Cranks but will not start

Hello,

This could be a problem with your vehicle's Crankshaft Position Sensor (CKP). Your vehicle's Power-train Control Module (PCM) use the signal from the CKP to determine the rotational speed of the crankshaft for engine rpm's and misfire monitor. If the PCM doesn't get the signal from the CKP, it won't realize that the engine is turning and therefore will not start the engine. I have included a few links for you to go to down below:

https://www.2carpros.com/articles/how-a-crank-shaft-angle-sensor-works
https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor
https://www.2carpros.com/articles/crankshaft-angle-sensor-replacement

Please go through these guides and get back to us with what you are able to find out. I have also included in the diagrams down below the description of the CKP and it's location on your vehicle.

Thanks,
Alex
2CarPros

i checked the crank shaft sensor and is good. it keeps turning but wont start. also the starter when i try to start the truck it keeps starting until i close the ignition switch.

Hello again,

Okay, you probably have a problem with the Bendix gear on your starter. The Bendix gear is what pops out and engages the flywheel to rotate your vehicle's engine when you start it. If it doesn't pop out enough to engage the flywheel or stays engaged, then the starter is bad and will need to be replaced. I have included a couple of links below for you to go to, please:

https://www.2carpros.com/articles/starter-not-working-repair
https://www.2carpros.com/articles/how-to-replace-a-starter-motor

I have also included in the diagrams down below starter diagrams for operation, and location on the vehicle, as well as wiring diagrams for the starting circuit. Please go through these guides and get back to us with what you are able to find out, please.

Thanks,
Alex
2CarPros

i already check starter and it good. also check the wires and they are okay.

Hello again,

Okay, so the starter is good and the wires are also good, but the starter stays engaged when it shouldn't. Then your vehicle Engine Control Module (ECU) has failed. Your vehicle's ECU or "computer" is what supplies power to the control side of the starter relay, energizing the coil and closing the switch allowing battery voltage to go the starter. Please check out the wiring diagram I have sent earlier and get back to us with what you are able to find out.

Thanks,
Alex
2CarPros

Good evening, i replaced the crank sensor and i took the starter to AutoZone to check it and it is good.

Can you hear the fuel pump come on in the tank for 5 seconds if you turn the ignition key on without cranking the engine over? Pleas let me know here is a guide that runs down the possibilities in order from easy to more difficult.

https://www.2carpros.com/articles/car-cranks-but-wont-start

Also can you use starting fluid to see if it will run a bit? Also how does it sounds when it is cranking over normal?

Had Timing chains replaced at 20,000 and again at 106,000. Started having random misfires at 110,000, had a friend (ASE Certified) check why, he found that the front cat was clogged. I replaced but during the replacement found a chunk of catalyst stuck in front of 3rd cat. Repair completed.
Within 200 miles as I was driving- everything seemed normal, came to a stop at an intersection when I tried to accelerate I had no power. Made it maybe 100 yards and it died.
Hooked up scanner - P0343 and P0367. I swapped cam sensor to see if problem would move from bank 1 to bank 2. It did not. GM garage said it was highly unlikely that this is related to timing chain- that it is most likely a short in the harness (or to ground). May I have your opinion and maybe some trouble shooting advice (maybe a schematic or pin-out at the ECM?)

Thanks,
John

It may not be related to the timing chains itself but it could be that the trigger wheel for the cam sensor is loose or has a broken tooth or to much of a gap between the sensor and the trigger wheel, and yes it could be electrical too.