My wifes 92 LT1 automatic is about to drive me crazy, kind of long story. Took it to a dealer to get the cruise control fixed, car was running fine, get the car back and it picked up a miss in it. Took it back for them to fix what ever they had screwed up, they decided it needed the opti replaced. Going down the road the car runs fine, put the motor under a load it misses or shakes and then takes off (like kicking it down into passing gear) . Even idiling it is just fine until you nail it and it will miss a little. So I had my regular mechanic replace the distributor, cap, rotor, plugs, and wires, still doing the same thing. Runs fine except when you get on it or taking off right off of idle but the motor is under a load right then. Mechanic noticed that when it was cold it didn't do it right then, drove around the shop and it started again. Could it be in the vacuum system or the injectors, I don't want to start throwing money at it. The car has 100,000 on it so everything I had replaced didn't really bother me, but I don't want to just started replacing stuff untill I find the problem or go completely broke, which would happen first anyway. Thanks for any help I appreciate it.

David

 

Sounds like you need an Opti.

 

I also have a 92 and I remember back years ago when I had a similar problem;
-at idle there seemed to be no problem unless you reeved it and there would be a light miss
-when under normal driving, stop and go at lights(intown) no problem
-only when the car was warm did it act up when you tried to excellerate from normal driving speed to a get up and go fast speed or excellerating to get onto the highway speed.At that point it seemed like the car would almost die or loose all excelleration and it felt like the car was bogging or was starving for gas and then after a few seconds or until it finally started to get to a certain speed it would drive okay again, until you tried to put the pedal to the floor to excellerate again.

Long story short (maybe to late) but it was my opti and after replacing it , it didn't act that way anymore. I never had any noticeable leak from my water pump, but it had a small or slow leak that affected the opti. Had the water pump changed also.

Good luck with finding the problem!
Any questions feel free to ask me, I've owned mine for 17 years and we have gone through alot of things.

Chris

 

Sounds like it never needed the opti replaced. Assuming the Service Engine light is not on, try..

Process of elimination-

Check fuel pressure (idle and under load)

Check injectors (ohms and noid light)

Check every plug near the throttle body- unplug, blow out, replug.

Someone with an Autoxray 6000 or similar scanner for OBD1 (most dealers don't have anymore) can give you info on the voltages to all your sensors

I found one plug not connecting well along with a scan using AX6000 told me my Water Temp sensor is not reading right (even though tempurature read correctly). This will effect how the ECM controls the fuel (lean/rich).

 

There are no codes showing but I do believe it is something simple that we are over looking. Just trying to find it with out pulling out the rest of my hair.

 

Quite often when a problem shows up after some other work is done, it is no coincidence. It is likely that the dealer tech disturbed something while doing the original work. I agree that a complete scan of sensors, etc. and also for history codes should be your next move.

 

How old are the spark plugs and wires? coil or IGN module? Sounds like a no sparks issue or very weak spark.
The only other thing they screwed with doing the cruise control would be tha vacuum lines that go to it if it is like my 91. I assume you did not have the skip before the cruise control work.
Dave

 

The dealer serviced the car.
The mechanics are trained to fix the problem.
They didn't fix the problem,and still made their money.
I would go back and insist they solve it and I would contact the GM rep to ensure they don't clean out your bank account in the process.


Geeeeez !!!! What happened to service.??????

 

The dealer I took it to won't ever see me and my money again. I already took it back to them and nothing came of it. I also realize that it is my word against theirs as far as how the car was running before. I had to put a battery in it this morning, then went for a drive, it will still sit you back in the seat it just has that studder/miss when you first get on it. The mechanic that I have been taken it to wants to check the injectors next. I'm going to try and read up on every thing I can on it and try to do what I can here at home on my own. I'll work on our 74 Stingray but I'm nervous about all the sensors and what not on the 92.

 

Do you have Champian spark plugs ? It really sounds like an eginition break down.
At night have someone start the motor ,put in gear an add a little throtal with their foot on the brake. Look and see of you can see spark jumping arround the motor. If you do you have a bad set of plugs or wires. I won't put Champion plugs in a wheel borrow. For that exact same problem.

 

When was the last time the fuel filter was changed? My car had similar symptoms and the filter was the culprit.

 

As far as working on your '74 vs. the '92, yes, it's a whole new ballgame, heavily dependent on electronics. However, if you're inclined to work on the '92, and do some background reading, some aspects of the newer diagnostics are easier than the way we used to do it in the "old days". If you decide to go this route, I would buy a copy of the Facrory Service Manual for '92 (not Chilton's, etc.). With that in hand, and a scanner if you can swing it, you will be able to do at least as well as a repair shop (you already had a bad experience there) especially if you look for guidance on the Forum. I have a lifetime of working on cars, trucks, and construction equipment, from back when you could look under the hood and see the ground on either side of the engine, did my share of clutch changes on the ground in the snow, etc, but I continue to learn from Forum members. In the end, it's comforting to know how your car works instead of fearing in the back of your mind that you're sunk if something fails.

Remember, these cars are old enough now, and never mainstream enough, that most techs working now have never been under the hood of a C4. The driveline mechanicals are not that specialized, but a lot of the electronic controls call for more model-specific knowledge. Even some shops use the "replace parts at random" approach and you pay the bill.

 

If you have no codes it could be the ICM or the wiring harnesses from the opti and / or ICM.
If you have codes post them!
With a factory service manual, a little mechanical ability and the C4 tech forum you can fix most issues yourself. The FSM will be the best $100 (or less) you spend!

 

So very true, even at Dealerships.

OP- buy a fuel pressure tester ($30) a volt/ohm meter ($40) and a noid light set ($15 ebay) and you can test the basics.

Fuel injectors should all be in the same ohm range (remove fuel rail cover, pull injector plug (push in on metal tab) and put black/red from ohm meter (set to 20k) and they should read in the 12ish range. Put noid light on injector while engine is running (one at a time, quickly) to see that they are firing.

Fuel pressure gauge-(connect to passenger side shraeder valve (black cap looks like a large tire valve stem cap) and turn on key (not engine first). Should read 41-43 immediatly. If it does, tape it to the windshield and take a drive, have a passenger monitor the gauge when you punch it etc. This will help you see if a fuel filter or pump may be needed.

 

So far I have replaced the distributor, wires, plugs(ac delco), fuel filter, water pump, and battery. No codes are showing and I will look and get a service manual because I would rather do the work myself. I just don't like getting in the situation where I don't have what I need to do it properly. Whether it be knowledge or tools or both, older cars like the 74 or my Nova I'll work on them with no problem. Guys I do appreciate all of the advise and hopefully weather permitting this weekend I can do a little more trouble shoting on it.

 

Hi David, if you have access to a hand held o'scope it will help isolate the cylinder(s) causing the misfire. The fact that you replaced all the tune up parts leads me to think that you may have an injector issue or fuel pump problem. Take a fuel pump reading and if you can while you are under light acceleration. Also if a scope reading leads you to a particular cylinder,measure the resistance of the injector to a known good injector. Connect a vac guage to manifold and make sure your reading is steady,a large swing indicates a valve issue. But I don't think thats the problem. Didn't mean to over do it. Hope this helps

 

This car is about to drive me crazy on top of the on going problem the cooling fan motor is trying to go out. It will make all kind of noise when it kicks on, I can tap on the top of the support and make it stop. I am looking at the fuel system now, was going to work on it this weekend but have to many other honey do's right now. I'll get it figured out but we are looking to go to Bowling Green in a month or so and I don't know if we are going to be able to drive it or not.

David

 

I found mine on e-bay $66.00...a must have

 

You mean your regular wrench replaced the optispark? It's all in one piece. It's easy to do you just have to pull some stuff out. I sort of know what you're talking about like you're in 1st gear and you give it a little gas before it kicks in. It doesn't do this at any other speed only pulling out of the driveway and going down the street is when I sometimes feel it. Mines been doing it for years but I replaced my Opti and she's alive again so race on. There's a post on here somewhere that shows you step by step of how to replace the Opti with HD pictures. Hook you car up to a scanner and see if anything pops up.

 

Found a solution for my problems with my wifes 92 today, traded for a 2004 that only has 11000 miles on it. The 92's A/C went out today and that was the last straw, got on line and found the 04 on a local lot went to look at it and now it is under the carport. As we pulled up to the lot the cooling fans on the 92 went to screaming, the sales guy looked at us kind of funny.

David