Fault codes 81, 82, 83, 84 with LA3 ecu

[MaxiHP]

I had an issue with the 87 tc T5 the check engine light came on the engine ran on 2 cylinders and would continue to run at 70 but would not accept loads more than 10% greater than the current throttle command. The engine would not idle without part throttle typically 2000 rpm or more and I can smell raw fuel. The check engine light went out and all went back to normal. This happened more frequently and lasted longer. When the check engine light is on and the key is in the run position engine off the fans are on. if the check engine light is off the key in the run position engine off no fans.

I got out the trusty KOEO test and with the check engine light on ran the test. Got codes 81 through 84. Let the car sit and the check engine light out tested it again got code 11. I have a couple of 8UA boxes so I installed one and the issue has not come back at least 2 days of 35 mile commutes to work each way so 140 miles. I installed the LA3 box and the problem is still present. It does not appear to be coolant temperature related but it has not happened when the engine is cold. I have not tried to cool the box or warm it up to see if there is a thermal issue with the ecu. I did open it up and see no traces burnt or obvious cap/amp issues. All the joints look good but I have not given it a real deep dive.

I read the 8UA is a different animal than the LA3 auto vs man but there may also fan relay and Boost Control differences having that in mind did I really isolate the issue to the ECU. I haven't found any technical details on the pin outs or the updates to the mid year release to the 8UA. I know the processor speed is faster but are there actual differences in the pin assignments? Does the 8UA run the relay control box the same as the LA3 or is there an updated interface that was also part of the 8UA?

To run the fan I bypassed the ac pressure switch and the single fan runs continuous with the engine running (long story car has no ac pump or condenser). I believe if the root cause is in the vehicle it is a ground issue and or a signal return I am looking to split the issue in half and test the most likely path. As a last bit of information the Alternator is charging @ 17V and the feedback wire is sensing 17V so there is a regulator issue that I need to dig into, dose the vehicle reference voltage get in the way 17V is iffy or is this an isolated issue? I could get it hot run it with the regulator not wired and see if this impacts it but that is only if there is a reason to. What /where are all the ground points that need to be addressed.

First things first fix the basics, I don't want to bypass the fan or the boost controller the car should run right then go after the mods.

Whew that was a lot I hope it is a clear path to the issue I have and someone can point me to a logical fault tree.

[Stinger]

Sounds like a faulty ECU to me. It's 30 years old so it's common.

8UA is very similar to an LA3 but with trans control and small changes to the timing curve and boost control to make up for the POS auto trans. You can swap them back and forth without issue though. I'd just run it and assume the ECU is bad unless the problem returns.

Charging voltage should be an isolated problem but needs to be fixed before you burn up anything else, including the battery.

[MaxiHP]

I took a closer look at the ECU and one of the caps looks to be leaking cheap enough to change I'll get that done and post the results. Just so someone else has a path to the root issue or can eliminate it. There are a lot of gremlins in a 30+ year old original car thankfully it is from northern cali so it is clean but the paint is sun beat to death.

Just for clarity the 8UA and LA3 pin assignments are equal except for the pins 42 & 53 3-4 shift control? You know the internet never lies but the people who post on it add misery to the equation I can't trust what I read so I come to the expert.

Thanks for the help

[Stinger]

Pinouts are the same for all 87-88 TC ECU's other than what's not used (trans control) and nothing needs to be done to swap an 8UA in place of an LA3.

[MaxiHP]

Solved the problem by replacing the capacitors finally got the chance to swap the ECU and drove it for a couple of hours so far so good.