Electronic Fuel Injection for the Slant Six

by Bob DiBiase

Fuel Injection EmplemIf you want to bring your Slant Six along with you into the twenty first century (at least for the next 200,000 miles!) and if you’re not interested in a by-the-numbers restoration, then you should seriously consider an Electronic Fuel Injection (EFI) conversion. This is true whether your beloved SL6 is a daily driver and must co-exist with today’s gasoline, or your goal is real performance. Remember, this engine was designed in 1958! Technology has come a long way in the last forty plus years, and now is an excellent time to take advantage of some of this newer technology. An electronic fuel injection conversion is also the first logical step to efficiently turbo-charging the SL6.

There are a number of ways to accomplish this conversion. You can purchase a complete new setup for either throttle body injection or multi-port injection from aftermarket sources such as Accel, Holley, or a host of other suppliers, or you can design your own setup using salvage yard parts, or use a combination of salvage yard parts and new parts.

My view is that if you’re going to convert to EFI, then you might as well go all the way with multi-port fuel injection, and forget the already obsolete throttle body injection. After all, the auto manufacturers only used throttle body injection as a transition technology when converting from the carburetor to modern electronic fuel injection. Also, throttle body injection does nothing to address fuel distribution problems, while multi-port injection eliminates these problems.

A new multi-port EFI setup can cost you over $4000. This would include a modified intake manifold, custom fuel rail with a pressure gage, injectors, a high-pressure electric fuel pump, adjustable pressure regulator, throttle body, all the required sensors, a wiring harness, and a programmable Electronic Control Module (ECM). It would not include an ignition. This would be a Speed Density system (more about this later), and as such would require programming with a laptop computer. It would also be an excellent setup, as it should be for that kind of an investment!

So now I'm going to tell you how you can have a setup almost as good as that new one, and have more fun building it, for about $1000, or for around $500 if you modify your own intake manifold and fabricate your own fuel rail.

As it turns out, there is a factory multi-port fuel injection system that could have been made for the SL6. This is the batch fired EFI setup used on the early to mid-eighties GM V6 engines. I’ll be concentrating on the 3.8L engine and a 225 CID SL6 conversion, but suitable GM setups can be found for the 170 and 198 CID engines as well.

According to The Haynes Fuel Injection Manual by Don Pfeil and John H Haynes, the batch fire 3.8L engines can be found in 1982 thru 1985 Buicks, Cadillacs, Chevrolets, Oldsmobiles and Pontiacs. My own experience is that they are most commonly found in ’84 and ’85 Buicks and Oldsmobiles. These engines are easily identifiable because they still used a distributor. I chose the GM setup mainly because of the abundant supply in most salvage yards, and the potential for possible upgrades later. After all, GM did make a 3.8L turbo V6. Most aftermarket systems are also based on the GM design.

Adapting the GM setup to the SL6 is not nearly as complicated as it may seem. Because these engines are batch fired and not sequential, you can use your stock distributor along with a good square wave tachometer trigger source, such as that provided by an MSD 6A ignition box, or even the stock GM ignition module, and don't need a crank trigger or cam position sensor. I'll first describe this EFI system and how it works, and compare it to other closely related systems. These other systems are used in various GM 3.8L engines and are for the most part model year dependent. Don't be intimidated by the different systems and the intricacies of each. I'm only including this as background information and for those of you who may want to deviate from doing exactly what I did, and hopefully to avoid confusion when you are searching for parts. You don't need to understand in detail how each system works, but rather just realize that there are different setups out there in similar cars.

Batch fire fuel injection, sometimes called "group fired", does just that; it fires (opens) the injectors in groups. Sequential fuel injection, on the other hand, fires each injector individually just as the corresponding intake valve opens. Supposedly, sequential EFI provides better idle quality and smoother part throttle characteristics, but you couldn't prove that from my experience. From what I've read the engine can't tell the difference between batch fire and sequential fuel injection at full throttle or high RPM. With the batch fire system, the injectors are not fired to correspond with the intake valve-opening event. As it turns out, this is not critical because even at idle RPM the fuel stays vaporized outside the closed valve and has little time to puddle. This is especially true as engine speed increases. It is this batch fire concept that allows us to keep our stock distributor. With batch fire, the ECM only needs to know the RPM of the engine to determine how often to fire the injectors. Even many programmable aftermarket systems, such as Accel's, can be run as either batch fired or sequential. This would depend on whether or not a cam position sensor is available in a specific application. Sequential fuel injection needs a cam position signal. Of course, a distributor can be used as a cam position sensor, but for this it must be configured with the proper electronics to signal the ECM when the intake valve opens.

The 1982 through 1985 3.8L batch fired engines also used a Mass Air Flow (MAF) sensor as opposed to the Manifold Air Pressure (MAP) sensor that is used with the later and much more common Speed Density systems. The MAF sensor makes this setup very flexible for adaptation to engines with different volumetric efficiencies. This is because the sensor actually measures the mass of the air entering the engine. The ECM (computer) then uses this information, along with information from the other sensors, to determine how much fuel the engine needs at any given instant. The effect, then, is that this setup is self-tuning, at least for a limited range of engine variables. With a speed density system the ECM uses the Manifold Air Pressure (MAP) sensor (which measures manifold vacuum), an air temperature sensor, the engine speed (RPM), and the known volumetric efficiency of the engine that is stored in the ECM memory to calculate the amount of air entering the engine. Change the engine volumetric efficiency with the Speed Density system and the whole equation is thrown out of whack, unless of course you have access to the ECM's internal memory. This is why all of the aftermarket systems, which are speed density systems, require a laptop computer to tune for individual applications.

OK, so now we've decided that we want to use a batch fire mass air flow system, and we're ready to go and butcher one of the General's cars to get the only good stuff on it! Here is what you'll need to salvage from a 1982 through 1985 GM 3.8L engine that has a distributor, along with some tips on how to best accomplish this, and the approximate cost of each item. Of course, you might be able to negotiate a package deal and save yourself some money. (Remember, the fact that the engine has a distributor means that it is batch fired, is not sequential, and therefore does not have a crank trigger or a cam position sensor. All of these engines will have a MAF sensor.)

ECMElectronic Control Module (ECM) This is an unpainted metal box with two multi-wire connectors that is located under the glove compartment (remove the plastic kick panel). It will have a sticker on it with the Serv. No. 1227065. Remember to get as much of the wiring harness as possible. This will reduce the amount of wire splicing that you will have to do later. Pry the plastic wire harness holder out of the firewall and cut the wires as far into the engine compartment as possible. BUT, and this is very important, make sure that you unplug the plugs at the ECM before you cut the wires. The reason for this is that the ECM is extremely sensitive to static electricity and you will be well charged after sliding all over that seat. If you zap the ECM through one of the connectors it may not look like it's been toasted, but believe me, it will be toast. Typical cost: $25 (toasted or untoasted!).

MAFMass Flow Sensor (MAF) This is a tubular plastic device, with a three wire single connector, located in the air duct going to the throttle body. Get as much of the wiring harness as possible, but again unplug it from the sensor before cutting the wire. This sensor is also static sensitive, but other than the ECM, it is the only other static sensitive device. This item is in big demand because it costs about $300 new, and it is often missing on salvage yard cars. However, it can also be found in 1986 and, I believe, 1987 and 1988 3.8L engines with sequential fuel injection. I avoid some of the later versions that have a Venturi outer shape because they look like they would be more restrictive. However, I’m pretty sure that they would work. Get two of these while they are still available. Typical cost: $25 each.

Throttle BodyThrottle Body This is what is used instead of the carburetor with Multi-Port fuel injection. In fact, by the way it is mounted on the 3.8L engine, it looks like a side draft carburetor. The throttle body will have the Idle Air Control (IAC) motor and the Throttle Position Sensor (TPS) attached. Again, get as much of the wiring harness as you can (no static worries here as long as the ECM has been disconnected). Also, bring a pair of heavy-duty wire cutters to cut the throttle cable, because it’s difficult to remove from the throttle body with everything in place. An Exacto knife will also be handy for cutting the coolant hoses and removing the vacuum lines without breaking the plastic nipples. Typical cost: $25.

Oxygen SensorOxygen Sensor This is a spark plug size device located in the exhaust manifold. I usually get these from GM four cylinder engines. On these engines they are located on the exhaust right in front of the engine, and are easy to remove with a 7/8-inch open-end wrench. Get only the single wire model. Be sure to cut the wire on the far side of the plug that is about a foot away from the sensor. Typical cost: $10.

 

Fuel Pump RelayFuel Pump Relay This is a small rectangular plastic box, usually located on the passenger side firewall, but sometimes found on one of the strut towers. It will be with a group of three or four other relays that are usually all under one plastic shield. You can identify the fuel pump relay by the four wire colors, only two of which are always the same, independent of year. All fuel pump relays will have a pink/black (i.e. pink with black tracer) wire and a dark green/white wire. Then, depending on the year and model, they will also have either a gray or a tan/white wire, and a black or black/white wire. If you’ve lost track, there are a total of four wires. As you can see Mother is not the only one trying to confuse us! The number on the top of the relay I’m using is 10038490, but I have also seen different numbers. Good luck, I hope it will take you less time to identify this item in the salvage yard than it took me look up all the possibilities and to compose this description! Typical cost: $5.

Fuel InjectorsFuel Injectors To salvage these you'll need to remove the fuel rail and then pull the injectors from the intake manifold. They are often stuck on both ends so bring a tire iron or a large screwdriver to pry up the fuel rail after removing the hold down bolts. Then use Vice Grips to pull the injectors from the manifold. I would recommend getting twelve of these. You'll have to clean and test them (more on this later), and after 15 years of service the "yield" may be disappointing. Also get the fuel injector harness, and as much of the main wiring harness from its plug back to the firewall as possible. Typical cost: $5 each, plus $5 for the harness.

Fuel Pressure AccumulatorFuel Pressure Accumulator (optional) This is a device that reduces noise by absorbing the fuel line pressure surges that are created as the injector groups fire. I used one so I don’t know how noisy it would be without one. Not all models used this component. It is located in the incoming fuel line between the steel line and the flexible line that goes to the fuel rail, and is close to the firewall. You will need a mini tubing cutter to cut the steel fuel line just behind the accumulator, and an Exacto knife or heavy-duty scissors (the kind that will cut a penny) to cut the reinforced flexible fuel line on the engine side of it. You will also have to explain what this is to the bewildered counter man! He’ll say "about $5…. I guess."

ALCLAssembly Line Communication Link (ALCL) connector This connector is located just under the dash, and usually just to the left of the steering column. It is at this connector that an On Board Diagnostic I (OBD-I) scanner can be connected to monitor all of the ECM functions. Don't panic, you're not going to have to go out and buy a scanner! But this connector will be nice to have when you find one of these soon to be obsolete scanners for peanuts at your local swap meet. In 1996 all automobile manufacturers changed to the OBD-II format and now use a different scanner. This connector is also the point where all of the ECM trouble codes can be read using only a paper clip. However, if you do as I did, you won't need this connector for that purpose. I'll explain that later. Typical cost: $2.

Air DuctAir Duct This includes all of the ductwork that will be used between your air cleaner and the throttle body. It will also house the MAF sensor. It is important that this ductwork be air tight, especially between the MAF sensor and the throttle body. Any air leak here is referred to as "false air" because the MAF sensor will not detect it. This condition will result in poor engine performance. There will probably be as many ways of configuring this ductwork, as there will be EFI conversions. The one piece that's critical is the piece connecting directly to the throttle body. This piece must make a sharp turn to allow for hood clearance. I found the one I used (pictured) on a 1985 Buick Park Avenue with the 3.8L engine. It seems to be unique to that model and engine. You'll have to plug the hole that was used for the crankcase breather tube. In our application this piece is used after the MAF sensor so a breather tube connected here would introduce false air. If you use a breather tube it will have to be placed before the MAF sensor. Typical cost: $10.

GM Igmition ModuleGM Ignition Module (optional) This module is located in the distributor and can be used in place of the MSD ignition if desired. A discussion of this option, along with the required wiring diagram, will be included later. Typical cost: $5.

 

 

Electronic Spark Control Electronic Spark Control (ESC) module and Knock Sensor (optional). The ESC module is located on the passenger side firewall and looks like an electronic voltage regulator. The one I have has a sticker on it that reads BTN 882604, and has four wires going to it. The knock sensor looks like a temperature sensor and is located on the upper front left side of the engine. This option will also be discussed later. Typical cost: $15 for both.

 

 

 

Cleaning the Salvage Yard Injectors

The fuel injectors that you got from the salvage yard should be tested, cleaned, and the rubber o-rings should be replaced. You can have this done or you can clean and test them yourself if Tester / Cleaneryou have access to an air compressor. I did this by building the tester/cleaner pictured here. It consists of a Sure Shot spray can from Harbor Freight (www.harborfreight.com) P/N31059-OUHH ($30), with a 1/8" NPT pipe thread to ½" hose barb fitting in place of the spray nozzle (use Teflon tape). Two worm gear clamps are used to attach ½" ID reinforced braided PVC transparent tubing (Home Depot) to the Sure Shot and your injector. You can make-up a wire harness by using part of an injector harness from the salvage yard and attaching a push-button switch and some alligator clips large enough to clip to a 12V battery (wiring diagram below). Use carburetor cleaner (the kind that comes in a spray can), fill the Sure Shot as described in the instructions that come with it, and pressurize the tank to 80 PSI. At first, only release a small amount of cleaner into the hose. This is important in the event that the injector is bad and will not open when energized. If this happens you'll have to loosen a hose clamp to release the pressure and you don't want a full charge of cleaner in the hose when you do this (this happened to me…not fun!). Be sure to use this Wiring Diagramcontraption outside and wear safety goggles! Once you've determined that the injector will open when energized you can fill the hose with pressurized cleaner, and then intermittently fire the injector into a clear plastic bottle to give it a thorough cleaning, check the spray pattern, and insure that they don't leak when under pressure and not energized. Don't fire the injectors continuously because they may overheat and be damaged. You can use the cleaner collected in the plastic bottle many times over.

New Parts List

The remainder of the parts need to complete your fuel injection conversion are listed below. I've included links that you can access to view these items and check the current prices. Simply click on the link and enter the part number in the search box. The exception is with some of the Accel parts. To view most of these you'll have to download their catalog at www.mrgasket.com/acclcat.htm. The catalog doesn't list prices but the link listed here with the part number will.

Intake Manifold and Fuel Rail You must first decide which manifold you want to use, and then decide whether or not you will modify the manifold and/or fabricate the fuel rail yourself. A little later Doug will explain how you can do this if you have access to the right equipment. If you decide to do your own machine work, Racesearch (www.racesearch.com), sells the Accel fuel rail raw stock in 12-inch increments (P/N 74734, $16) up to 6 feet long. You'll need about 21 inches, so figure about $32. Accel also makes the injector bungs, which are available from Summit Racing (www.summitracing.com) as P/N ACC-74740, $86 (for 8). Another source of components needed for converting your manifold to fuel injection is MSD (www.msdignition.com). They use a different approach than the typical extruded aluminum fuel rail. When you're on their web site click to the fuel management section and then open the flex hose file and the flex rail file.

I've been told that the Clifford manifold would be best for converting to fuel injection because it is supposed to have better flow characteristics and already has the injector bosses cast into it. However, this manifold must be used with headers and that's something I didn't want to do. It is my understanding that headers are not the best choice for a turbo setup, which is my ultimate goal. Based on this, and the cost, I chose the aluminum Offenhauser 4-BBL manifold. This manifold is still available from JC Whitney (www.jcwhitney.com) as P/N 73ZX7653A for $230 (wrong picture on web site), and Performance Automotive Warehouse (www.pawinc.com) as P/N 5720. Of course, the least expensive alternative is to use your stock cast iron manifold, or even the stock aluminum manifold. For my setup I had Rance Fuel Injection (www.rancefi.com) do the machine work and weld the injector bungs and fuel rail brackets on my Offenhouser manifold. The total cost for the machining, welding, and the fabrication of the fuel rail was $460. Rance is also an Accel and Offenhauser distributor.

Electric Fuel Pump The stock fuel pump used with this GM system is mounted on the fuel pick-up line inside the fuel tank. To use one of these would require significant modifications to your tank. Instead I used an aftermarket pump that could be mounted on the rear sub-frame. You'll need a high pressure electric pump capable of supplying 45 PSI of pressure, at a flow rate that will sustain whatever horsepower you are ultimately hoping to achieve. I chose the Accel model 74701 which will support up to 500 HP. This pump is available from Rance Fuel Injection (www.rancefi.com) and Summit (www.summitracing.com) as P/N ACC-74701, for about $140. This pump uses barb type hose fittings.

Fuel Pressure Regulator The pressure regulator controls the fuel pressure at the injectors and is usually attached to the fuel rail between the rail outlet and the fuel return line. Fuel that isn't used by the engine is by-passed through the pressure regulator back to the fuel tank by way of a return line. By controlling this flow, the regulator maintains the proper pressure in the fuel rail and consequently at the injectors. Actually, with the stock GM regulator, it is the pressure differential between manifold pressure (vacuum) and the fuel pressure in the rail that is maintained by the regulator. This regulator keeps a constant pressure differential across the injectors. The regulator uses a manifold vacuum reference signal to determine the differential pressure. The stock fuel pressure regulator is pre-set to maintain a specific pressure differential and is not adjustable. Because we are using this setup on the SL6 with different volumetric efficiency than the donor GM engine, an adjustable fuel pressure regulator should be used. This allows us to fine tune the pressure differential, and consequently the air fuel ratio, independent of the ECM during open loop operation. The ECM operates in open loop during acceleration and full throttle. Some aftermarket regulators do not have the manifold vacuum reference feature, even though they are adjustable. I would avoid these regulators since they do not maintain a constant pressure differential across the injectors, but rather only allow you to increase the static fuel pressure in the rail. This means that when you "floor it", and manifold pressure goes up, that the pressure differential across the injectors actually decreases! Not what you want.

I used an Accel adjustable fuel pressure regulator. This is available from Summit (www.summitracing.com) as P/N ACC-74750 ($73). This is a GM style regulator, and as such, mounts directly on the fuel rail via an O-ring interface. For this, the fuel rail must be specially machined. Also, the fuel line fitting on the regulator, for the return line, is the GM Saginaw type, and required a special adapter to transition to the flexible part of the return line. If I were to do this conversion again I would probably use a regulator like the Aeromotive fuel pressure regulator from Summit Racing (www.summitracing.com, P/N AEI-13101 ($130) or the very similar Paxton universal fuel pressure regulator from Jeg's (www.jegs.com, P/N 780-8001690 ($143). These regulators are more expensive but they can be mounted anywhere and provide a convenient common location for the fuel line from the fuel tank, the fuel return line and a flexible line to the fuel rail. These features would be a real advantage if you're fabricating your own fuel rail. They also eliminate one of the flexible fuel lines going to your engine. You will, however, have to adapt the AN type fittings on these regulator to your fuel lines.

Fuel Pressure Gauge You could use a hand held fuel pressure test gauge to perform this function. But one permanently attached to the fuel rail is definitely the "trick" way to go. These are available from Jeg's (www.jegs.com) and others. Jeg's P/N 918-153003, $21.

Air/Fuel Ratio Gauge This gauge is connected to the oxygen sensor in the exhaust manifold and allows you to monitor the fuel/air mixture. For a fuel injection conversion this is needed to insure that the fuel/air mixture is correct under all conditions. This gauge is very useful when making fuel pressure adjustments. It is especially needed to insure that a dangerously lean condition does not exist. Get one! Summit (www.summitracing.com) P/N NRD-M7009, $30, (www.jcwhitney.com) P/N 81ZX5401X, for picture, ($36).

Oxygen Sensor weld-in Fitting (optional) This is the fitting that can be welded in your exhaust pipe for the oxygen sensor. I've listed it as optional because for my application I drilled and tapped (21/32 drill, 18mm-1.5SP tap) the exhaust manifold for an oxygen sensor a number of years ago. I used the oxygen sensor signal to check my fuel/air mixture when I did a 2-BBL conversion.

The oxygen sensor must reach 600º F to operate properly. So, if you use the weld-in fitting it must be placed on the exhaust pipe as close as possible to the exhaust manifold. The fitting is available from Jeg's (www.jegs.com), P/N 764-60406, $9.

Fuel Pump Safety Switch In this application this switch does not serve as a safety switch. It does not turn the fuel pump off with a loss of oil pressure. The ECM performs that safety function because it turns the fuel pump off when it no longer senses a tach signal. Rather, this switch keeps the fuel pump running in the event that the fuel pump relay fails, and in this way takes the place of the oil pressure switch that GM used in parallel with the fuel pump relay for this purpose. This is a "belt and suspenders" approach, and is good insurance. You can imagine what would happen if you were on the interstate, in the passing lane, when the relay failed and you didn't have this back-up system. I used a Mr. Gasket fuel pump safety switch from Jeg's (www.jegs.com) P/N 720-7872, $13.

Electronic Voltage Regulator If you are still using the original style mechanical voltage regulator you should convert to an electronic unit. The mechanical regulator could generate voltage spikes that may damage the ECM.

The electronic voltage regulators provide the solid output that the ECM likes to see, and swap right in for your mechanical regulator with no other changes. The electronic regulator can be identified by the lack of external wire wound resistors on the underside of the unit. They are available from J C Whitney and others. (www.jcwhitney.com), P/N 73DY7133U, $9.99

I had also converted to the later dual field alternator a few years ago. I'm not sure that the earlier single field alternator will support the electrical current demands of EFI.

Injector Seal Kit This kit contains new o-rings, plastic washers and plastic tips for your salvaged fuel injectors. Tomco Inc., P/N 27007, most independent auto part stores (not discount), $12 (enough for eight injectors).

Spectre universal fuel filter This filter will be located between the gas tank and the electric fuel pump. It is important that it have both the 5/16" and 3/8" hose fittings included. The fact that this is a low pressure filter is OK. It will be used on the suction side of the fuel pump. Jeg's (www.jegs.com), P/N 865-2368, $6.

Inline high pressure fuel filter with integral 3/8 hose barbs This filter is used in the flexible high-pressure fuel line at the output of the electric fuel pump. It is available from Summit (www.summitracing.com), P/N SUM-G1512, $18. This filter is rated for 100 PSI.

AN-06 Stainless Steel Braided AQP Racing Hose This is the flexible fuel line used between the 3/8" steel fuel line, (or the accumulator if used) and the fuel rail. Also used between the electric fuel pump, the high-pressure fuel filter and the 3/8" steel fuel line. You'll need about three feet. Aeroquip AQP Racing Hose. Jeg's (www.jegs.com), P/N 023-FCA0603, $16.

Reinforced Rubber Fuel Injection Fuel Line (5/16") You'll need about 18" to use at each end of the 5/16" rigid fuel return line. Any automotive parts store, $8.

Fuel Return Line Kit When I replaced my gas tank a couple of years ago, I had soldered a 5/16" nipple near the top of the tank for the fuel return line. I then used a 5/16" steel return line between the flexible fuel line at the pressure regulator and the flexible line at the tank. Jeg's sells a kit made by Moroso that allows you to plumb the fuel return line into the gas tank filler tube, and is an option if you're not replacing your tank. Of course you could also fabricate a similar adapter yourself simply by soldering a 5/16" hose barb fitting into a filler tube (remove the filler tube from the tank first!). Jeg's (www.jegs.com) Return Line Kit (optional), P/N 710-65385 ($40).

Rigid Fuel Line (3/8" and 5/16") You'll need enough of each to basically go between the fuel tank and the engine. I used steel line but aluminum would be an option. The 3/8'' line is for the feed line and the 5/16" line is for the return line. This can be purchased at any automotive parts store. About $20 total cost.

Jumper Line (Saginaw flair to 5/16") This is needed to adapt the regulator output to the return line if you are using an Accel GM style fuel pressure regulator. Summit Racing (www.summitracing.com) P/N ACC-74731B, $11.

Jumper Line (Saginaw flair to 3/8") This is needed to adapt to the feed line if you use a Fuel Pressure Accumulator from the donor car. Summit Racing (www.summitracing.com) P/N ACC-74731A, $11.

Potentiometer - 20K ohm (optional) The ECM normally monitors the engine temperature by reading the electrical resistance of a temperature sensor. At start-up the engine is cold, the sensor resistance is high, and the ECM provides a wide injector pulse width for an enriched cold start fuel mixture. As the engine warms the sensor resistance decreases, and the ECM reduces the injector pulse width to lean out the fuel/air mixture. One of the performance modifications often suggested for fuel injected engines is to use a lower temperature thermostat. This "fools" the ECM into maintaining a rich mixture for maximum performance. With our custom fuel injected SL6 we can do better than this! By using an adjustable resistor (potentiometer) in place of, or in series with a GM temperature sensor, and with the aid of our air/fuel ratio gauge, we can have manual control of our fuel mixture during open loop operation. By mounting the potentiometer on the dash we can use it at start-up just as we would use a manual choke (if we don't use a temperature sensor). And, we can also optimize for performance at the stoplight (with or without a temperature sensor)!

ChartIf you do decide to use a temperature sensor your stock one will not be sufficient. The GM temperature sensor has a much broader resistance range than the SL6 temperature sensor.

You could locate the GM temperature sensor in the upper radiator hose. I have seen these hose inserts used for temperature operated vacuum switches on certain late seventies SL6 engines. Again, we can still use the potentiometer even with a temperature sensor. With the potentiometer adjusted at 0 ohms the sensor will send a signal to the ECM just as it would with the sensor alone. A suitable 20K ohm potentiometer is available from Allied Electronics (www.alliedelec.com), Allied stock # 753-1216, $9. A good knob for this potentiometer would be Allied stock # 296-1215, $3.

Double row terminal strips These are used to organize and splice the wires from the ECM to the appropriate circuits, and to provide convenient access for troubleshooting. Allied Electronics (www.alliedelec.com), Allied stock # 607-1213 (12 circuit), $2.22 each, Allied stock #607-1253 (16 circuit), $3.35 each, and Allied stock # 607-1123 (3 circuit), $0.60 each. You'll need two of each of these. If you place solder terminals at certain locations they will provide convenient places to connect your analyzer or DVM (Digital Volt Meter) while testing. Allied stock # 607-1003. 20 for $2. The use of these components will be covered in detail in the installation section of this article, which will also include the ECM connector layout and wiring diagram.

Toggle Switches You'll need two switches. One for the main fuel injection system switch, and the other for the diagnostic/field service mode switch. When the fuel injection switch is located in a discreet location it will also serve as an anti-theft device. The engine will turn over but without fuel it obviously won't start. Allied Electronics (www.alliedelec.com) Allied stock # 683-0050, $4.27.

Electrical Test Equipment The only electrical test equipment that you will absolutely need is a Digital Volt Meter (DVM). However, if you don't have a DVM don't run out and buy one. Instead spend the extra $30 and get a $60 digital engine analyzer. With this you will have all the functions of a DVM and the additional capability of measuring injector duty cycle by using the dwell function of the analyzer. You can also use the RPM function to measure frequency and troubleshoot your MAF if that's ever required. I'll explain both of these functions later. Of course, you can also use a DVM and a separate dwell meter if you already have these testers. The Sunpro Model CP7676 Engine Analyzer is an excellent unit and is sold by Northern Auto Parts (www.northernautoparts.com) for $59.

Miscellaneous Items

Wire terminals and crimping tool. Most electronic, home improvement, and department stores, $15.

Soldering iron and electrical grade solder. Most electronic and home improvement stores, $15

Neoprene grommets. To protect wiring that passes through drilled holes. Individually as needed from a hardware store, or as set from JC Whitney (www.jcwhitney.com), P/N 14ZX2737R, $15.

Heavy-duty mini fuse holder (Buss Fuses). These are weather tight mini blade type fuse holders that can be used in the engine compartment environment. You'll need four. Wal-Mart, $2 each.

Mini-Fuses (Buss Fuses). 10amp, 20amp, and 30amp. Wal-Mart, $3/ box of 5.

Installation

Copyright © 2001 Robert DiBiase, All rights reserved