I have a 1993 Chevrolet Z28. It starts and idles fine, cruises along fine. But when light acceleration is done, it starts hesitating and stumbling. If you get on it, it does it at about 4000 rpms to redline. If you drive it light, it starts at 2000 rpm. This has been a persistent problem, only did it high rpms at the track until recently when it started doing it at low rpms as well. It been doing this in high rpms for a month, and started doing it in the low range for a week. So I had the filter changed, and the spark plug wires and fuel pump checked. So the dealer tells me it might be the optispark. I'm just surprised that it would go out so early. My car has 102K miles on it, is this about right for the life of an optispark. Also, the dealer would use a new optispark, but my f-body buddies tell me the dynaspark is the way to go. Sorry so long. Any imput is appreciated.

 

Have you cleaned your MAF yet?

Joe

 

It's a 1993 Z28, so no MAF. When I wrote filter, I meant fuel filter, the air filters were just cleaned a couple days ago.

 

Duh lol.....tested the map sensor?

 

I am having the same kind of problem as you and I replaced my Opti which only had 3000 miles on it and it didn't cure the problem. If you have over 100k on your Opti you are one of the fortunate ones. I would try to narrow it down before you replace it. If the dealer does it it's big $

 

You can check the coil...and also space it off the head (prevent heat-related problems) and be sure to put thermal grease on the back of the module.

 

It's doesn't seem devastating, just really annoying. I really want to get it fixed. If it is the opti, I'm willing to do this myself, along with a new water pump. If it's off, why not? But if what RCF925 is saying is true, what other possible things could it be besides what we've eliminated.

 

I changed my fuel filter and one of my fuel injectors (had the car scanned and the #5 injector was leaking) last week and the car has no stumble now The fuel injector really made a difference.
The coil trick works too from what I understand.

BTW: check to make sure your throttle body butterflies open all the way when you floor the gas pedle. Every 93 I have seen has had the buterflies only open 3/4 of the way at WOT. If you want to know more PM me. I have pics of an easy fix.

 

If you had a code that said your injector was bad, wouldn't your SES light come on. THere are no lights on, so I don't think it's the EGR. So I've narrowed it down to opti, injectors, or some other freak problem. I just don't know. But I want to lean with opti, but don't want to spend that kinda money if it doesn't fix the prob.

 

Did you thoroughly check ALL of the WIRES and PLUGS??

I strongly advise doing this before you shell out your hard earned money on a new opti. I went through the same problem as you. First, high rpm stumble, then it got worse and worse.

I did the opti, coil, icm, egr (cleaned), TPS (cleaned)...yada yada

Finally turned out that one of the wires was melted right where rouutes around the accessory bracket. I couldn't see it arching because it is so cramped in there. Anyways, I could have saved a lot of money and time if I had done a more thorough check of the wires.

 

All problems don't cause codes. If you rely on getting a coded or SES light , you may never fix the car . When you look at diagnostics, you can read what is going on. I don't know if the person above with the leaking injector had a code, but I doubt the computer will give a code all the time for a leaking injector unless it's something in the circuit or injector electronics. A bad seal or something similar could cause a leak , but that would have nothing to do with the computer. Just like a dirty sensor could cause a stumble hesitation , but the computer would not throw a code because there is nothing wrong with the sensor , besides the fact that the dirt, oil, etc could be effecting it's readings. Plus sometimes codes or SES lights don't come even when they should because of computer problems and who knows for what other reasons. You have to look a diagnostics.

Codes do help fix the problems sometimes, but just by the fact that some people have some sensor issues and bad running cars with no code or SES light tells you that they are not always the answer to finding the problem. It could be dirty sensors, vacuum leaks etc.

I would have the car scanned in real time by a dianostic program with laptop or good scan tool by you or somone who knows about the sensors readings. This way you can watch the readings, especially when the hesitation/stumble is happening. It might save you a few hundred or more on the opti and other parts.

 

No, my fuel injector never threw the ses light. The shop I went to is one I have been many times, and since I know the guys they let me in the back when they ran the test, it was done on a laptop with one of those softwhare things you can by on the net (datamaster or something, sorry I suck with computers.)

 

Oh ok, well it's been a little over a week since the stumbling began in the lower rpm's, and just today, the stumbling kinda went away, but only after a significant power loss. It feels like a six cylinder, so I though a cylinder might be out, but my friend said if that is, it would run rough, but it runs just like it did with the stumble. Cruises and idles fine, but now I notice the power loss. It started stumbling again later on, but the power loss is still there, I don't even feel power come back, just stumbling and the loss of power. This is getting really annoying. Thanx for all your replies.

 

If you are losing power to only a cylinder or two then it is most likely a plug/wire issue. Check them before you spend any $$$.

 

I just pulled apart my opti, it had 135k on it and the cap and rotor were in a dreadful state of burnt up.
The studs were halfway eaten through and the bearing in the optical part was toast.
the car started and ran and I got no codes but it was stumbling a little at first and just got worse and it was off on power as well, not much but not what it should be with my mods.
You have alot of miles on that opti and trust me the cap and rotor do get worn just like any other, its just so hard to replace on these cars most don,t do it.

I am not saying this is your problem but just letting you know what I found.