Causes for high Knock Retard? (KR).....

[Mark B]

Hey Everyone,

I recently got a Scan tool for my 1999 Grand Prix GT and have noticed that my KR is pretty high up there! I have been getting up to 8.0 degrees at the shifts and up to 6.0 degrees in the middle of the gears. Thats on 93 Octane Pump Gas!! I obviously want to bring those numbers down. These are the modifications that I have done.....Cat-Back exhaust, Fenderwell Intake, 180* Thermostat, New ACDelco plug wires, and Bosch Platinum Plugs. Do I need to go to lower temp plugs? Keep in mind that this is not a Supercharged Motor. What else could be causing such a high KR. Thanks for taking the time to read this. I would appreciate any help.

[PiercedJD]

normally factory range plugs are fun, unless you are spraying or supercharging/turboed, then you want to go colder, as the combustion chamber temps are increased, and the lower range plugs can still reach their self cleaning heat range.

it happens all the time? if it happens during normal driving/part throttle cruising, I would suspect it to be false knock. check the knock sensors and make sure they are screwed in snuggly and that there is nothing obviously physically wrong with them. with the engine on the neanderthal way to check and see if they are working properly is to run the motor, and then watch your ignition timing, or on the scan tool watch for knock counts, while tapping near the knock sensor with a hammer or wrench. it should pick that up as knock and retard the timing and show knock counts.

if the knock sensor is functioning properly, and you don't suspect the engine is running lean causing actual knock, check ignition timing and make sure it's not too far advanced.

[Joe 1320]

Knock can be caused by a lean condition, a rich condition, hot spots on the combustion chamber, excessive timing relative to boost, ignition breakup, too hot of a plug, low fuel quality.

Various mechanical noises could also be picked up by the sensor and interpreted as knock. (false)

If you want a quick diagnosis, add a 25% by volume Xylene to a tank of unleaded premium and add 1 ounce of marvel mystery oil per gallon of Xylene. So for a 16 gallon tank, 12 gallons of pump 93, 4 gallons of Xylene and 4 ounces of marvel. This will give you 100 octane unleaded without having to search. Xylene is available at paint supply houses. Us Buick guys have been brewing the stuff for years. If you still are getting knock, it will most likely be ignition or false knock. Since you don't have the blower, my bet is either false knock or ignition related rich condition.