My 2006 Hummer is showing random multiple cylinder misfire on the tester.It runs fine until it gets warm then it starts running rough, missing and sputtering,at times you can smell gas.It has never quit but is very stressful to drive.This is my daily driver does anyone know what could be going on with it?

 

 

A VERY common problem is plugged cat(s). And it behaves exactly like this. How does it accelerate uphill? Lugs, or runs like new? Plug cats cause random codes and noticeable loss of power.

 

a bad temp sensor can cause fueling issues or no start condition.

 

it usually does good when you give it more gas straightens out for a bit however it’s getting worse the engine light flashes quickly and it sputters alot. I don’t trust it anymore to drive. When sitting still the vehicle shakes some.

 

Thankyou I will have him check it

 

Unscrew 02 sensors before and after cat, and measure pressure difference via those 2 ports. If cat is plugged, the upstream pressure will be much higher than the downstream pressure.
Both sides. If cat is good (i.e. non-restrictive), the pressures not be significantly different.

This is the only way to test the cats that I know of.

The other is to look for a sock in your exhaust pipe

You are likely going to break at least one sensor, so make sure you are ready with an easy access to a replacement. They are 20 years old and brittle. And rust-welded into the exhaust. Soak threads in Kroil or acetone/trany fluid a day before attempting this.