My car ran great but after breakin there would be a bad stumble during WOT, around 5K rpm. Also, the idle was high and sounded erratic, like a miss. We checked the valvetrain, no loose rockers (Hotcam kit), No starting problems, and checked spark 1 plug at a time seemed ok maybe low on 2 plugs (new wires/plugs). All problems were intermittent. I did notice the water pump was occasionally leaking lightly from the bottom spout, leading me to worry about the Opti. The PCM did not throw any codes when scanned and has a tune from madz28 (the motor is a 97 z28 LT1)

Would a reprogrammed PCM stop it from counting error codes like misses? We felt for sure when we pulled the plug wire to check spark it would throw a code.

I am going to have the motor checked by my machinist before I reinstall it in the car (leakdown test to be sure of no sticking valves) and would like to be sure my practicly new Opti is good before I bolt the front accessories and new water pump back on and put it in the 70 vette I'm building.


Looking for advise and recommendations, and not "go spend $500" for a dynaspark. I'm hoping to get away with a cleaning and inspection deal on the opti. Any NY area reccomendations are best, but shipping works too. I'm assuming my problem was the opti, any other possibilities come to mind from my symptoms feel free to chime in.

Thanks in advance
SD

http://www.cardomain.com/ride/2055655/1

 

Gee... I would think there is a problem with the high voltage side of the opti.

I would check to be sure the coil wire is ok. That's my first guess.

As for testing the high voltage, there isn't any that I am aware of. Short of using a scope or a spark plug tester.

I can't see how the reprogrammed ecm would not count misses, unless that was programmed out.

Also, what knocksensor are you using? with the hotcam you would want to get LT4 knock sensors.

 

If the optical section of the Opti-Spark is bad, I would think there is a good chance the ECM would detect missing pulses and issue a trouble-code.
When the high-voltage side of the Opti-Spark carbon tracked on my '92, there were no trouble-codes.

The way I determined the Opti-Spark was the problem was by taking a "snapshot" (also called a "data capture") with my Vetronix Tech-1A scan-tool. I waited until the problem happened and triggered the snapshot.
When I graphed the data on my computer (Vetronix TechView for Windows software), I could clearly see that there was a tremendous amount of knock and the ECM was trying to compensate by retarding the timing (if I remember correctly it was by about 25 degrees). And, this was at only about 10% throttle opening and low rpm.
After seeing this graph, I diagnosed the problem as a carbon tracked cap. I took the Opti-Spark apart and confirmed the problem.
The cap was tracked in a way that allowed the next cylinder in the firing sequence to fire prematurely (90 degrees before it should have).

Although I didn't try it, this could probably have been seen on an ignition system oscilloscope (as Bogus pointed out) by viewing the "parade of cylinders" of the high-voltage firing sequence.
However, since this problem didn't happen all the time and not at idle without a load on the engine, it would have been difficult to see this on the O-scope at the appropriate time.
With the capability of triggering the Tech-1A snapshot when I wanted to, I was able to capture the data at the correct moment while driving the car.

Tom Piper

 

I have had some success with trouble shooting the HV side by useing a spark tester. I picked up a spark test tool from Auto Zone about three years ago and it works prety well. Check several plugs, one at a time. with the tool set to the correct gap, it will show weak or intermintant spark if the cap is arching.

 

I'm using the stock knock sensor, but supposedly the tune desensitizes the PCM knock settings. Do I still need an LT4 knock sensor? Again, no codes, but am not sure, does knocking set off a code?

If I opened up the opti, would I notice water damage inside? It only has 4K miles on t so I'm assuming it should looke like new inside, is this easily doable?

Thanks again.