I don't know what is mechanically wrong with the engine, EVERYTHING is new including the engine. Data log showed weird spark advance numbers, see screen shot below. Turns out the weird numbers in TunerPro RT is because the spark advance is a negative number ( used a timing light with a dial to confirm negative advance).
Anyway, I disabled all spark retard programming in the $OD PROM Chip. Now the data log shows normal spark advance. Truck runs much better with spark retard disabled!
I'm open for suggestions as why or what causes the spark advance to go negative. I define negative spark advance as degrees AFTER TOP DEAD CENTER. In this case, the negative spark advance was 5 degrees ATDC. Typically spark advance is degrees BEFORE TOP DEAD CENTER.
Tried different computer, same result negative spark.
Tried different Memcal, same result negative spark.
Knock sensor measured 4K ohms. Knock sensor wire, computer to connector measured 0.6 ohms.
Tried different (KNOWN GOOD) GM ignition module, same result negative spark.
Tried different coil (stock GM), same result negative spark.
Disable ERG in PROM, same result negative spark.
Tried different MAP sensor, same result negative spark.
Tried different CTS, same result negative spark.
Weird, weird, weird problem!
dave w
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