Finally got the GN figured out.


Senior member
FOUND my problem and reason for ecm getting hot, bubbling my ignition module and all the weird readings on the ScanMaster and OTC. Internal problem in the negative battery cable. Passed ohm readings and continuity tests originally. Got it to stumble and act up in the garage. It was near where the passenger header is closest to it (3" away). Cable sheath is fine. Grabbed the cable while idling and it stumbled pretty bad. Repeated it to verify and yanked that puppy completely out. Cut it in pieces so I would never be tempted to use any part of it for any reason. Put in a monster 00 negative cable ($9.99), routed it a little further from header and secured to head. Every single symptom is gone. Car pulls very hard again and now I am ready to turn it up to 25psi and see what she does now. ME-R system back in with the 83#ers. Best the car has run so far was a 11.4@117 with 20 psi and there is more in it.
I've seen all kinds of weird sensor readings when grounds are bad, I've even had car throw multiple 'nonsense' codes that was eventually traced back to a bad ground. It's good to reinforce how critical good quality grounds are on a preformance motor. Thanks for reminding us to look there:cool:

I think it was Sport Compact Car a few years ago that added one of those 'daisy chain' grounding systems to like 5 long term project cars. Every one of them made more power and had a smoother dyno graph. THe RXA made like 18WHP more:eek:

Good job there, buddy. I'm filing this away for future reference/reminder that our cars can be a pain in the ass.

Bruce '87 Grand National
Two years and 7 months I have been chasing this. Over and over every part of the car without spending money on it throwing parts at it. Had all the extra parts for my Vega project so I decided to start trying different things when the voltage tests and ohms readings all were within specs or nothing outrageous. Only money actually spent was on a new 340 pump since that one was probably over 10 years old and the battery cable. Was out late last night driving. Drove for over half an hour this morning before I had to go to work. Drove around my whole lunch break just throwing everything at it up to the 16psi it is running at now with the RJC boost controller. Pulls like a mother so it is time to turn it up again to where I originally was when this all started. :)
What a nice thing to read! Man, that's great. Sure wish I could write a page like that before I die.

Bruce '87 Grand National
Thanks guys. It was truely a great day when I found the stumble/hesitation. Now it is all progress again and smiling like there is no tomorrow. This car has woken me up again to actually enjoying/craving to drive the car. So much time wasted fighting it that I was starting to believe I would never find it but I am not a quitter. :D
Isn't it a great feeling when you, yourself, find the problem and all goes right with it? Like waking up to a beautiful day, rays of sunshine and a big bank account because you won the lottery!!!!! Man, it must feel good..give yourself an "attaboy" pat on the back because you deserve it!!!!!!:smile:

Bruce '87 Grand National
Thank you Bruce. I am not one to take my car anywhere. If I haven't done something, I WILL learn. Been ASE Master certified since 1990 and I can do anything and everything on this car...besides paint and body work. Tried that when I was younger and just don't care for the chapped/cracking and dry hands that I was getting. I don't generally like electrical but I have the experience and knowledge to do it. Hopefully on the road to 10's now. :D
I can relate what you went thru & it sure feels good when you find it!
I had a bad ground in a MAF plug wire & I thought I kept frying out MAF's all summer. They were all fine but it made me crazy the whole time. Now I have more grounds than needed but it's only some wire & ring terminals for $20 & no ground issues so far.
Good job finding your problem....

This is why I don't check resistance on electrical problems.
You'll find wiring problems much faster by checking voltage drop. I have a eight inch positive cable from a Taurus in my tool box that shows no resistance, but has a 2.45v drop. I keep it to show people the difference.
I also tried voltage drops and could never find a problem. I ohmed out wiring from computer to component and checked the reliability of the wiring with wiggle tests on every single wire on that car. I checked hot and cold and but never got it to act up except under boost and I never gave it boost when cold since oil pressure would blow the filter Oring out with the bypass blocked. (don't ask how I found that out. ;) ) Had my Fluke meter here more times than I have used it at work in that time. It drove me crazy thinking I would leave it alone for a while and then go back and look with a fresh set of eyes and start from "square one" every time I checked it out.
Eric, what was the voltage drop for the ground cable? I am fighting a very bad tip in stumble and was wondering if perhaps that might be my problem also?
Good Find... I've dealt with a few "bad cables"- Started pulling stock stuff out and swapping for new 2 and 4 gauge cables - both pos and neg. No more issues!

It's nice when you can discover the problem and get back to the fun stuff;)
I'm filing this one too...:biggrin:

I've had this on/off gremlin for awhile where the battery light would flicker under light/moderate acceleration and the volts on the ScanMaster would drop into the low 12/high 11V range when it happened.

A couple weeks back it got far more repeatable and would happen every time I drove and lightly accelerated. Checked out the charging system and battery a couple times to no avail.

Finally, after getting some advice in the electrical forum to check the cables, I disconnected the batt cables, cleaned them and the terminals up with a steel brush (there was minor oxidation), the did the same to the alternator wire and poof...problem solved.:biggrin:

On one of my former cars (a '93 GMC Jimmy) my ABS stopped working. The place I took it to wanted to change the ABS brain which I could not afford at the time (would have been a couple $K).

After reading up on it a bit, I learned that the ABS brain needed a minimum voltage on the input or it shuts off and throws a code and light. On a hunch, I went ahead and replaced the + battery cable which looked a little shady and corroded.
Problem solved...:biggrin:

Bad batt cables can cause lots of crazy stuff to happen.:rolleyes: