Could be your ecm.

I had that dang misfire code a couple times, ended up being the $600 in Holley red top coil packs from Summit Racing I put on. Went back to stock AC Delco, problem solved. Finicky engines.

 

I caught the p0300 11+yrs ago, induction cleaning corrected to this day! SEAFOAM WORKS!

 

I purchased high milage sea foam put that in that tank. After that I Put 16 gallons of 93 in the H2. Ill run the sea foam in the engine 2mrw. Fingers crossed.

 

You've replaced a good number of parts, why not find a local tuner or someone with logging capability and have them log all the OEM sensors while driving.
Then have a look and see what the issue is.
I would start with a cylinder balance test and see if anything shows up.
The fact that its a P0300 says its a random issue effecting all cylinders, the crank sensor measures accelerations and decelerations of the crank at each firing to know if something is wrong.

Have you tried pulling the trans down to 3rd and see if its as bad,

Neal

 

Hey Neal, I have not attempted pulling the trans in 3rd. Ill do that this evening. Ill report back and let you know how it goes. Great idea going to tuner.

Did run the seafoam into the vehicle. Will be going for a joy ride this evening to clear up the intake a little more. Found out more information on the spark plug wires as well.

The plugs Inside the H2 are showing .975 ohms.

The ac delco wires I purchased are 9748HH are showing .430 ohms on the fluke multimeter which is correct for these plugs. They are listed incorectly on auto sites saying they should be 1000ohms.

Also crossed my mind that the current spark plug wires in the H2 are incorrect.

Read multiple posts online saying the .430 ohms for 9748HH are correct for the H2.

The battle against P0300 continues! Thank you everyone who has joined the fight! Chat soon.

 

Gentlemen, we have success!!!! Massive success! H2 Hummer is back! Full review :
The H2 would get better with each part installed. Could feel the power growing with each upgrade but would be bogging down under load. This was on going for the last 6 months. At one point I had ordered new spark plug wires off Amazon but they were fake parts I received. Box looked identical to the real box, but when testing the cords they were all over the place from 400ohms to 7000ohm. Couldnt even get the boots on, cords were so jacked up. Learned my lesson. Only buy from auto stores. No fakes that way or at least reduce chance considerably. Also will only will buy parts of Ebay if the user has 100% feedback. The spark plug wires in the H2 were showing .975 average on the ohm reading. The new ones that are installed are .435 ohms Part # 9748HH. It shows online thar 1000 ohms is the correct for H2 on auto websites. This is false information. Found a few posts oNline were H2 owners stated .435 ohms are correct.It just fired up super quick. Im guessing that at some point the wrong Ac delco wires were installed in the Hummer. I took the vehicle on highway at 55mph for 25 minute drive. The shifting was incredible. Was shifting about 5 to 8 mph less than the bad spark plug wires. Full power from stop to go. No bogging making turns. The engine was super quiet. I couldn't even hear the engine. The final test was going up a massive 2 miles hill. Very steep grade. H2 just took off going up the hill. No knock codes appeared no P0300. Just raw power. I also completed the cleaning with seafoam in the tank and seafoam into the engine. The spark plugs wires were the main culprit. .435 ohms is correct. There is a lot of mis information online have read regarding ohms too. Just want to say thanks again to everyone for assisting in getting my H2 back online. Going to an incredible upcoming snowboard season with the H2!! Cheers!!

 

 

Thanks for updating this thread, now anyone that reads it will have solid info when working to resolve the P0300

Glad you got the h2 back to good health

Neal

 

great

 

question i have for anyone .. i would i measure the ohms of the sparkplug if its not removed??