P0300 Chevrolet -

Question

Last week i threw a cylinder #3 misfire ... I replaced all plugs and cables now I'm throwing a p0300 random misfire ... I replaced the coil and removed / cleaned the throttle body.. Then ran tank near empty to do a fuel treatment and replaced with high grade gasoline ... Nothing has helped .. It only misfires under a load so I checked the fuel pressure while driving under a load and the pressure is in the 40-50 psi range so fuel pump is good to go ... Any advice ? I'm guessing compression is the next thing to check but just seems odd it only misfires under a load. And it misfires violently btw not just a stutter
Thanks for any help
Will

Answer 1

Misfire just only when under load, Then this is a ignition misfire condition . There has to be enough ignition coil voltage for a ignition to occur on the next event. you can be looking at a failing ignition coil. As for the fuel pressure the specification are key on engine off 50-60 psi, At your pressure setting you would only have a lean code for both side of the Bank not a misfire condition. As for the compression test if it idles good and misfire only under load save your time the compression will not be any issue. With this type of engine and this year make and model. if the misfire issue is not resolved you can expect the catalytic to have problem such as plugging up, and you would have another misfire condition and no power during acceleration.