Odd problem rough running (Page 1/1)
weaselbeak DEC 16, 11:42 AM
I have an odd problem. My NA 3800 is running rough, misses badly & pukes on acceleration. It will run up smoothly if you do it slowly with no load. Fuel pressure is good, new pump, new injectors, new sensors for tps, map, & maf, & idle air control. The only code it throws shows intake air temp. I put that sensor on new as well & it doesn't change. The odd part is that it runs better, still not good, with the intake air temp sensor unplugged. A good bit better, but not really driveable. I can probably limp it off to a better mechanic without a trailer, but thought I might ask around here 1st. I am at the point where it's over my head. There are no vacuum leaks either. Any new ideas?

[This message has been edited by weaselbeak (edited 02-27-2022).]

Mike in Sydney DEC 16, 06:24 PM
Fuel Filter?
weaselbeak DEC 17, 10:03 AM
New pump, filter, regulator. pressure never drops below 50 on acceleration. 60 at idle.
Dennis LaGrua DEC 17, 10:11 AM
My 3800SC had all the symptoms that you described. It turned out that it was a bad ground to the ignition module. Removed ign module connector, removed coil packs (5.5mm socket required) and coil pack and module was now free. Cleaned bottom of ignition module with alcohol, then with very fine 600 grit wet dry paper, coated module bottom with a light coat of conductive thermal grease. Put it all back together, ran a 14ga ground wire direct to battery ground with a ring wire lug. Started the engine and all was fine.Second one we saw with that problem. The other one had actual corrosion below the module on the mounting plate. Both triggered a DTC p0300 .
BTW, any trouble codes show up? Reset the PCM by disconnecting the battery cable. If you are still getting the IAT code then something else is wrong.

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" 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 12-17-2021).]

weaselbeak DEC 18, 04:39 AM
I will try that. The only code it throws is P0113, the IAT code.
weaselbeak DEC 24, 11:24 PM
Well, that didn't work, but it was fairly corroded under there.
weaselbeak FEB 27, 10:55 PM
Up date. Pretty weird tho. I offered a hotshot mechanic 100 bucks to come look at it and just tell me what he thinks. Best money I ever spent. Even tho every coil tested ok, he was of the experienced 3800 opinion that they were not up to snuff. He also was sure that my brand new MAF sensor was faulty, based on his experience with the 3800. So I got coils, plug wires for the heck of it, and another MAF sensor from fleabay. It got better with the coils, and back to good with the MAF sensor. It now pulls like a banshee thru all gears, no miss. I still have a couple of issues, but we'll get that figured out somehow. It really doesn't want to run when cold, acting like a vacuum leak, which it doesn't have. OK warmed up. His code reader refused to play with my computer. Mine shows only one code, PO113, which is intake air temperature sensor. A new one was no help and and still shoots the code. Used a new plug in on it as well. But that is small potatoes I can work on as I have my driver back. I told him I did not mind blindly throwing on new parts, because now I have new parts & that's comfort to me. I had to edit my original post, as I had inadvertently typed idle air temp instead of intake air temp.

[This message has been edited by weaselbeak (edited 02-27-2022).]

theogre FEB 28, 12:05 AM
Check EGR valve even if is a "digital" one.
Vac valve can have problem on vacuum side but any can weak/broken springs etc. making a "vacuum leak" to the rest of engine.

See my Cave, Vac Leaks
Read even after you look for them.

pull spark plugs and keep in order. Plug(s) cleaner then others can be problems like coolant leak from iffy intake parts.

Is DIS engine? see http://www.fiero.nl/forum/Forum2/HTML/145876.html
Iffy plugs & plug wires can kill coil(s) and ICM
Iffy power or main ground can wreck ICM too.
Other "ground" isn't for ground the ICM. See my Cave, Ground "Myth" notes

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

weaselbeak FEB 28, 06:17 PM
Thank you. I was at a loss as to where to look next.
weaselbeak MAY 26, 11:42 PM
Well, all is pretty good now.

[This message has been edited by weaselbeak (edited 05-27-2022).]