Help..3800 Running Rough

jefferylackey · #1 11-04-2006, 10:08 PM

Please help. I'm at my wits ends. I've got a 1990 pontiac bonneville with the 3800. the car is barely running. here's the deal. for about a month, it would intermittently miss while driving down the road. then one day it went. car was running so rough i didn't know if i was going to make it home. it seems that if you keep it light on the throttle it almost runs fine. i'd say that you can give the gas peddle about 10 percent of it's travel. if you go past that it will start to spit, sputter, pop and cut out. Here's what i've done so far.
NEW PLUGS/PLUG WIRES
NES GAS FILTER
NEW AIR FILTER
NEW O2 SENSOR
NEW MAF SENSOR
REPLACED THE CAT
CHECKED FULE PRESSURE AT RAIL = 45PSI
CHECKED COILS, #3 WAS BAD AND REPLACED IT
RAN ALCOHOL AND FULE INJECTOR THROUGH TANK
RAN 2 TANKS OF 93 OCTANE, I USUALLY PUT THE 82 AND IT RUNS FINE.
CLEANED EGR VALVE OF CARBON DEPOSITS
CHECKED FOR VACCUM LEAKS
CHECKED TPS...used ohm meter, movement was smooth

even at idle, it kinda runs a little rough, but if you get to going down the road, as long as you stay off the gas, it will drive like nothing is wrong but like i said, there's a thresh hold that if you cross, it will cut out.. once you get it up to speed, say 70.. it will maintain that speed just fine without cutting out, as long as you barely give it gas. all this leads me to think about the TPS but as i said before, i've checked it. I replaced the crank sensor about a year ago, it was an aftermarket one. Any help would be greatly appreciated. thanks.

LMP · #2 11-05-2006, 06:13 AM

A few comments....lacking a definite explanation...
...doesn't this light up the CEL?..
TPS is OK, no doubt..this device is mostly used for transients (rapid throttle changes), not really for steady state throttle.
I'd suspect exhaust invasion...leaky EGR valve, leaky gasket or most possibly burnt exhaust valve. IN fact...were it not for the weird access to spark plugs...I would go for a compression test, at least to confirm or clear the valve option.

This can also be related to poor spark quality--spark has more problem going through denser atmosphere, which happens when throttle is more depressed.....and then the only remaining item in the loop is the ignition module...But this should give a CEL

jefferylackey · #3 11-05-2006, 07:29 AM

I don't know what a cel is. Uncle has a compression checker, i'll get it today and check it out. thanks for the help. It's not throwing any computer codes. For checking the coils, first did a ohm test, they were all the same, .56 ohms... then uncle came over to pull plugs one at a time, first we let the car warm up then started pulling plug wires from the coil one at a time, all were firing a bright blue and made a pretty loud pop sound while arking, except for #3, it was a yellow spark and not so loud, so i put on a new one. when i cleaned the egr valve, i didn't put a new gasket on it, just used the old one.

LMP · #4 11-05-2006, 11:12 AM

Quote:

Originally Posted by jefferylackey

I don't know what a cel is.... It's not throwing any computer codes. ..

OK you did it anyway : CEL = Check ENgine Light

ChemMan · #5 11-05-2006, 12:16 PM

Dirty fuel injectors?

jefferylackey · #6 11-05-2006, 01:53 PM

i've run a bottle of that fuel injector cleaner in my tank... i've also head that these cleaners don't really work, any input on them. is there any way i can take the injectors out and clean them?????thanks..

LMP · #7 11-05-2006, 03:21 PM

THe probability that ALL injectors start blocking at same time is very remote....dirty injectors can limit MAXIMUM power, but not normal driving..at least, not on a sudden...
...there has been a case of broken exhaust valve stem...almost similar symptoms...but, needless to say, very rare....not a high probability, but just to know it happens.It still can be a fire problem..but to me it does sound like intake contamination by stray exhaust. Since you have recently removed the EGR valve, I'd make a temporary gasket to totally block the valve..at least to make sure none of the 3 valves blocks open and test. Stray exhaust can sep through damaged lower intake manifold gasket...at least there were exhaust passages through intake manifold with carbs...may be I'm wrong now..just tell me...
THe burnt valve syndrome is also exactly like that..had that once long time ago...
Keep us informed of any findings, jeff......all the time someone comes with something totally unexpected..and we all learn for the next time.

sixsmiles · #8 11-06-2006, 01:48 PM

I had this exact condition on a 95 Bonneville after all the things you have done and a little more I found that the ground between the block and the H-Frame was lost. Not battery to engine but engine to chassis ground (H frame on the bottom of the car.) There is also a ground just below the coil pack I have heard of going bad. So... check the resistance between the engine block and the H Frame should be a few Ohms (1 -10), mine was 30MOhms.
Best of luck!!

jefferylackey · #9 11-16-2006, 11:11 AM

checked ground wire, got good grounds. i've run another bottle of fuel injection cleaner through it. still no changes, running like crap. hard running on start and go... but once it's going, just giving it a little gas and it'll run like a champ... push that gas pedal a little too far and it goes to cutting out, spitting, coughing, back firing... anyone else with any ideas.... i replaced the crank sensor about a year ago, when it would get hot, it would stop running...well, a couple days ago i was running around town, it got hot.. so i stopped, poured some water on the crank sensor, no change in the way it runs... so i don't think that's it..... rpm's have nothing to do with how it's running, i can do 70-80 with no problems, so long as i go easy on the throttle.

maxwedge · #10 11-16-2006, 02:25 PM

Quote:

Originally Posted by jefferylackey

checked ground wire, got good grounds. i've run another bottle of fuel injection cleaner through it. still no changes, running like crap. hard running on start and go... but once it's going, just giving it a little gas and it'll run like a champ... push that gas pedal a little too far and it goes to cutting out, spitting, coughing, back firing... anyone else with any ideas.... i replaced the crank sensor about a year ago, when it would get hot, it would stop running...well, a couple days ago i was running around town, it got hot.. so i stopped, poured some water on the crank sensor, no change in the way it runs... so i don't think that's it..... rpm's have nothing to do with how it's running, i can do 70-80 with no problems, so long as i go easy on the throttle.

Have you checked the fuel pressure as the problem occurs?

jefferylackey · #11 11-16-2006, 04:08 PM

how do i check the fuel pressure running down the road... can i leave the fuel pressure checker plugged up, with an extension, and run it outside the hood onto the front windshield.. that'd work i guess... if it's not raining tomorrow, i'll try it... been raining for 2 days now..

auto trainy · #12 11-16-2006, 06:51 PM

Max, what about the TPS ?,could it have a bad spot?

auto trainy · #13 11-16-2006, 07:02 PM

Sorry ,reread the original post about the TPS.

jefferylackey · #14 11-16-2006, 11:21 PM

forgot to mention, if i floor it, trany will down shift, engine will rev... but it sounds as if it's missing a cylinder.

jefferylackey · #15 11-17-2006, 03:41 PM

OK, took ignition control module off and went to autozone, they ran a test on it and it came back good. did another volt test on the tps... works fine... did another pressure check on fuel system. left pressure valve hooked up for more than 10 minutes, no drop in pressure... anyone with any more ideas.... please... at a dead end... maybe just junk it... but it runs great so long as you're up to speed and not giving it any gas. thanks, jeff out.

POST REPLY TO THIS THREAD