Electronic Fuel Injection 101

General Info | Injection System Components | Swap considerations | Engine types | Transmissions
Modifying Current Systems | Troubleshooting | More Info

(Please note: I'm still working on this page. I know it looks like hell.)

General Information
One of the things I get asked all the time about is converting non-injection cars to TPI. Since I'm going to be doing this myself (on a couple cars?) this will help me also. Since this is the case, this page will be written with the focus onto what's required to retrofit (swap) a newer engine (powertrain) or injection system into an older, and probably non-injected engine. (as opposed to swapping TPI for TBI which imo is a waste of effort/time/money - IMO).

Also, sprinkled around in here will be information about fuel injection in general.

ALSO, let me put this in now. Before you shoot your wad on a TPI plenum, we need to understand that the injection system consists of MANY SPECIFIC PARTS. Make sure you get them all, otherwise your TPI Plenum will be an expensive garage ornament.

Why install injection?

TPI - Makes more power up high, Looks really cool, More expensive than TBI
TBI - Makes power off idle, Easier to install, Cheaper to purchase.

Both are generally similar, the main difference is the LOOK, and the fact that TBI has 2 injectors mounted on the intake manifold (looks a lot like a carb), while TPI has injectors which feed each individual cylinder. In reality, TBI is not inferior to TPI.

Swap Considerations
WARNING: READ THIS PLEASE. If you're going to spend $xxxx on an engine, spend the $50 to $100 to get the service manual for the year engine you have, or will be making/emulating (if unsure, pick one and build to that.) The shop manual will tell you everything you need to know about how your particular engine needs to work.

The trick is to make the ECM & power train THINK it's in the car it came from and it will work properly.

You bought it, you own it. Neither I, nor anyone else (who's offering "advice") will come over to your house to fix to help you sort out your mess.

Retrofit (swapping) newer engines into older chassis
It is cheaper to obtain a COMPLETE engine up front, rather than piece together an engine. This also helps so you can get the correct manual for troubleshooting.

Converting from TBI to TPI (often) requires converting accessories too, since the air ducting won't clear the TBI accessory and fan belts.

Older accessories often not compatible with newer engines (put a serpentine belt on your 1972 power steering pump).

Also, the accessory brackets may not fit correctly onto older heads, due to the fact that newer heads have the correct bosses for the brackets while older heads may not.

Pre-1987 heads, (or post 1986 small block heads) have a different intake manifold bolt hole location. You can grind the holes so the bolts line up correctly. Be sure to use a washer under the bolt if you do this.

Distributor drive gears must match the cam being used. Newer engines have roller cams which require the correct distributor drive gear. While the gears look the same, the roller cams require a harder gear otherwise the gear will wear out prematurely.

If using a Donor Car: Record the VIN from the donor car, so that you can retrieve recall or diagnostic information from the GM diagnostic system at a dealership if necessary.

Also, keep in mind that most cars that decide to donate engines have been wrecked. This can cause problems such as cracked or bent items on the donor engine.

Fuel injection calibration. Transmission shift point calibration. ********************************************************************** Understand what you're working on. The easiest way to do this is to study the service manual for the engine you are working on.


Realistic Expectations:
Engine swaps can get costly if you don't plan correctly, don't understand what you're working on.
Injection won't make a slow engine fast, or improve economy.
The way to make an fuel injected engine powerfull is to concentrate on the short block of the engine (more later - cams/compression/cylinder heads)....
The way to improve economy is to lower engine speed by adding an overdrive transmission to the engine or building the engine to make low end power.

Fuel injection offers precise air/fuel distribution.... Due to the fuel distribution, oil isn't washed off the cylinder walls which helps the engine last longer.
Diagnosing engine problems is simple, just dump out the codes.
The engine is smoother at low RPM.

While complex, they're not difficult to work on and troubleshoot if you sort out all the systems and understand what they do.
Reference the particular service manual for the engine.
Get the complete engine if possible otherwise you will spend a lot of money chasing down the appropriate accessories.
In non-standard chassis, be prepared to fabricate items....

General, a small block is a small block, BUT TPI accessory drive belt routing, fitting into the frame, computer & wiring harness. oil, cooling, air intake ducting, exhaust clearance, linkages, fans, hoses

Engines - Considerations and gotchas
Corvette engine is WIDE and low to fit under the hood of the vette.

Heavy (8600GVW) 3/4 ton and 1 ton truck engines are designed for sustained, full throttle usage (i.e. towing). As such, they don't lend themselves to performance street use. They are built for heavy duty durability (low compression, small valves, heavy valvetrain).

TBI = mild cam, strong off idle performance. TPI begins to make power above 2000 rpm.
TPI is more difficult because you have to consider the air cleaner & ducting. Also, many TPI cars (not trucks) have pass-key systems & cooling system fans which add to the complexity of the wiring harness.

1985 - 1987 TPI engines use fan belts.
1988 - 1992 TPI engines use serpentine belt.
(air conditioner/air pump considerations)

1990-1992 TPI (LT-1) don't use a MAF sensor.

Distributor interchangability
1985-1986 - Old style big cap, internal coil, 8mm wire
1987-1992 - New style small cap, external coil, 7mm wire
Wiring is the same, but the electrical connectors are different. Ignition advance is controlled via ECM, so neither distributor has a vacuum or mechanical advance.

Injection System Components
ECM (Engine Control Module) / starting in 1992 renamed to PCM (Powertrain Control Module) "the computer".


The only thing the ECM drives on the dash is the SES light Definitions of sensors/Systems VATS/Pass-key Knock sensor 350 PROM or custom prom. **************** Wiring Fuel system Cooling - overheating will ruin your new engine. Oil pressure fuel pump switch VSS Vehicle speed sensor - if equiped. Air Injection hose routing Throttle cable - make sure throttle opens fully, doesn't bind. TV (transmission throttle valve) cable

Modifying the Injection system
The hot ticket or money mods to spend on "improving" your injection system is: Larger throttle body. Larger plenums I'd say spend the money and install a fuel pressure guage. Bolt on "better" heads Switch the cam Install headers Larger engines require the following: Standard engines are either 305 or 350 cubic inches. So, if you plan on building something larger than a 350, you should AT A MINIMUM install a 350 knock sensor and PROM. Depending on compression/cam, will require Custom prom (links to this). larger fuel injectors or increase fuel pressure and use a fuel pressure regulator.

USING NEW TRANSMISSIONS Retrofit (swapping) newer transmissions into older chassis. Pre 1986 700R4 tranmissions are considered junk. Avoid them if possible. Using an older, non-overdrive tranmission will hurt the low speed drivability of your fuel injected system.

Transmission wiring, Lock up converter, 4th gear switch. grounded or ungrounded. (other stuff if electric trans in use)

Prior to 1992 the ONLY THING THE ECM CONTROLS IS THE torque converter lock up. The ECM has nothing to do with shift points.

The "electric" (4L60E and 4L80E) must be used with a computer. Speedometer cable provisions. cable driver and/or electric speedometer. VSS.

The 4L60E doesn't use a governor.

Truck splines are longer. Corvette uses independent rear suspension, while the Camaro uses a live axle. PNR (park neutral reverse) switch. Tailshaft housing 700R4 and TH350 use the same output shaft. The 700R4 is 3" longer than a short shaft TH350, and the right side of the valve body is wider. The rear mounting pad of the 700R4 is 1.75" further back than a TH350. This will require using either a TH400 crossmember, or a crossmember from a car that had a 200R4. For more transmission info. See over here.....(?) or from there to here?

Common Troubleshooting
Fuel pump croaked
Ignition coil croaked
ECM Diagnostics - dump the codes and see what they say.

Fuel Injection links:

DIY Fuel Injection

Last updated: 6/11/1998
Author: MadMike Maciolek
Email: iracez28@stc.net
Email: m_maciolek@vmsnet.enet.dec.com

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