Ok I have an 06 H3 when it sits for an extended period of time it doesn't want to start. After several attempts to get it to start it will barely even run. it is mis firing really bad. after about 30 sec of running like crap the idle smooths out and runs fine. you can shut it off and it restarts without any issue. It comes up with p0300 (random misfire) and p0326 ( Knock Sensor 1 Circuit Range/Performance (Bank 1 or Single Sensor). but once you get it started and runs 30 sec to a minute it runs fine no misfire and it does not have a knock.

Ok I have an 06 H3 when it sits for an extended period of time it doesn't want to start. After several attempts to get it to start it will barely even run. it is mis firing really bad. after about 30 sec of running like crap the idle smooths out and runs fine. you can shut it off and it restarts without any issue. It comes up with p0300 (random misfire) and p0326 ( Knock Sensor 1 Circuit Range/Performance (Bank 1 or Single Sensor). but once you get it started and runs 30 sec to a minute it runs fine no misfire and it does not have a knock.

Really weird. There are so many things this could be, likely a combination of things.

Here's what I know:

The batteries in the H3's especially the early models are known to be bad. However unless you are under warranty, it will not be covered.

p0300 can be from a few things, dirty injectors, bad plug, and or depending on the mileage of the truck, more commonly it is the head issue. The valve guides did not seat properly and caused a defect in the cylinder head in the early '06's and some 07's caused a misfire code. (It was an issue in the Canyon/Colorado's too)

You are likely no longer under warranty, however, I have seen this issue fixed with enough persistence. It is known issue with all the I-5's.

Call a dealership and ask them to run your VIN to see if the head has been replaced. If it has, find out the who what when and where. If not...it increases the chances that this is the problem.

Call customer assistance 1-866-HUMMER6 and let them know what's going on and they will set you up with a dealership. Remind them the exact same engine in the Colorado/Canyon's had an extended cylinder head warranty issued (75K). Don't take NO for an answer. It is a well-known problem with early made H3s.

You can eliminate and isolate the issue by changing the plug with OEM plugs, cleaning your fuel injectors, and replacing the battery. See if that cures any of the symptoms.

How many miles and when did you purchase? Do you have an extended warranty?

thanks for the info. I have already changed out the factory battery. I have autolite Iriduim plugs. I have replaced all 5 boots. I did all this when I first purchased the H3. I was having probelms with a cyclinder 1 misfire. The Hummer dealer did a leak down test on it and it passed. My vin does fall into the category of I-5 heads that had issues. Came to conclusion that the cyclinder 1 injector was bad or casing the misfire code. I ran lucas fuel treatment in it every tank for a while and problem went away. I may have to break down and just replace the injector now. I now have 85k on it

thanks for the info. I have already changed out the factory battery. I have autolite Iriduim plugs. I have replaced all 5 boots. I did all this when I first purchased the H3. I was having probelms with a cyclinder 1 misfire. The Hummer dealer did a leak down test on it and it passed. My vin does fall into the category of I-5 heads that had issues. Came to conclusion that the cyclinder 1 injector was bad or casing the misfire code. I ran lucas fuel treatment in it every tank for a while and problem went away. I may have to break down and just replace the injector now. I now have 85k on it

Get rid of the Iridium plugs. Get OEM. Have another leak down done on it. They have been known to go on a few hi -mileage H3's.

It sounds like the injector, but you need to get rid of those plugs first.

Get rid of the Iridium plugs. Get OEM.
What Bebe said, I have heard of others having issues with these plugs.

Ill give it a shot. Just find it hard to believe its the plugs its been running fine for the last 10k

as bebe said I would start with the plugs. They will set the same code and cause it not to start. I just fixed a friends truck that was doing the same thing.

It makes sense use to have to change or clean plugs in my drag car back in the day it was doing just about same thing.

Well it was not the plugs runs exactly the same

Then I guess it's dealer time. Make sure you call the number above and get a case started before you go to the dealer.

Sorry I couldn't be of anymore help.

Bebe

Thank's I'm trying to avoid the dealer.

Well, replacing the injectors or the head. That's about all that's left to do. The Knock sensor is what is saying it's in the top end ie "Bank One".

It might be the injectors but I really don't think it is the head. It runs fine it is just a hard start after sitting for a couple hours. The only reason it is popping up codes is due to the hard start. When it first starts it sounds like it is firing on maybe 2 cylinders. Which would make sense as to why it is registering a random misfire and knock sensor code. The first minute of run time it is running like crap. Today once I got it warmed up and running I cleared the codes on it. Drove it for about 100 miles and didn't get a single code. But The computer wouldn't run all the system test. Everything is checking out except for the EVA. Which I also noticed that before I cleared the codes was the only one that hadn't registered before after about 200 miles. which to me sounds like a sensor or something in that system not working.

Damn Hummer started up fine all day today. I think it is the injectors. Just gonna replace all 5 and be done with it