I have a 2006 H3 with about 150,000 miles. I replaced the fuel pump in October 2013, as I had issues with pressing the gas and it delayed picking up speed so a local shop ran a diagnosis and found reduced fuel pressure. It ran fine for a few weeks, then I noticed that when I filled up with fuel it would stumble...the tach would bounce between near 0 and 1500 RPM and eventually turn off. This did not happen every time I got gas, but 75% of the time. I would get the vehicle to a parking spot and let it stumble to see if it would smooth out, it never did. So I turned the vehicle off, all the way to the off position, and restarted. It always started smooth again and allowed me to drive off.

After this happened three times I had an episode in my driveway where the Hummer would roll over but not fire. I tried it three times, no fire but the engine rolled. It started later that evening with just letting it sit. I did read that the battery terminals could be bad so I replaced them after finding the stock positive and negative terminals were broke and were loose. The vehicle ran fine but I did notice the vehicle did not automatically lock the doors when in drive. I drove it about 2 hours and stopped to pull all the fuses, they were all good and once I checked them and put them back the door lock issue resolved itself. At this time I also notice a vacuum line on the driver side had broke as it came out of the rubber grommet and got pinched by the hood hinge on the firewall. I fixed that issue, but the Hummer has stumbled three more times since then.

After more research I pulled my plugs and replaced them with AC Delco Platinum plugs and cleaned all my ignition coils. I did have one coil that had some discoloration so I replaced it and sealed all the ignition coils with the recommended grease as I know there is an issue with the hood ornament and water leaking on top of the engine that gets in the ignition coils and had corroded them.

I had no issues after doing this for about three weeks then tonight I got gas and went to pull out and the engine stumbled and stopped. I had the key in the "on" position so I just started it and the engine stumbled and then stopped. I then turned the key to the "off" position, took the key out and restarted. It restarted fine and was able to drive home with no issues.

This leads me to think I have an ignition issue with the unit in the steering column. I have not had any check engine lights or any other information displayed on the DIC. The symptoms I mentioned have occurred inconsistently, causing me to scratch my head.

Any advice you may have is greatly appreciated!

 

Wild guess but you may be having a PCM that is going bad. When you start a vehicle and it has issues, then shut down and restart without those issues you cleared a brain fart (like restarting a computer with an issue). You can have it scanned to check the PCM.

Sometimes a PCM just dies immediately, sometimes they have intermittent problems and then die?

Good luck.

 

If it is the PCM, what is required after I purchase and install the part? Does the dealership have to reprogram it?

Thanks!

 

Wow you got my head spinning...lol

Did you scan the computer for codes? Scan it, some codes will not trigger the cel.

Start with the basic issues the H3 is known for:

Check the battery terminals (poor connections causes electrical issues, and have the battery tested)
Clean the throttle body
Clean the maf sensor
Use top tier fuel
Clean the injectors


Warm restart issue, I would check/replace the coolant temp sensor.
Could also be a leaky fuel injector and cleaning could correct (professionally cleaned=immediate results, or add techron or any quality fuel injector cleaner to the tank at fillup= may take a couple tank fulls to correct).

Now on to the no start, starts later, another common issue: ignition switch (the black switch on the end of the ignition housing with the passlock sensor)

GL

 

Thanks for the reply.

I did change out the battery terminals, had the battery tested and checked all ground wires.

I cleaned the throttle body, this is actually the third time cleaning it with the approved cleaner and a tooth brush. I also used MAF cleaner to clean the MAF and it is spotless.

Every oil change I use Lucas fuel injector cleaner, and I just don't think that is the issue as my symptoms are not consistent.

If it is the PCM would it throw a code? And do I need to have it reprogrammed if I replace the PCM?

 

Also, I did not scan the computer. Is this something that can be done at Autozone or do I have to go to the dealer?

 

Get your computer scanned. You can go most anywhere and get it scanned for FREE.
If you have a defective pcm, you would have alot more issues! I have had many that needed to be "flashed" (updates installed) however, I haven't had 1 that has totally failed with your symptoms.
Is your coolant clean? Where is the temp gauge when you reach operating temp?
Communication is the issue, could be a defective temp sensor, or a "sticky" fuel injector. It wouldn't hurt to clean the injectors again.
If you are unable to correct this yourself, take it to a shop and have them interface or you could just buy a genisys touch and do it yourself.



You can see it in action here:

 

Thanks for the info, I will see if I can have it scanned tomorrow.

The coolant should be clean, I did a full flush last spring and then my thermostat went bad so I replaced that and then used all new coolant (again). My temp runs right above half way almost all the time, and during the summer just slightly higher.

I am going to try more injector cleaner, some with every fill up for a while to see if that is the issue.

I will keep you all posted, thanks for all the info!

 

Any word on a solution, sir?

 

I do want to update this situation. I have put three tanks of gas in the H3 since I last posted, and I have added Lucas fuel injector cleaner to each tank. I noticed that at the first fill up the engine stumbled and I had to shut it off and restart. The second time it stalled when backing up and upon restart (I simply restarted it, I did not turn the key back to the off position as I had previously) and it stumbled real bad forcing me to turn it off. Once the key was in the off position I restarted with no issues. My last fill up the tach did move but it was virtually unnoticeable. I will keep putting fuel injector cleaner in each tank full and post again in a few weeks unless I have a problem before then.