Code 0300 Random Misfire Help Needed

CorvetteGeorge · October 17, 2008

I am setting a code 300, random misfire. This is on a 2003 6.0L V8. The scanner says cylinders # 1, 5, 6, & 8. I have changed spark plugs, wires, moved coils to other cylinders to see if miss moves, it doesn't, fuel filter, fuel injectors, intake manifold gaskets (aqua gaskets), all to no avail. The code does not set at low speed operation, under 50 mph. It will definitely set when running 70 mph,

but it seems to be running just fine (cannot notice any miss).

Anyone have any suggestions?

Thanks for helping a newbie,

George

merlin5577 · October 18, 2008

I am setting a code 300, random misfire. This is on a 2003 6.0L V8. The scanner says cylinders # 1, 5, 6, & 8. I have changed spark plugs, wires, moved coils to other cylinders to see if miss moves, it doesn't, fuel filter, fuel injectors, intake manifold gaskets (aqua gaskets), all to no avail. The code does not set at low speed operation, under 50 mph. It will definitely set when running 70 mph,
but it seems to be running just fine (cannot notice any miss).

Anyone have any suggestions?

Thanks for helping a newbie,

George

Does the truck have an EGR valve? I cant remember what years had them/didnt have them.... Anyway, pull the valve and check for carbon build up. I have a P0300 code on my Suburban for a few months with nothing noticeably wrong, pulled the valve and it was pretty well coated with carbon. Changed the valve and voila! Code went away. Hope this helps.

CorvetteGeorge · October 18, 2008

I am setting a code 300, random misfire. This is on a 2003 6.0L V8. The scanner says cylinders # 1, 5, 6, & 8. I have changed spark plugs, wires, moved coils to other cylinders to see if miss moves, it doesn't, fuel filter, fuel injectors, intake manifold gaskets (aqua gaskets), all to no avail. The code does not set at low speed operation, under 50 mph. It will definitely set when running 70 mph,
but it seems to be running just fine (cannot notice any miss).

Anyone have any suggestions?

Thanks for helping a newbie,

George

Does the truck have an EGR valve? I cant remember what years had them/didnt have them.... Anyway, pull the valve and check for carbon build up. I have a P0300 code on my Suburban for a few months with nothing noticeably wrong, pulled the valve and it was pretty well coated with carbon. Changed the valve and voila! Code went away. Hope this helps.

I'm not sure if it has an EGR system or not, but I will check to see shortly. Thank you for the suggestion.