97 eldorado etc with a stumble

[scottym]

can anyone offer any assistance, 2 weeks ago i got mobil super unleaded at the local station, and about 30 miles later a service engine light soon came on. the car ran fine, and light went out after 60 miles. the next day after the light went out i noticed at idle at a stop light with the a/c on, when i took off the car had a very minor stumble, i figured might be water in the gas. i drove the tank empty and filled with another brand premium, and still stubled, (keep in mind, it does not stumble at all with the a/c off.) i took it to the local cadillac dealer, and the computer stored codes for a o2 sensor that was bad. i replace it, knowing it would have not effect on the stumble. the car has 76k miles, has been maintained RELIGOUSLY since new, i decided to try changing the original plugs with ac delco replacement, replaced the coil pack with ac delco, the wires were replace with ac delco last year, because of a burn thru causing a similar problem, only a worse hesitation and stumble. the dealer thinks perhaps maybe the a/c compressor bearing might be on its way out????? they wanted to play the swap and see game, and i said no, if you cant figure it out, i will . any other guys with a eldo, deville, seville, had/having the same trouble, should i try replacement wires again? any help is appreciated. scott in maine

[Ranger]

If the wires are only a year old they sould be fine but try misting them in a dark place at night and look for arcing. If the are bad, they are warrantied for life.

[scottym]

can you offer any other things i might check, i will try your suggestion, however i think the problem is located elsewhere. it happens when i take off from a light, or when i stop, and put in reverse, and back up, its off the idle, rough. can you also tell me what the little wire that appears to be a ground, under the coil ground on the block, mine appears to have been sheared off on the other end at one time or another. i think what makes me mad is the dealer and the lack of educated people working on these engines. my northstar was always so smooth till this problem, you could balance a glass of water on the cover of the engine, and race it, and the water would not move. help!! scott

[Eldyfig]

If you did get h2o in the tank, it will take more than one tank of good gas to clear it out. My wife used my ride once last year. It was getting low and she filled it up with gas from the local pan handlers station (a gas station at the bottom of my list for the look of quality). My car ran like crap for a while. It finally worked out of the system after two full tank loads and some prestone water remover.

When this was going on, car was very rough at idle and made alot of noise. Very scary, thought my ride was dying.

[scottym]

well, hopefully your right, tank is getting low again, so i will fill with exxon premium again, and add some prestone stuff like you suggested. im becomming discouraged with this, i have never had a problem with this car since new, always run preimum gas from one of th ebig guys, normally sunoco ultra, car loves it, however in the northern part of maine here, there is no sunoco. when we resided in boston, sunoco was a dime a dozen, and the car had been run on ultra for 7 years. I maintain this car mint, oil and filter every 2000 miles with penzoil oil, any time there is the hint of a problem, it went back to the cadillac dealer in boston, colonial cadillac in danvers mass, they were great. im going to try your suggestion, and i think i will replace the wires again with ac delco, and return the ones on the car back to the dealer for a refund. if you think of any other things that might be causing this, please post so i can read them. i appreciate all your input. scott

[Ranger]

Originally Posted by scottym

can you offer any other things i might check, i will try your suggestion, however i think the problem is located elsewhere. it happens when i take off from a light, or when i stop, and put in reverse, and back up, its off the idle, rough. can you also tell me what the little wire that appears to be a ground, under the coil ground on the block, mine appears to have been sheared off on the other end at one time or another. i think what makes me mad is the dealer and the lack of educated people working on these engines. my northstar was always so smooth till this problem, you could balance a glass of water on the cover of the engine, and race it, and the water would not move. help!! scott

I cannot think of anything else but the gas idea sounds plausible.

Did you have the fuel rail recall done? I think the wire you are talking about is the old ground wire for the old fuel rail. Since the new rail is stainless steel it is grounded at the mounting points. Since mechanics make their money by beating the clock, it is simply faster to cut the old ground off rather than removing it the way you or I would on our own cars.

[scottym]

yes the fuel rail recall was done on my 98 sedan deville, and the eldorado. i didnt have any problems after the recall being done, the car ran perfect. my wife, however on the deville, she had a gas odor for long time, and after many trips back to the dealer, the discovered a rubber o ring had not seated properly. this wis discovered after 1500 mile trip, imagine, the car could have burnt up, and the dealer would have been responsible. does it seem logical that the a/c compresser is somehow linked to my stumble like the dealer is suggesting. i tried again this am, and with the heat on to clear the fog off the windows, it seemed like it didnt stumble, but when i fliped over to a/c when arriving at work, and backed into my spot, it appeared that the stumble was there on acceleration while backing into the spot, and putting it into park, ran a little rough, and when i shut off the a/c and reved it a little, the idle was a smooth as possible...this is really becomming annoying, i know lots on automotive repair, but just can't figure thos out.

[Raze]

You've said you notice the 'stumble' (I'm assuming it's a misfire, but have you checked the codes?) when you turn the A/C on, but do you ever notice it at other times, such as when the engine is cold? If your plugs, wires, ignition coil are all ok, you could check for a vaccum leak on the intake manifold, or oil leaking from the o-ring gasket in the plugwell between the valvecover & head. If it's persistant over all driving operations it's most likely an ignition related issue. If it comes and goes, it's more likely a leak or fouling I would think but my knowledge is limited.

[scottym]

the dealer checked for codes the other day, and suprise, none stored in the computer. it only stumbles from s stop with the a/c on, never at any other speeds, the car runs exceptional at all speeds, and never when cold. i checked the manifold bolts, and all were tight to specs, and on one plugwell i did notice a small bit of oil when changing the plugs, but it looks like it had been there for a while.

[Eldyfig]

Is it possible that when at idle, the load being minimal, you do not feel any stumble? But, turn the a/c on, you put enough of a load on the engine to feel the miss. You wouldn't feel a slight miss while accelerating because the rpms are high enough. I would suspect a coil pack then.

On OBD I cars, you can go into pcm override to ps04 to disable specific injectors. The test can also test your spark to each cylinder while the car is running. When you disable the injector you should hear a change in the sound from your exhaust. No change in sound, bad coil pack. I have done this test to find my previously bad packs. I do not know if this works on an OBD II, or if it is a different override code from ps04.

[scottym]

coil pack is all new, as are the plugs, all ac delco, i'm going to drop the dough for a new set of wires, i was checking again tonight, and upon removal of the engine cover, it seems that when the recall was done, the dealer put those ribbed sleeves on the wires, as part of the fuel rail recall, and i noticed a crimp and the pack of wires where they come out of the back of the cover, the wires seem fine, but i think the smallest crimp perhaps may have pierced the wire, and causeing an arc. will replace them tomorrow, and let you know.

[STS 310]

That very well may be the cause of your problem.