2004 GMC Envoy, intermittent spuddering, stalling, back firing, hesitation, & poor acceleration?

by Eddie F Keel
(Camden, SC)

I have a 2004 GMC Envoy XL, 4.3L V6 with the extended wheel base. Within the last month my vehicle started this intermittent spuddering, stalling, back firing, hesitation, & poor acceleration mainly when at operating temperature. There is no OBD code associated with this action. After pulling over off the roadway and sit for a spell the vehicle runs normally for 10 - 15 minutes and start the same actions all over again. After the vehicle is parked for an extended period it operates normally until driven 15 - 20 miles and then starts the cycle all over again. During stops, the engine will shut down due to an abundance of engine misfiring, but normally will start again and run smoothly for a couple of minutes. It burns approximately a 1/4 tank of gas in 60 miles. The fuel pump has been replaced and the issues continue to exist. The garages are at awe about the diagnosis. Hopefully, you can provide me with some helpful information and thank you...



Steve Says,

Hi, Eddie. Thanks for using my website.

This type of car problem is always difficult to diagnose even when I'm right there with the car and able to run the tests I need. With that in mind there are some things that you could try.

I don't know what the other auto repair shops have tried to do to diagnose this problem, but I'll tell you where I would start.

The first thing that I noticed from your post is that your truck problems all start after it has had a period to warm up. This means that the problem is happening after your truck starts running in "closed loop". All that means is that while your truck is warming up the computer does not get its fuel mixture from the sensors. It uses information that it has stored in its memory to determine how to mix the fuel. After your truck reaches a certain temperature it then goes into "closed loop" mode and starts reading sensors (o2 sensors, MAF, etc.) to determine how to mix the fuel.

What this means for us is that the most likely cause of your problem is one of your sensors, the wiring from the computer to the sensors or possibly (yet unlikely) the computer itself.

The first thing that I would do if I were you is get some MAF sensor cleaner (you can get it at any parts store) and clean the MAF sensor. It is located in the duct work between the air cleaner and the throttle body.

The mass airflow sensor (MAF) will cause many of these same types of problems when it gets dirty and often times it will not set a code. Even if it still does it after you clean it that could still be the problem.

Another way you can check this is to wait until your truck is acting up then unplug the MAF sensor. This will cause the computer to revert back to its stored memory as to how to mix the fuel. If it starts to run normally then you know that you most likely have found the problem.
Some of the other things that could be causing it are the oxygen sensors (though usually they will set a code), crankshaft sensor (sometimes it will cause these types of problems without setting a code too), camshaft sensor.

These are some of the likely things that could be causing your problem. Please leave a comment and let me know what you try the tests above and let me know what happened. I'll try to give you more help as you give me more information.