i have a '94 z28 with an auto and about 95k miles on it. about a month ago my car died on the side of the road. i towed it to a shop and it sat over night, the next morning it ran fine and the mechanics couldn't get it to die again. So i've been driving it since then, now whenever it warms up, when i go to accelerate hard the motor starts to fumble, has no power at all. If i floor it, it will take off then around 3500-4000 rpm it starts to stumble, it will go like hell and then stop then go again, then stop, etc. It only does this when it is warm, and the hotter the engine the worse it is, at 210 degrees fahrenheit its terrible, that car hardly works. I put a fuel pressure gauge on it and even when it was stumbling it still has over 40 lbs. the car isn't showing any codes. i've tried unhooking the MAF and the IAT sensors with no luck at diagnosing it. at the end of december the car was tuned up and had cap, rotor, wires, and plugs replaced. They also found the water pump was leaking and replaced it. i took a look at the back of the cap and there was green dust on it from the anti freeze. any way, i'm out of ideas. i just discovered this site and have been reading through it, which has been very useful. sounds like other guys have had this problem and it has been the optispark, or the O2 sensors. if you have any suggestions they would be more than appreciated

 

Optispark sounds like the source of your prob, but its weird that it died and came back to life, usually they just give out. Get it scantooled at a dealership and check the O2 voltage, should be between 400 and 500 mv all the time im pretty sure. Im guessing by cap and rotor you mean the optispark was replaced, since we dont have caps and rotors persay. Let us know, go from there.

 

Welcome to the board. This is one of the best sites on the internet in my opinion.

As far as you Z goes, I tend to lean toward the Opti as well. It is blamed for a lot of things, and most of the time it isn't the culprit, bit in your case, I would recommend looking at it. Make sure your water pump isn't bad again. The weep hole is on the back of the housing just above the cap on your distributor. If it has a white residue, it is leaking.

Also check the obvious things like plug wires. Also check the back of the intake manifold for leaks.

Your O2 sensor milivolts should be around 900 or less at WOT, 400-500 is lean, scary lean. The don't stay constant unless you are at WOT.

Good luck. Also search under "hesitation" and "miss" in the LT1 Tech forum, you well be shocked to see all the threads on this subject.

Scott

 

no, the opti wasn't replaced, when the mechanic did the tune up he said there was a bearing somewhere in the distributor that was in rough shape, he lubed it and that made it better. i was away skiing while he was working on it and he wasn't able to get ahold of me while he was working so didn't replace it.

 

I have heard of people changing their plugs and wires only to find one of the new plugs had a crack in it thus causing arching. Open the engine compartment when it is doing it and you will visibly see and hear it if it is the plug wires. I would check the basics before jumping towards the opti. You might also think about the coil itself. Just some ideas, I hear the opti can get pretty expensive.

 

unhooked the o2 sensors today and was driving around, car seems to work good, will drive some more and see if it continues. Transmission's slipping on shifts now. do i ever get a break

 

does any one know if you can buy an opti separate from the rest of the distributor

 

You mean can you just buy the insides of it, not the casing?
I doubt it, check at autozone though, thats where I got mine, it was like $260 after I turned the core in, maybe 160, cant remember. I may have bought it as two separate pieces, so check, not sure.

 

I just had the exact same problem(s) on my 95. It would run almost perfectly (stumbled at high revs though) and would die without warning. Sometimes it would run 2 weeks without a problem and then die 8 times in an hour. I took it to the garage 4 times and each time it ran perfectly so they couldn't find a problem. Here's what I did and now my car runs perfectly (knock on wood).

Replaced opti, plugs, plug wires, coil, coil module, ignition switch. ($400 parts, did 30 hours labor myself) Started up car and idled perfectly. Stepped on throttle and engine sputtered.

This happened 3 times and then it wouldn't start again. Towed car to mechanic who 1 hour later told me that my PCM was toast. Towed car to dealer who also told me that my PCM was toast. Replaced PCM. ($650 parts & labor)

Started car and it idled perfectly. Stepped on throttle and engine sputtered. Although fuel pressure going into engine was good, the exhaust pressure was high, indicating blockage. Replaced Catalytic Converter. ($159 parts and labor) Car now runs perfectly.

In retrospect here's what I think caused it all. Original problem was a tired opti brought on by old age (80,000 miles) and a couple of engine shampoos. I noticed a small amount of fluid (oil or coolant) in the opti area when I removed it. The poor running opti caused unburned fuel to enter the Catalytic Converter where it then burned and melted it. That caused an exhaust blockage. The PCM was damaged by the mechanic who hooked something up wrong and shorted it out. (just my opinion)

BTW, I replaced the ignition switch because it has feedback to the PCM controlling fuel and I was having trouble nailing down if the problem was fuel or electrical.

 

Call up Jason Cromer for you Opti. I went to my local dealership and they said it would be 400+ for the Opti. I called up Jason and got the Opti for 278.50. So call 1-877-726-8295 and as for Jason Cromer will save you a lot.