I have a 91 camaro rs with tbi. I recently purchased a tpi manifold and intake to upgrade. I beleive it is a MAF type. I have a few questions. My first one is how do I tell if I have a MAF or Speed density type intake. 2 I was reading the Tbi to speed density repinning thread and was wondering, if I modify my harness to wire the injectors and I have a MAF type intake, do I still have to repin the harness or just change the chip in the computer. 3 Do I need to change my distributor or will my tbi distributor work just fine. If this is not the correct area to ask these questions could you please direct me to the correct place. If I think of anything else I will ask.

 

1985-1989 MAF / 1990-1992 Speed Density

MAF TPI setups have 9 fuel injectors. The ninth one operates during cold start conditions to make the run richer. The speed density cars just pulse all 8 injectors more to compensate for lower engine temps. The ninth injector is in between the runners on one side of the base plate. Can't remember which side. It's easy to spot as it has an aluminum fuel line that runs out of it into the back of the fuel rail. The speed density ecu and harness will work with either intake as it does not NEED that extra injector. The MAF ecu and harness will not work with the 90-92 speed density setup as it NEEDS the ninth injector.

You will have to get a different harness for either setup. A TBI ecm cannot drive a TPI setup. The injector driver circuits cannot handle the load of the extra six injectors and will burn out. You will need the appropiate ecm for whichever TPI control you decide on (MAF of SD).

Your TBI distributor is the exact same unit used in all TBI/TPI 305/350 cars and trucks including TBI 454's, but excluding the 1985 corvette.

 

I have an 85 IROC 305 TPI WITH MAF Burn-off relay that sits above/below the ECU. What wires connect to it, color, and clip?

 

- TPI intake manifolds that used a MAF sensor have no bracket on the side of the plenum for a MAP sensor.
- All speed density manifolds have only 8 injectors
- 85-88 manifolds have 9 injectors
- 89 manifolds have 8 injectors, but used a MAF sensor

 

Incorrect. The MAF ECM (1227165) will work just fine with 8 injectors. Simply update the calibration in the prom to 1989 TPI.

GM did away with the 9th injector in 1989.

As info...the cold start injector circuit is bundled with the rest of the fuel injection harness, but the ECM does not control the 9th injector. The injector is controlled by a temperature switch and only receives power during crank.

 

the pinouts on the bulkhead connector (c100) were different from 89 -91 if you use an 89 harness the connector will need to be repinned. If you get a harness from a 91 tpi and use the sd computer you won't need to worry about it.

 

Cool. I never heard that. But we never went any further than swapping stock parts to make a system work.