sorcerer jinxed

[sorcerer]

I got a '94 T/A M6 with 90000 KM on it. It start to jerk and detonate between 1500-2000 Rpm only. If i rev it, it ping and detonate also.It's worse once warned up. The OPTI-SPARK was replaced 10000KM ago with a rebuilt one, could that be the culprit? Any advices appreciated,thanks.

[Benm109]

Is the check engine light on at any time? Have you checked the codes if there are any?

[Injuneer]

If you can hear detonation (post ignition knock) or ping (pre-ignition auto combustion) you're in big trouble. The PCM should be pulling up to 15deg of ignition timing to eliminate knock. You should not be able to hear any knock. Might want to get a scanner on it, and observe the PCM value for "knock retard", to see if it is responding correctly.

What grade fuel are you using? Is the coolant temperature running unusually high? What heat range spark plugs are you running? Has any "programming" been done on the PCM? Any chance pairs of adjacent plug wires are cross-firing?

What did your "rebuilt" Opti include - cap/rotor only, or cap/rotor and optical module.... IOW front half or complete unit? What brand?

[Joe 1320]

Knock can come from a lean condition, it can also come from a rich condition. A scanner would help...... if the ignition is cutting out from either a defective opti or coil/driver module you can expect knock and it may not set any codes. usually the coil/driver module can be subject to heat soak as they are mounted right on the driver's side head. Usually, that manifests itself in higher rpms, so my guess would be either opti or plugs and wires. A scanner would be of help to read the sensors to see what the computer is reading. I would be interested to see the fuel trim, 02 values and timing.

[sorcerer]

It begin to act 2 months ago. Hard to turn over cold but not all the time,same feeling as too much advance. Battery is OK. Once running, engine was fine most of the time. Until last sunday,i went out for a ride 135 miles away, at 60 mph, took 3.25 imp. gals., so i made about 40 mpg. On my way back, it start to act weird, like stumbling and detonate between 1400 to 2000 rpm,over that rpm, no more stumbling and deto. When i engage the clutch from a stop,it would also cut or kick suddenly.To past low rpm in third, fourth,fifth and sixth,i have to feathered the throttle. So, IMO,since i got good fuel pressure (37 idle,43 full throttle), recent plug wires replaced, new spark plugs,fuel filter and tested many sensors with another car,i look to replace th OPTI-SPARK with a new one from GM. The one I'm taking off is a rebuilt unit from winnipeg. It got only 6000 miles on it and it did not come with cap but a used rotor was on already.