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Hummer H2For those who like a little more gleam to their Hummer, the H2 offers a similar rugged look as the H1, but as a lower cost, and with more added features, making it almost a massive luxury SUV.
From experience, plugged cats on the H2 do indeed throw P0300, and a lot of other unseemingly related codes. Because nothing works properly if the engine can not breathe. No point in chasing all these codes.
You need to check for plugged cats first. The GM cats are garbage, and plug up. Very common H2 problem.
One easy way to test is flooring the vehicle going up a hill. Does it bog? If you can not get RPM up, check for intake obstructions first (like air cleaner), then plugged exhaust (cats or gerbils in pipe).
Were you buying garbage gas lately? After you replace, change your gasoline brand. That fixed it for me. Switching to Chevron from S-Hell.
Neal thanks again. Few questions for you or anyone for that matter.
Will the VX Nano with the Tech2 Win software allow me to see and graph all cylinders mis-fires? Injector and coils firing and will it only be 1 at a time or can I have all 8 showing on any of the graphing/ logging? Same with O2 sensors or anything else, will it allow me to see the wave form up and down as it cycles or fires depending what its function is. Pressures or temps for visualization. Anyone that has one could you possibly post a picture / screen shot showing how it looks?
Is there anything the VX Nano setup can't do that we would need to perform on our H2's? Crank relearn, or TAC module or other programing/ setups one might run into?
What else would cause these after cat O2 readings to be high if the cats are not plugging? Can a cat be bad and still not have plugging/ back pressure seen on a pressure test? How do you all interpret the before and after cat temps I posted earlier?
And what is made of the STFT B1S2 & B2S2 each at 99.2%? What is that telling me and the difference between that STFT and the ones shown earlier in list where it shows STFT-LTFT B1 & B2?
Just recently-like last 15 miles or so power and poor running have become issue and our front drive is going up decent hill and she struggled. I didn't floor it though just not to abuse it but it took considerable more effort to get up it.
Neal thanks again. Few questions for you or anyone for that matter.
Will the VX Nano with the Tech2 Win software allow me to see and graph all cylinders mis-fires? Injector and coils firing and will it only be 1 at a time or can I have all 8 showing on any of the graphing/ logging? Same with O2 sensors or anything else, will it allow me to see the wave form up and down as it cycles or fires depending what its function is. Pressures or temps for visualization. Anyone that has one could you possibly post a picture / screen shot showing how it looks?
Is there anything the VX Nano setup can't do that we would need to perform on our H2's? Crank relearn, or TAC module or other programing/ setups one might run into?
What else would cause these after cat O2 readings to be high if the cats are not plugging? Can a cat be bad and still not have plugging/ back pressure seen on a pressure test? How do you all interpret the before and after cat temps I posted earlier?
And what is made of the STFT B1S2 & B2S2 each at 99.2%? What is that telling me and the difference between that STFT and the ones shown earlier in list where it shows STFT-LTFT B1 & B2?
Thanks much for the help and education. Roy
Regarding vx nano: you are essentially using a tech 2 hand held, with all its capabilities except imulator will display in windows. So Google what you are wanting to see with tech2 included in search. For example, this came up with search of "tech2 cylinder misfire graph" https://caddyinfo.ipbhost.com/topic/...misfire-graph/
I think the VX nana will be more convenient than my current MDI. I just ordered from Amazon be here Tuesday I'll let you know how it goes. I ordered Wi-Fi version
My drivers side cat was dead not clogged. My random misfires code stop showing when i replaced it. Prior to that I replaced all O2 sensors to confirm pre/post cat readings. I still need to do a valve job to eliminate a mis that i feel but doesn’t throw a code
I'VE NEVER REPLACED A CAT TO FIX A P0300(including my vehicles, and thousands of my customers vehicles over the 30yrs in the auto repair shops, worked, managed, & owned)!
Throw parts at it, or
LOOK HERE>>>>>Bulletin No.: PIP5029
Some customers may complain of a MIL and/ or engine misfire, rough idle, extended crank, or crank no start in some cases, the misfire may be more apparent on a cold start and may run rough for up to 5 minutes after starting the engine, may count on a single cylinder or several cylinders, and may or may not be felt by the driver. Upon inspection, the technician will find one or more misfire codes (DTC P0300-P0308) stored in the ECM and SI diagnosis may or may not isolate the cause of the misfire depending on whether the intake/exhaust valves are sticking at the time of the diagnosis.
This may be the result of major carbon build up on the intake and/or exhaust valves due to fuel contamination or incomplete burning of the fuel as shown below so the misfires should not have appeared until accumulating at least 5,000 miles or more.
I agree with Hummerz, p0300 by itself has nothing to do with plugged cats or bad gas. I got some bad advice on the same in this link: https://www.hummerforums.com/forum/h...0-p0131-44815/. If you have bad cats it will throw low-performance catalytic converter codes, and these 6.0 Vortec will take just about any gas you can throw at it. They are not Ferraris.
Review your other codes, and if it's only a p0300, really look at the cylinders that are miss firing, ensure your crankshaft sensor reset, and data your o2 sensors are sending. Most likely if it's a single bank of misfires, then the first O2 sensor is falsely requesting more fuel (lean condition) through the entire bank (one side of the engine) creating a lopsided situation as was the case with mine.
I do believe I have other issues besides cats and will be working to resolve them, but I also feel it would be neglectful to not get back pressure checked and cats verified as good while I wait on VX Nano/Tech2Win to arrive. I've had a Valvoline Induction cleaning done and it always has fuel stabilizer and Seafoam cocktail in the tank. I did a Seafoam spray and heavy mix in approx 5 gals left in tank when I started this about 2 months ago. Less than 100 miles. I will be surprised if carbon build up is the issue. I won't get much done this week as its deer season and our gun opening weekend starts this coming Friday. I had my A-frame apart and blasted/ painted so I got to get it together and back in the shop to aid in pulling the hood by myself so if I need to pull intake I have it out of way and I am also going to be looking at the tranny lines and add cooler / eliminate radiator internal run. Thanks again all for the input and educational material and rest assured it will all be looked at. It might take me a month between hunting and Thanksgiving, but it will be figured out whatever I got to do or pull off. Roy
11-12-2023, 08:54 AM
