I am working on a friends 2003 suburban 2500 lq4 6.0, he had a p0300 code for a while and another mechanic talked him into replacing the engine with a rebuilt one. He also replaced the crankshaft position sensor and connector since it looked damaged, he has also replaced the computer twice. Currently I am only getting a p0307 generic cylinder 7 misfire, rpm check engine light comes on at between 2-3k rpm. I swapped coils, new spark plug, new spark plug wire, checked for vacuum leaks, leaking fuel pressure regulator all check out fine. He normally runs 87 octane, I put in a few gallons of 91 to see if that would help and it did not change anything. I replaced the fuel pressure regulator, and fuel injector for cylinder number 7. Also found 2 cracked vacuum hoses, one was for the fuel pressure regulator and the other was manifold to valve cover. fuel pressure with new regulator is 44 psi key on engine not running, engine running at idle warm is 48psi. I can hear what might be an exhaust leak on the left bank, can not tell if from manifold or to collector flange. Would a crankshaft relearn procedure help or fix this? Any other help with this would be greatly appreciated.
Well figured I would update this since the misfire is fixed. Turned out to be caused by back pressure in the exhaust system from bad catalytic convertors on both sides.
Thanks for posting back with the fix. Do you please mind sharing how much did it work out to?
You could try crankshaft relearn but for my experience of those older ones when they start getting these random misfires often you have to replace the wiring harness for the fuel injectors they degrade on those as a relatively cheaply made and will cause those problems and the wiring harnesses themselves just for the fuel injections are pretty easy to change
the wiring harnesses themselves just for the fuel injections are pretty easy to change
Thanks for the response, by changing the fuel injector harness do you mean just the connectors or the whole engine harness? The injector connectors are part of the complete harness and have to be removed with the complete engine harness.
I tested the injector harness it is getting 12v with key on, engine off. Also hooked up a noid light and the fuel injector is getting a signal to fire. I did a spark test and that checked out. I swapped in a coil from a ls6 I have and the p0307 code went away, but a p0300 code came up instead. I collected some data from the engine once warm, short term fueling -1.5 to 2.5, long term bank 1 is at 14 and bank 2 between 24 to 27. oxygen sensors are getting the same voltage and percentage readings per side and pre and post cats.
Correction bank 2 is at 17. Also fuel pressure at idle is 48psi.