p300 with no misfire - odd soloution found

[yngstr]

Truck: 2006 2500hd 6.0 2wd 5spd

 

I have had the p300 code for a number of years. No actual misfire just the flashing mil and sometimes it would set the light and eventually go off on its own.

Injectors, plugs, wires, vacuum checks, driving around town with a mechanic and snap on diagnostic scanner - yup light flashing and no misfire on his computer...

 

Problem can be duplicated in the driveway- set the brake, start the engine, clutch in, run the rpm up to 2600 and hold steady for a minute or so and viola! Flashing mil light.

 

Finally put in a new motor as mine was shot. New sensors, crank relearn, waterpump, fuel pump, new injectors and harness.... and the flashing mil is back.

 

Did a whole lot of thinking on this one and thought about harmonics from the belt setting the crank sensor off. My stock belt was so tight it barely went on..

 

Had a friend hold the rpm at 2600 while I watched the belt. You could hear a vibrational hum but only at that rpm.

 

Changed the belt to one just a smidge longer and the flashing light is gone. I can't duplicate it as I used to. No more hum.

Just thought I might share an odd soloution to a common issue

[Swimmer8366]

I've seen this happen before....

 

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