Hey gang, first time in the sight hopefully I can get some help. My 2005 H2 Hummer it started running rough so I changed the spark plugs and the driver side if looking looking at it from the front all the plugs look fine burning clean the passenger side they’re all black but not wet. Ran fine for about 20 miles started sputtering again. Also I’ve noticed when I first crank it in the morning when it’s cool it runs fine until it warms up and starts sputtering again. I can also be on the Highway make it downshift to go up a hill , it will start running fine on all cylinders again and then start stuttering when I lay off, Engine light is always like it most of the time. Very strange has anybody ever had this happen. Googled it they talk about 02 sensors and airflow sensors. Any suggestions would help.

 

You might have a plugged catalytic convertor. Or you will soon if you don't get it figured out. Have you checked fuel pressure and fuel pressure regulator?

 

Hey Phil,

Thanks for writing me back and I should have highlighted that I had the catalytic convertor taken off by a mechanic. It was a cloudy day yesterday and I drove it for about 20 miles and drove fine, still idled a little ruff but if it gets real hot, like it does in Atlanta then it starts to run very ruff and the engine light starts blinking. The engine light stays on all the time anyway because I took the catalytic convertors off but it is strange. When I'm on the highway and give it gas to pass or go up a hill, it will at times clear up and take off like there is no problem and then when I let up on the pedal it will starting running rough again. I have not checked the fuel pressure or the regulator can I get a tool for that a typical parts supplier.

 

Check codes and see if there’s one for the mass airflow sensor. That’s what it sounds like to me. But also removing cats can screw up the way your engine runs in some cases. Someone else mentioned fuel pressure too.

 

I have heard that taking the catalytic convertors off can cause it to run ruff, I took them off about a year ago and it ran fine but I understand it can change things. I have spent hours on google and YouTube and just like you stated it says to clean the mass air flow sensor and 02 sensors. This is what I'm going to do and thank you so much for writing me back.

 

bad intake gaskets, dirty maf sensor and dirty throttle body are all things to look at. but if one side is running richer than the other i would suspect the intake gaskets on the side thats running cleaner. sounds counter intuitive but the pcm is compensating fuel mixture on the side it can control. so it adds fuel making the better side run richer.

 

The intake manifold on our engines (and in all of the GM trucks and SUV's) are known to over the years deform the intake gaskets and potentially start sucking air in. One way to check is to take a propane torch and slowly blow it around the intake (obviously not lit, just gas) while the engine is running. If the idle changes noticeably anywhere you have a leak. But as mentioned could be any number of other things as well.