High Rpm Detonation

DTS419 · July 6, 2009

My engine seems to detonate- you know, good old fashioned spark knock or ping like the timing is too advanced- at 4,000+ RPMs. I tend to notice it more if I really punch it like to pass someone and force an abrupt downshift.

If this were the good old days, I would simply get out my timing light and back the distributor off a couple degrees.

But, since this is the "Information Age" and everything is now computer controlled, is this detonation normal, or is there anything I can do about it? Knock sensor maybe? The check engine light is not on and the engine runs like a champ otherwise.

Draenor · July 6, 2009

How long has this been happening? Are you getting the same fuel and the same place? Could be bad gas.

Next, how many miles? Try running some seafoam. You might have a buildup of carbon in the cylinders.

..and dont run the engine hard, any pinging heard is not good and you could ruin a piston.

bill190 · July 6, 2009

Speaking of computers (and engine computers specifically!)...

Sensors for the following things input to the computer and can change the timing based on their input. However, if one of the sensors for this is giving the wrong information, then the timing would not be set by the computer as it should.

Each of these can be tested for proper operation. Instructions for testing and what the test results you should get are in a GM factory service manual set for your year/model vehicle.

Crankshaft position

Engine speed (RPM)

Engine load (manifold pressure or vacuum)

Atmospheric (barometric) pressure

Engine coolant temperature

Also there would be one or more "knock sensors" somewhere. These retard the timing a great amount when they sense knocking, then slowly the timing advances bit by bit until the computer figures out the best timing adjustment. (Or so it should.)

The factory service manual would also say where each device is located.

DTS419 · July 7, 2009

I've only had the truck for a few weeks so I don't know if the truck has done this since the factory, or if its the reason the last guy got rid of it. It only has 66,000 miles. I did put some lucas fuel system cleaner in it tonight so maybe that will do the trick. Can carbon build up cause detonation? I've only ever experienced detonation during light throttle, going up hills, etc- classic wrong fuel detonation. never before at full throttle like this. I have a 1999 Plymouth Neon that detonates when the engine is cold because I am too cheap to use the higher octane gas that the owners manual calls for, and I have put 130,000 miles on it that way so I'm inclined to believe that minor pinging does no harm, but I have no experience with these new aluminum engines either. My last Chevy engine was a bullet proof cast iron 350.

redvett · July 7, 2009

Does the SES light work? If not fix it first it should go on when you start up the engine. Have vehicle checked for codes. If its a real spark knock problem you will have these codes.

DTC P0325 Knock Sensor Module Performance

DTC P0327 Knock Sensor (KS) Circuit

DTS419 · August 28, 2009

Update for anyone who ever comes across this thread while searching: The problem was the MAF sensor. When I took the truck back to the dealership after several attempts to clean carbon from the engine, they test drove it with the Tech-3 and saw a glitch in the MAF signal during the detonation. Turns out the MAF had been contaminated by oil from my K&N air filter. I even cleaned the MAF with a bottle of special spray cleaner but that did not fix the problem and the MAF had to be replaced. You can bet my first stop on the way home from the dealership was to pick up a Wix paper air filter and the K&N went into the trash.