Beauty: Car runs fine for maybe an hour (no heavy traffic), then the Bitch appears out of no where. I can tell from the sudden jerking and stalling, then back to perfection, that the miss/stumble is ignition related. Also, when the problem is obvious, the idle is erratic...very high, then normal, then high again.

I have gone thru the normal routine for the Opti - The water pump coolant sensor has proper ohms, the 4 pin connector is clean and there are no shorts; terminals A & D each has the 12v, B has 3-4v, and C is grounded. Spark plugs are new and look OK as do the wires.

Car is a '96 Corvette LT1, 115k miles and all stock and does not appear to have been abused. I have 3 sets of manuals, including Helm's.

1. I know how difficult tracing intermittent shorts are, but what sensors or other items would you suggest looking at before I place an order for a new GM opti?

2. I'm thinking that it's time to replace the entire opti anyway, so I should just do it along with whatever problems I find while I'm in there.

3. Along with the new opti, I know I'll need 2 water pump gaskets. Anything else? O-rings for the water pump shaft?

4. I think a new set of plug wires makes sense, especially after 10 years.
Any recommendations? I don't want to waste money on some cheapie wires from a discount house, nor do I want a gold-plated $1000 set. What is a good brand to buy and where to buy 'em?

5. Anything I missed?

Thanks,

 

1. Your car is old, might as well replace the opti. The Coil is cheap, you could replace that.

2. Good idea

3. You don't need o-rings, you don't mess with that at all. You just need to make sure you have gasket sealant for those water pump gaskets. You might want to replace the waterpump too. You can gut that one and put in an electric one. However there are mix reviews on those.

4. . I really don't think you need to spend a lot of money on wires, OEM replacements should do. I saw a review in I think it was GM High Tech Performance where they did a dyno with high performance plugs, and it did not even increase one horsepower.

5. You will be draining the coolant from the radiator so you will need more, you could replace the thermostat while you are at it. You will also need a special tool to remove the harmonic balancer, and a special torx like device to remove the opti. You might also want to consider replacing some hoses that might break. Every listed in this catagory is pretty much optional but you might as well do them since you will be taking so much stuff off.

- Z28WannaB

 

If it is not consistent, I wouldn't blame the opti just yet. Especially with no codes. I would suspect a coil if you are sure it is ignition related. Have you checked your wires visually? If one or more is cracked, it may be fine one minute but arcing to ground the next(I had that problem once on wire #1).

Also, take a look at your iac valve. You can clean it and reinstall. If it is dirty, it can cause a poor or fluctuating idle.

Is the car loading up during the rough running? Or is it leaning out due to a possible clogged fuel filter? How does it run at WOT when the car is running good at low rpms?

Mike

 

You didn't mention codes, and whether or not you checked for any. If you haven't it's worth a try. Also, if you have something that can view the live data, to try to see what the computer is reacting to when it changes the idle.

I had an idle issue, and viewing live data showed the IAC was doing as it was told. After much more watching I discovered that the computer was reading occaisional huge rpm spikes that weren't true, which in my case is why the computer was opening the IAC, thinking it was at much higher rpm than it really was.

 

my car had a similar situation, i would start it up in the morning and it would misfire like crazy and shake and almost stall in gear, then all of a sudden it would smooth out, and once and a while start doing it again. it got worse and worse untill the car wasnt even driveable anymore.

I finaly bought some new wires... turns out when i took off one of the old ones i looked inside and it was all burnt up, i cut off the boot and the wire crumbled in my hand. funny thing is the wires looked fine on the car, no dry rot or anything.... changed them and the car runs great. if your wires are the originals id change them anyways just as preventitive mantnence.

 

Thanks for all the replies! The new Taylor plug wires and new GM opti have been ordered and are on the way. Forgot to post that there were no codes.

The last few times I've started it up from cold, it runs fine (the beauty). I'm afraid to travel too far not knowing when the bitch will bite me.

There are a million posts about how bad the opti is, but I can't stop from thinking this motor is very susceptible to grounds not grounding. Even had reports from someone else with my same symptoms that were eventually traced back to a bad Alternator Ground!

The only other oddball item was something called a "Tach Filter". I expect to know more about that item than I care over this weekend.

This is a sweet piece of machinery, but there are times that I think the old points distributor and a 4-barrel wasn't all that bad.

 

im on my original opti... 121,000mi, i dont think its too bad

 

one other oddball thing to check is your catalytic converter. wouldn't happen to have the problems w/ power after you turn a corner or anything? I had a catalyst come loose in my converter, engine would run fine till the catalyst plugged the exhaust, kinda stupid scenario..

might find someone in the area w/ autotap to watch the sensors to see if there's anything going on.

 

I'll try "tapping" on them with a dead blow hammer and see if I can detect any rattles. Thanks for the tip.