Mr. Kilmer. Need your advice. I have a 2004 gmc yukon xl 5.3L with 163,000 original miles. About a year and a half ago my vehicle started stalling while idling, and when on the highway if I tried to abruptly accelerate to pass someone, etc the vehicle would stall. It would start back up and run normal sometimes immediately or sometimes I would have to wait up to 5-7 minutes. I took it to the mechanic and he replaced the mass air flow, fuel tank, fuel pump, throttle body, crank shaft positioning sensor. It ran better initially, then same symptoms.

Took it to a different mechanic and they said the catalytic converters were bad, so they hollowed out 1 and cut the 2nd out all together. In doing so the left side rear o2 sensor was eliminated. I can't afford to put 2,000 dollars into replacing the cats.

I am being told now that the correct course of action is to either pay a specialist to have the ecu " tuned", or install a y pipe out of the manifolds and add a true dual exhaust system, and possibly a performance mod chip, and possibly a performance air intake. At this point I have invested so much into this engine I can't really walk away from the vehicle.

When the outside air temperature is below 40 degrees the engine runs noticeably better( meaning much less stalling) at 60 degrees or warmer the engine barely idles, but there is definitely a significant reduction in power, acceleration. Whenever the vehicle stalls you can smell gasoline inside the vehicle. The codes that show up on the computer always say that it's the o2 sensors, but I am getting advice that if the cats have been removed the o2 sensors shouldn't cause that dramatic of a runability problem. Then I changed the purge valve up near the throttle body and the vehicle would run almost normal for a week or so, then the symptoms return each time damaging the mass airflow sensor, and causing the purge valve to stick. I can't seem to find a mechanic that can come up with a solution.

I have watched several videos where other people have removed their cats and their vehicles ran better? I really need to come up with a solution to make this truck run like it was before removing the cats. One problem was just reported that the lower left bolt stud was broken when the throttle body was replaced. So it is only fastened with 2 of the 3 fasteners. This mechanic is saying that symptoms replacing that 3rd stud so I can install all 3 nuts on the throttle body could be the root of the problem, and that the over poor performance could have also caused some or all of the spark plugs to go bad. He is suggesting we replace the plugs, fix the throttle body 3rd connection and believes this may solve the problem.

I have watched most of your videos and value your knowledge. If this were your problem and money is a limited resource right now, what do you think I should do? Any help you can offer would be appreciated and I would certainly support your site and / or post any comments and/or videos to help you if you could find the time to offer a strategy, or even guide me with the right questions or suggestions to pose to a mechanic. Is there any other simple things, or other sensors that I didn't mention that I should check? I have attempted to check and tighten any ground wires.

It just feels like this is a simple problem that everyone is failing to diagnose because they can't get past the o2 sensor codes. If I thought replacing the 2 out of 3 remaining o2 sensors would solve the problem I would do it. The part is $60 per sensor, but everyone is saying that because I removed the cats, that it wouldn't solve the problem. When I look under the truck, I see where 1 of the cats was removed, but on the right side of the vehicle I still see the shell of a converter. They may have hollowed it out and re-installed it or maybe they only addressed 1 of the cats. I found out that removing the cats is illegal where I live in Illinois which is why I am assuming that garage doesn't want to help or provide me with any more details on exactly what to do.

I am praying that you can recommend some tests or something I can try to solve this problem, as it has cost me jobs and money making opportunities because I can't pursue anything more than a few miles from home out of fear that I will end up stuck on the side of the road. Is there a specific accredited certification of mechanic that I need to find? I know if I took it to GM they would simply tell me to replace the cats, which at this point I just can't afford. I have watched videos where you have came up with amazing simple solutions. It seems like I need a reasonably priced person with your type of diagnostic skills. Whatever next step I take has to be the right one. My family and I would greatly appreciate any advice you are willing to offer my number is <personal information removed>