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Elder User
Joined: May 2008
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The problem is probably that your ecu isn't retarding the timing since your knock sensor may be bad, causing a ping since it cant "see" the knock.
Postmaster
Joined: Jun 2008
Posts: 2,564
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From: Wayyy NoCal, USA
That's possible, but the way it comes and goes at steady throttle leads me to believe it was the ECU adjusting the timing trying to get to optimal.
My theory is that it keeps trying to advance to the hard coded "optimal" timing setting, but then knock sensor detects it starting to ping so it has to back off. Then it tries again. A continuous effort to maximize hp/mpg without excessive knock.
As I understand it, that is how most ECU's operate with regards to timing.
My theory is that it keeps trying to advance to the hard coded "optimal" timing setting, but then knock sensor detects it starting to ping so it has to back off. Then it tries again. A continuous effort to maximize hp/mpg without excessive knock.
As I understand it, that is how most ECU's operate with regards to timing.
Senior User
Joined: Jun 2007
Posts: 283
Likes: 0
From: Minnesota
A couple of other things to consider on trucks with higher miles is:
The computer temperature sensor may be out of parameter.(slow to adjust air/fuel trim)
The thermostat may be sticking open or opening too soon. (cold condition)
The O2 sensors are out of parameter (slow to adjust air/fuel ratio)
Eventhough these will set a MIL light (check engine) when totally shot they can still be bad and NOT set a MIL/CEL light.
O2 sensors are especially prone to this. The heaters go bad and they won't adjust the computer signal for 2-3 seconds. Not 5 app. times per second as required.
The MIL light wont be set off until app. once every 5 sec. is detected.
Go to a service garage and have them look at your "live run" parameters.
You will be very surprised at what they can see.
Operating temp, Fuel trim, O2 response time, oil pressure, cylinder balance, Timing, plus alot more.
If all else fail bring your truck to the dealer and reflash your PCM to your local area tune. (your truck may have been at sea level -vs- high altitude or vise versa)
Good luck and thanks for reading my 2-cents in advise.
The computer temperature sensor may be out of parameter.(slow to adjust air/fuel trim)
The thermostat may be sticking open or opening too soon. (cold condition)
The O2 sensors are out of parameter (slow to adjust air/fuel ratio)
Eventhough these will set a MIL light (check engine) when totally shot they can still be bad and NOT set a MIL/CEL light.
O2 sensors are especially prone to this. The heaters go bad and they won't adjust the computer signal for 2-3 seconds. Not 5 app. times per second as required.
The MIL light wont be set off until app. once every 5 sec. is detected.
Go to a service garage and have them look at your "live run" parameters.
You will be very surprised at what they can see.
Operating temp, Fuel trim, O2 response time, oil pressure, cylinder balance, Timing, plus alot more.
If all else fail bring your truck to the dealer and reflash your PCM to your local area tune. (your truck may have been at sea level -vs- high altitude or vise versa)
Good luck and thanks for reading my 2-cents in advise.
Last edited by Move over I'm coming; Sep 19, 2008 at 05:43 AM. Reason: spelling
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