My Gn's Running Bad - Need Help


My '87 GN sat in the garage for about 5 months. Wasn't driven but started up at least 2 times and backed out of the garage and then back in. I recently had to move it 30 miles to put it in a different garage and it ran terribly bad. No power whatsoever, got quite warm and backfired and died several times. It had been low on gas but I filled it up just prior to the move and prior to it running bad and I'm sure the new gas was getting to the motor. This is a Texas car but it is currently in California and my ex GN mechanic is in Texas. I'm a pretty good mechanic but haven't done much with GN's. The car has had extensive modifications done to it but always ran good prior to this recent move. Now, when I start the car up, while it is idling, there is a small pop or backfire (kind of like a cough) coming from the top of the engine every so often. Does anyone have any quick fix troubleshooting ideas that I might try? And if not, would anyone know of a good GN mechanic in central California near the coast, to wit in Paso Robles or San Luis Obispo or Santa Maria? Any help or suggestions would be appreciated. Thanks
Possibly bad MAF? You mentioned extensive modifications. Just what are the mods? We need to know these. Scantool?
Sorry, but I'm not that familiar with GN's. What's a MAF please? As for mods, I couldn't begin to list everything here. The complete drive train including the engine and transmission were completely redone. If you wanted specifics on something, I could probably look it up. Also, all the electronics were redone. I know this is vague but I don't believe the problem is internal engine related. It is going to be something either gas or electrical or air flow related, I think. And is a Scantool something you can hook up to the engine and tell what the problem is? :confused:
I read your thread and you said the engine is getting fuel, do you have a fuel pressure gauge to actually look at to verify this? i've experienced fuel pressure regulators sticking after prolonged sitting even the billet adjustable ones.

The maf sensor is located after the air filter in the piping / ducting going to the turbo.

John :smile:



OR Possibly a fuel issue as the others stated.
MAF = Mass Airflow Sensor. The symptoms you are describing sound much like a bad MAF. The original or rebuilt stock type units are all black. Does yours have one of these? And yes, a scantool such as a Scanmaster could tell you if it is your MAF gone bad.

Unplug the MAF and see if the car runs any different.

If you do find out that the MAF is the problem, be wary of the Autozone/rebuilt stock type units mentioned above as a lot of people have problems with them not being calibrated properly, etc. But, let's not jump to conclusions here. It could be something else. I do suggest that you invest in a Scanmaster. You'll need it eventually anyway.

Let the $ spending begin. Oh yeah...welcome to the darkside.
Answers Leading to More Questions

Thanks guys for the help. I'll check on the fuel pressure. I have 2 GN's and one is in Texas and this one is in California. I think one of them has a built in fuel gauge that I can look at under the hood but not sure which one it is. :confused: I will also try unplugging the MAF and see what happens. Since you said to unplug it and start it up, I asume it will run with it unplugged, right? If I need a new one, we have a Kragens, NAPA, and Auto Zone here (not a big town). You said avoid AutoZone so what do you think of the other two? Where can I get a scanmaster? How much are they? and where do they hook up to the car at? I think the Texas car has one built in under the dash.. Will the scanmaster pinpoint the problem kind of like a car analysis machine? I hope I can get this fixed in the coming week. The car is in the empty garage of a rental house and new tenants are moving in next saturday and I hate to have to put the car in a shop. :( Does anyone in know a good mechanic in central California near the coast?? :wink: Thanks again for your time and help... :)
The car will run with MAF unplugged, just rough. Thus, if you unplug your MAF, drive/run the car and it doesn't act any different and/or symptoms do not get worse, this would be a good indication that the MAF is the source of the problem. See what I'm sayin'. The MAF is vital to engine operation.

All of the store you mentioned sell remanufactured units, so don't just stay away from the Autozone ones. It is possible to get a properly calibrated one, you would just need a scantool to verify this.

Scanmaster just uses three wires: Red for 12v power (i.e.-fuse box)/ black for ground/ white (plugs into diagnostic port under dash). Numerous vendors sell the Scanmaster. Try here:


Using the link you can also check out the Translator which allows you to use the modern GM MAFs with our cars.
What would I be looking for to verify that the rebuilt MAF I just put on is calibrated correctly? I have a ScanMaster in the car and have an OTC 4000e.

On Scanmaster, AF reading should be anywhere from 4-7 at 800rpm idle. Should also max out at 255 at WOT. If it doesn't, it's bad.