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P0300 Code...Where to start?


papashaq
10-26-2009, 10:40 AM
Hi guys, I've been having some problems with my 2001 Silverado 2500HD Crew cab with the 6.0 and 4 wheel Drive. I was having hard start and stumbling problems almost like it wasn't getting enough gas. It would drive fine, no loss of power, but stumbles on idle and 1/2 of the time I have to push the pedal all the way to the floor to get it started. I replaced the plugs about 6 months ago and ran great until about 2 months ago. So far I replaced the fuel pump, fuel filter, pcv valve, and the fuel pressure regulator (which made it run worse so I put the old one back in). I was gett pressure drop at shut off before I replaced the pump. It ran better for just a little bit after the new pump, but now it almost seems like it is getting too much gas. My gas milage is terrible now and it stinks when it is running, burns nose like it is burning too rich. I finally got a SES light when I was idleing at a stop sign yesturday and it was a code P0300 that comes and goes away. So I was wondering what would be the best procedure to eliminate this code and get her running smoothly again? I know it could be a whole lot of things, but was wondering if there was more logical place to start. Thanks in advance for any advice.

Airjer_
10-26-2009, 11:13 AM
The first thing I would do is look at the O2 sensor Data and Fuel trims. Something you can try is unplugging the upstream O2 sensors. It is not uncommon for them to be "stuck" in a rich or lean signal. Unplugging them will let the PCM set default values. If the idle returns to normal than your on the right track with O2 sensors giving wrong readings.

wafrederick
10-26-2009, 08:14 PM
Check for vacuum leaks and even around the intake gasket area.The intake gaskets are a huge problem with the 6.0s,blow out sucking in air and causing a miss.Where I work at,we get this with a missfire with the 5.3s and 6.0s replacing the intake gaskets and it is fixed.Most parts stores stock the intake gaskets for the 4.8s,5.3s and 6.0s knowing they are a huge problem.Yes the intake gaskets are made out plastic and I have heard Dorman might of came out with upgraded metal intake gaskets for these

j cAT
10-27-2009, 08:28 AM
vacuum leaks are a a possible cause of this 300 dtc..
however it appears that with your description of engine operation I would look at the injectors leaking. dirty and dumping fuel excessively into the combustion chamber...also remove plugs to confirm that it is running too rich ,,and it is very possible only one cylinder / injector is the problem...since installing the new regulator caused a more rich condition..
check that the vacuum line to regulator has no smell of fuel if it does this regulator is bad..

this 300dtc could be caused by just about any fuel control device including any grounds,,especially the computer/PCM/injectors...

restricted exhaust,leaks on the air intake after the MAF..plug wires should be resistance measured to ensure there ok ...

with inspection of the componets involved this should reduce the cost to make this repair, as the info gathered will narrow down the problem[S]..

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