I'm starting this thread so future searchers on the P0300 code can easily find it. I asked for help on choosing a scan tool and because it was immediately for the engine mis-fire issue the thread evolved into great input from several of you on troubleshooting the P0300. As such I didn't what your time and input to be wasted in a thread with a label for something else.
Here is link to that thread for those looking for more info to help them. https://www.hummerforums.com/forum/h...-2023-a-47498/
Please continue further input here on the subject if you have something to suggest or offer on engine mis-fires or other issues that can throw that code.
I have re-attached here the history pdf on mine and what it's doing and what the history is. I'm original owner so no mystery on what else may have occurred or been done to it.

Thanks all!

 

HUMMER DTC P0300

The PCM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission or catalytic converter damaging levels to exceed mandated standards.

 

With the absence of codes other than the normal P0300 I would look at the cats, as Bronxtech has said
Some good reading on troubleshooting the CAT's on an H2,
https://www.wheelsjoint.com/hummer-h...and-diagnosis/

also being able to see the fuel trims in real time is invaluable to understanding possible issues with the truck,

Neal

 

or bad knock sensors or wiring to them.

 

Thanks again guys. This am I was able to get back on troubleshooting it. 1 other thing I failed to mention earlier and on my list was fuel pressure/ regulator tested good back when I tested coils, injector drop test and ran compression. Back to todays tests. Fired it up and scanned for code looking to see if mine gave the throttle position code like NAPA got. Yep I got P0300(again as expected) P2108, P1516, U0107 which all 3 of those are throttle control related. Once it started warming up I went to Live data and recorded the attached clip. When done I checked the temps on the cats(see pics), and as such I have appt Monday afternoon at muffler shop to get back pressure tested and new cats if he concurs the cats are plugged. I found this youtube on testing cats with both O2 sensor readings and temps- . I'm not messing with the throttle or anything else till the cats are replaced. Once he is done with back pressure test and declares them junk I'm going to clear the codes and then I am going to disconnect battery for the time he has it on lift welding. Then when started back up afterwards it can reset and pray all is good. If not then it will continue depending what the code directs towards. Still am going to clean MAF and Throttle body etc no matter the outcome.







Pre cat bank 1

Post cat bank 1

Pre cat bank 2

Post cat Bank 2

 

YouTube didn't work-trying again.

How To Test A Catalytic Converter

Jimthecarguy
190K subscribers

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Inspect/clean connector/contacts TAC Module

P2108> TAC module is damaged or it has failed
P1516> TAC module throttle actuator position performance. The actual throttle position does not match the predicted throttle position for greater than 1 s
U0107> TAC module is not receiving or transmitting messages on the CAN bus.

 

Thanks Hummerz. Here is a bulletin from years back related on these as well.

 

Is it running rough? If not my bet is catalytic converters need replaced or I read you can clean them. Is it more difficult to start once it's been warmed up? If memory serves me correct, with a true diagnostic tool, you would also be getting Bank 1 Bank 2 as well as front and rear in each bank. Regarding scanner I've used for the last 13 years tech to win and GM MDI. MDI was a China clone.

 

Thanks for input bknap, going Monday afternoon to muffler shop to get backpressure checked and I'm sure it will be getting 2 new cats. Pretty sure I will end up with the VX Nano/ tech2win software-scanner package, I like the idea of running it off laptop for larger interface.