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livesayx14 1/15/2018

2005 GMC Savana 3500 Base 8 Cyl 4.80L


truck loses power til fault code reset

dreaded p0300 code .. sometimes says cyl 3 or 4 along with system fuel lean faults,,, ive changed, MAF, throttle position sensor, o2 sensors, plugs, wires, coils, alt, truck runs great... idles rough now and then ,, will lose power and struggle on the highway now and then ,, but if I clear the code while driving it instantly regains full power?? ECM? I have fuel injectors but haven't put them in .... it runs great just seems electrical

1 Answer


HouseCallAuto 1/15/2018

Intake manifold gasket is the cause mostly of P0300 on this engine. Vacuum leak. If you start it up cold and dump a gallon of water on the intake manifold the engine will likely run rough as a small amount of water gets sucked in at the source of the vacuum leak which will confirm the vacuum leak. If there is no vacuum leak the engine speed will not change at all. You could also use a propane torch without igniting it but the result will be higher idle speed.


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