I have a 5.3l swapped into a 89 c1500. I just put a new motor in the truck do to a cracked block an every since I put it in the truck don't start an throws a p0336 code.

Truck mods:
216/224 cam
918 springs
New timing chain
Tuned by Blackbear

Iv replaced the crank sensor didn't fix it, checked fuel pressure good, did crank relearn didn't fix it, checked wiring all checked out good

Anymore opions I can try

 

Where did this "new" motor come from???

Where did the new sensor come from???

Have you checked the crankshaft end play???

 

Yes checked crank play an the motor came out of a wreaked 02 Silverado an the sensor came from my local parts store

 

Anyone have any ideas

 

How did you do a crank sensor relearn if it won't start?

 

It will start an run sometimes but you have to hold it around 800 to 1000 rpms for it to stay running because it serges.

 

Got the problem fixed ended up being the ecm