And to add..... the typical variation in the idle speed for a healthy engine is +/- 25 RPM from the target. There is even a column of data showing the variance as a %. What you are seeing may be drivable, but it wouldn’t be considered “acceptable”.

 

Fred, the voltage at the alternator output, and at the battery itself holds pretty steady. I had disconnected the battery last night and left it on the trickle charger all day while I was at work. I connected it and immediately cranked the car. I was getting a reasonably steady 14.63V at the battery and at the alternator output terminal. It only varied a few hundredths every few seconds.

If I can get a few hours this weekend I plan to find every wire and pin that is on that 5 V ref circuit and ohm them out. Really beginning to think it may be something gone wacky internal to the PCM.

 

Injuneer, when you looked at my 2nd log did you notice the differing O2 voltage readings between banks? They differed a lot, and seemed to start tracking closer together after I revved the throttle. That seemed to 'clear it out' a bit.
I have no doubt the plugs are in bad shape and I intend to change them. I think I may have a few leaky injectors as well. I have cranked the car 15-20 times since I got it running again, but I'm not able to drive it (clutch issues). I think it's loading up the plugs and fouling the O2's on top of everything else.

I think in the entire history of the car I have replaced only 1 of the O2 sensors probably around 2010 or so.

I should probably put some new O2 sensors on it shouldn't I?

 

Fuel for each bank of the engine is controlled independently. In closed loop, they will not match. When you go full throttle, or even part throttle at lower RPM, the PCM enters “Power Enrichment” (PE) mode, it drops out of closed loop, and both banks will tend to match. That is when you start to see both O2 sensors approaching or above 0.900 volts, because PE mode targets a much richer (typically ~11.8:1) A/F ratio, as opposed to 14.7:1 in closed loop.

On cold start it sets a very rich A/F ratio, and in the second log O2 readings were very rich on startup, and never seemed to drop as the engine warmed up. But that's when you were commanding higher RPM, etc., so that may explain what was going on.

 

It is smelling rich when I run it. It has the stink that gets on your clothes and stays with you. (No cats). It's not to the point of puffing black out the tailpipe though. It's misfiring here and there until I do plugs and wires. Hopefully that will help that a bunch.

I've been holding off doing as little as possible until I get that idle situation under control.

 

I haven't disappeared, just regrouping. I have been reading in the FSM, and studying the PCM wiring diagrams and connector pinouts and writing a list of wiring items to check when I get several hrs to spend with the car. I have checked and cleaned all the grounds near the front of the engine, and am preparing to ohm out the PCM ground by the starter and the sensor grounds from PCM to the sensors. So many sensors share the grounds in a fairly convoluted way that it is hard to get a good handle on where a problem could be. I have prodded and shaken the plugs/harnesses with the engine running and logging and then studied the logs to see if I can see any inconsistencies but that revealed nothing.

Meanwhile, I drove the car up and down my road (1/4 mi or so) about 8 times and it is running pretty well despite the slipping clutch and fluctuating voltage issues. Need to get some better tires, and insure it so I can put some miles on it.

I will report back when I have done the electrical testing.

 

Was there ever a resolution for this problem? I seem to b having the same issues.

 

No- no resolution. Never got it running well enough to insure it and try to drive it regularly. I still have it, but future is unsure as it will take so much to 'get it back'. I got to the point that I want to try and replace the computer- but have not done so yet mainly because everything to do with my ability to tune using old software and known tunes are serial-number-tied to my current PCM.

I wish you luck with chasing down your issues!

 

I followed this thread but never saw that you checked the PCM grounds as suggested early on. Did you ever do that? And you can buy a new PCM and have your VIN programmed in if you need to for LT1 edit.

Good luck!