Unexplained knock retard.

[Cerwin Vega Fan]

I have done two WOT runs where the scanmaster has recorded a knock retard of 10 and 12 degrees. Other times whenever I take off from a stop the scanmaster starts to read a knock retard under very light throttle conditions and it goes up as I give the car more throttle (0.1 to about 1.8 degrees of retard). The odd thing is that some days the scanmaster will record 0 knock retard even under WOT. At first I thought it may be because the engine might be running to cold (160 T-Stat) but I know for a fact when the scanmaster recorded the 10 degrees of retard at WOT my LT1 was at operating temps. Any input on the subject would be appreciated.

Thanks

[Joe 1320]

The only thing I can offer based on that info is it happened to me once. Upon the next tank of gas it mysteriously went away. I suspected that "premium" was switched to something of lessor quality due to all the hurricane relate gas shortage.

[brothapig]

Remember, octane ratings are always MINIMUM ratings, so you may get a little higher octane than what you pay for.....

[DeWynter]

The only thing I can offer based on that info is it happened to me once. Upon the next tank of gas it mysteriously went away. I suspected that "premium" was switched to something of lesser quality due to all the hurricane relate gas shortage.

Hahaha...shortage, I hardly call a few days running the refineries at 25% capacity a shortage. The oil/gas transfer lines from Canada were so full half the plants around here couldn’t even ship oil. Its all a scam from the oil companies. If in fact they are swapping lower grade for premium its not because of shortages. Refineries aren’t like cars you cant just shut them off. Once running they never take them off line completely. They send home all but a skeleton crew to run the plant and bring down production so that as few people can run it as possible. While katrina was rampaging less than 15% of the entire US production of oil/gas was affected.

[fastTa]

Remember, octane ratings are always MINIMUM ratings, so you may get a little higher octane than what you pay for.....

Yep. It was interesting....here on one of the local news channels, they hired a reputable and professional company to test the gas from the pump. Supreme (93) actually tested out to be 93.3-93.5 octane.

[Kevin - Blown 95 TA]

That kind of knock retard had driven a lot of guys crazy (including me). There is some predictive knock code in the PCM that no one has ever found, and it lets the car get one good WOT run after startup, then it anticipates the conditions under which knock will occur and pulls timing, and you can verify this because it will do this without the knock count increasing. If the knock count is increasing, the knock sensor is telling it to pull timing, and you may have real or false knock. But this 'phantom knock retard' is in addition to the low octane knock retard, burst knock, and the sensed knock retard that the PCM is programmed for. It might do it when you whack the throttle the second time after startup - I think it sees a massive change in air flow and pulls timing to react to a probable knock condition. It will also then pull timing on light cruise, light accelleration & gear changes, and it may eventually subside & return to normal. If you solve the mystery, you're the man, because the LT1 Edit group has worked on this for years to try to figure it out. Some guys just set the max retard to 3 or 5 deg, or disabled it altogether for racing, or went to an aftermarket management system. Some just lived with it & turned the car off before making a run, although the burnout can again mess things up if it gets activated. The car tries to protect itself, sometimes to the detriment of it's performance. Don't know what else to tell you about this problem, except that you are not alone. If you want to learn more you can do a search on the LT1 Edit archives & download the giant 85Mb or whatever file and search thru it. I don't think anyone ever figured it out.