I have a 2006 hummer h3 that has a misfire problem on cylinder 3 I changed spark plugs a few months back also changed coil packs and alternator cause of a recent stalling issue i cant seem to figure out why the truck is stalling when I come to a stop after replacing all these thing i also cleaned the throttle body but I'm out of ideas what could possibly be the issue besides the misfire on cylinder 3 if someone could tell me what is going on would be awesome

 

I had a similar problem. It sounds like you've already done all the basics. Your next step is probably a leak down or compression test. My misfire ended up being from a bent valve. Unfortunately was not cheap to fix.

 

Well thing is I ran some seafoam threw it about a month back and it stop stalling and got rid of rough idle for sometime then it came back so now I'm thinkin its gotta be the fuel injector not fully spraying when I come to a stop because when I drive she runs dammn good so ima run BG44k threw since its supposed to be alot more powerful and if that doesnt work Ima have to take the manifold off and manually clean the injector cause the hummer has sat for some years and from what I heard if I had a bad valve I would have alot more issues than just stalling I dont have rough idle or bad vibrations just rpm drops and sometimes its stalls sometimes it picks back up but it hasn't stalled on me while driving and engine light says cylinder 3 misfire so I'm guessing its injector for shure I just want the dammn thing to be finally fixed GM makes it a nightmare to work on especially when you not professional mechanic lol

 

Search feature works here at this site.

Do all of the things suggested in this thread and then ask questions if you still have issues.

Acts like it wants to stall/rough idle -No CEL -What To Do:

PS... ain't no such thing as a mechanic in a can so instead of buying wonder juice, save the cabbage for actual parts or tools. Notice how the linked thread does not include pouring miracle magic mechanic in the tank.

What does an alternator have to do with stalling? Go back and revisit your plug and coil pack work at #3, make sure the coil pack is properly in position on the plug and connections to the wiring harness are straight and solid.

 

Mechanics use wonder juice all the time. Today's base fuel is crap so suppliers put in all sorts of additives, including ethanol. Problems develop when a vehicle sits and all those additives breakdown into other compounds and cause problems. BG44K is designed get those additives back into fluid forms and move the crap out of the fuel system. I would try 44K first, but will probably need a fuel rail injector service or injector replacement.

 

Agree 100%
First and foremost, only use fuel from the best fuel suppliers:
https://www.toptiergas.com/
If you have a performance issue, I recommend to start with:
Lucas or Techron fuel additive.
If that doesn't correct the issue, it's time to do an induction service.
Bottom line, the "wonder juice" (used in fuel injection, tbi, & induction cleaning)can correct the issue, that removes all the "carbon deposits" causing the driveability issues, which was caused by using a poor grade of fuel, and no need to look at replacing the engine nor anything else to try and correct.

 

Stuck valve due to carbon deposits, induction clean would have solved it. Sorry for your loss.

 

i second the bg44k that **** is amazing. its actually warranty used by subaru for fuel system cleaning or was a few years ago. the stuff is simply amazing.

 

Well I have a downstream 02 sensor that is no good and its giving me p0303 and p0036. I'm just wondering why I'm getting a misfire code when it's the downstream o2 sensor?