420A 1996 Possible Bad ECU?

[Goreb]

Hey guys,

Finally deciding to post here to find any guidance on the electrical issues on my 1996 420a Talon, I've been having since June. I am at the point where I'm wondering if the ECU is failing. I have read through all the forums trying to find a related issue, yet was unable. So, here I am posting..

I'll describe the few problems I'm having and then what I have done to try to fix it. My main problem is that my alternator seems to periodically stop charging, I'll get a battery light, then when I park the car and shut it off and start it again the battery light more often than not will stay off. Eventually the alternator would stop charging completely and the car wouldn't start. So, I replaced it back in June, twice actually which it ran fine for months until recently this month I started getting a random misfire code P0300, the light has been flashing ever since. I also have a rough idle, and battery light which is still very periodic. Sometimes weeks without the light turning on. I have a 12v reader for my cigarette lighter which would read 11.8-12.3 but stays in that range when the battery light is on, but when it's not on it charges like normal. 13.8-14.1 depending on throttle.
The misfire isn't noticeable 99.99% of the time, It only is when I am downshifting I do occasionally get a piston slap like misfire or something similar.

At an attempt to fix the idle surge I replaced the intake, plenum, and TB gasket to make sure there was no leaks. I also replaced fuel injector o rings, and tips of the injectors while I was there and cleaned the IAC valve and all other sensors attached. My revs don't hang when not on the throttle at freeway speeds anymore, but still hangs when coming to a stop, it stays about 2000 then decays to a normal idle. I did order a new IAC to see if that will fix the surge, I have noticed the surge when starting the car as well, it just sounds like it revs higher when it starts.

The only other related electrical issue I have is a bad taillight ground or something similar because I have been told it is periodically dim or just out when I am driving. Surely that wouldn't be the culprit for my problems right? but I know I should fix it.

OBD2 Codes I have.
#1 P0300 - Random Misfire across all cylinders
#2 High voltage on bank 2 sensor (I don't have a cat)
#3 One for the EGR (I haven't added the resistor since I did the EGR block off well before all of these issues.)

All of these issues combined really leads me to believe the ECU is going out. Back in June when I was having the majority of the charging problems I did try to read the voltage on pins related to the alternator on the ECU, they had proper voltage, but I was using a 97 wiring diagram which doesn't have the same pinout as a 96 right?

I know there is a lot of information in there, as well as a lot of questions. Any help, guidance or assistance is greatly appreciated, thank you all for your time.

 

[BLACK'98DSM]

Possible? Yes. Likely? No.
Most people will never see a faulty 420A ECU. They don't normally get taken by corrosion or leaky capacitors like some computers, mostly due to being a fully sealed and insulated unit. While it isn't impossible for one to go faulty, I wouldn't say that's your case. In the event of failure, it's going to be a total loss of functionality. Not a progressive decline.

Have you conducted a compression test? I've seen low compression readings be a big cause of random misfire codes.

I'd venture to say that replacing the IAC valve will help with your idle and revving issues. The timing of issues that you described perfectly aligns with when the IAC is at work. I've fought with many screwed up 420A IAC valves.

 

[Goreb]

Possible? Yes. Likely? No.
Most people will never see a faulty 420A ECU. They don't normally get taken by corrosion or leaky capacitors like some computers, mostly due to being a fully sealed and insulated unit. While it isn't impossible for one to go faulty, I wouldn't say that's your case. In the event of failure, it's going to be a total loss of functionality. Not a progressive decline.

Have you conducted a compression test? I've seen low compression readings be a big cause of random misfire codes.

I'd venture to say that replacing the IAC valve will help with your idle and revving issues. The timing of issues that you described perfectly aligns with when the IAC is at work. I've fought with many screwed up 420A IAC

Hey man thanks for the tips, and sorry for the late response life's been hectic.

I've been meaning to go borrow a compression tester but there have been some other problems I've wanted to address first.
For example the problem with my battery light was with the connector to the altenator with the 2 wires back to the ecu. It seemingly would slide out of place slightly and when I would go press it back into place I would get charge again. I just ordered all the wires from the altenator fusible link back to the altenator and other sensors. Since I have a 96 and had to rewire my crank sensor awhile back, I was hoping the P0300 code was to do with crappy wiring job, but I still have the code for the misfire. But hey, we fixed something at least.

I got the new IAC valve in, and it ran great at first, but started idling poorly once again, I'm going to try to adjust it a couple turns clockwise. It only revs high when I blip the throttle, or put it in neutral when coming to a stop which is progress from before.

I did find some new problems I wanted to address first as I mentioned, I see that I must have over torqued my egr block off and bent it causing a leak, I'll try some rtv until I can fab up a thicker one.

I also found my pcv valve was rattling so I'm getting one of those today, after I get the pcv I'll do the compression test.

You know I did my head gasket 3 years ago now, and I regret not using the thicker head gasket people reccomend because I have a feeling I'll get low compression in cylinder 4 because of that damned head bolt.

 

[Goreb]

Hey man thanks for the tips, and sorry for the late response life's been hectic.

I've been meaning to go borrow a compression tester but there have been some other problems I've wanted to address first.
For example the problem with my battery light was with the connector to the altenator with the 2 wires back to the ecu. It seemingly would slide out of place slightly and when I would go press it back into place I would get charge again. I just ordered all the wires from the altenator fusible link back to the altenator and other sensors. Since I have a 96 and had to rewire my crank sensor awhile back, I was hoping the P0300 code was to do with crappy wiring job, but I still have the code for the misfire. But hey, we fixed something at least.

I got the new IAC valve in, and it ran great at first, but started idling poorly once again, I'm going to try to adjust it a couple turns clockwise. It only revs high when I blip the throttle, or put it in neutral when coming to a stop which is progress from before.

I did find some new problems I wanted to address first as I mentioned, I see that I must have over torqued my egr block off and bent it causing a leak, I'll try some rtv until I can fab up a thicker one.

I also found my pcv valve was rattling so I'm getting one of those today, after I get the pcv I'll do the compression test.

You know I did my head gasket 3 years ago now, and I regret not using the thicker head gasket people reccomend because I have a feeling I'll get low compression in cylinder 4 because of that damned head bolt.

I guess the rattle is normal, I'm ignorant so ignore that, but I believe that p0300 code was from the egr blockoff leak, it was a pretty gnarly gap.