anmar A

I just changed my opti spark on my 1993 z28 to MSD and kept the stock coil, the car idles and runs very good, but for some reason i feel a slight loss in power when comparing to the older opti (which it was stock), what could be the reason, no DTC no misfire again the car runs just fine, i just feel like it is not as fast as before the MSD.
i didnt change the screw on the opti for advance spark.

BTC

The MSD opti doesn't have the greatest reputation.

Did your opti need to be replaced?

anmar A

oil got into the older opti caused it to fail, so i replaced it with the MSD, again the car runs good no issues, it is just feels like i lost some power not alot i still beat other cars, but am thinking maybe am running lean or rich, i don't smell any fuel but i don't know if i am over thinking it or maybe i need to adjust the screw, what does the adjustment screw do, i thought that the pcm is responsible for advance or retard the timing on the spark, so whatever i adjust the screw too the pcm will offset it, right?

shoebox

No, the PCM cannot adapt to what you do with the screw. This is why you should never mess with the screw (IMHO). Some people have reported the screw mechanism to be faulty and skewing their timing. The bad part is that there is no decent way to verify what it is doing. My preference is that MSD should never put it on there in the first place.

Injuneer

That screw is only useful if you have offset the camshaft relative to TDC. Problem is, there is no defined "0" point on the screw, so you sort of have to take their word for where the 0-point is.

anmar A

so how do you know if the timing is messed up, can it be messed up just a little bit? how can you make sure that it is right?

shoebox

With the PCM continually adjusting timing it would be hard to tell, even with a timing light and a pointer. Very problematic.