Random misfire code P0300? H2
 

Hello all,
2003 H2 with P0300 random misfire code. The truck was running fine. Then I stopped to take a phong call and sat with the engine running for about 45 minutes. When I went to leave the engine started popping and backfiring and died. I tried to restart it for awhile it would kind of start but was rough and only like 300 rpm then die. Had it towed to a local shop after-hours. A few hours later I went to get something from inside the truck. I tried to start it again and it started. It ran but still had some misfiring and rough running issues. The shop checked the engine codes and it had a P0300 (random misfire) and also a knock sensor code. They replaced the plugs and wires and it still doesn't run right. When you push down on the accelerator it has no power and pops and misfires. Any suggestions on what might be the issue (s)?
Thanks!

i have this same problem-- but only in the morning till it get warm...then for the rest of the day its fine... i changed the plugs-wires and coil packs. everymorning the code will come back- i get to work- take out my dianostic tool and clear the code-- does not come back till start up the next morning

I have the exact same problem and replaced the same items as PDMILLER. Does anyone have have a fix ?

This is interesting.

There are dozens of hits on Google, but there seems to be no single cause.

In my case it was a "plugged" CAT causing P0300 but with a range of other codes too, however the CAT was like a "bucket of sand"

Not saying its this but maybe woth considering.

If it is running rich it sounds like the fuel regulator which is a very easy fix. See my post: https://www.hummerforums.com/forum/h...-solved-40327/

If youve got a knock sensor code and the motor is popping and has no power. It is because the knock sensors will put your truck in limp mode to prevent further damage. I went through a slight misfire issue at idle for months and it was driving me crazy as it took a month and a half to throw a code. Multiple trips to the shop. Seafoam, plugs, maf etc. Still misfiring. I had suggestedit wwas the intake gaskets but my mechanic wouldnt listen to me. Then i made him do another leak and smoke test. Which he soaked the motor so much that water got into the knock sensor bowls and fired that code.

I then ordered 2 new AC DELCO- important- knock sensors as well as the ac delco harness( dont replace one without the other). Also two new steel fel pro intake gaskets. The oem are plastic and known to fail causing misfires. Its not a bad job if you take your time and clean everything up. I used painters tape over the intake ports to keep the debris out. Siliconed the heck out of the knock sensor caps including the wire hole and built dams around the knock sensors to divert the water around. I would also recommend removing the hood. I didnt and had to lie across the battery and hold yourself up with one arm while trying to dissassemble the intake. In the end my misfire was gone and my baby was back to normal. Very frustrating though. There is a long list of things it could be.