Missfire on cylinder 1 and 4 only while driving

[Steven5568]

Missfire with code p0300 p0301 p0304 only while under a load , if you start car up and let it idil it will not give any codes ,but if you drive it . It will eventually throw those codes, I have replace plugs , plug wires , coil pack. Can’t find any vacuum leaks , I do need to replace fuel pump seal but I wouldn’t think that would cause a missfire

[EAD15]

Try checking the "air hose" starting at the air filter. A number of people get nearly undetectable cracks in it, in the folds, that causes unmetered air to enter the engine.

[Steven5568]

thanks for the idea but that's not it either.

[andyfisk]

Weird idea, crank position sensor, VSS?

Or if you would like to join in the continuing hunt for misfire codes how about a your crankshaft pulley (harmonic balancer). I have to say though, I would be looking at the coil pack (just 'cause 1 and 4 fire off the same coil. Did you replace the mounting plate when you replaced the coil pack? Maybe a crappy ground (had it happen on a Saturn a couple of years ago).

[slayerized6]

How did your plugs look when you replaced them? Cover in oil? Being that its the outside 2 cylinders, I might suspect a bad valve cover gasket which is letting in oil