Oh boy has this been a endeavor. We own a Non Profit and this 2002 GMC 2500 (non HD) 6l gas, has been given to us. Its never ran good, previous owner said it one day started to run rough and die. He thought it was a fuel pump and had cylinder 2 and 7 miss fire. Oh and when you would get out of the truck the truck would instantly die.



When we got ownership of it, it had the following codes. TPS Low voltage (short) and Misfires on 2 and 7.



So TPS didnt have 5v, so i spliced into the 5v at the MAF and TPS code is gone now. Still was running rough. Would die at idle, and still if you left the seat of the truck it would die. Removed the bed of the truck and changed the fuel pump. Had a rotten cross member and changed that. Still nothing has changed, truck still runs bad.



Okay now we get a code after this, Bank 1 and 2 is running lean. I spray break clean around the Intake manifold and it revs up. I change the manifold gasket, the code is gone. ran good until i got out of the truck and it died. Now it will not start at all. I turn the key everything works but the starter wont engage. I hear the click at the Fuse box. Ran out of daylight to test for power at starter.



Newest codes i have are for a Cam Position sensor and U1026-19. Im a bit reluctant to continue down this rabbit hole. At this point i just want to put a Carburetor on it and call it a day. But unfortunately per Ontario safety rules i cannot. I can only assume its an electrical issue. Is there a work around or should i just get started on ripping out the old Wiring Harness or maybe try a new ECU?

 

Here's an updateI managed to find the issue. But still have starter issues now. When i pulled the PCM i found 3 wires were exposed and shorting out. So now all my check engine lights are gone. Hurray!



I managed to get the truck to start once since i fixed the wires. I changed the starter and bought a new battery and still didn't work until i fiddled with the ground on the battery and it fired up. I cut the end of the battery ground cable and re attached it with no avail.

Not sure how to approach this one really. Relay clicks. I am getting 12.6v at starter. I jumped the starter with a screw driver and all it did was spin (didn't grab the flywheel). Ill check the grounds tomorrow from the battery.



I keep seeing this Vats i think its called that causes issues with these trucks on a lot of the no crank research I've done. Security light doesn't stay on once i turn the key to the ON position, it just shows a battery on the little screen.



i don't know if this related or unrelated. But the light on radio doesn't work in the ON position just when the key is turned backwards from the off positions. Also headlights, when i turn the dial from running lights to night lights it doesn't change at all. If i remember correctly i was able to keep the head lights off prior to the starter not functioning.

 

I can't help with many of your issues, but if you jumped the starter and it spins, but did not engage with the flywheel, that implies that the starter solenoid is not activating to push the pinion gear forward to engage with the engine's flywheel. I've never changed the starter on my GMT800 (2006) but did about a year ago on my GMT400 (1996), and recall there being two wires to the starter - the small one from the switched key activated circuit, to control the solenoid, and the large one from the battery to the starter.

Sorry if I am just stating the obvious. 7AM and on my first cup of coffee here.

Good luck working out the gremlins. Shorting wires and such - you've found and fixed a lot so far. If you get it running, should be a good truck for you.