2003 2500HD 6 liter Miss fire

[SJ75]

All I know right now is that it has a random miss fire. 0300 0500 0600 are the codes. Only does it at idol. Except a rough run between 45 and 50 on the highway. I replaced the MAP (which had oil on the sensor end). The throttle body was replaced as well. Not sure where to go from here.

Thanks

Shane

 

I have to add that I have noticed that the rpm's do not drop at highway speed indicating it is not dropping into overdrive. When it does, as soon as I have to back off speed then come back again; it doesnt go back to overdrive. It shifts smooth, rpms are usually the only way I can tell it shifts.

[dewfpo]

Besides the random misfire code P0300

 

P0500 is a speed sensor code

Possible causes :

- Faulty Vehicle Speed Sensor

- Vehicle speed sensor harness or connectors is open or shorted

- Vehicle speed sensor circuit poor electrical connection

- Faulty Engine Control Module (ECM)

Read more: https://www.autocodes.com/p0500.html

 

P0600 Loss of Serial Communication Link

Possible causes :

- Faulty Engine control Module (ECM)

- Engine Control Module(ECM) harness is open or shorted

- Engine control Module (ECM) circuit poor electricl connection

- Low battery voltage :

Read more: https://www.autocodes.com/p0600.html

 

Sounds like you may have a wiring/dirty connector issue. Start with the speed sensor wire and work your way back to the ECM.

DEWFPO

[Formulabruce]

Either a ground issue or a EMC reboot, or a dealer ECM reset.

I would first try to unhook the battery for 30 minutes.

How many miles on your rig? Oil on the MAF bothers me some...

[davester]

The OP mentioned oil on the MAP sensor, not the MAF sensor. The MAP sensor is screwed into the intake manifold itself, and can get oil on it because some oil gets into the intake manifold via the PCV hose.

[SJ75]

OK so the MAP sensor with a coating of oil is normal? Considering it was original and the truck has 190300 on it right now.

 

Over the weekend I will disconnect the battery for an extended period.

 

The battery is a year old.

 

Thank you I will look at the wiring and connectors. I am open to other ideas too.