Stumbling and Studdering

[SeaFoam]

54 = failure of ACT/IAT. VAT throws a 58 on LA3. 54 is an expected code unless you've added an ACT sensor with the LA3 swap. so that leaves ..

the 66, which is MAF/VAM went below .4v during operation, there are a few things that can cause this. since you already eliminated the VAM as a possible issue, the problem likely lies in the harness. did you check the VREF as well as the VAF pins as documented in the troubleshooting guide that navy posted in the other thread? VAF should be 1-5v full sweep. if you're getting .255v at the VAF pin at the VAM, vane closed, with both new and old VAMs, something else is wrong. either VREF is low at the VAM, or VAF is shorting to ground.

either of which likely points to something busted up in the harness. if i were in your shoes, id just start unwrapping the harness starting at the VAM connector and surveying the damages. 84s are not known for their quality harness insulation; most likely that chunk of harness is turning to dust.

Here's the thread I was talking about that says the VAM should be .25v closed and 4.5 open.

http://www.svoca.com/forum/showthread.php?t=23783

So which is it??

[Alex L]

So which is it??

according to the ford manual: .15-.5v with engine off, 1.5-2.7v at idle. so my statement of 1-5v full sweep is incorrect, its .15~.5v ~ ~5v full sweep. my bad, sorry about the confusion. diagnosis is still the same. undervolt/open circut on the VAF signal.

[NOTACARLO]

this may not help you but I had the same thing happen to me after a 70 mile jog about two months ago. I replaced the coil and have not had an issue since. I also replaced the 24 year old pick up, and TFI this week amongst some other preventative things.

I could let the car rest for 15-20 minutes and it would start right back up and run like a top for about 10 minutes. Then it would start to do it again. Once the car died on it's own you could not restart it....was like it was starved of fuel. I had correct fuel pressure and good voltage so it perplexed me a bit. I went to the coil first as I noticed it wasn't Motorcraft. Figured it was just an old heat soaked coil.

[fast65]

Ok, here's an update.

The VAM and the TFI have been replaced so far and there has been no improvement. I just got home today and my dad told me that after he replaced the TFI it ran great except for it would occasionally die when he would come to a stop. I went to adjust the base idle and TPS before I took it for a test drive and I noticed that when I moved the TPS wire it would change the idle. Then I took it for a test drive and it did the same thing it has been doing, I also think it might be running a little rough, but I'm not sure.

I really have no idea where to go with this, I can't seem to find a TPS harness and I just don't know what else to look for. There was no wiring problems leading back from the VAM either. Do you guys think it could be the LA3? Maybe the IAC? Btw, fuel pressure isn't dropping at all.

[fast65]

Well after taping the TPS wires up and another test drive, it drove fine for the first mile and a half or so, then I went to put my clutch in and it died.

[GAboySVO]

The 84 model is notorious for having wire insulation issues. If your problem is intermittent as stated and wiggling wires changes how the car runs, then you have found your problem. Peel the harness back as far as you can to find the issue. My guess is that it is in the area above the turbo.

[1984GT350]

Any update on this? I'd like to hear the solution if you found one. I'm having a very similar issue with my 85.

Thanks