The patient - 1995 Z28 Camaro see sig for details. 143k miles

The problem - a miss under load.

The car has a miss just off idle and under load in any gear. Off the line the engine smooths out at about 2k rpm. I can cruise on the hwy without any problem but when I try to accelerate quickly I get a miss and stumble. If I downshift I can accelerate with no problem. Interestingly, the effect is much less when the weather is cold. In fact the colder it is the better the car likes it. The engine starts immediately when cranked at any temperature.

I've already replaced the spark plugs with AC Delco plugs. I also replaced the coolant temp sensor on the water pump and the IAT sensor thinking perhaps the car was getting the wrong mixture (due to the cold temperature preference). I've also run a can of Seafoam through the engine. I run premium gas only.

Some years ago I replaced the Optispark with an AC Delco unit and I replaced the ICM a year or so ago. I have an Accel high output ignition coil and Taylor 8mm spark plug wires.

I'm a bit befuddled by the problem. I would expect the Optispark to give a constant miss if it was the problem but I'm open to suggestions.

Hope someone can help me isolate the problem. Is this a typical way an Optispark fails, or could the ICM be failing under load?

 

It is usually the spark getting to ground through faulty insulation or another wire through bad plug wires or other high tension areas like coil wire or maybe opti cap. High load miss is usually insulation breaking down somewhere. I'm betting your opti is OK, maybe check your wires thoroughly and don't forget the coil wire - matter of fact you might want to look at that one first.. Back when people were working on these engines more than now, people used to report occasionally that they had problems with misfire after installing Taylors. It seems like they had problems with purple or pink designer wires when there were so many other good choices out there. They were always a big name in racing and I don't get why they had a problems with wires unless they were sourcing them some where cheap for consumers to buy. I never used them, but have read enough problems to not ever want any. Again, that doesn't come from direct personal experience, but then I never had that type of failure with the wires I've been using. Keep that in mind as you do your troubleshooting.

The ICM doesn't like heat but it isn't sensitive to load. It is on the primary (low voltage) side of the ignition. Good practice to keep it alive is to space it off the head a bit with some washers.

 

have you checked the fuel pressure ???
Not sure what happens when the opti goes bad ?? Shoebox has a way to prove your getting a signal from the opti ..... My car is having the same problems as yours and I cannot find a shop that
Knows what is wrong with it and they tell me that they suggested that I replace all things related
for a stupid huge bill ... I have also replaced plugs , wires , I.C.M.

 

When my 1993 z28 would do that my fuel pump was going out. Drove it for a year like that then finally got tired of it and cut the fuel pump door and replaced it. And boy was it an all new car.

 

Thanks guys for the input.

 

Bad plug wire(s) comes to mind.

 

Guess I'll go with the wires first. It seems the least of the evils. I just have to find some yellow over the valve cover wires.

 

Have you looked at the wires at night to see if there is any kind of spark or glow around them?

What part of town do you live in?

 

Yeah, I keep forgetting to do that.

The car's in the body shop now getting repaired from a lady backing into me. Needs a driver side fender, front bumper cover, headlight mount, and hood repair. Just had it repainted and had the bumpers replaced this summer. Fortunately she came into the store and let me know and she has good insurance.

I'm in J-Town near Hurstbourne and Taylorsville Rd.

 

Did you ever figure out what was causing the miss?

 

No solution found yet. With the bad weather I've parked it for a while. Hope to tear into it sometime soon. With the comments I received I had decided to replace the plug wires. I've been looking for another set that can go over the valve cover. Then I received a message from someone who has/had the same wires and he said he never had any trouble with them at all. So I really don't know what the problem is. I'm going to have to start replacing stuff I guess until it is fixed. I'm still open to suggestions.

 

I have the same problem here is a list of parts that have been put on in the last 2 weeks.. Opti spark , plugs, wires , fuel pressure reg, fuel pump, map sensor, throttle pos sensor, starter,battery,engine temp sensor, coil, and water pump.. All ground wires and positive wire to starter...still has stumble problem..hope this will help you on the parts I've replaced and still have the problem...

 

Mine was caused by bad O2 sensors. Unplugged them to see if they were causing the issue, and sure enough, problem went away. Check engine light was on until new ones were put in and plugged back in LOL, but no more stutter.

 

Ben, that's quite the list of repairs you've made. Hope you can find the problem soon.

Revmarc - did you have a Check Engine light on before you unplugged the O2 sensors?

I've not gotten back to the problem. It's been parked about a month. I'm getting ready to work on the header leak I have at the head. Hopefully new gaskets and retightening the bolts will do the trick. Anyone heard of headers warping? I have Mac mid-length headers.

While I'm working on the header problem, I plan to replace the sparkplug wires.

 

It's not unusual to find that the header flanges are not straight when new. They need to be checked with a straight edge and straightened before installing if needed.