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Junkyard Fuel Injection Conversion

Posted in How To: Engine on January 9, 2018
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Photographers: Trenton McGee

Fuel injection, it’s the wave of the future. Well, at least it was in the late 1970s and early 1980s. This was really the dark ages of fuel delivery in cars and trucks. Carburetors worked pretty well until automotive engineers had to worry about fuel economy and vehicle emissions. The first band aid to improve economy and emissions was to load engines with emissions-choking devices like smog pumps, huge EGRs, stuffy catalytic converters, and computer-controlled carburetors. None of this worked too well until electronic fuel injection introduced atomized fuel and electronic feedback systems. Efficiency went up and emissions went down with a system that could properly self-regulate fuel air ratios.

Enter Dino the Dinosaur, our 1970 Chevrolet Suburban 4x4 with a long story to tell. Predating both emissions controls and expensive fuel, Dino drinks gasoline like a fish. The truck originally came with a 307 V-8 fueled by a one-barrel carburetor. In the late 1980s the tired 307 was replaced with a remanufactured Chevy 350 and the one-barrel carb was swapped over to the new engine, which delivered fuel to the newish engine for the next 31 years without too much drama. Recently the carb was in great need of a rebuild, but we wanted to give Dino more power and better fuel economy and to improve drivability. We dabbled with the idea of adding a Motorcraft/Autolite 2100 two-barrel or even a Quadrajet four-barrel carb, both of which are known as good off-road carbs.

Another alternative that would bring Dino up to the standards of the late 1980s and early 1990s was to do a junkyard rebuild and install a GM throttle body electronic fuel-injection system. We have dabbled in GM TBI a few times on other projects and knew it was a simple, reliable, and fairly efficient system. The best part is there’s aftermarket support for GM TBI and the systems litter our local junkyards. Unfortunately it’s not quite as simple as bolting a throttle body onto the engine, but with a little research we were able to piece together a running system that could be replicated for virtually any V-8 with a displacement around 260-400 ci. Also GM TBI has a rudimentary onboard diagnostics system that can help indicate any problems with the system, and the system can be modified to run on a wide variety of makes and sizes of gasoline engines.

After gathering the parts needed to add GM TBI from our local junkyard we began piecing the system together. If used parts make your skin crawl, you can order a full TBI retrofit kit from a company like Howell EFI, which bases its system off the same tried-and-true GM TBI system we pieced together. We decided to do a little bit of both using some new and some used parts to piece our system together.

Scouring the junkyard yielded a ton of different TBI trucks and cars. We like to focus on the 1987 and 1995 trucks and vans since they seem to be more consistent and plentiful than TBI cars. The main part you need to find is a throttle body with injectors that gets close to your engine’s cubic inch displacement. Since Dino has a 350 we want to find a truck with a 350, although many of the parts from a 305 truck and some from a 4.3L truck could work. Ideally you can find a totally complete truck with wiring, sensors, throttle body, and even ignition parts. In that case grab everything from the one truck. In our experience you will probably need to piece things together from multiple vehicles, as people pirate just one or two parts. This truck has the wiring, throttle body with injectors, ignition, and some of the sensors. That’s a good place to start.
Snagging the injectors and computers seems to be popular with junkyard scroungers. The injectors are specific to the engine size and are color-coded to indicate which engine they came on. These systems came on everything from 4.3L V-6s to 454 big-block engines, and the injectors have two colors of paint on them depending on how much fuel they flow at a given pressure. The color-coding paint seems to be fairly fragile, so it can be difficult to tell which injector is sized for which engine. These injectors are blue and yellow, indicating a 4.3L. So this throttle body with these injectors would be good for a V-6 of roughly 3.8L to 4.3L displacement. By the way, the actual throttle bodies are the same for 4.3L and the small-block V-8s; they interchange. The throttle body is physically larger for big-blocks, although the injectors will swap between the bodies along with the sensors.
The throttle bodies are generally very dirty from the junkyard but are easy to rebuild with a kit from just about any local auto parts store. You’ll need some small Torx bits to disassemble everything. You can send the injectors out to get flow tested and cleaned if necessary. We used WitchHunter Performance. Keep track of how everything goes together. We removed all the gaskets and sensors and cleaned the metal portions of the body with carb cleaner. Sensors can be cleaned with electronics-safe throttle body cleaner. These throttle bodies are marked 4.3L and V-8 and ready to be cleaned up and rebuilt. The spring and diaphragm in the back of the unit regulates the fuel pressure and is critical. If the spring is damaged you must replace it with the correct spring for your application. There are also kits that allow you to modify the pressure regulator so that it’s adjustable. That is desirable if you want to run the system on a modified engine.
Some of the many sensors are critical to the system functioning, and some are critical to the system functioning with all of the onboard diagnostic functions. You’ll save yourself time and money by grabbing the manifold absolute pressure (MAP) sensor, knock sensor, knock sensor control box, O2 sensor, EGR solenoid, and some of the ignition wiring, including wires, coil, and ignition control module (ICM) if you want the computer to control ignition. Alternatively you can have the computer control only the fuel system. You absolutely have to have the O2 sensor, MAP sensor, TPS, and temp sensor. The system will run without the VSS, knock sensor, and/or EGR parts, but the check engine light will be illuminated and the system will record faults associated with those missing sensors. Here you can see part of the wiring harness, the TPS sensor on the left, the EGR control solenoid in the center, and the MAP sensor on the right. Some sensors vary from early to late TBI systems so mixing and matching sensors can get complicated.
You can run GM TBI with lots of ignition systems, but by far the easiest is to run it with an HEI style ignition like the factory did. For Dino we needed a GM small-cap HEI distributor, which you can snag at the junkyard or get from the aftermarket. In our case junkyard parts would work, but we wanted the reliability of new parts in Dino’s ignition system. We used this PerTronix Flame-Thrower EST Distributor (right). Next to it is the PerTronix Flame-Thrower Stock Look Cast Distributor (left) that we would have used if we were keeping Dino carbureted.
We also used a PerTronix Flame-Thrower HEI Coil. We reused a GM factory coil mount and modified it to fit the PerTronix unit. We also grabbed an ignition control module and the pink and white wires (shown here on a computer) that run from the coil to the ICM and from the ICM to the distributor.
Speaking of wiring, you can either trim down a factory wiring harness to work with your TBI conversion or you can buy a harness from the aftermarket. Several websites explain what to trim and what to keep, but we prefer the threads on the topic at Binder Planet (binderplanet.com/forums). After all, if it can make GM TBI run on an old tractor engine it should work on just about any gas engine. We went with the Standard Length GM TBI new replacement harness from Painless Performance Products (PN 60101, $520).
If you are pulling the harness from a junked truck you’ll want to start at the throttle body and follow the wires to the fuse block and to the firewall. You’ll have to pull part of the harness from inside the truck through the firewall. This bundle of wires follows down to the firewall grommet. You will need to remove and pull the interior wiring through the waxy weather-seal material and plastic firewall plug with hot water or a heat gun. You will trim most of the wires out of this plug. Take your time. When in doubt, follow a wire to its end before cutting it. Chances are one way or another you’ll have to make repairs to any harness, but that’s not a big deal.
Newer trucks will have an underhood power distribution center that you can partially reuse. Older trucks will have these relays, fuses, and fusible links. Take all these off the firewall and bring them home; just don’t count on using most of the fusible links.
You will also need to pull the computer that runs this whole show. It’s usually behind the glovebox liner on the passenger side of the dash. You generally want the one with PN 1227747 and, for our 350 Chevy, the broadcast code (BCC). Unplug the connectors from the computer and you can cut the wires under the dash. You will need to splice in new wires for the check engine light and the ALDL connector. Also grab the ALDL and 6-8 inches of its wires from under the dash near the steering wheel.
Once home, it’s time to research how to pare down the wiring harness. That’s best done by reading lots of the TBI tech threads on Binder Planet (binderplanet.com/forums). The most useful thread is called “Step By Step Real World Build Up” in the Injection Tech section of the forum. Special thanks to the folks who assembled all this info and maintain the site. Here is a harness we pared down and some of the wires that we pared out after trimming off all the wire loom and electrical tape. You can also see how almost all of the wires are labeled, including the ones we pared out. See the black plastic box under the wires? That’s the bottom of the underhood power distribution box from a 1995 Chevy truck.
Mechanically, getting the TBI onto your engine should be pretty simple. There are tons of adapter plates for two- and four-barrel manifolds, and let’s face it: You can “machine” an adapter out of aluminum on a drill press with a little knowhow. We got in touch with Edelbrock for one of its Edelbrock Performer T.B.I. Intake Manifolds (PN 3704, $344.95). We did have to modify the intake to work with our early small-block heads by ovaling the four center bolt holes and using special hex-head bolts on those four holes.
Fuel delivery is easy for us because we just installed a new gas tank from a 1990s Suburban, which had factory TBI fuel injection. We used a new AC Delco in-tank pump. In our experience these systems generally work better with in-tank pumps, but since they are low pressure you could get away with an external inline fuel pump like an e2000 (from a 1989ish Ford F-250. For an external inline fuel pump we usually run a clear prefilter between the tank and then a high-micron, fuel-injection-ready fuel filter ahead of the fuel pump. This helps keep the fuel pump happy and still filters the fuel for the fuel injectors.
Connecting the fuel feed and return line to the system should be pretty easy. You true junkyard scroungers can reuse the fuel lines from your donor truck, or if you want to run push-lock hose or the like with -AN fittings you’ll need two adapters: one 12mm-by-1.25 O-ring seal to -6, and one 14mm-by-1.25 O-ring seal to -6.
Wiring the system should be pretty straightforward after you tackled paring down the harness. It was simple for us with the Painless wiring harness because all the plugs are in place and are clearly labeled. We used a hole-saw to drill through the firewall near the passenger-side valve cover.
Here is the harness laid out on Dino so we can fine-tune where everything needs to go. The part of the harness to the right will be inside Dino’s cabin, and the wires on the left will go to the throttle body, O2 sensor, fuel pump, VSS, and so on. Speaking of VSS, you will need a two-pulse, square-wave signal. We were able to find one on the internet. Howell EFI, Novak Conversions, and others should be able to supply one if you want to run it.
We plan on mounting Dino’s computer in a reproduction glovebox. We mounted the ALDL and check engine light under the dash close to the ignition witch. Again, to ensure that the onboard diagnostics work in Dino without the check engine light on, we are running all the factory sensors, including a VSS, an EGR solenoid (which is not hooked to vacuum or an EGR since Dino doesn’t have one), a knock sensor, and a knock sensor control box.
To finish off our install in Dino, we scrounged up a GM TBI air filter housing and wrapped the new wiring with Painless Performance ClassicBraid. We did our best to hide any evidence that Dino is fuel injected. We probably should have painted the intake manifold to match the engine and valve covers. After all, we want it to look the same yet function as well, if not better, than it ever has.

TBI Parts We Used on Dino

… except for those we forgot. Many sensors and parts can be sourced from the internet or your local parts store for a 1987-1995 Chevy 1500 Suburban with a 5.7L V-8.

• Throttle body with injectors (junkyard)
• Throttle position sensor or TPS (mounts to TBI) (junkyard)
• Idle air control motor or IAC (mounts to TBI) (junkyard)
• Wiring harness (Painless Performance)
• Temp sending unit (parts store)
• O2 senor (parts store, or junkyard if you’re feeling lucky)
• Oil pressure switch (we didn’t bother; Dino has an idiot light, but you could acquire the switch from a junkyard or parts store)
• VSS (Internet, Howell, Novak)
• Intake or adapter plate (ours came from Edelbrock)
• Knock sensor (junkyard or parts store)
• Knock sensor controller (junkyard or parts store)
• Fuel pump (parts store; ours is for a 1991 Suburban in-tank unit with tank; for inline use, a late 1980s Ford F-250 fuel pump)
• Fuel filters (parts store)
• Fuel line and fuel fittings (parts store or online)
• Coil (PerTronix)
• HEI distributor (PerTronix)

Sources

Painless Performance Products
Ft. Worth, TX 76105
800-423-9696
www.painlessperformance.com
PerTronix Performance Products
San Dimas, CA 91773
909-599-5955
pertronix.com
Edelbrock
Torrance, CA 90503
310-781-2222
www.edelbrock.com
Binder Planet
binderplanet.com/forums

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