2004 3.8L NA in my 88 GT - engine stuttering (Page 1/1)
qwikgta MAY 31, 05:22 PM
2004 NA 3800. Ran fine with no issues. I used it as a daily driver and it never let me down. Then... the Fuel Pump (FP) went south, but, it was not the FP it was the FP relay.

Short story: The PO wired up the FP using "Sinisters" FP hot wire diagram. I didn't know there was two relays, so when I checked the stock relay and the FP did not run, I assumed it was the issue. Replaced the relay and still could not get the pump to run, so I dropped the tank only to find the "hot wire" setup and another relay. Once I checked that relay I found the problem. Because I did not know what this extra wiring was at the time, I removed it and made the FP run off the stock wire diagram. Also, since I had the tank on the ground and a new FP I decided to replace the old stuff w/ new stuff. OK, so i put it all back together and now it runs like crap.

It will start fine, and idle fine, but when I try to drive it and push down the accelerator pedal it starts to stall and "kick". I can feather the throttle back and it will run again, but if i push the gas it runs like crap. If I let the car sit and idle no issues until its been running for about 10 min, then it starts to run like crap and no matter how much gas I give it, it wants to stall. The engine actually starts to "jump" around and I have to turn it off before it blows up. I have checked the Fuel Pressure and its getting a solid 42-45 PSI. Even when I push the throttle, and it starts to stall, the pressure stays at the 42-45 mark, so I don't think its fuel.

The first thing I thought was the Cat Converter/Muffler was plugged, so I dropped the exhaust and it made no change. Still wanted to stall. It has air, so it must be spark.

I replaced the ICM and it made no change. I have another set of plugs, wires, coils that I plan to swap. I also have another FP, hose, screen ready to drop in if needed.

What am I missing???

Thanks in advance.

Rob
La fiera MAY 31, 10:36 PM
Make sure the TPS is working properly. Also, did you change the fuel filter as a precaution? Make sure the MAP sensor hose to the sensor is not cracked or crimped.
Frenchrafe JUN 01, 03:35 AM
I had a similar problem with a replacement fuel pump fitted too low.
The fuel pickup/mesh filter was squashed up against the pump inlet. This caused the pump to act up and not pump enough, especially at WOT.
Check the depth of the tank and adjust accordingly the pickup height.
I had to raise my pump 5mm to get clearance. (Slight mod on the pump hanger/level sender.)
Regards,
Rafe

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qwikgta JUN 01, 06:39 PM
Good ideas, i'll give them a try

Rob
Raydar JUN 02, 08:25 AM
Are you taking your pressure readings at the fuel rails?
If so, that would seem to eliminate most everything upstream. (Pump, filter, etc.)
Maybe some crap got sucked up or knocked loose, and is clogging the injectors. Maybe try connecting a noid light to one of the injector connectors to make sure the ECM is firing them correctly.
KissMySSFiero JUN 03, 12:24 PM
Unplug the MAF and see if it goes away.
Just replaced mine for similar issues.

I had dropped the tank to fix the fuel level sending unit.

Put it back together and before I got through half a tank, it had stumbling and stalling issues.

The MAF was "Sticking" on a reading, then jumping when it registered again causing what felt like the fuel pump cutting out.

it should still run without the MAF.

Likely not the problem, but an easy check. If the tank isn't venting properly(letting air in) it could cause stalling issues. Common with boats when someone doesn't open the tank vent, or something clogs it.
An easy check is to take off the fuel cap.

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SSFiero@Aol.com

qwikgta JUL 02, 04:32 PM
So got it running again. Replaced the air filter, its a CAI type that sits just behind the Archie Rockers and was rusted and filled with dirt. Thought that was it, but after installing a new K&N it still ran bad.

I noticed after letting it run for a few minutes that it was finally flashing a code. Checked it and found a P0300 which is a bad coil. Found that the 6/3 coil was not making spark. Put on a new coil and it runs so much better.

Took it for a spin, drove it about 10 miles and it drove fine. Started slow going around the block a few times, had to get the rust off the rotors. Then went out on the main roads. I didn't push it until it was warm and after a few "3/4 throttle" blasts I was happy, no studder. Then I did a full "balls to the walls" WOT blast and it started off fine then started to studder again. I did a few of them, and each time it drove great up to about 3/4 throttle and once I pushed to the floor it would studder. Backed off and it went away and drove great.

After about 15 min of driving I noticed the coolant temp was HOT, over 220 on my gauge, even started to vent from the overflow bottle. Was able to nurse it home and after I let it cool it was over a gallon low on coolant.

UPDATE: After letting it cool and filling it with coolant I took it for another drive. I taped the fuel pressure gauge to the back window and watched it as I did a few WOT blasts. Two things I noticed, one, it didn't studder under WOT and the two, the fuel pressure didn't drop at all. As for the temps/coolant, I think that my radiator fan is not working. Temps started to increase even though it was much cooler out. Was watching the temps on my phone/OBD app and they would go up to 200+, then down to 185, then go back up to 200+ and then back down to 185. I'm going to have to troubleshoot the fan next.

Rob

[This message has been edited by qwikgta (edited 07-02-2022).]

Dennis LaGrua JUL 02, 08:47 PM
I would advise putting a quality scan tool to the OBDII connector and monitor the performance of all the sensors while driving. If the engine is going lean the O2 readings, STFT and LTFTs will tell you that. I would also check if the swap has a ground wire to the coil pack mounting plate. If not, put a 12 ga wire there right to Bat+ Make sure that plate is clean for good contacts with the coils.
I also recommend cleaning the MAF sensor with a MAF spray cleaner. . You are using a K&N Filter that is oil saturated. When new those filters will emit a small oil mist that gets on the hot wire in the sensor and messes up the MAF readings.

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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 "

qwikgta JUL 07, 10:39 PM
all fixed.

Turns out the bad coil was it. swapped out a new one and it runs great.

The overheating issue was a bad fan motor. Did the usual troubleshooting for a fuse/relay/motor and found out it was the motor.

Swapped out the fan with one from my parts garage and presto, works great.

Drove it for about 25 miles and the temps never got over 190.

Feels so good to drive a Fiero again. Now I can start to fix/update all the other stuff I need to do, but its a driver again.

Rob