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Discussion Starter #1
I've got an issue I've been working on on the Tbird for the entire time I've had the car; and I know it's a wiring issue somewhere.
I've swapped a bunch of stuff, but can't find it.

I have all the drawings, datalogging, electronic skills, everything I should need.

The problem is it runs rough sometimes at low end, until it warms up, or always Sometimes in the rain. :)

Here's what I've swapped:
EEC, Coil Packs, Plugs and wires, Wiring pigtail to EEC from under the hood, wiring pigtail to transmission, O2 sensors (all).
Probably more stuff I'm not remembering right now.

It does not show in a datalog as anything other than missing on random cylinders.
I can see when it commands 2nd gear; but I don't see any sensor changes that would cause it.

The weirdest part is that it will occasionally throw the tranny back into second, commanded by the eec, even at 70+mph. That's fun. :)

I've swapped the eec with a good one from another running car; still does it in the wet. Occasionally.
It did this with the original EEC, that eec went bad with another tranny related problem, which was fixed with a new EEC.

I have tried other EEC's same problem, and this problem doesn't occur with those EECs in another car.

I thought I had finally found it with water in the plug wells, but it recurred after the last rain, and there's no water in the plug wells. :)

The car runs Great 99% of the time, which is the thing that makes it hard to find.

Suggestions for additional things to datalog, things to check, voodoo rituals to perform; all useful suggestions are welcome.
 

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Reminds me vaguely of something mine used to do, over 10 years ago. Then randomly one morning, it stalled as I was on my way to the wife's (then GF's). It ended up being that a bunch of the wires in the harness at the back of the engine, running along where the EGR valve is and down to the passenger side O2 sensor is, were all melted together and shorting out intermittently causing all sorts of weird goodness.

When it throws the car back into 2nd, what is your TP sensor saying? Aside from that and the VSS (and going into limp mode), I don't know why it would command 2nd gear randomly...
 

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Discussion Starter #3
VSS reads normally, as does TPS; the VSS freaks when it shifts and the car slows rapidly, but it's after, not before.

I'll look carefully at the wires behind the engine, but I inspected the wiring back there that last time I did a tranny swap.

I changed the section that goes to the tranny when I changed the first tranny; it's easier to repin that section, then install it, than to do it under the car.
It had the problem with both.

It's done it on all three trannys. Yes, I'm that hard on them, lol.
This one I built, so it is doing pretty well; I put it in after finding out about the 127mph shift bug. :)

I'm going to clean the top of the engine, clear out the EGR ports, and swap the injectors for a set I cleaned, just for giggles soon; when I do I'll look over all the wiring going to the engine.

Could this be a crank sensor problem, maybe?
I'd expect that to just die...
 

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The harness that was giving me trouble was part of the engine harness going to the front O2s, not the tranny harness. YMMV, of course...

I agree, don't think it's the CKPS. No CKPS signal, no spark... though I suppose if it was intermittent for milliseconds at a time it could cause a miss but I've never heard of that.
 

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Discussion Starter #5
This acts like the plugs are dirty, misses down low rpms, but clears over ~2000 rpms.

It has new plugs, new wires, less than 200 miles on both.
I'll pull one, just for giggles tomorrow.
Those usually cause problems on the high end, not the low.
It's done this the last two days, that's the longest it's done this in years.

I'm down to fuel feed, although I think I'd see that on the o2 sensors.

It set a code earlier today, I haven't had a chance to read it yet.
I don't keep the Xcal in the car; it would suck if one got stolen.
I'll check that in the morning.
 

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MLPS on the Transmission?
 

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Discussion Starter #7
I've replaced it once, it was originally the old style. And reset it each time I replaced the tranny after that. I've done that a lot, lol.
Lazarus has had four trannys, Red Cougar two, and Tbird three, lol.
I built the one in the Tbird, and the one in Lazarus.

It did have the problem with the OG tranny/mlps.

But the missing / bucking starts before the gear change thing happens. Usually.

I seriously think Brandon is on the right track, with a wiring problem, but I just haven't found it yet.
Possibly the eec sees the misfiring, and decides to gear down.
I think I'll pull the intake off, and pull the top part of the engine harness apart, and look for problems.
To miss, it's got to be Fuel or Spark, and the EEC says all is good.

I think before I do that, I'll swap the EEC just for shits and giggles, and see if it acts the same as when I parked it today.

It hadn't done it in a year, and two days ago it started doing it again out of the blue.

I appreciate the help, guys; I've done everything I can imagine without untaping harnesses.
I've swapped everything that is related that will swap, except for injectors.
If I take the intake an all off, I'll wash out the fuel rail, and swap to a clean set of injectors.

Not the 39# ones, lol.

Hmm. This one still has the stock MAF; I have another 02 maf/inlet/airbox, maybe I'll do that first.
I could swap a stock maf in, I have a couple.

Wetness, a crack in the maf somewhere; that could cause it.
IDK why it would fix itself, tho.
Heatsoak drying it out?

That I have not tried!

Car should run with the maf unplugged, right?
I'll see if it runs better with it unplugged.

Thanks guys, for the suggestions!!
 

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Discussion Starter #8
Took the car to the store today, weather has been rainy on and off.

Can ran fine, not a burble; acts like it's brand new, lol.

The code light was out when I started the car, I still haven't looked at codes.

This is really scorching my Grits!! :D
 
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