Wagon running terrible

My wifes car has suddenly decided to give me fits. It starts up and idles ok but any kind of load on it and it spark knocks pretty bad and stumbles. Driving down the road if I try to get into it it again spark knocks and stumbles. One thing I noticed is that the temp guage barely moved. 85 degrees and I drove the car about 10 miles both in traffic and in the country. The needle never went above the first mark. If the thermostat is stuck open would that cause the car to run too cold and give me these probs? The cel is not on. Could it also possibly be fuel? Any suggestions would be appreciated. I probably need to do a full tune up but right now time and money prohibit that - I just need to get it running better this weekend if I can. By the way, it's a 94 RMW.

Thanks
Jon

Open the hood at night with the engine running. Look for fireworks. A cold engine will not cause knocking, but even if the thermostat was missing, the temp would get to about 125. Could be a ground as well. Probably not the fuel, unless you put diesel in it. The temp sensor for the gauge and the ECM are not one and the same.

I opened the hodd last night after I posted, didn't see any arcing. I drove the car first thing this morning (cold), it ran fine at first but after about a mile or so I got one quick spark knock. it seems to do it for a brief time when I ease into the gas. I didn't notice any power loss this morning but I didn't drive very far. My wife said it's been acting up for a few days and takes about 6 miles or so. I'm going to try the coolant temp sensor although I changed it not long ago - I guess I could have got a bad one. I believe it's temp related and not fuel also. (I HOPE it doesn't have diesel in it LOL). Thanks Fred.

Jon

As fred posted in his other thread check for a bad ground,..
stone cold or not the car should run fine,. even at minus f*kkity F8ck around here in the winter the old gold run of the mill woody roady fires and runs fine,.never misses a beat,..

Nick

Ok, chned the thermostat and coolant temp sensor, car runs just as bad, guage still not right but I put the temp on the cc and it is running 165-170f. When I went to drive the car, the a/c wouldn't come on. i had brought my scanner home (cheap one, no real time data but it will read obd-1) and I had an a/c pressure switch code. I tried to jump the compressor but wouldn't work. I went ahead and drove the car, NO power on take off, terrible rattling from under the hood but once it gets going seems to clear up some and at wot it does ok although still feels a little sluggish. Now to the point of my rambling - I get down the road and the a/c suddenly works again, I get back and tell my wife and then she says "that car has electrical probs in the dash because sometimes the radio cuts off when she puts the car in park" I think fred and Nick are right. Now my question is, where are the grounds I need to check. I know theres one on the coil stud but where else?

Thanks
Jon

Ok I'l try and make this easier to read. I feel like I'm chasing my tail here. I'm still having issues with the car. This is especially aggrevating because now 3 out of 4 of our cars have problems. This morning I checked what grounds I could find, checked to make sure manifold bolts were tight, plug wires on tight, didn't find any probs. I went ahead and changed fuel filter since it had been a while. I still have the same problem with the car stumbling off idle when it gets some heat in the motor. Cold it's fine. When it stumbles, I also hear a momentary "rattling" coming from somewhere on the ds. I haven't been anle to pinpoint it. It also bogs while I'm hearing the noise. When I try to drive it under light throttle it wants to bog and rattle. Once I get past that it pulls good. I'm at a loss here!

Jon

Did you check your fuel pressure regulator?

No, do you think low fuel flow could cause this? I can't get my hands on a guage until tues unless there's another way to check?

certainly sound like a lack of fuel problem,. which can happen from bad O2's,. bad maf (i,d look at it first see if the wires are good,. not too dirty)
The ects will also cause these problems,. (you are changing the ects in the front of the water pump right?)
as was mentioned the temp sensor in the head simply runs the guage,. the ecm gets its temps from the sesnor in the water pump,.
a vacuum leak will be very pronounced when the car is warm,. not so when its cold,.
It,s very difficult to diagnose anything over the internet ,..

Nick

My wagon did the same thing 2 years ago and it was the MAF, but it had a code. It seems like it was about 50.00. I know you probably hate to change parts but it might be worth a try.

Well, I wish I could say I fixed the car but if I did I don't know what I did. This evening the power was mostly back and it doesn't have the stumle to it. I went ahead and swapped the maf with one from the other 94 just so I can see if that makes any difference. I'll know tomorrow after driving it again. The only thing that changed today was putting more gas in. Is it possible that this whole ordeal was over some bad gas?


Jon

Probably not the gas. Gas has to meet government standards, and they can not sell it if it does not. Sometimes we move parts without realizing it, and it temporarily fixes a problem. The issue with that is that we do not know what we did. The problem usually reoccurs at a later date, and we start all over again. You will know in the next few days if you actually "fixed" it. You might check your vapor recovery canister, and associated parts. I would still check the fuel pressure. You may have covered a split hose between the pump and the exit pipe in the tank giving you more presssure temporarily. I had that happen to my 92, and it about drove me nuts. I have "experience" now, you are getting some whether you want it or not.

LOL Fred you're probably right. I feel like this isn't the end, but we'll see. I will keep this updated.

Still no better. So far I have changed thermostat, coolant temp sensor (in the wp), fuel filter, maf, and today had fp checked and new plug wires. The same thing - car runs great cold but as soon as it starts getting heat in the motor it starts losing power and spark knocking. The more it's driven the worse it gets. It's also not storing any codes. Would the coil or icm cause it to act this way? If O2's were bad wouldn't it throw a code?

Thanks once again
Jon

I have heard that the ignition module can cause strange behavior, and the coil can have ground problems, so it could also be the coil. I am not as familiar with LT1s as with the LO3/5s

i suppose its possible that as the coil heats up it will run bad,.
certainly sounds like an odd problem,..

Nick

Okay, I know this is far out but could it be stopped up cat converters? Cold they contract and are somewhat open but when hot they expand and close up.

I'm going to 2nd the cat(s), if one or both cats are braking apart inside, those chunks can move around in there as the exhaust flow increases and decreases. That would cause similar problems you are experiencing. Quick hard acceleration when the engine is warm could cause a bad stumble, light easy throttle input may allow the engine to run (breath) fine even at WOT. The spark knock is heat related, 2 or more flame fronts in the combustion chamber running into each other, plugged converters will build up heat in an engine quick.


Give the cats a good smack with a hammer and see if you hear some rattleing in there. Or go out tonight, get the car to act up for a little bit, pull into a parking lot or what not, and check and see if the cat(s) is glowing. If so you have a pluged cat(s). If this is the case you may even see the manifold(s) glowing Orange/red. Hope this helps in some way, good luck.

Mike

Todays adventure: Since the fuel pump went out on the black 94 and I quit driving it, I guess it's now a parts donor. I changed the icm, no difference. Changed the coil, again no difference. Changed the pcm, still the same. Went ahead and put new plugs in even though the old ones weren't very old and looked fine. No change. Took the car to the muffler shop and they said neither cat was plugged. Actually he said the pass side was already empty but there was no restriction on either side. Anyone think it might be the opti? I'm running out of things to try.

Jon

Sounds like an EGR problem to me. The EGR system does not operate when the engine is cold and will cause an off-idle stumble and spark knock if it is not working properly at normal operating temperatures. The EGR valve is vacuum operated.

To test the EGR valve; remove the vacuum line that is connected to the valve, apply vacuum using a vacuum pump to the valve while the engine is running. If the engine stalls the EGR valve is working, if not, the EGR valve may have failed or the passages may be plugged with carbon deposits.

If the valve is working, you could have a vacuum leak prevening the EGR system from working.

I swapped the EGR this morning with the other car and in dong so the plastic line to it snapped almost as soon as I touched it. Changed the lines too and drove the car. It seemed to be doing better but still not right. I had the temp on the cc and after driving about 5 miles and then letting the car idle it never got above 164. Moving it was around 156. I changed the thermostat again and now the temp is staying around 178. Car runs much better although still a slight miss. I'm wondering if I got a bad thermostat last week.

Thank you everybody who responded with suggestions. I really appreciate the help and I hope I will be able to pay it forward!!

Thanks again
Jon

Update. I've cleared up the spark knock so I assume it must have been temp related. However, the car is running worse than ever. Skipping and missing like crazy. It doesn't matter whether it's cold or hot any more. Since the opti is the only thing I haven't changed, I'm leaning toward that. Does anyone have any experience with any brand other than delco? I've seen a pretty wide price range on whats available. Thanks.

Jon

TRUST ME!!!! I have done 4 in 4 months [You must be registered and logged in to see this image.]

thepartsladi on ebay. Best OEM parts.

I read through this quickly, so excuse me if I am redundant. Did you check the engine grounds.

Main ground from the battery.............
Ground strap to the back of the drivers side head............
and the three grounds by the coil.............

Tim

Yeah, check the grounds by the coil, a few times.....

If you are going opti, thepartsladi is the way to go.

Robert - 4 in 4 months? You ought to be a pro at this!

Tim and 2000Z - I did check the grounds over and over. I feel like I've checked EVERYTHING twice. Yesterday I started with the basics again, checked spark and had no fire on #8 cylinder. I swapped the wire (pita - pass side) and still no spark. I then spent 2 hours removing the opti from the black wagon. Poor car, I guess it's now officially my parts car. Anyway, got the opti back on the ldm but haven't put the water pump or fan back on. I cranked it just long enough to check and see if I had spark on #8. If this fixes it I'll probably go ahead and order a new opti to be ready.
BTW I looked up thepartsladi and it looks like they're now thepartspros.

Jon

Everyone should be glad to know after chasing my tail for all this time I FINALLY caught it. Now I'll quit bellyaching about this problem. After changing everything but the tires (and I would have if I thought it would have helped lol) I did a compression test today. All 8 cylinders had right around 120 lbs but in doing that I discovered 3 of the new plugs I put in last week looked terrible. #1 had such a big chunk of carbon on it there was no way it could have fired right. I put the older ac delco's back in and the car runs great.
I think I probably had more than one problem at the same time and thats why this has been so aggrevating. Probably the combination of running too cool and the opti going created the carbon. Anyhow, thanks for all the suggestions and again I hope I can return the favor.

Jon

Ignition module issues are usually crap like starts ok but won't restaqrt when it's turned off. Or no freaking spark! When you checked for codes... Nothing?

What was the fuel pressure at the valve on the fuel rail?

You say it starts up and idles ok. For how long? At about the three minute mark it should be changing over from open loop mode and going into closed loop operation. One of the parameters to get there is temperature. Is there a correlation?

If you stomp on the pedal right away after you start, does it bog, or only after a few minutes has elapsed and things have supposedly warmed up? If the ECM doesn't know it has warmed up, there are still fuel issues envolved.

Is there black smoke from the exhaust after it warms up? unburned fuel?

Get a pin out diagram of your ECM. it will help you trace connections, particularly if the several issues are tied to the same ground.

One other thing I did was check the aux battery post. Someone previous to me had replaced the battery cable to it. It had a brass post but when I took the cable off to clean it I discovered 3 wires connected to the back that had been vey hot at some point. I'm not sure what they are for and even with the fsm I couldn't figure it out. I replaced the terminals, cleaned everything, and put it back together. I think that along with proper operating temps and the car running on all 8 cylinders finally got it. It's running the best it has since I've had it and seems to be much better on gas (haven't checked the figures). One other note - when you switch the pcm from a 2.56 non tow car into a 2.93 tow pack guess what happens to the speedometer. Gotta remember to change it back lol.

Jon