Another P0300 Problem

nojamin4 · September 13, 2012

I have a 2001 Silverado 1500 Z71 5.3L 190,000 miles and trying to get it to pass inspection in new york is a pain in the ass nowadays. You can't have more than two of the drive monitors tests inconclusive in the computer. The cat monitor test will not run, which I was told by the mechanic that i've been getting multi misfires on 1 3 5 7, and that is causing the test not to run, and the EVAP test will not run either, not getting a code there. I've replaced all of the O2 sensors (noticed a significant increase in mileage), changed all the plugs and wires, and still get the P0300 code as pending. Engine idles smooth and starts fine and I'm not noticing any misfires. If you rev the engine above 2500 rpms the light will flash and go out, but on the road if you get right on it, it won't come on. Not sure what i should look at next. Any help would be appreciated. By the way, if you live in new york, don't clear any codes before you get your vehicle inspected. That's what the computer is l;ooking for now.

TJay74 · September 13, 2012

Have you checked the ground cable for the coil packs? When was the last time the injectors were cleaned? Either you are not getting the correct spark on that side or not enough fuel.

As a test you could try swapping the coil packs and see if the misfire moves to the other back as a test.

txab · September 13, 2012

Also check for intake leaks.

hockeypro1411 · September 13, 2012

Have you checked the ground cable for the coil packs? When was the last time the injectors were cleaned? Either you are not getting the correct spark on that side or not enough fuel.

As a test you could try swapping the coil packs and see if the misfire moves to the other back as a test.

Same thing happened to me. One coil pack is bad and it causes a few cylinders behind it in the firing order to misfire as well. Start it up and pull the plug wires off and see if any of them don't have spark.