misfiring im stuck i tried everything :( help please

[silverado98]

well this my dilemma my 98 silverado 5.0 vortec has been misfiring the last couple of weeks, and so far i have changed fuel injectors, spark plugs, wires, ignition coil,fuel pump, fuel filter,mass air flow,cap and rotor. im still misfiring under load and at idle and when im cruising the check engine flashes and obd scanner just says random misfire p0300 thats all i really dont know what else to do guys please help or has anyone has any similar issues. thanks love this forum by the way

p.s also i replaced all the o2 sensors too and i tested the compression test came out good

 

[magimerlin]

Throwing parts at it can get expensive.....lol... did you change where you got your fuel recently?? Check all the vacuum lines... take some brake clean and spray all around the vac lines, intake gasket areas, etc and see if the rpm/sound changes.

And what was your numbers on each cylinder for compression. Did the engine get hot recently?

sent from what use to be a great country...

 

[silverado98]

dont remember what exact numbers where on cylinder and no my engine didnt get hot recently plus i changed all the in gaskets when i did the spider system as well and also had the heads redone a yr ago as well

 

[Jrgunn5150]

Spider failure

 

[silverado98]

just changed it a week ago brand new

 

[Big D]

has the timing been set since all this work has been done?

does it have a hard start issue?

have you tested the Ignition control module? what did the rotor and cap look like when you swapped it out?

 

[silverado98]

i have not tested the icm yet but it doesnt have a hard start issue yea and the the timing has been set

 

[Big D]

I had an ICM that would misfire under load, and then became hard start, and then didnt start at all.

have you checked to see if your getting consistant spark to all cylinders? a easy way to do this is using a timing light.

PO300 is gonna take some trouble shooting to narrow it down.

 

[beardeddummy]

Do a leak down test

 

[Justin S]

Check fuel pressure?