I have a 2008 sierra 1500, code p0300 it went from running great to shit in one second any ideas? Have replaced crank and cam sensor


Asked by Apr 09, 2017 at 01:47 PM about the 2008 GMC Sierra 1500 SLT Ext. Cab

Question type: Maintenance & Repair

I was driving at 50k or 30 miles per hour on dry road, while cruising the truck went from running great to shit in one second magic code says P0300 random multiple misfires and by the way it feels it is hitting all 8 cylinders, truck runs really rough and seems to be sending gas out the tailpipe as it leaves stains on the garage floor, have replaced the crank and cam sensors, getting 60PSI gas pressure and just noticed the battery may be weak, had headlight on for 5 min and would not start so will be replacing that today, the truck runs so shitty I will not take it out of the garage for fear of breaking something else

3 Answers


P0300 GMC - Cylinder Misfire Detected Random Cylinders...Possible causes; Faulty spark plug (s), Faulty ignition coil (s), Clogged or faulty fuel injector (s), Intake air leak, Fuel injectors harness is open or shorted, Fuel Injectors circuit poor electrical connection, Ignition coils harness is open or shorted, Ignition coils circuit poor electrical connection, Insufficient cylinders compression, Incorrect fuel pressure...The P0300 code means that a cylinder(s) is misfiring or is randomly misfiring. Start by checking for intake leaks, intake gaskets are common caused of multi-cylinder misfiring. If no leak are found the next step is to replace the spark plugs. If the problem persist more tests needs to be done to diagnose problem...Also check this out... https://youtu.be/QdWd68bVm30


so in the end all that was wrong with the truck is a broken exhaust valve spring on the number 2 cylinder and the computer tried it's best to fix it thus taking all the remaining cylinders down too as it ran really bad and spitting gas out of tailpipes


That would cause the misfire code. Thanks for following threw to let me know what the problem was.

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