HISTORY: I have an LT1 1994 Camaro Z28, automatic. I bought it used without much information on it's history. It seems very stock. It came with a leaky h2o pump, bad wires, 97K miles on orginal opti, badly slipping tranny between 1 and 2, a very bad vibration and stumble, and it sat 6 months before I came along.

I immediately gave this car a tune up (plugs, wires, PCV, fuel filter) but didn't do the cap and rotor. I had never heard of opti until I owned this car. Expensive and hard to get to. I also didn't change the coil wire because I didn't see it behind everything (DUH). I did have the tranny rebuilt with a slight shift kit. That works great.

I just put on a new water pump, new distributor (and cap and rotor), new coil, new ign. Module, new coolant temp. sensor, new fuel injector, new starter, new battery, cleaned all contacts, and more. I still have the same coil wire (DUH) because I cannot find one yet that is sold by itself (Kits only). I lost the new one from the kit. I checked for vauum leaks-NONE.

PROBLEM - finally: Very bad vibration. Slight stumble on acceleration, especially from a stop, and vibration through all ranges of RPM.

What did I miss? What could this be? I know every other person on this site asks this question. They try everything, then go to a shop. They say they will keep us posted, but I never see anything else. What are some of the reasons you out there have found to cause this? Could this be a bad crank pulley dampener? My vacuum guage doesn't show any issues internally. I don't have bad gas smell. It does it in both open loop and closed. Could this be a bad computer? How about dirty injectors?

Any help or advise would be greatly appreciated. It runs, it drives, it is not my everyday driver. But I would like it better (smoother) than this.

Thanks!!!

 

bro you really should have changed your opti out while you were doing the water pump, the leaky water pump probably caused your opti to crap out. Thats probably what the stumble and hesitation is from. It's not really as big of a pain in the *** as most make it seem, but i gaurantee you once you change out ur opti it'll run strong.

 

thanks for responding gt8249, I just wanted to clear up my orginal complaint. I am usually accused of talking too much and I wanted to keep it short. Here is the short version of the whole story...

I bought this car 6 years ago from a man who has died. He wanted me to buy it because his son was neglecting it. Believe it or not, his son wanted a cavalier instead. Anyway, I had the tranny done immediately and I did the plugs, wires, cap and rotor, pcv and fuel filter. I had a horrible stumble and vibrtion that actually shakes the dash. After using my vacuum guage and fuel tester, I suspected a fuel injector; but was wrong. I drove on the bad h2o pump, since it wasn't leaking, for 4 years. I put up with the vibrtion since I didn't drive it much. It had sat for 6 months prior to my owning it. It also would not run good at all on humid or rainy days. Finally, on a heavy rainy day in October of 2004, it stopped running. When I tried to start it, the starter broke from a backfire. I was flat bedded home. I bought everything to do the job at that time but the car sat in my garage since October 2004, while I never had a chance to get to it. Finally this year I said it will run, and I put on a brand new opti distributor, cap and rotor. Not sure what to expect when I started it again, it ran good. It seems stronger than it used to be, but the stumble and vibration is still there. I also changed out all of the things I stated before (coil, module, cts).

I know others have complained about this, but I must have missed their replies once they fixed their cars similar problems. I am hoping there is one typical thing that I have missed.

Thanks for any input.

 

Could you describe the stumble and vibration more in depth? Does it only happen at certain RPM ranges? Only when accelerating hard? More info on this could help people to diagnose the problem sooner. I know how frustrating it can be to replace all those things and still not hvae a smooth running car

 

My stumble is when accelerating from any speed. On the highway, I punch it at say 70 and the car responds by acting like a cough and slowing down. I back off and slowly accelerate, and the car will feel like I took my foot off of the gas, cough a couple of times, then shift down, and now the thrust. If I am stopped and want to peel out, the car won't. It acts like it has no power until it gets moving, even just slightly. Instead I take my foot off of the brake, let the car get moving a little by the idle, then step on it...but not punch it, and the car will accelerate quickly. If I punch it at an idle and moving a little, the car will bog down. I may say it seems like a backfire through the intake. It did this before and after the new opti.

The vibration is like a heavy miss. I know the wires are correct. The car runs and starts too good to have a crossed wire. After warmed up, at a stop light, the tack needle drifts about 100 to 200 rpms, on a down drift the lights get dim on my dash and an up drift they get bright. It was a cool night tonight, around 60 degrees. The car ran better than it did before. Responsive, less harsh of a vibration. It seems like the new opti did some good things, but the vibration is elusive. The vibration used to be so severe the dash plastic used to rattle with it. Now it is less severe but still there. You really feel it in the steering wheel, the seat, all through the car at an idle, and any acceleration. It is there at crusing speed too.

The vibration and stumble were there before the new torque converter. Could this be a dirty ground cable connection? Could it be as simple as a bad coil wire? My vac guage says steady vacuum. Could it be internal or mechanical?

 

Usually the situation to it running funky/bad is the opti -- it can do some really screwy things to these cars.

I would double check the coil wire -- and also double check the spark plug wires in general. I had issues of a bad stumble at high RPM which eventually creeped lower, and then finally my car would totally shut off at highway speeds. I replaced the coil and it still did it, all along all it needed was a new coil wire.

I've also been through my fair share of plugs/wires. I had a issue with it running incorrectly and I got the car back up on the jack stands and the diagram in the Hayne's Manual was actually upside down for the wires. So double check that, and actually refer to the numbers on the opti itself on how to route them. Try that out and get back with us.

Also, because the car isn't your DD -- check out the fuel pump. If it was owned and neglected its possible that the son didn't take care of it and ran the car to empty frequently. Just something to think about.

 

Make sure the plug wires are not arcing.

Spray some water on the wires, look and listen for spark arcing. I had this problem a while back. My wires were arcing cause severe misses and the car would shake violently. It looked like fireworks under the hood from faulty wires.

I now have MSD 8.5mm with no arcing issues at all.
Double check that coil wire.

 

I appreciate all of the advice. I see we are leaning toward the wires. I can believe that. I bought new wires but never put on the coil wire (couldn't see it). That was 6 years ago. I am not normally cheap, but 6 years ago I didn't know what I was buying when I bought this. I put on a set of AUTOZONE wires...yikes!! Maybe I need to buy some wires from the neighborhood engine shop (National Machined Automotive). Still the vibration was there before and after the new wires, and no change. I know the importance of wires. I will start there. I dread the thought of changing the passanger side wires.

I will keep you posted!!

 

You need at a minimum a REAL (no auto-zone bargain baloney) set of Ignition Wires. Grab a set of 8.5mm MSD Super-Conductors (not cheap:~$80.00) that will actually work as well if not better than factory wires. This wire set includes a coil wire....don't lose it this time !

 

The Autozone wires work fine on a near bolt-on car. Spending $80 for pretty red/blue/yellow wires is pretty ludacris if you asked me. I used autozone wires on my car for almost a year until I stepped up the car completely with a cam and nitrous. The biggest pro to Autozone wires is that they will replace them for free for the life of the car as long as you still own it, I can't say I'd complain too much about that one, and they do include a coil wire -- if not just take them back and get a whole new set.

The best way to see if the wires are arching is to start the car at night with the lights off in the garage or just in dark outside. You'll definately be able to see whether or not you've got issues with that.

From my experience, the easiest way to take care of the passenger side is actually from below the car. Make sure you pay attention to where the wires are supposed to go, but just snake your arm up along the y-pipe into the passenger side and just be patient with the whole process. Then from the top use a ratchet or something to the equivalent to sort of push them on as far as you can by using the body of the car as a fulcrum.

 

I didn't buy the wires yet. I plan to today. National Engine said $50 to $140. They have to order which will take another day. I use Autozone wires on my cars with pretty good results. I believe my Z is near stock.

I wanted to meantion that the car runs almost perfect when it is cool out. Last night it got down to the 60's and the vibration was almost gone, and the performance was there. How about a MAP or Baro sensor? DO I have one of those? What would be dependant on the weather and would cause this vibration-stumble? I have decided the vibration and stumble is much better since the new Opti.

 

Yes your car does have a MAP. Have you seen if it will run okay in open loop? Try unplugging your MAF and starting the car and see if the car runs fine in open loop.

That'll tell you if its sensor related, or if it is ignition related.

 

cschevy, where are you located? If you are lucky, you may be close to someone on this board who has experience with these cars or better yet, someone who has a laptop and scanning software.
If not, I would pay up to $100 to have it diagnosed at a dealership. Let them know you are going to fix the car yourself and that you just need to know what the problem is.
Since you replaced most of your parts 6 years ago, I would certainly replace the fuel filter again (it's cheap). The problem seems more like a misfire though. Pull a couple plugs that are easy to get to and see if they are clean and still gapped correctly.
Also, do as most already said: Check those wires. There is nothing wrong with Autozone wires, but check them for arching or burns/cracks/cuts and make sure the terminals are not corroded.
Finally, as I learned this weekend, clean your battery terminals and apply some dielectric grease when you put them back in. With dimming lights and such, this certainly sounds like a problem with electrical current.
I'm trying to think of all the easy things that don't take much time. If you do these processes and you do not find anything wrong with your wires or plugs, then I would find a place which has good diagnostics capabilities. If you live near a large or newer dealership, they should be able to target the problem.

 

Hi group, I first want to say thanks for the advice up to now. I want to say thanks also for not treating me like I am a 'dolt'. I actually have a some knowledge with cars, but I was always weak in diagnostics of these newer ones.

I have had some success in pinpointing my problem. I have a cousin who is exceptional with Chevy engines. He was trained at the NASCAR school in Ohio, and works as a diagnostic and testing technician at the Chrysler Proving grounds. He is and always will be dedicated to Chevy. I have been very busy and have not had much money to invest into the car. So far I have done nothing, because I am afraid of wasting money on things that are not neccessary.

There have been a lot of cruises here, in Michigan, this summer. I left a cruise today and went to my cousin's for a graduation party. He was more than excited to slip behind the wheel and take my 'Z' for a ride. Here is his diagnosis:

Once he started the car:

He suspects my plugs are fouled because of my prior bad distributor.
He suspects bad wires and suggests good ones I told him you in this group suggested.
He suspects crossed wires.
He suspects MAF.

Upon a short diagonstic inspection, he found:

He determined that my computer is not talking to me. Bad ground is likely keeping my car from giving me codes. So we cannot rule out sensors.

He found my snorkel feeding my air intake was loose. He told me that will cause intake air from a source around the MAF and really confuse the computer. He tightened the clamp.

He found a cracked and arcing plug wire. I split it when I installed it 6 years ago. He feels I will find more bad wires as I change them. Too much vibration to be just one bad wire.

He suggested the fuel filter, just for kicks. Not a bad idea since they are cheap.

He told me to recheck the firing order. I may have a crossed wire.

He told me the enging is loading up. He pulled the plug on the injectors while the car was running and found no change with most of them. Some did make an apparent change. The engine shook more. With all of the injectors, when unplugged, the check engine light did not come on. This was unusual to my cousin and goes with the computer is not giving me the codes.

His suggestion:

Leave the car with him for the winter and he will go through it. I won't recognize it in the spring.

Or

Change the plugs, wires (checking the firing order), fuel filter, and see what happens with that. If still vibrating, take to a tech and have the car diagnosed. That may tell if an injector is leaking. If not, start trying to pinpoint a leaky injector. May be able to tell by the condition of the plugs. Having the car scoped will also tell if the computer is not grounding, or has issues. He still is suspicious of the MAF. It should throw a code, but the computer may not be alerting me.

That is where I am at. Many of his suggestions mirror yours in the group. I will keep you posted as I go on. I hope to help someone else who encounters this vibration condition.

 

Check your fuel pressure.Tape a guage to the windshield and go drive it. Try to make the miss happen like on the highway and see what the pressure is. Pressure should be 45/47 with the vacuum hose off of the regulator and about 37/39 at idle with it on.
If the pressure gets lower than say 35 while driving normal or 45 when on the floor, ya got a bad pump.