All;

Those that have been following the adventure as I get closer to being able to start the engine for the first time, I had a massive epiphany this afternoon while tracing wires. My questions here are directed at the 3.4 DOHC wiring harness gurus please.

Way back when I stated a 3.4 DOHC swap, I started with 94/95 engine. I had erik here build me a harness for the 94/95 with a 91/93 ECM. All great but I never ended up going forward with the 94/95 engine. I found a 96 crate engine that I grabbed. 14-15 odd years later, I am actually putting the engine into a Fiero project. Now, I went along my happy way completely forgetting that I had a 94/95 harness for a 96 engine swap. Right up until this afternoon when I realized my injectors were not firing at all. I did the D3 and D9 continuity tests and found that those leads went to completely different plug towards the engine than what the injectors are wired to....

Short story long, I realized/remembered I have a 94/95 engine harness trying to fit on to a 96 engine.

Questions for the gurus:

1. Should I just get FieroFlyer or Phonedawg to build me a new harness for the 96?
2. Should I go through the differences with someone to see if I can update the harness myself?

How much different are the two harnesses? Aside of course for that fact that the 96 has an extra plug in the harness which hosts one of the injector wires. How many other differences are in play for the plugs going onto the engine itself, and even maybe to the other sensors??

Thanks
Don

fieroking (Joe Sokol) did the DOHC swap for Nolan when he had the 88 GT.
http://www.fiero.nl/forum/Forum3/HTML/000127.html

He may be able to help you make the changes needed to the harness you have.
https://sites.google.com/si...ngcustoms/contact-us

Found this... 1997 DOHC ECM pinouts
http://www.mediafire.com/fi...onte3.4VinX.jpg/file

Someone here had same problem in 2017 (maybe you?)
http://www.realfierotech.co...4&hilit=dohc#p156814

------------------
My World of Wheels Winners (Click on links below)

3.4L Supercharged 87 GT and Super Duty 4 Indy #163

OK. Thanks for the links Fierosound. That was me over on the other site and I refreshed that site as well with latest progress.

For the 3.4 DOHC folks here, I am further along but into another issue now.

My current status of the wiring and troubleshooting. I believe I have everything wired correctly now but I am still not getting the injectors to fire.
I have confirmed the pink wire going to the injectors has 12V in run. I have confirmed that when putting power and ground to the injectors, they will fire. The three I can get to anyway. I just don't seem to have the signal coming from D5/D9 on the 91-93 ECM. That tells me I am looking to the ECM for next steps.

I have ordered an ALDL connector and hopefully it gets here soon. I tried shorting out the A and B terminals on the ALDL with a troubleshooting light but no lights or codes showed. Not saying there are no codes, just didn't come through with the trouble light.

One point I found in the troubleshooting was B10 in the ECM diagrams says power at all times but I don't get power on B10 until I put into Run?

Are there other sensors or triggers inside the 91-93 that I need to check out so I can get power to the injectors? Any other items anyone can think of that will help push me forward and troubleshoot the ECM before I get my ALDL cable? I will be using TunerPro as well to get the settings and codes out as a starting point.

Any help appreciated.
Don

See here:
http://www.gearhead-efi.com...d&highlight=16211539
http://www.gearhead-efi.com...s&highlight=16211539


Looks like ECM 16211539 was used for both the 3800 and 3.4L DOHC
http://www.gmtuners.com/fil...PCM_Fiero_wiring.pdf

[This message has been edited by fierosound (edited 02-01-2020).]

Its been a long, long time since I did my 96 DOHC into my 88 coupe using a 91 ECM/Harness. I did this b/c I had the low milage 96 motor and wanted to use a manual trans. I didn't want to go thru the process of figuring out all the A/T wires and "specific auto trans" wiring (yellow/purple wires come to mind). I found a 91 Cutlass w/ manual trans in my local Pick n Pull and grabbed the harness/ECM and the trans too.

So now I had a manual harness and 91 ECM and had to graft it with the 96 harness and the 88 Fiero harness. I created a excel spreadsheet w/ all the specific wiring from --> to with color codes and everything. The most important thing I can pass to you is you have to have the Factory Service Manual w/ wire diagram. 91 diagram is a little different than the 92-93. I found this out the hard way by using a 92 wire diagram and things did not line up. Once I got the 91 diagram it made sense.

Bottom line, I had to trace each wire (i think there were 51 of them) from the ECM to the connector. Some of the sensor ends were specific for the 96 motor and not the same as on the 91 harness, so those had to be grafted together. The injector wiring is one part I remember, I think its either the injector ends were different or maybe the batch fire vs. sequential thing??

It sounds like a lot, and it is, but its doable and kind of fun. I did it all on the kitchen table and it took about three days of on/off working. I had Ryan reflash the ECM with all the specific data needed and it worked perfect. No codes and ran great.

In the end I had no issues building my 3800 harness, and that one I did on the motor making each wire the correct lenght and all wires hidden as much as possible.

Good luck.

Rob

[This message has been edited by qwikgta (edited 02-06-2020).]

That Rob;

So, as it turns out, I have had this harness for over 15 years and I reran a pile of the wires making sure I used the 91 diagrams and I was still not getting the injectors to fire. In the end, I figured I would see what codes I am getting so shorted the ALDL and then checked the dash light wire and was completely dead. Oh, great, I have a dead ECM I am thinking. I open up the chip access panel and low and behold, after all these years, I find an empty chip receptacle. So, I never received my flashed chip from the original builder or I received it and put it aside for safe keeping and have since lost it. No idea what it was but in the end, I don't have the chip.

I have contacted Ryan and he has flashed a chip and sent it on Friday and I also found the factory chip from another enthusiast and that is also in transit. I hope to be starting the engine up in about a week or so.

All good in the end as I now know WAY more about the harness swap than I ever thought I would and I know all the wires are correctly run and I also took the time to route the wires a bit better in the end.

Thanks again to everyone for all the help.
Don

I felt I knew so much more about the swap after doing my own harness. Nothing wrong with "plug and play" but when you have to know each wire, what its for, how it works, where it goes, I feel you are just more in tune with the swap. Folks toss around the terms they hear or read on the net, but after you run the wires for each sensor and understand how each sensor works with the others you just in a better spot. It also helps with trouble shooting things. You get a better understanding of how the ECM and sensors work together.

Good luck with the new chip when it arrives.

Rob