I have a pretty stock 3800SC has been running great for years, no issues.
Suddenly on way home it would stumble upon acceleration, over 3000K as it was going into boost.
No codes, except I did get on the third ride, a P0300 (i think) which was multi-cylinder misfire.
First, thought it was bad gas, maybe poor octane, so I added some octane booster. No change.
Except from that mentioned above, no other codes. Idles well. Starts right up.
Fuel pressure good, 50psi, and holds after engine is off (no injector leaks). I can hear the fuel pump working. I did change the fuel filter.
Also, I installed new spark plugs, though the old ones were slightly worn they looked fine. Again no change.
I did install a new radio, have not had a radio in a while. Noted when I switch my engine coolant fan on I get a loud pop through the speakers which I thought was odd (and annoying). So I checked the battery grounds, re-did them. No change.
This seemed to appear around when I installed the radio, but a radio can be causing this?
At a loss, I thought it could be a MAP sensor, but everything is connected. Vacuum is normal, but I checked those lines, appeared good.
Any ideas?
[This message has been edited by RotrexFiero (edited 09-29-2025).]
My engine PCM sent a 0300 code a couple of times . The first time it was a bit of water in the gas but after some driving that passed . In the most recent case it was bad ground connection to the coil pack or a burned out coil. Replaced all the coils, put a new ground cable there direct to -12V and the stumble was gone. First check for good ground connection to the coil mounting plate as that could be it, but the coil packs do burn out. Coils detach with a 5.5mm bolt that is hard to find so don't lose them!
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
[This message has been edited by Dennis LaGrua (edited 09-29-2025).]
I ordered new coil packs....I guess those are pretty old by now.
So, the consensus is something electrical.
Question: Why am I getting feedback through my radio? It appears when the alternator kicks on, like when there is a high draw on current. I can see the blip in my voltage gauge. Shouldn't the battery absorb, or stabilize any surges? Again, is that a ground issue.
Yes, I am looking at new plug wires, but these are in good shape from a visual inspection.
[This message has been edited by RotrexFiero (edited 09-30-2025).]
Good guesses that the problem is in the ignition. Can't disagree with that but a small amount of water in the gas from long term storage will also set the P0300 random misfire code. Ask me how I know? If it were an ignition wire would that not just set a code for the affected cylinder? Judging from my last experience, I'll still go with my guess on a coilpack and wait until the solution proves me wrong.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
Okay, I ordered a new coil pack, and within only a few minutes I had them installed.
Dennis you are a genius, or some kind of Fiero savant.
So, it fixed the problem.
I am now worried that maybe the ignition module that is underneath the coil pack should also be replaced.
What is the life expectancy of these modules?
Glad that you got it fixed.Thanks for the good words but am hardly a genius. Just using my own experience in trying to help. For some strange reason the coilpacks on the 3800 engines seem to be a repetitive problem. Might be location close to heat and/or weather exposure. As for the big module itself, I believe that if it goes out the engine will die but there is always a possibility of intermittent operation. It might set a code but only if completely dead. Always keep a spare ICM just in case as no one can really say how long the ignition module will last. If you buy a spare I would recommend using a name brand like AC Delco, Delphi, Wells or Standard. They are expensive. Last tip. If you decide to test the coilpacks by measuring the resistance of the primary and secondary windings, they are might read within spec at room temperature but when heated in the engine compartment they can fail to produce a solid spark. This is why I replace in set of three.
------------------ " THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite. "THE COLUSSUS" 87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H " ON THE LOOSE WITHOUT THE JUICE "
[This message has been edited by Dennis LaGrua (edited 10-11-2025).]
I'm seeing the ignition module for around $50.....knowing what I know about electronics is "when they go, they go", and these were probably the original coil packs. So, it would be good to swap in a new one.
