Gemini EFI conversion

[Adam]

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GEMINI MULTIPOINT E.F.I. CONVERSION
by Paul Thorpe (Tooleeda)
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Version 1.1
Revisions: 1. Introduction - HP Increase
2. Hardware - Injectors
3. Electronics - Sensors (MAP or MAF sensors)
6. Other Details - Cooling System

Contents
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1. Introduction
-About cost
-HP increase
-Replacement parts
-Finding parts
-Wiring diagrams
-Minimum parts and sensor requirements
-Abbreviations in this text
2. Hardware
-Manifold
-Heater connections
-Plenum
-Distributor
-Fuel Rail
-Injectors
-Throttle bodies
-Thermostat housing
-Gaskets
-Donor vehicles for hardware
3. Electronics
-Computer
-Loom
-Coil
-Igniter/Spark Control
-Sensors
-Wiring
-Distributor Pickup
-Idle Air Control
4. Fuel Delivery
-Pump and Pressure Regulator
-Baffles/Surge Tank
-Fuel Lines and Diameter
-Filter
-Dampening
-Pressure and Injector Matching
5. Air Delivery
-Airbox/Ram Pod
-Ducts
-Plenum Size
-Port Sizes and Finish
6. Other details
-Head Machining
-Spark Plugs
-Parts Mounting and Wiring
-Self Diagnostics
-Cooling System
-Reprogramming
7. Credits

1. Introduction
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The conversion of a Gemini engine to Electronic Fuel Injection is relatively easy due to the abundance of bolt-on, and aftermarket parts available. That's not to say it's a weekend job, or not costly, but as with everything there is several ways of going about it. There are specialists around that offer a drive-in drive-out conversion, and if money is not a problem for you this would definitely be the way to go. When I researched a conversion I was quoted $2K-3K (pre-GST) for such a deal, needless to say I was happy when I finished my conversion for $700 plus tuning.

Firstly I want to dispel a few myths about EFI on the humble Gemini: If you are expecting neck breaking power gains from it, read no further and go and buy a big bore engine and some twin-carbs. What it will deliver is a smooth, economic engine operation with little maintenance and high reliability. The type of EFI that offers large power gains is one that injects fuel through the open valve in the firing order. (Sequential direct injection). Unfortunately there are no off-the-shelf manifolds for this available for the G-series Isuzu, which relies on the traditional 'batch fire' injection. This type of injection sprays the fuel at the back of the inlet valve, and causes it to vaporize for good combustion. Significant power gains are possible, but this comes from the basics of power tuning, i.e. good port airflow and fuel/air mixing, not necessarily the addition of an ECM controlled fuel delivery.

A DIY conversion is possible for your average backyarder with some careful planning and talking to people in the business. Most people are happy to advise you in your undertaking, and its invaluable to hear from people who have seen it all before. They save you money when you avoid costly mistakes. You need to consider the dollar value versus the performance gain because even $700 still buys a nice set of twin-carbs! My primary reason was not horsepower increase, but drive-ability, legality, and to add a bit of longevity to a vehicle that is 21 years old and done a quarter of a million K's.

Designing your system is the fist step in the conversion. You need to know what parts are available to you, cost of replacement parts, programmability of the ECM (Electronic Control Module) and any limitations the system might have - for instance you may wish to turbocharge the system later. The cheapest way to get the electronics done is to find a donor vehicle to scrounge the parts from, keeping in mind the ECM from such a car must be re-programmable. If the serviceability of some second hand parts is in doubt, you should buy new ones straight away. It is simply not worth the trouble of saving a few dollars on a sensor if it takes a few days to find it's causing a problem. I used the system from the late 80's Nissan Pulsar, and or Holden Astra/Camira. They also share the Delco ECM with the VN Commodores of the same era. This system is a popular choice because of part availability, especially the wiring loom which is a good length and generally the correct shape for fitting the SOHC Isuzu.

It is also a good idea to choose a donor system from a vehicle that has a lot of research material available for it. Wiring diagrams are essential for DIY conversions, and I must at this point give credit to Gregory's and their handbooks for the Gemini and Pulsar. They contain colour-coded wiring diagrams for everything and make it very easy to connect up the loom. On the topic of research - the public libraries also contain a lot of material on EFI and I suggest you read up on it - it is so much easier to work on something when you know WHY you are actually doing it.

The last step in the initial planning is to work out the sensors you will need. Electronic fuel injection works by a computer sampling various parts of an engine, and making very rapid calculations so it can inject the required volume of fuel. The fuel requirements vary immensely depending on what the engine is doing and the computer works this out by the signals from all the sensors. The minimum sensors you will need to get an engine running properly are: crank angle, throttle position, air temperature, coolant temperature, and a MAP sensor OR a MAF sensor. There are numerous others that contribute to the drive-ability and economy of the engine including the oxygen (O2) sensor, but the above mentioned are the minimum. The sensors you may want to run on your system may or may not match your wiring loom or even form part of your loom. Conversely some sensors usually signaling the ECM may be redundant altogether. Generally this won't be a problem and is sorted out when the ECM chip is re-programmed.

Abbreviations in this text:

AFM Air Flow Meter (same as MAF)
ALDL Assembly Line Diagnostic Link
ATS Air Temperature Sensor
CPU Central Processing Unit (same as ECU/ECM)
CTS Coolant Temperature Sensor
CAS Crank Angle Sensor
ECM Electronic Control Module (same as CPU/ECU)
ECU Electronic Control Unit (same as CPU/ECM)
HP High Pressure
IAC Idle Air Control valve
MAF Mass Air Flow sensor (same as AFM)
MAP Manifold Absolute Pressure sensor
MEMCAL MEMory CALibration chip
MPI Multi Point Injection (same as TPI)
NA Naturally Aspirated
OEM Original Equipment Manufacturer
O2 Oxygen sensor
SPI Single Point Injection
TDC Top Dead Center
TB Throttle Body
TBI Throttle Body Injection
TPS Throttle Position Sensor
TPI Tuned Port Injection (same as MPI)
WOT Wide Open Throttle


2. Hardware
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The hardware items required to convert the G-series Isuzu SOHC to EFI are listed and described as follows:

INLET MANIFOLD: bolts to the side of the head and replaces the old carburetor manifold. It contains the same water galleries as the old one but may not (depending on the type of manifold) contain correct heater connections. Turbo Piazza manifolds contain an additional gallery running against the head and around the ports but does not pose a problem and is left as is when bolted on. The small hole in the rear of the head that is part of the water gallery can be sealed against the inlet manifold gasket, or you can drill the manifold through to match it up. (Sealing it off does not appear to affect the heater or running temperature) The manifold also contains the four injector housings and 8 studs for the injector clamps. There is a rubber o-ring in the end of each housing which should be renewed for a conversion, and must match the injector head. Four longer studs are needed in the top row of the head for the inlet manifold, and by coincidence the four long studs used to hold the rocker cover to the valve train fit perfectly, so source some of these.

HEATER CONNECTIONS: On the Turbo Piazza manifold, the heater connections are on opposite sides to the Gemini. The press-fitted elbow and T-piece are also different diameters so cannot be simply pressed out and swapped. There are no commercially available alternatives so you simply need to get the old ones cut off and new ones welded on. A standard T-piece is available from most auto parts stores, and the elbow can be fabricated from steel tube.

PLENUM CHAMBER: The air reserve that bolts to the inlet manifold and supports the throttle body. It is simply a box that holds a reserve of air and stops fluctuations in air delivery to the engine. Contains various vacuum nipples and screw holes and contains an EGR-valve which can be removed and sealed off (The EGR valve may be required for legal compliance on TD onwards models, as they all used an EGR valve). Any defunct inlets need to be sealed off to maintain a tight vacuum seal. The plenum also supplies vacuum to the brake booster, vacuum gauge (where applicable), rocker cover, fuel vapor valve, and is fed by the IAC (idle air control) valve. Turbo Piazza Plenums (besides having the word 'Turbo' cast in them) have, in addition, a 50mm pressure relief valve in the front of them (this is an emergency pressure vent for the standard Piazza Turbo not a blow off valve). This valve can be left there on NA engines (it fills the large hole quite nicely) but must be removed and sealed up on modified turbo engines that run above standard boost.

DISTRIBUTOR: Replaces the normal distributor in the Gemini that usually contains the points. An import distributor can be fitted which is nearly identical to the stock one, but contains the magnetic pickup inside (similar to the RB Gemini). Make sure replacement caps are available if you use an import dizzy (RB Gemini caps usually fit them). Existing dizzies can be modified by removing the points and replacing with an inductive (Hall effect) pickup. Whatever the choice, the output signal must be compatible with the ECM and ignition module being used. There are aftermarket kits for breaker-less distributor conversions, but keep in mind you only need the sensor (pickup) not the entire spark module so see if you can purchase them separately. The vacuum advance mechanism will not be used in the EFI system and must be disabled. The rotating base plate inside the distributor must also be fixed so it cannot move - it can be clamped or tack welded. (I filled the ball bearing race with two-part epoxy, which also works well!) Make sure you mark the position of the base plate before you remove it so it can be re-installed correctly. Alternatively you can use the vac-advance mechanism to locate the base plate.

FUEL RAIL: connects to the injectors and holds a reserve of fuel for them to draw from. The fuel rail also works in conjunction with a pressure regulator, refer to chapter '4. Fuel Delivery'. The choice of rail is another tricky part of the conversion. Ideally a factory one from a Rodeo/Piazza should be used but these are increasingly hard to find. Alternatively you can make one from some thick-walled aluminium tube - fitting 7 screw in brass nipples for the four injectors, fuel in, fuel out, and pressure sensor connection. I used a JD Camira fuel rail. It contains a massive fuel reserve in the rail, and lines up well on the manifold. The outlets for the injectors need to be bent so they line up on a slight angle with the injectors.

INJECTORS: There are thousands to choose from so consider the following points if you are unsure of the required flow rates. Choose the donor vehicle injectors based on YOUR vehicles engine size, rev-limit, fuel pump and fuel regulator. As a general rule of thumb, if you have a 1.6L or 1.8L, source the injectors from a 1800 Pulsar or Camira; if you have a 2.0L then find a 2.0L Camira or VL Commodore. The injectors that fit the Rodeo/Piazza manifold are predominately BOSCH units. It gets slightly more difficult choosing injectors for turbo applications, so speak to some specialists. (Injectors from a Turbo VL Commodore work well but are impossible to find new).

The injectors must be of compatible impedance (resistance) to the ECM, and if you are scrounging injectors from a wreckers be sure to measure the resistance with a multimeter. Make sure the resistances for all the injectors are the same (to within a few percent) and they are the correct resistance (refer to manufacturers specifications). The injectors must also fit in the housing on the inlet manifold and can be adjusted slightly by changing the rubber grommet around the outside of them. E.g. injectors from a Camira will require a thinner O-ring around the body in order to fit the piazza manifold.

It is also worth having any second hand injectors cleaned ultrasonically and tested. Injector servicing specialists charge around 5-10 dollars per injector for this.

THROTTLE BODIES (TB): Again take your pick of the type of throttle body you want to use. There are three main types: Single butterfly; Dual Simultaneously opening butterfly; and Dual Sequentially opening butterfly. The merits of each one I can only guess at. I would assume the 'single' is more simple and therefore more reliable; the 'simultaneous' narrower but bigger volume of airflow and may not be as smooth on acceleration; and the 'sequential' is built for economy with small primary and large secondary butterfly creating higher airflow speed. If you want to use one that doesn't fit the plenum, you will need to fabricate an adapter plate. The standard accelerator cable will not fit the Plenum/TB and you will need to have one lengthened. This costs about $60 depending on where you go so make sure you measure it carefully - you need the outer shroud length and the throw length (distance the cable travels when the accelerator is depressed fully) as well as the neutral cable length. Make allowances for any adjusting nuts the cable has on it already.

THERMOSTAT HOUSING: A new housing is required for the conversion, as it has to bypass the No.1 injector to the radiator. You can get one off an import engine, (or possibly the Piazza or Rodeo) or have one made up using a stock housing base. A new top radiator hose may be required if the old one cannot be shortened or touches the distributor cap. A standard thermostat that has previously worked well with the engine can be fitted.

GASKETS: The thermostat and inlet manifold gaskets are standard G-series Isuzu, the latter needing to be trimmed slightly (refer to chapter '6. Other details') the throttle body to plenum, and plenum to inlet manifold gaskets can be made from gasket cardboard. And an appropriate sealant (oxygen sensor friendly NO SILICONE!) can then be used on all mating surfaces. Note that in turbo applications the gaskets are not cardboard and need to be made from a different type of material as they are under more pressure - speak to a specialist about what to use in this case.

DONOR VEHICLES FOR HARDWARE: There are 3 sources, and four types of hardware you can use for the EFI induction system: Rodeo, Jap-Isuzu imports, Turbo Piazza, and NA Piazza. Whilst generally speaking, they all 'bolt straight on' they all need a few minor modifications to suit a Gemini. Sensors and throttle bodies can be obtained from many vehicles, by simply measuring the required dimensions, and specifications in the case of sensors. My conversion shares parts with RB Gemini, VL&VN Commodore, N13 Pulsar, JD&JE Camira, Piazza, and Jap- imports; its just a matter of finding the right part and the right price.

3. Electronics
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COMPUTER (ECM): The size of your wallet will dictate what type of computer you will need. They cost as little as $50 for one that will do everything you'll ever need - the downside of this is that the chip needs to be re-programmed and the hourly rate for programmers and dynamometer work is quite high. The other alternative is an off-the-shelf kit, which contains computer, wiring, and usually an array of startup programs so you can get the engine running by yourself. Expect to pay about $500-1000 for a kit such as this, or around $600 to have a factory computer reprogrammed. The computer chip contains a fuel map, which is a reference table the computer uses to determine the correct amount of fuel to inject for a given engine load. Some of the cheaper kit computers contain very simple fuel maps with only a few reference points, and some control only fuel delivery, not ignition timing. You'll need a computer that can handle both. As previously mentioned, I used the Delco ECM because of its cost, and the fact it has a removable Memcal chip for easy programming. This was a second hand unit straight out of an '89 Astra and it can handle all types of input signals and control many vehicle systems: Idle air control, speed sensing, thermatic fan control, air-cond compensation, ignition timing, and MAP sensing for both NA and turbo applications.
LOOM: By far the easiest way to go with a loom is to get one complete from a wrecked EFI donor vehicle. Don't bother with a cut loom, or one that you have to make yourself. It is so easy to make a mistake when making a loom, and so hard to trace afterwards; and any joins must be spliced, soldered, heatshrink wrapped, and taped which is a hell of a lot of work when making 50+ connections. An added bonus is that the Gregory's people have already made a colour coded wiring diagram for most Australian sold cars as well. The best source of a wiring loom is a late 80's Astra, Pulsar or Camira, the Camira having a slightly shorter loom length. When getting a wiring loom, be sure to get as many sensors from under the bonnet as possible - these are suited to both the computer and the connectors and are the best to use if they are in serviceable condition.

COIL: The original low-voltage ignition coil could be used but you shouldn't bother. You can get a High Energy EFI coil that plugs into your wiring loom in most cases. Again source these from the same vehicle as your loom. The more plug-in parts the better and more reliable your system will be. There are different sparkplug lead terminations on some EFI coils, so a new coil-to-cap lead may need to be purchased.

IGNITER/SPARK CONTROL: Commonly referred to as the ignition control module, it is essentially a transistor that the ECM uses to switch the massive current to the coil. This unit forms part of the distributor of the Family II (Pulsar/Astra engine) and needs to be removed from under the distributor cap. It takes the output from the crank angle sensor (the distributor in most cases) and tells the ECM when to fire the coil. These are relatively delicate components and require a fair amount of heat-sinking to ensure reliability. The two wires from the pickup coil inside the distributor connect to the input side of the device. The connection is polarised so if you're using a RB pickup and Delco ignition module, connect red wire to yellow, and white to green.

SENSORS: As already mentioned there is a minimum number of sensors you need to get the EFI working properly. The more you connect the more drive-able the engine will be. The following is a list of sensors easily compatible with the Gemini configuration:

Oxygen Sensor: Commonly referred to as Lambda or O2 sensor, it monitors the exhaust gases and signals to the ECM a rich or lean state. They are 'poisoned' and rendered inoperative by silicone, and lead from petrol or avgas. Even silicone used in manifold gaskets can end up poisoning an oxygen sensor so don't cut any corners or risk it to save a few dollars. A new Delco sensor will cost about $80 and will last around 10 years in a properly tuned engine, be wary of this if searching for a second hand one. There are several types of oxygen sensor, made from different materials etc, but the most common difference is the number of wires coming from the end of them. A single wire sensor used to be very common but is less so today; it requires the engine to be at operating temperature to function correctly. Multiple wire sensors have an inbuilt heating element, so it can work properly while the engine is still cold thus reducing emissions. In most cases the heated sensors can be used to replace a single wire sensor, as the + and - wires are simply connected to 12V through the ignition switch. The sensor needs to be mounted in the exhaust manifold at a point nearest to the ports (for good heat conduction), but after the manifold ports have become a single pipe. This is so the sensor is reading a mixture from all cylinders not just one, as it is possible to have just one cylinder running too lean or too rich. In most cases provision will need to be made to mount the sensor, unless a Rodeo exhaust manifold with the O2 sensor mount is used. This is relatively simple if you have extractors, as you can weld a matching nut on, and drill out the hole. A cast-iron manifold (stocky) cannot be modified and the sensor would need to be mounted way down the line in a steel section. In this case a heated sensor would need to be used, as the pipe is a lot cooler at this point. When choosing a mounting point be wary of where the sensor and wires will run so they do not catch on underbrush and road debris, or wires will not melt on red-hot parts. The O2 sensor is non-essential in getting the EFI system operational, but is an important tuning aid. It allows the ECM to inject the precise amount of fuel over all load ranges, so if it is omitted only fuel economy will suffer, and the engine is tuned only for WOT.

Coolant Temperature Sensor: Looks similar to the sensor for the heater gauge, but has a 2-wire connector. It is the only reference for engine temperature that the ECM has, and helps determine the mixture of injected fuel. It is an essential sensor and the system cannot function without one as it is used in the cold starting of the engine. It is screwed into the water gallery anywhere in the inlet manifold, but most often under the thermostat.

Crank Angle Sensor: In most cases the pickup in the distributor is the crank angle sensor, but many systems use this in addition to a sensor on the flywheel or crankshaft, that tells the ECM exactly when the #1 piston is at TDC. The distributor gives a sufficient crank angle signal, but the output needs to be doubled (the crank rotates twice for every distributor revolution) to be used as a CAS. The distributor sensor is a minimum requirement to get a Gemini running EFI.

Knock Sensor: A knock sensor will detect pre ignition (Pinging) or miss firing and signals the ECM to retard the timing to eliminate this condition. It is not an essential sensor but a valuable one in extremely modified engines, and can detect knocks unable to be heard by ear. They are prone to false readings through noisy valve operation or vibrations though, and performance may be inadvertently lost due to this.

Throttle Position Sensor: There are two types of these sensors, a 3-position sensor, and a variable resistance sensor. The 3-position sensor tells the ECM when the throttle is at idle, partial, or full throttle only. It is not compatible with the Delco and was mainly used in BOSCH systems. The variable sensor is a large potentiometer, whose resistance varies in proportion to throttle position. It helps deliver a smoother fuel delivery and throttle response. These sensors are mounted on the TB and use the butterfly shaft to move them. This is an essential sensor for the EFI conversion.

Air Temperature Sensor: basically a thermometer that tells the ECM the temperature of the air entering the TB or entering the inlet ports. The sensor is mounted in the plenum chamber on a setup using an air filter box. On an engine using a ram air feed (ram-pod filter) the sensor should be mounted in the ram tube before (but as close as possible to) the throttle body.

MAP or MAF sensors: Only one or the other is needed in an EFI system, although various manufacturers have experimented using both. The MAP sensor works in conjunction with the ATS to determine the volume of air entering the engine, as it calculates the air pressure (a vacuum in most cases). Pressure and temperature readings are then used by the ECM to calculate the volume of air, so the correct proportion of fuel can be injected. With this system, any dimensions of air intake or TB can be used as it will not affect the calculations of the ECM. An alternative to MAP is the MAF system, which uses a relatively complicated device to determine the velocity of air entering the throttle body through a fixed (known) diameter. From this information the ECM can calculate the air volume. Generally the factory airbox and air induction must be used with the MAF sensor. The MAP system is very simple and hence more reliable and is the system utilized by the Delco ECM. A MAP sensor can operate erratically at low revs if too large a camshaft is used, as idle vacuum is reduced and the fuel delivery is enriched. This is not a problem if the ECM is to be reprogrammed, but may cause high fuel usage with a standard chip, and a higher idle speed may need to be set. A final point to make about the induction sensors is that turbocharging creates a negative vacuum (boost) in the induction, so a special MAP sensor that can detect this is required. Either MAP or MAF is required for EFI.

Vehicle Speed Sensor: Does as its name suggests, and tells the ECM this information. It is used because fuel requirements are different when the vehicle is constantly changing gear ratios, even though engine revs may be the same. It is not an essential sensor, but one that enhances drive-ability, especially when going from idle to motion etc. Vehicles without a speed sensor may experience stalling occasionally, when coming to a stop. On a Gemini the sensor connects in-line with the speedometer cable and the gearbox. The sensor from a 'Speed Alert' device is used for this as it is manufactured to fit onto the box, then drives the speedo cable. Other vehicles use sensors on the driveshaft or output shaft of the gearbox.

WIRING: In addition to connecting the computer's loom to the engine, other connections need to be made to the fuel pump and battery, via various switches, fuses and relays. This sounds complicated but in fact is not, and there is only one wire from the loom to the battery. When making connections it is essential to use good quality auto connectors (the crimp on type) and where a connection does not terminate (i.e. a join in the wire) use plenty of insulation tape. With the exception of fuel problems, wiring is the number one cause for EFI failure or malfunction. Relays are used in two areas: to supply power to the ECM, and the ECM uses a relay to supply power to the fuel pump. Power to the ECM relay comes from the ignition switch, and power to the high-pressure fuel pump comes straight from the battery. The Delco system has a 'check engine' lamp that you can mount on the dashboard somewhere and this is connected to the ALDL connector. The ALDL connector is used to determine fault codes in the ECM and is displayed by a blinking of the 'check engine' lamp.
A complete wiring diagram for this is available from the Gregory's Automotive Handbook #250 for the 1987-1991 Pulsar and Astra.

The final wiring point you may want to consider is an emergency fuel cutoff switch. This is a feature omitted from all production engines because of the 'idiot factor' but is an important safety device nonetheless. The switch kills power to the fuel pump and ECM, because in the event of an accident the engine may die, but the ignition could still be powering the pump and therefore circulating fuel through the lines. If a line were to have broken from the accident, there would be pressurised fuel spraying a hot damaged engine and no way to stop it - not a good scenario.

DISTRIBUTOR PICKUP: As already mentioned there are several devices you can use in a distributor to make it compatible with an ECM. It is not necessary to find a long shaft distributor from an import engine (though it is easier), but the points can be removed from a stocky, and the system work just as well. There are three options for this, the first two require parts from a speed shop and are common in converting points-distributors to breakerless type. The points can be replaced by an infra red sensor that uses a chopper on the rotor to break a beam of IR light, signaling the computer. The chopper is a disc with four slots cut into it that allow light to pass through each time a spark is required at the plug.

The second system uses an iron vane as a chopper, and the rotating vane is detected by a Hall Effect pickup on the baseplate. Both of these systems work in a similar way, the latter being not as susceptible to dirt contamination. The last design uses a square block (similar to the rubbing block on the standard dizzy) from an RB Gemini distributor, screwed down onto the distributor shaft. This block spins next to a magnet, and each corner creates a signal in a pickup coil every time it passes. There is no real difference in the performance of any of these systems, but as with everything, the less homemade, and more-bolt on the parts are, the more reliable the system becomes.

IDLE AIR CONTROL: It is similar to a choke on a carburetor engine, the IAC valve delivers extra air (and hence fuel) to the engine whilst it is in warm up mode. It does this by raising the idle speed slightly to overcome the friction of the cold engine. Essentially the valve lets filtered air bypass the throttle body into the plenum chamber. There are two main systems designed to do this: computer controlled IAC, and a timed/temperature based IAC. The computer-controlled system determines the amount of idle speed increase, via a stepper motor in the throttle body, which increases or decreases the idle RPM. It can compensate for such things as increased alternator load or the air conditioner compressor load, as well as the cold start idle. The second system is a mechanical valve, usually containing a heating element that slowly reduces the idle air bypass as the engine warms up, to a point where it is completely closed off. This valve is powered by the battery through the ignition switch, and the engine heat keeps it closed once operating temperature has been reached, thus enabling warm starting without large engine revs.

As for which system to use it again comes down to cost. The computer-controlled valve usually forms part of the throttle body and therefore the entire air bypass is proportioned to the engine size of the original vehicle. This means that the capacities of the donor vehicle and the Gemini should match. Camshaft timing will also wreak havoc with IAC settings, usually due to a lack of adequate vacuum at idle. All these problems can be ironed out with the reprogramming of the ECM, but as always this requires time (and money). The mechanical system is fine in 90% of applications but some time is required to find the ideal mounting location of the valve as it is heat dependent and can close too quickly or too slowly causing stalling or fast idle respectively. There is an adjusting nut on the base of the valve that is used to vary the duration of closure, but once the optimum setting is found it needs to be fixed in place with Loc Tite.

4. FUEL DELIVERY
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An EFI system relies on fuel forming a vapor (atomizing) as it is injected into the airstream. The only way the fuel can disperse into small enough particles to combust properly is if it is sprayed through a nozzle under a sufficient pressure.

FUEL PUMP: the fuel pump supplies All this pressure, and the nozzle is the fuel injector. The EFI fuel pump is very different to the standard pump located inside the fuel tank, and is singularly the most important part of the entire system. A circuit of fuel is flowing constantly while the engine is running: from the tank, through the fuel lines, through the fuel rail, through the regulator down the return lines and back to the tank. Only a small part of the fuel being pumped is injected at the inlet manifold, the rest is returned to the tank. This allows simplicity in the fuel pump operation, i.e. it runs flat out all the time - the pump speed does not need to be regulated against fuel demand. A vacuum operated regulator located on or near the fuel rail controls the fuel pressure. As the vacuum increases (i.e. at idle) fuel demand is lower so the regulator allows most of the fuel to flow back to the tank. Under WOT conditions the vacuum is near zero, and the demand for fuel is greatest, so the regulator closes off and all of the fuel pressure is fed to the injectors. On turbo vehicles a different regulator is required because the engine is under negative vacuum. The regulators for turbo engines usually have two feeds for separate vacuum and boost activation. The regulator should be mated to the injectors so source it from the same vehicle or engine type as this.

The most common and easiest pump to use in a Gemini conversion is the bullet-style, 'external', high-pressure pump from a VN Commodore. The N13 Pulsars use an 'in tank' pump which is not suitable, but the Commodore pump is mounted outside and is easy to mount anywhere. Fuel pumps are susceptible vibrations and need to be mounted well away from any heat also. They are also noisy when operating, and if mounted in the boot or wagon may be irritating whilst driving. Insulating all mounting surfaces with grommets or rubber sheets will reduce noise.

The stock Gemini 'internal' fuel pump must be kept and be in good working order as it feeds the high pressure pump. No rewiring is necessary for the stocky pump, so it will still fail if the alternator fails (the age-old Gemini problem). The high-pressure pump is connected via a relay to the battery and the ECM controls the relay. It is most important that the pump is powered from the battery, as it needs a minimum of 13 volts to operate reliably, so do not run it from the accessories or other fuses.

BAFFLES/SURGE TANK: Baffling inside the fuel tank reduces movement of the liquid fuel hence reducing surging in the pick up of fuel by the pump. There are two types - metal plates welded inside the tank, or a foam substrate which can be pumped in. they are very expensive and used mostly in racing and not necessary for street use.

Surge tanks are a device that holds a reserve of fuel to feed the high-pressure pump, in the event that the 'in tank' pickup temporarily runs dry. Gemini sedans have a unique advantage in their fuel tank design, in that the tank is mounted vertically, so the movement of fuel is comparatively small. This negates the need for a surge tank in the delivery system and it will operate without problem in hard corners or steep ascent/decent. If you can afford it though, it is still a good idea as a fail safe, as the smallest air bubble in the line can cause a lean fuel delivery. A surge tank is absolutely necessary in a Gemini with a horizontal tank though, be it a panel van, wagon, or a drop-tank setup, as they notorious for running lean stock standard.

FUEL LINES AND DIAMETER: From experience the steel fuel line diameter is sufficient to operate an EFI G200, a turbo EFI G180, and a G180 EFI Twin-Cam without problem, the latter two being in panel vans. However the standard line diameter is on the minimum side of normal. All EFI vehicles I sourced parts from had bigger diameter line than the Gemini - a 1.6i Pulsar having the same size fuel hoses as a 3.0i Commodore. Symptoms of an engine with too small a fuel line are a loss of power at high engine revs, and it will tend to surge rather than completely cut out. (Monitoring the oxygen sensor with a mixture-meter will indicate a periodic lean condition such as this.) All rubber fuel hose between the HP pump, and the fuel rail must be upgraded to EFI standard high-pressure hose. The hose is available by the metre from most autoparts places and will have a pressure figure stamped on it somewhere. You can also obtain fuel line from a wrecking yard from an EFI vehicle but check the condition thoroughly. Typically the hose needs to handle a pressure of 250 kPa under WOT. Return lines don't need to be upgraded to HP but it is essential to fit the screw type clamps to all joints in the fuel system instead of the spring types.

FUEL FILTER: The filter in the system needs to be upgraded and the old plastic filter under the bonnet removed completely, due to the increased pressure running through the system. The filter required is the steel EFI type that cost about $15, but have a life of about 100,000 km. The filters for most Australian cars are very similar and it doesn't really matter what vehicle it was made for, but ideally buy one made for the vehicle your HP pump came from. They can be fitted anywhere in the fuel system on the inlet side of the system. Commodores have them near the fuel tank on the underside of the floor-pan, whilst Pulsar's are located under the bonnet. It is a good idea to obtain a mounting bracket for them from a wreckers, as they are quite heavy and should not be putting a strain on any fuel hose through any movement.

FUEL DAMPERS: Some production vehicles experience 'hammer' in their fuel system (similar to water hammer in old houses) and the manufacturers utilize a damping device to eliminate this. As yet I have not experienced this in a Gemini conversion, but it is quite simply solved if it occurs. A pressure damper is fitted in line and smoothes out the flow and pressure delivery of the fuel. It looks similar to the pressure regulator, but without a vacuum nipple and its placement in the system has a bearing on its effectiveness. For instance it may need to be placed close to the HP pump, mid-line, or near the fuel rail to stop a hammering problem.

PRESSURE AND INJECTOR MATCHING: As previously mentioned the selection of injectors is important in smooth engine running, but there are other dependent factors. The pressure regulator, injectors and HP fuel pump should all be rated to similar pressures. Fuel economy will suffer due to injectors leaking at the tip if there is too high a fuel pressure. The regulator may respond improperly if different vacuum conditions exist compared to the OEM design. Idle quality may suffer if the injector is too big. Some experimentation may be necessary to determine the correct combinations of these components, but as always, source as many parts from the same vehicle whenever possible.

5. AIR DELIVERY
===============

AIRBOX/RAM FEED. There has been much debate over the merits of these two air induction systems and I will outline the operation of both. The air filters are connected via ducting to the throttle body and contain renewable or washable elements to do the filtering. An airbox draws air from inside the engine bay or mudguard and passes it through a high-flow or paper filter before it reaches the TB. The airflow is slower than with a ram feed and consequently so is the throttle response. The advantage it has over a ram feed is in drive-ability and idle quality, (and it is also a legal requirement in S.A.), as a consistent flow and air temperature is obtained. Tuning is also easier for these reasons and there is a torque increase. It is impossible to tune a ram-feed system perfectly, as wind conditions cannot be simulated on a dyno. The power gains to be made from a ram feed are mainly due to the cooler air being inducted, and not necessarily the fact that it is under pressure, and these gains are at the expense of idle quality. Provision needs to be made in the ducting for the ATS in the latter system.

DUCTS: The diameter of the ducts depends on the TB diameter and should be no smaller and as short as possible to obtain a better throttle response. All joints must be airtight and flexible in the direction of engine movement. PVC storm-water pipe can be used, with any elbows being glued, (Remember, no Silicone sealant!), and then sanded down for the smoothest interior as possible. Remember to wash all ducts thoroughly, as any debris will enter the engine. Rubber connectors can be sourced from a wreckers, but again inspect well for tears or perishing, and secure all rubber joints with large hose clamps.

PLENUM SIZE: For most applications the plenum size cannot and should not be changed, the Rodeo/Piazza chamber being good enough, but there are problems associated with incompatible plenum chambers such as stalling, or resonance. In general the throttle response increases inversely to the plenum size; but too small a plenum and flat spots may appear in acceleration from idle; too large and response will be slow. There are infinite formulas around for calculating your plenum size, so look at something where the math has already been done - production vehicles. Do not choose based on engine capacity alone, find the volume associated to a similar bore and stroke, and inlet port diameter as your Gemini.

PORT SIZES AND FINISH: All inlet manifolds should be match ported to the head, as a mismatch that may not cause problems on a carburetor engine, can wreak havoc with the ECM operation. It is also worthy to note that the inlet ports can now be polished (when ported) as only air passes through them and fuel condensation will not occur.

6. OTHER DETAILS
================

HEAD MACHINING: The inlet ports of the head need to be grooved slightly to allow the injector to spray properly. This is easily done with mounted stones on an electric drill using the inlet manifold as a template (with head removed). The procedure for this is as follows: Trim some standard G-series inlet manifold gaskets to the shape of the inlet manifold ports. Transfer the gaskets to the head face (keep careful note of the orientation of the gasket) and using a felt tip marker, trace on the groove outline. When grinding the head go about a centimeter deep and run-out into the port gradually, not just dig out a big chunk. (Needless to say, wash the ports out well before refitting the head and manifold.)

SPARK PLUGS: The standard plugs should no longer be used, as they are usually of the non-resistor type. A resistor plug must be used with any ECM controlled system as electrical feedback can affect the computers operation. NGK denote resistor plugs with an 'R' in the plug part number as the third letter. For example standard Gemini plugs are BP6E, and the equivalent resistor plug for EFI is BPR6E (the other letters denote the plug dimensions). The number '6' is the temperature rating of the plug and doesn't need to be changed, with the possible exception of a turbo setup. (Note that these are all NGK part numbers and they vary for different brands, I have got the best results from some V-Groove NGK's, number BPR6EY)

PARTS MOUNTING: There are a few sensors and devices that need to be mounted off the engine somewhere in the engine bay. Considerable care needs to be taken when mounting these for the following reasons: heat transfer, engine vibration, engine torque movement, and water ingress.

All wiring should be periodically tied down along its length to minimise movement of the loom, and run a course that is far removed from heat and water. Wires should not be under tension of any kind and must be lengthened if required. When making connections use quality crimp connectors and insulate well with tape. Where soldering is absolutely necessary, all joints must be heat-shrink wrapped as well as taped. Wiring is the second most common failure in an EFI system next to fuel.

The earth wire to the engine must be in mint condition and any other earth connections required need to be made properly. Sand or wire brush the area down to bare metal to make a good contact with terminals, and paint afterwards if required.

Vacuum tubes must be allowed to flow freely to avoid crimping, and steel or brass elbows should be used for extreme curves. All hose connections including fuel should be clamped with quality screw clamps.

Air Induction pipes need to be insulated from the exhaust headers either by wrapping the manifold in heat tape, or shielding the manifold with sheet aluminium.

The spark control module should be mounted as far away from any other wiring as is practical, and needs to be bolted to thick panel steel, or a heatsink. HT (high tension) leads should be directed well away from other wiring also, as should the coil, as the voltages in them is about double the standard, and interference in the radio or an amplifier may increase.

A catalytic converter on the exhaust is required by law on all vehicles running unleaded petrol, and will need to be fitted to comply. Fortunately high flow converters are available but at large expense. The catch is you cannot legally run an EFI system on a Gemini with leaded fuel (including avgas) without an O2 sensor (for emissions reasons) which will be destroyed rapidly. The use of unleaded fuels also requires that the filler neck of the fuel tank be reduced in diameter to fit the petrol station pumps.

Use fuses wherever possible, do not run wires to the interior fuse box. Go straight to the battery and use quality bar-fuse holders. Typically 10 Amp fuses are all that is required for the ECM and fuel pump. Refer to an EFI wiring diagram for the fuse locations.

SELF DIAGNOSTICS: The Delco ECM is equipped with a self diagnostic program that runs when the ignition is switched on, and periodically when the engine is running. It will blink a warning light in a certain pattern to indicate a particular problem, namely sensor malfunction. A table of codes and error signals is available in the Gregory's Manual for the Pulsar/Astra N13, and probably from Holden or Nissan as well. The ECM also contains several 'Limp Home' modes that will enable the engine to run adequately with a variety of malfunctions.

COOLING SYSTEM: the temperature of your engine needs to match as closely as possible, the temperature of the donor vehicle originally running your EFI system. For me this involved playing around with a few thermostats to actually make the engine run hotter, to match the Pulsar temperature. This is because the CTS is calibrated to the donor vehicle, and may be completely different on your engine. It pays to have a larger radiator (either 3-core or rodeo) which can handle the additional cooling requirements also. It is not a bad thing to have the engine run warmer; anything up to about half on the temperature gauge is fine. A hot engine is often confused with causing power loss and pinging, when this has more to do with air/fuel temperature and combustion chamber design. On the other hand a massive radiator and no thermostat causing an engine to constantly run cold is extremely bad. The pistons, rings and bearings have not thermally expanded to their tolerances, and the engine is actually operating under more stress. A warmer engine will often return better fuel economy as well because more complete combustion is occurring in the chambers.

REPROGRAMMING: The last stage in the conversion to get the EFI system running the way a Gemini wants it, is to reprogram the MemCal chip, or computer. This involves dyno work and as for programming details, I have only minimum knowledge. Essentially the fuel map is reprogrammed to suit the engine - when I first got my engine started it was running on a 1.8L Astra chip and ran massively rich, returning 12 miles per gallon, or 4 km for every litre of petrol! After reprogramming there was a slight power gain and a huge jump to 13 km per litre average, so it is an essential part of the conversion. I have heard rumors that the 2.0I Camira MemCal chip matches pretty well to the Gemini engine, but it won't ever be at optimum without dyno tuning.

Remind the programmer to turn off possible defunct systems on the chip that you are not running, as they may trigger errors within the ECM. For example, you may not be running a speed sensor or O2 sensor, and the ECM will be processing incorrect values. Also the Delco has rev limiting capabilities which is around 6500 rpm standard, so be sure to have it shifted if required.

CREDITS:
========
In conclusion I'd like to reiterate that I've written this article based on what I have read and what has worked for me in my conversion. There are many paths to the final destination; this is only one of them. I hope as a guide, specific to the mighty Gemini, it stands up well, but no doubt there will be additions made to it in the future as information comes my way.


Now, in no particular order, is a list of fine people and organisations that helped me reach my goal:

Rob and Tim at Motor Traders, S.A.
Universal Fasteners, S.A.
Steve at Just Gemini Spares, S.A.
The infinitely knowledgeable people at the DIY_EFI website.
The NGK website.
Gregory's Workshop Manuals for the Pulsar and Gemini.
U-Pull It wreckers, S.A.
Andrew and Paul - for doing it all before me.

And to Melissa, for making room in the wedding budget!

Cheers,
-Paul Thorpe (a.k.a. Tooleeda)

[TXcoupe]

hmm if you had the time or budget why not buy an aftermarket progammable ecm like a wolf3d or motech?
but yeah pretty sweet for $700