Ok folks,

Here I am again reporting another cylinder 5 misfire. This time the Check engine light came on, so I scanned it. Scanner detected a P0305 code again. I don't notice a change in idle, nor is the fuel economy different. I;ve only gotten 14 mpg on average for the last year.
Also, I just recently filled up from EMPTY to FULL with Thornton's fuel. (apparently isn't Top grade fuel, tier 3?). That's the only variable that can be included in this ordeal.
My cylinder 5 misfire has been on and off since the summer of 2014. Has anyone else had the Check engine light come on with a P0305 code and go away in the same day? I want to sell this thing ASAP

Any feedback or help on this issue would be appreciated. I can't seem to locate the root issue to this cyl 5 misfire. My coil on pack plugs are replaced, spark plugs are relatively new, throttle body cleaned, MAF cleaned. 71k miles. Never offroad. New shocks and replaced radiator. This 06 looks mint. seriously i'd bet mine looks better than most 2009 H3s.

 

What about plug wires? I'd be suspicious of them wayyyy before the plugs themselves. I've had plug wires look new but there is some undetectable damage to the insulation and they are sagging or kinked just right and they're arching off the block instead of sending spark to the plugs.

 

One tank of cheap fuel is likely not the problem, but if that is your regular use brand, get away from it. I am not saying this is your problem, but a dirty fuel injector can throw a misfire code intermittently.

Seams like you covered all the basics otherwise. Drive it for a while and see what happens.

Yes, H3s can occasionally throw a misfire code, more likely the random misfire P0300 (mine never has, but I know others have).

I always use Marathon fuels with King Petty's STP already included.

 

I'll take a look at the plug wires. I'll also run sea foam treatment through the gas tank.
I recorded my exhaust after just starting the vehicle. Sounds like it's ticking ? Expanding metal or the exhaust manifold problems ?

 

most likely the latter. the cast iron manifold under the the heat shield retains heat under it and causes them to crack

 

I don't think I want to attempt to extract the bolts.. I don't have the proper tools. So that, a recurring misfire, odd bump like wobble from the rear axle, leaking cv seals, and engine oil seeping from the block.. this thing is aging fast this year.

 

My check engine light came on in Dec. Took it in code read misfire cylinder 5. They did a pressure check and it was leaking out of the exhaust. Had to have the head replaced. During this time of the engine light. It ran fine no noises. They showed me the head where No. 5 was bad. Also during the R&R they found a crack in the exhaust manifold so that had to be replaced also. Shoot drive it till it dies if you want to chance it. I love my hummer so I got it fixed. Only issue now is I just replaced the resister for the heater/blower and it works fine except it does not blow on setting number 4. So no Idea. I did search here but just comes up changing the resister and wire harness. Any clues? Thanks

 

Phil, if you don't mind me asking , how much did it cost to replace the cracked head and exhaust leak?

I bet mine has the exact same two problems. As for your fan speed issue, I have no clue how to fix it. Inspect the harness and make sure it's all connected?

 

I had a dealership do it. They gave me the parts list and I ordered the parts from GM parts outlet. Which made the parts half of what they would have cost. It was around $3000.00 give or take a few hundred. I didn't mention that they had checked the coil pak, plug wires and all that prior to doing the compression check. I have spent a fortune on my hummer since I have owned it August 2014. New head, manifold, radiator, heater resistor, wire harness, u-joints, thermostat and housing, Not to mention tires and a battery. But I love it so I guess Its worth the extra. I am sure you could have a small time garage do the work for cheaper but I wanted the warranty of 12/12 which they accepted cuz of the GM parts. Good luck.