Installing a new ECU harness (1 Viewer)

[alia176]

Happy weekend everyone, just wanted to share some random thoughts with you regarding our aging ECU harnesses. Several weeks ago I swapped out the ECU harness, while doing other things like a radiator swap, fuel pressure gauge hookup solution, catch can install, turbo exhaust leak fix, rear heater delete, ABS/LSPV delete, TBI coolant hose delete etc.

I've had a turbo for a few years, and even before that, I was experiencing random lean codes. The O2 sensors were just fine, regardless, I still swapped them out with the appropriate Denso units for the upstream and downstream. Not that it matters, the downstream sensor really doesn't do anything useful.other than let you know your cat is not efficient.

In any case, I made some interesting observations that I wanted to share with you and it's applicable whether or not you are forced induction or not.

First and foremost, all check engine light codes went away and stayed away. No more lean codes, no more any other naggingnfault codes. Additionally, this engine literally woke up from a long slumber. I realize that I have a turbo for additional horsepower, but it was the way the engine management behaved that I found to be astounding.

She simply runs much more smoothly. She holds harder gear going uphills even longer than she should. I used to have this annoying random miss during idle, that totally disappeared. I bet my MPG improved by a fractional amount, but who cares!

Some tips that you might find useful. Do this project when you are taking the upper intake manifold clamshell off for other projects like vacuum hose replacement, , etc. Plan on taking an entire day for this project and having a second pair of hands is really useful. In my case, I needed my daughter's narrower elbows and fingers to get to some of the things. Additionally, she can hunch over an engine bay for a lot longer than I can! Whenever I do any projects under the hood, I remove both front wheels then drop the whole thing down as low as possible, practically resting on the front radius arms on top of 2x4s to make it easier on my back.

I did shoot myself in the foot by not taking great care at disconnecting the transmission / transfer case harness from the main ECU harness. This is where I want you to pay close attention to what I'm writing. Absolutely disconnect the transfer case / transmission harness completely and pull it to the driver side of the transmission tunnel then let it hang. Afterwards, climb into your driver side wheel well, then take your time at disconnecting the two harnesses. Seriously, take your sweet ARSE time here.

I totally mucked up the connectors on the transmission side by being impatient, which made me lose the speedometer signal, as well as the center diff lock signal. Basically she refused to go into four-wheel drive mode while I was inside the Maze district of Canyon national Park. I was able to work around it by doing some manipulations manually, but it was still a PITA to deal with in the dirt. Thankfully I had the EWD with me on this trip and was able to hot wire the CDL actuator motor. Not having cruise control REALLY sucked on a six hour one way trip. The turbo allows one to use their cruise control easily as you might know!

My local U-Pull-&-pay had an 80 so I robbed that transmission / transfer case harness from it and I'm golden once again.

 

[Bludozer]

You're not the first to report a performance difference with a stock ECU replacement. I don't have any intermittent codes so I'm curious to see if I feel any sort of difference once I finally get around to tackling this.

 

[Kernal]

FWIW: Engine Wire 82121-60343:

 

[baldilocks]

Yep, I bought one of the last if not the last 93-94 engine harness available back in 2015 and did notice a difference not to mention had no further concerns about crusty connectors and future issues.

I now own a 96 that is solid but got ignored for a few years. It’s currently waiting refurbishment and build up but the new engine harness is on the parts list already just because it makes sense. Nearly 30 years in a hot, chemical rich environment is a hard life. I’m in the camp that has no problem spending money and time now to very possibly avert an untimely and even more costly break down later many miles from home or a paved road. It’s peace of mind for someone who ventures out alone regularly and, as you’ve learned, can mean restored performance that we didn’t know was lost because we bought the car a couple decades or more after production.

 

[ZackR]

My 94' runs a lot better after replacing the harness, 02 sensors and doing all of the PM under the intake manifold. My old one was pretty wrecked by the EGR pipe and was in such rough shape (crusty with 330k miles on it) I couldn't justify repairing it.

The harnesses for 93-94 are extremely hard to find new since they were discontinued. It took me over a year to find one while the cruiser was torn apart in the garage. I ended up getting one from the classifieds on here.

If you have a 95-97 and plan to keep the truck for any amount of time I highly suggest buying a spare harness while they are available to keep on the shelf.