Got a mail order tune, fine the first day, and now CONSTANTLY cutting out?!?!
 

Alright,

Well my car was down for a few days since I got the new Comp 918's, so while I was busy replacing those, I thought it'd be a good excuse to send out my PCM for a mail-order tune (bolt-ons, baby cam, m6) to squeeze out a few more HP. Ok, fast-forward to the day I fired everything up, fired up perfectly, drove GREAT, pulled HARDER than before, way more low-end, nothing to complain about. So yeah, I basically drove it normally for 30 minutes to heat up the new springs, let them cool down, and then drove it around again for a while, beat on it for about ~15 minutes or so, drove it around for about 10 more minutes, then shut down.

A couple of days later I decide to go to LA to pay my friends a visit, so I hop in the car, get on the freeway, and it just starts cutting out, hard, and constantly, like literally every 3 seconds (sometimes a bit more random), the car will cut out and jerk the car. First thing I thought- I broke a valve spring. So after I got home, I pulled off the valve covers, NOTHING bad at all, no stress cracks, no signs of anything bad... weird...

Well, here's what I've done so far:

Checked the ECU for pulled pins
Replaced fuel pump relay
Ran new fuel pump wire
Inspected fuel pump sock
Redid ALL grounds
Checked if injectors were firing (felt for snappin')
Tried looking for shorts
Checked PS spark plugs/wires for tears/rips- none
Checked some of DS spark plugs/wires for tears rips- none yet

Only things left:

Coil packs
Rest of DS spark plug wires
Fuel filter
PCM
Suggestions?

Can my PCM really have acted 100% perfectly one day with the new tune, then act like complete crap a couple days later? I don't know, I'm lost. And I have an event at Willow springs road course on Satuday, so I'd really like to see if it's maybe something on my part. Thanks guys.

-Andrew

Can you check for engine codes on the pcm? It should tell you a hint of what the problem is? When you turn the key on the ignition, all pink wires in your engine harness should have 12V. I would check that also on both sides of the engine. If it was a PCM problem, i would think that after you pulled the harness to check the pins on the computer, the engine should MIMIC exactly how it ran the first time you plugged it in and had no issues. So that rules out the pcm. The only thing left is for burnt wires, or a bad fuse, or missing power somewhere, or a bad spring ect......

Hey Jesse, I tried calling you last night, but no luck. The last code I got was the p0118 code which was the high coolant temp output I told you about, but I got a new connector for it, so it should be good now. I checked the codes when I was on my way to LA.

I have yet to drive the car after popping out the PCM and plugging it back in, I hope that'll fix it. We'll see...

Mine did the exact same thing. It ran fine for a day then started cutting out going down the highway the next and would barely run at all. I switched my PCM back to the stock PCM and it ran fine. This actaully happened to me two different times. Each time the stock PCM fixed it...

Damn :( I'll test drive it tonight after unplugging/replugging the pcm back in. But I've been borrowing the battery from my '93 because my redtop died a while back, so wouldn't that have automatically reset the pcm since I've been unplugging the battery and swapping it everytime I use it?

IF you are unplugging the battery then it should run exactly like it did that one time, due to it using the base starting point that i have had set. So if it dont work exactly the same then there is something wrong on the vehicle. Wiring, ect..

Looked at the crank sensor wires, no burnt wires, cam sensor wires, same thing, looked under the car, nothing melted/burnt. I'll check coilpacks next. I'm also gonna see how 02trns_am's theory works today by swapping PCM's with my friend's.

I just stumbled across your thread and figured I'd put in my 2 cents since I just had the exact same problem on a different motor. My van did the exact same thing. It ran fine all day and I just started it up and it was doing that bucking or jerking and really running like crap. It was pretty bad. It didn't throw a light and I plugged it in to a scanner and it gave me no codes, the scanner didn't even register a misfire. I had this problem before and it was a coilpack. I pulled them off one by one (for 4.6 with coil over plugs) and checked the resistence on the primary and seconday terminals. One of the coils was off a little so I replaced it and it completely fixed the problem and it runs fine again. I couldn't believe that 1 coilpack would cause such a severe problem. hope this helps

I 2nd the crank sensor wires. I just went through something similar to this and it ended up being the the male end on the crank sensor wires, the part that snaps into the crank sensor itself. I bought a new pigtail, soldered it in and that fixed my problem.

Well this is so weird... I was checking wires, most of them were fine, I came to the crank sensor wire, they weren't really melted to each other, but I did have to pry them loose from each other, no metal-metal contact from what I can see, but one wire (the blue one) did have a couple of exposed areas. So I replaced that section of wire, checked around some more, cam sensor wire was fine, etc. etc.

So... fast-forward to today, I met up with Brismo7 to borrow his PCM, go to my car, put it in, fires up right away like always, I drive it, drives perfectly! Ok, I call Steve, he tells me to make sure that my old PCM was the problem, so just unplug my neg terminal, swap PCM's, then drive it and see if it runs like crap, so I did it... It ran great too?!?! Oddness...so was it the crank wires just waaay too close or something? We'll see tomorrow if she works fine or not...