Misfire problem

[Jeremy the 3]

I've got an 03 Denali xl that is giving me misfire problems. Changed the plugs and wires before I had my buddy hook it up to his readers. Cheap reader gives P0300(random misfire) and P1380(misfires repeated) codes. His other reader is a little bit more in depth. Shows all the cylinders misfires. This cant be all the coils CAN IT? It's got to be further in then the coils right? Any input helps thanks

 

[Tonyrodz]

Curious myself.

 

[Scottydoggs]

clogged cats would do this, how high your miles?

 

[Doubeleive]

possible intake leak, try to do a leak test, spray some starter fluid or something volatile along the edges of the intake and see if the idle changes

 

[Bear77]

Also got the p0300 code on mine and was going to change plugs on it tomorrow


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[SnowDrifter]

Things to check in no particular order:


Vacuum leak

Bad MAF

Low fuel pressure - pressure regulator, filter, or pump

Worn cam

Skipped timing

Worn timing chain

EGR issues

Poor fuel quality

A horrifically clogged air filter

Bad plug gap. You did gap them right?

Bad ground(s)

Exhaust issues

 

[SnowDrifter]

Also: I see it's -39 degrees where you are. If you have a flex fuel vehicle, e85 doesn't do well in the cold

 

[Jeremy the 3]

Also: I see it's -39 degrees where you are. If you have a flex fuel vehicle, e85 doesn't do well in the cold

The -39 was because I forgot to plug the radiator temp sensor back in. plugs are new and pre gaped as well as the MAF 6 months ago. It has 175K on it. Was also told the fuel filter or pump. How do I check the fuel pressure?

 

[M1Gunner]

The engine coolant temp sensor can royally skew A LOT! The sensor can even keep a truck from starting. If the computer thinks it’s that cold outside it’s going to dump fuel to that engine to compensate. You need ALL sensors plugged in for proper data.

 

[Doubeleive]

ya thinking it is -40 below certainly cant be helping the matter