PFF - Pennock's Fiero Forum, PDA Edition

3800SC Running Issues (Page 1/1)

LukasMC

SEP 23, 12:19 PM

Hi everyone!

I bought an 4 speed 86 with a blown 2.8, but the seller also included what I believe is a 98 Regal 3800sc with unknown mileage. The swap is done (Thanks to the great info on here), but I'm having issues getting the engine to run properly. Before I committed to this engine, I did a compression test and all cylinders checked out at an even 150 psi. I also did the intake, valve cover and pan gaskets while I had it on the stand. When I first ran it in the Fiero, it had a couple dead injectors and some vacuum leaks (Injector O-ring and cracked egr tube) that I have sorted out.

I believe I have a couple problems I am trying to track down. When started, the engine seems to run well, but as it goes into closed loop the pcm commands very high negative trims (~-20 LTFT and -14.84 STFT). From what I can tell, the engine isn't running that rich, there is little fuel smell and no black smoke. I have tried 2 O2 sensors (From junkyard) with the same result. Additionally, the engine will occasionally start surging badly (It will eventually die if I don't hold the throttle open). I replaced the IAC which seemed to help a lot, but it will still sometimes begin surging at idle, and when driving the engine will occasionally surge and die when clutching in to stop. I can't seem to find any vacuum leaks with a smoke test machine, and a large vacuum leak seems inconsistent with the negative trims.

When driving the car bucks if I give it much throttle, feels like lean bucking to me which seems weird given the pcm taking away fuel. I have tried resetting the fuel trims and leaving the o2 disconnected, and the bucking seems to still be there. No codes are present in the pcm.

Having a hard time deciding where to look next, any ideas greatly appreciated,
Thanks for the help!
-Lukas

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86 SE

Dennis LaGrua

SEP 23, 06:21 PM

First off I would not use any junkyard sensors, especially the O2 units. I would only use the Denso O2 sensor that has proven effective. Also your MAF sensor provides the main fueling signal on the 3800 engine PCM. Try cleaning it with MAF cleaner and insure that its working correctly. What DTC's are you reading on your scanner, if any?

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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 "

LukasMC

SEP 23, 06:42 PM

Thanks for the Reply! I agree on the junkyard o2s, just figured they would be worth the couple bucks to test before ordering a new one in. Right now I've got a delco 02 in there, but I also tried a bosch. I'll try to get a new one on order. Forgot to add, I did clean the MAF with MAF cleaner, and its readings seem reasonable at ~4 g/s at idle. I have tested with the MAF unplugged and there doesn't seem to be any improvement, instead it had a hard time starting. No pending or verified DTCs show on the scanner.
Thanks!
-Lukas

Dennis LaGrua

SEP 24, 10:58 AM

If your negative fuel trims are running that high check the fuel pressure. Should be about 43 psi. at idle. Also could be a bad injector.

Spoon

SEP 24, 05:26 PM

Pull your spark plugs and check for wetness. Could be evidence of a stuck open injector. Use a noid light to check the injector firing.

Spoon

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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut