I could never get my 1985 305 tpi engine to run correctly. If I got the engine, harness, ecm, and tune port system out of an 1989 350 tpi, would it go right in no problems? It had the same trans as well.

 

The 1985 ECM harness is a 'independent' harness in that it's separate from the ENGINE harness. The 88-92 Harnesses are a huge 1-piece harness that merged the ENGINE & ECM together. If you were to swap , keep in mind that you would be swapping almost all of the wiring in the engine bay. This includes the Headlight harness and Wiper motor too because the wiper wiring was moved from ENGINE harness to the Headlight harness in 88 and the wiper assembly was redesigned that year too. ( 88 Wiper will bolt-up OK, but the plug is different.)

There are other things to keep in mind depending on what year your replacement harness is:... ( 88 was cold start - 89 was not for example), and there were probably some minor changes to the C100 and C207 connectors too ( Dash harness-to-Engine,.... and Dash Harness to ECM Plugs ). You migfht have to re-pin / splice some of those wires to make everything fully compatible.

Al that stuff CAN be swapped over,....... but don't expect it to be plug and play.

 

I have an 86 that I purchased without and engine. The ECU was missing and the previous owner had hacked all of the wires off of the engine bay. I bought a 89 for a good price with the engine and transmission in it. Engine and transmission were good. The previous owner started restoring it. So, the 89 was mostly taken apart. A lot of missing body parts. The interior was stripped. Anyway, I decided to put the engine and transmission from the 89 to the 86.

Currently, I have the engine and transmission installed. I have also transferred the engine and ecu wiring. I started transferring the dash wiring. That's when I ran into an issue. As stated before, the 89 wiring is pretty much one piece. The harness goes from the dash back to the fuel pump. It's been a pretty major job so far. Hopefully, I will have it done before spring gets here. LOL.

 

So would it be easier to get a 86-87 ecm, harness and everything?

 

Yes. If you could get the 86-87 ECM, harness, and everything, that would be easier. The body wiring is what's been a pain for me.

 

BINGO !

The ENGINE harness in your car right now is separate from your ECM harness and the ENGINE harness can remain in place if it's OK. ( Starter, Distributor, Gauges, Wipers, Alternator, Starter, E-Brake, HVAC )

If you get an 86-87 ECM harness you'll only need to watch for 'little things' such as if the ECM & harness is made for Auto/Stick compared to your car. ( Auto version needs the Tranny TCC plug on it; reverse light wiring different) The 85 was a one-year ECM system, but almost all it's wiring is directly compatible with the 86-87 plugs, accessories & connections. Some 87 TPI harnesses are made for single fan and some are made for duel fans. ( * 87 ENGINE harness changed due to small cap Distributor and Alternator wiring changes )

The 85 TPI was one of the strongest 'seat of the pants' TPI Thirdgens I've ever owned; too bad your not feeling the same thing. The 86-87 had a 'better' ECM so if you're 85 engine isn't "DEAD" yet you could/should consider the 86-87 ECM/Harness as an "upgrade" and convert the ECM/electrical before resorting to a complete Engine swap. ( just a thought )

 

Why not just repair the TPI system the car already has? You may get in way over your head if you attempt to replace the entire harness/computer with that from a different model.

 

I bet that 90% off the parts for my tpi setup are new parts or parts that have been changed. You name it, it has been replaced. I have tried three correct different ecms and proms and nothing has changed. I am actually out of ideas and anybody that I take the car to, asks me what I have already done, and then they decide they don't won't to mess with it either.

 

Do you have a GM factory shop manual for your car?

 

I don't have a GM one, but I have a Haynes and Chilton one.

 

You need to find (ebay, craigslist, etc) a GM shop manual, and then go through the troubleshooting steps to find the problem. Those aftermarket manuals are notoriously incomplete; if any of them contained everything you need, they'd be the size of a Helms manual.

The point I'm trying to make is that if you've been unsuccessful at finding the problem with your existing setup, trying to completely replace it will likely not end well for you. And as far as finding a repair shop willing to work on a 30+ year-old car, that's a tough nut to crack; shops specializing in such work are few and far between, are very expensive, and not all of them are as good as they claim to be.

 

I agree on the Haynes manuals. The are usually missing information. Years ago I purchased a fuel injection manual that helped me out with diagnosing those systems. I think I still have it around somewhere. I'll have to look for it.

 

 

I have an '87 harness and computer for sale PM me if interested

 

Just curious; ever Pull the intake off ???

Passages get full of carbon crud and that crap can - and does - block the EGR ports. If you ever pulled the intake you would/should have noticed the carbon build-up. If you never pulled the intake than you would probably never notice it.

 

Yes sir, I have. Well not the base intake, but the plenum and runners. And they were full of carbon. I eventually plan on pulling the intake off and getting it dry ice blasted like I did on the plenum and runners.