Help ! WOT electrical problems

[Scott Atk]

Well it happened again at the track last night. Time to turn to my brothers for help.
I have an intermittent electrical problem that only rears it ugly head at WOT. I can drive the car on the street at part throttle all day and it will never happen. Here goes...
The car will be pulling great and then just fall on its face almost as if its shutting off for a second then pick right back up. Sometimes it will do it three times within a quarter mile sometimes once, sometimes not at all (rare). When I playback TLink I get all kinds of crazy data for one frame corresponding with the stumble. Stuff like TPS goes to 2.xx when I never lift, battery volts go to 6.xx, P/N switch turns on, MAT goes to 47 degrees, then everything is back to normal for the next frame. Here's what I've checked so far. Battery cable to starter is good, grounds at back of head are good, ECM has been swapped. I really feel like its a ground problem but not sure where else to check. Im running the MAX EFFORT 16 pos. chip, 55 lbs injectors, PT54 turbo, PTE front mount, vigilante "0" pump, anything else that anyone thinks might be pertinent just ask.
Thanks !!

 

[Lee Thompson]

?

My best friend has the same problem. When you solve this problem PLEASE let me know.

 

[stormy]

ttt please

 

[John Larkin]

Since it happens at higher than normal RPMs, what are the chances that it could be alternator output? Maybe hook a DVM to the back of it and do some WOT testing and see if the output ever drops. Free test and would isolate one component.

 

[myclone]

Im fighting a similar prob on a non turbo FI vehicle right now...

Alt could poss be your prob. On the other hand it could be a bad connection some where. If it was me Id check the following once you verify the alt is good to go:

*Fusable links (check em close for being broken inside the insulation. PIA to do but Ive BTDT)
*Connectors at ECM (make sure no individual pins are loose/broken on each connector. Specially +12 and GND)
*GND connections at the frame/body/eng
*Connections where the fuses plug in at the fuse box (Ive fought this on TWO GM vehicles so far)
*Fuel pump relay and its connector/wiring

This ones gonna be WIERD..... I fought almost the exact same prob/symptoms on a buds GN and finally traced it down to a corroded Scotchlock connector back at the fuel tank that was cutting the fuel pump off at diff times. Id check for ANY kind of non stock connection that is either a crimp connection or other type of splice. If its not soldered and/or heat shrinked it can corrode without being visible. Especially if its exposed to the under car enviroment that his fuel pump was. Id still like to slap the person that used a Scotchlock on a outside connection (or ANY connection for that matter).

Lastly. Does the stumble ever appear when you encounter rough road conditions like a bridge expansion joint or the like? Id do some WOT/part throttle tests on less than smooth pavement to see if the vibration and the stumble coinside with each other. If they do then you have a bad connection/broken wire prob somewhere.

IMO the WOT only appearance of the stumble might only be showing itself due to the vibration of the eng/drive line at high RPM but doesnt happen at low RPM/MPH. Hence youd only think its a WOT prob.

HTH

 

[Scott Atk]

Thanks for the replies guys ! Ive pretty much ruled out the fuel pump and ignition due to the fact that there is all the weird ECM data associated with it. Im thinking if the fuel pump momentarily cut out or the ignition started to cut out at high boost, I wouldnt get the strange data ?????
The alternator is an option, I will check it today. But is it possible for the battery volts to go to 6 or below if the alternator cuts out momentarily??
Keep em coming please.

 

[G McCall]

I 've heard of the same problem; will be interesting to here what caused this.

 

[myclone]

Originally posted by Scott Atk
Thanks for the replies guys ! Ive pretty much ruled out the fuel pump and ignition due to the fact that there is all the weird ECM data associated with it. Im thinking if the fuel pump momentarily cut out or the ignition started to cut out at high boost, I wouldnt get the strange data ?????
The alternator is an option, I will check it today. But is it possible for the battery volts to go to 6 or below if the alternator cuts out momentarily??
Keep em coming please.

I would have to say that the actual battery voltage isnt going to 6v but where your scan tool picks up the voltage measurement very well could be. Symptoms of a bad connection or broken/breaking wire.

Im not familiar with the scan tool your using but if it was me Id try a little experiment.. If your scan tool requires a seperate 12v/GND to operate (doesnt get its supply power from the ALDL/ECM) then Id disconnect scan tools power wire and proceed to RAPIDLY touch the wire to the place your picking up the power. All the while watching the scan tools data. If it shows the same or similar "garbage" readings you have just discovered why the erronious readings are showing up.

Try the same "touching the connection" with the GND too. This will tell you if the probs in the "hot" side or the GND side.

Since the car is actually nosing over then its just not the scan tool thats flaking out it would be the ECM too. That would tell me to start checking ECM connections, GNDs, fuse connections in the fuse panel, and every other connection/wire that could interupt the power to the ECM.

Intermittent electrical probs are a HUGE PIA to find/troubleshoot. Trust me... I have to do it for a living...

HTH or least gives you some place to start.

 

[Scott Atk]

Thanks Syclone dude !

 

[BLACK MAGIC RACING]

A friend Of mine had a similar problem. I suggested the volt booster from casper's. I'm not sure if that's what did it, but his problem is gone, and i never had a problem and i have the booster. Just my input.

 

[Scott Atk]

Here's some more info. I pulled the ECM and took some voltage readings and checked the grounds. Here's the results:
C16 - 12.5V
A6 - 12.5V w/key on

A12 - 9.5 ohms to ground
D1 - 9.5 ohms
D6 - 9.5 ohms
D10 - 9.5 ohms
D12 - 15 ohms to ground when running. shows open when off

Do these grounds seem poor, or are these normal numbers?? Also does anyone know where the ECM grounds go specifically, so I can check the other end.
Thanks Again !

 

[salvageV6]

D6 and A12 go directly to the back of the head pass. side.

D1 goes to S668 which is near the relay bracket then to the back of the head. Spliced with others in the harness first.

D10 goes to engine harness near left hand valve cover then to the back of the head. Spliced with other grounds near the knock sensor first.

Last one that changes readings isn't a ground to the ECM.

 

[bose]

battery

Why don't you try a different battery and see what happens.Bruce

 

[Scott Atk]

update: I was measuring the grounds back to the neg. battery terminal. I tried measuring back to the cylinder head and they dropped to around 1 ohm. So I relocated my negative battery cable... now all ECM grounds are around 1 ohm. Unfortunately I just took it out for a rip. It seemed to run better but did freak out a couple of times.
SALVAGE: thanks for that info, Im going to check all of those.
BRUCE: Although its a high dollar fairly new OPTIMA battery, you're absolutely right, I shouldnt rule it out.

 

[tta1401]

Yes, resurrecting a really old thread!

Scott,

Do you happen to remember what caused and fixed your problem?

Thanks,
Sean

 

[Scott Atk]

Been a while but if I remember right it was the fuel injector harness connector. It was tedious soldering in a new connector but that fixed it. I also recommend a new injector harness from Caspers. HTH, Scott

 

[Bescurred]

I had similar problems but it was my positive battery cable rubbing against the exhaust...once the wire loom melted and got to the copper it was going nuts on me.

 

[tta1401]

Just pulled the cable out and it checkedd out good.