P0300 Help

Bruinsfan · Aug 21, 2016

I know there has been a lot of discussions about this, what seems to be the most likely cause and fix, mine is not cylinder specific, the dealer changed wires, plugs, PCV and doesn't really know, I can't afford to let them continue to easter egg it, I'm leaning towards starting with the upstream O2 sensors, any thoughts ?

05 2500, 5.7L
No EGR Valve installed

B-Shot · Aug 21, 2016

What symptoms does the truck have other than a code?

Bruinsfan · Aug 21, 2016

Runs rough till the engine starts to warm, no issues through upper rpm range, only seems to happen at idle when first started then goes away. No other codes other than random/multiple misfire

jotin · Aug 21, 2016

Worst case scenario, your lifters are losing prime and not pumping up correctly causing a misfire.

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dexter · Aug 21, 2016

Could be fuel injectors - try running sum Gum Out engine cleaner for a few tanks of gas.

RonJon '06 · Aug 21, 2016

If it only happens on cold starts, like after sitting overnight, I would suspect a leaking intake manifold gasket.

Bruinsfan · Aug 24, 2016

Thank you all for your help, it turns out that I had , what my mechanic termed as a "lazy" or intermittent O2 Sensor, (right side, upstream) starting to fail, but not enough to throw a code, but just enough to cause the motor to run rough until it came up to full temp, swapped it out and runs perfect now.

P0300 Help

Bruinsfan

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B-Shot

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Bruinsfan

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jotin

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dexter

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RonJon '06

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Bruinsfan

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