Ok new user here,


Ok, I know the P0304 is a generic misfire code related to cylinder 4. However, along with the code the hummer idles real rough. The H3 idles rough at start, when parked, and at stop lights. I have a complete headache because last year I dropped $1600 on 4x4 then another $400 for encoder motor two months ago. This code 0304 came on and I replaced spark plugs, boots, switched coils, replaced with new coil and then had a mechanic look at it while dealing with the 4x4. He stated that a TSB was out for the intake manifold bolts being loose. The bolts were loose... 3 threads from coming off. He tightened the bolts the code went off for a week maybe, but still persists to this day. He said that if the code persists then the intake manifold might be warped. It is plastic after all. I now have the funds to get this looked at, but wanted to check this forum just to make sure I don't waste $500+ to get new intake manifold and it be the dreaded head problem I have seen on so many forums.


While I don't do 4x4, I know my way around a vehicle good enough that I think I could replace the intake manifold. I did do a full rebuild on a Chevy inline 4. So if this is the best option what are reputable sites to purchase the intake manifold from? If I do replace the manifold what should I look for to see if it could be a problem with the head? I want this fixed I am tired of looking at the check engine light when I drive her vehicle.


She has a 2006 hummer h3 inline 5


Sincerely,


She got a hummer I got a headache

 

Just a question. Have you cleaned your throttle body You can get random or specific misfire codes just from having a dirty throttle body. It's a simple job you can do yourself just by removing a few bolts and then removing the throttle body and cleaning both sides with carburator cleaner and a brush. Just a thought. get that cleaned and your MAF sensor too and see what happens before spending the big bucks at the dealer. This diy job will cost you around 15 bucks. and is something that should be done anyway.

 

The only way to know if it is the valves is to do a pressure leak down test.

-If the manifold bolts are not tight (again) that will also cause the same codes again.
-Clean the TB (front and back).
-ACDelco plugs only. The I5 is a very picky motor when it comes to plugs.
-swap the coil from cylinder #4 to #1 and vice-versa. Clear the old codes and see if the code changes cylinders. If it does then you know that you have a bad coil still.

Let us know if any of this helped.

 

What Tainter said.

I do have a question. You said the code persists, but do you still have the rough idle symptoms?

 

I had the same problem and it was the coil.

 

Dont think its the coil. I have a similar problem. It is more likely the mass airflow sensor. Or tps. Throttle position sensor. Sometimes they f-up for a while before burning out.

 

P0304 Hummer Cylinder 4 Misfire Detected OBDII Engine Light Trouble Code | Engine-Codes.com

 

I can tell you that even thou I did not get any codes I has the same rough idle. I spent so much time and money going to the dealer and getting fuel system cleaned , diags ran , changing gas and so on. I hated my H3 by now. I have 98k miles on it and I was ready to throw in the towel. I cleaned my Throttle body and the mass airflow sensor and man she runs like a baby now. I cant believe that $15 and 30mins. of cleaning would be my saving grace. The dealer could not even find this.. I would try that before you spend anymore money. I picked up a bottle or CRC TP cleaner and the MAS cleaner. Worked like a charm .

 

For once I agree with Tainter...seen way too many I-5's with the head removed at the shop I work at....

 

Wow, I don't think I would recommend your shop, if you are just pulling heads with a p0304?

Seriously, that code automatically calls for the head to be taken off?