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GM Throttle Body Injection 1987-93 LO3 (5.0L) and LO5 (5.7L) engines..

This page is dedicated to the owners of these vehicles equipped with GM's dual point fuel injection (model 220 tbi). Although just a small number of cars were equipped with tbi in 1987, this changed very rapidly in 1988 when it was introduced on the F bodies (Camaro and Firebird) and expanded to include the Chevrolet Caprice, Monte Carlo and the truck lines as well. 1988 was the last year of carburetors  on GM's passenger cars.

Many vehicles were also equipped with the 2.8L V6, 4.3L V6 and 7.4L V8 (trucks) with the model 220 tbi and many  procedures are the same as for the 5.0L and 5.7L engines.

Although basically ignored by performance enthusiasts because of their limited performance potential, these systems perform extremely well, requiring very little maintenance of the tbi itself and is very simple in design.  They still suffer from the same mixture distribution problems as a carburetor, because of the wet manifold design, but since the mixture is very closely controlled by the ecm, the calibrated fuel requirements can be adjusted much more rapidly and with greater precision than ever could be achieved by an carburetor. 

Many are discovering the tbi is a cheaper alternative to the more exotic tuned port, readily available, easy to install, and the same brackets and accessories originally on their vehicles can be maintained. One note here is that if you plan on using the tbi on your 1986 and earlier heads, the two center bolts on each side of the tbi manifold (4 total) will have to be machined angle to match the earlier heads. Other than installing a electric fuel pump (15 psi maximum), fuel lines and adding the proper harness and computer, the system is very simple to install and maintained.

ECM Applications: This will help you identify the different ecms so you wont get the wrong type for V8 applications.

Page of 1228746 ecm schematic

Page of 1227747 ecm schematic

Page of 16136965 ecm schematic

All Chevrolet TBI's use a speed density fuel calibration, using a map sensor, much like the speed density tuned ports. They also use a tps, mat , cts, and have a idle air control system. They also use a esc module similar to the 86-89 maf tuned ports and require the proper knock sensor to mate with it. The tbi esc modules are different between the engine sizes and families.

The est distributor module sends the signal to the ecm to synchronizes the injector pulses, alternating the injectors pulses from right to left. There is also two pulses for each injector per engine revolution so the correct mixture is present when the intake valve opens. This is the reason given the SBC  firing order you don't have a miss or lean out with two adjacent cylinders firing on the same bank (cylinders 8-4, 5-7).

One thing about tbi, is that if you suspect a faulty injector, you can hook up a timing light and point the beam at the injector and see the spray pattern, and see whether or not it is correct or not.

The same troubleshooting techniques for a no start is the same as for tuned ports. See troubleshooting page.

Throttle body assembly

As you can see from the above diagrams, compared to a carburetor, the tbi is much simpler in design.

The injectors are designed to allow possible fuel vapor to rise to the top and dissipate through a channel to the return line, which the pressure is controlled through the regulator. That way only liquid fuel which is heavier is allowed through the metering point on the injector.

The regulator has four screws that hold the pressure spring against a diaphragm much like a tpi regulator. The same principle of operation applies. There is an adjustment screw inside which is held in place with a large spot of solder. Although it is possible to raise the fuel pressure it is a harder procedure to adjust it because you would have to removed the injector assembly.

Be careful in pulling a distributor to use on your TBI engine. The distributor to the left is used on the 1987-1992 Caprice,  Camaro/Firebird. Note the smaller base as compared to the distributor on the right, these larger base distributors were used on some 1992 and all 1993 TBI equipped engines, such as the Caprice. They use the TBI throttle bodies which are held down with two studs for the air cleaner, and the manifolds are machined for the large base distributor they use. They will not interchange.

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