94 GA GT with surging engine and dancing gauges

[daswansinator]

So my 1994 Grand Am GT is giving me a bit of a headache as of late. It has been showing a few symptoms but yesterday it actually scared me. I was making the trek from louisville, KY to chicago, IL, and once I got north of Indy, the car developed a "hiccup". I had the cruise set for like 67-70 mph, and when it started hiccuping it was almost like it was cutting out power to the engine for a fraction of a second. I thought I was crazy but the further I drove the more and more common this hiccup got. Once I was in IL, much closer to chicago, my speedometer needle started jumping around. It would drop down then shoot back up to my speed, all within fractions of a second. The closer yet I got to chicago, it seemed like my tach and the other smaller guages were doing it too, with the engines hiccup becoming rather frequent. Once I got back in my area, I stopped at autozone and had them do a scan on the computer and of course it came back system fine. So I continued home and on the road outside of my subdivision the engine just died. The strange thing was that my instrument cluster was frozen in the image of what the car was just before it died/ I wouldn't have noticed the engine died if it wasn't for the fact that the cluster got dim (no running alternator) and that the battery idiot light came on. I parked it in the middle of the street, and tried reseting the ignition, but the cluster remained frozen in that view with the engine not starting. It would crank but not start. Finally it started and I made my way into my subdivision.

I had thought prior to my trip that the engine ground was getting corroded because the speedo seemed to be "reseting" itself while driving, so I cleaned the only engine ground I could find, where the negative battery terminal bolts on to the enigine/tranny stud on the front side of the engine. But this didn't seem to help.

Any ideas are greatly appreciated since I have to move this weekend and it is hard to do with a car that seems like its been going out and drinking to much! Sorry for the long post, but I welcome your help!

1994 Grand Am GT
3100 3.1L V6 w/automatic

[xeroinfinity]

Welcome to AF.

When was the last time you changed the fuel filter ?

With your cluster dancing it is common that these go bad and short out.
It is a dealer part new, you can find them on Ebay or salvage yards for around $50-60 used.

hope that helps

[daswansinator]

I wish the problems I am experienceing were that simply to remedy. I know the cluster is fine because I tried the SE cluster from my 95' Grand Am (I hated not having the tach and other guages so I put a GT model dash in) and even the SE model cluster which works fine normally acts strange in this vehicle. The cluster is also lighting up strangly. As you are probably well aware, there are bulbs in the back of the cluster to illuminate the guages at night. What happens now is that when I put the key in the ignition, it turns on part of the guage illumination bulbs, ever so faintly. This happens regardless of whether the the light switch is in "headlamp", "parking", or "off" modes. The connection I have also noticed with this is that when the guage background lights illuminate inappropriately, the fuel pump does not run for the usual "bulb test" type period to build psi in the fuel lines. I am assuming that this is why the engine won't start, no fuel.

So I was doing some electrical testing. I decided to replace the ignition switch since they seem to fail rather reguraly on these cars. The ignition switch seemed to operate fine. It had a full 12 volts in and gave 12 volts back out in all the proper modes. So next I checked the fuel pump relay, and found that it is only receiving 9 volts. But the weird thing is that it is being backfeed the 9 volts up a ground. The lead that is supposed to power the relay goes straight to the PCM, and doing a continuity check showed to not be shorted, but yet recieved no voltage from the PCM. Is it possible the PCM could have gone out? I'm heard from some that those PCM's are indestuctable and theres no way to fail, but from others that there could either be a cracked circuit board or faild capacitor or I/C chip since manufacturers used less than quality electrical compnents during that time period. Or is there something else telling the PCM to not bother powering up the fuel pump.

On a side note, the other thing I have noticed is on my console mounted shifter, the indicator lights light up as usual just as you turn the key, but as soon as you hit the run detent, the gear indicator lights go completely out, regardless of gear.

This is driving crazy.

[daswansinator]

Well, I got the problem fixed, but I had to break down and take it in to the dealer to do so. Ended up being a ground to the PCM that became broken somewhere in the engine harness. Cost me $400 to get a new wire installed, but I guess the shop guys took pity on me and didn't even make me pay for the wire, just labor. It probably wasn't worth it to tally on the 50 cents worth of wire it cost. But shes running good again now and I am thankful because I really did miss her.

[xeroinfinity]

Yeah it did sound like a short and the pcm ground(s) do get damaged for some reason.

I know many who have replaced hundreds of dollars worth of parts and never found the true troubles.

Glad you got it going, sorry you had to pay so much.
Trouble shooting is timely!