hey fellas im interested in knowing if i can mod the harness out of my old 86 iroc to work on my 89 formula 350 tpi. im looking to put this motor into my 90 gmc chevy pickup. thanks for all your help. Btw i used to have a name here and i cant remember what it was lol

Henry

 

As long as the harness from your 86 was a TPI also, and the 89 is MAF also (dont remember when they changed to MAP) it'll work.

Matt

 

You will need to bypass the VATS relay under the drivers side up in the dash, and use a VATS disabled prom to use the complete harness. Otherwise it's very similar. Best bet is to find the pin-outs on the ecm for VATS and splice in your old harnesses connections and keep VATS.

 

I tried using my 86 tpi harness in my 89 application--it didn't work for me! Car ran like crap--blew black smoke, over heated and had no power! I went w/the right harness. I had to completely wire the whole car tho.

 

A harness has nothing to do with how a motor runs. You didn't have everything hooked up properly, or there was a problem with the harness that you weren't aware of. Other than the position of the alternator and a/c compressor plugs, the fan plug(s), the distributer plug, and the cold start plug, the two harnesses are the same.

 

Maybe the guy who did it originally didn't have everything plugged right-because it did run like crap! I had to re-do the complete harness. Motor runs great now.

 

Another difference I though of is where the distributer hooks up. The 86 has the coil-in-cap setup and the later has the divorced coil.. The plug is different but is simple to adapt.

 

on the 85 TPI I had, it was an external coil

 

My 85 has the coil in cap. I have an adapter harness to run the 89 computer in my 85. Not usre everything is set up ok on it because the car runs leand and gives weird codes like the A/C is on when it isn't. (According to the guy who hooked a scanner up on it. I'm going to modify that harness to work with an SD computer.....