p0307 code
Thread Starter
Teching In
Joined: May 2012
Posts: 12
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From: South San Francisco
p0307 code 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. Would a crankshaft relearn procedure help with this or would a fuel injector cause this? Any other help with this would be greatly appreciated.
Thread Starter
Teching In
Joined: May 2012
Posts: 12
Likes: 0
From: South San Francisco
Fuel pressure at the rails with key on not running is around 45psi. Running at idle is around 48psi. Does sound like the engine has an exhaust leak, but that wouldn't cause a misfire right?
Fuel pressure should be 58.
I would try swapping injectors with a different cylinder if you have not done that.
Also check compression on 7. Compare to a known good cylinder.
I would try swapping injectors with a different cylinder if you have not done that.
Also check compression on 7. Compare to a known good cylinder.
Thread Starter
Teching In
Joined: May 2012
Posts: 12
Likes: 0
From: South San Francisco
I haven't had a chance to do a compression check on the engine yet. I replaced the fuel pressure regulator with oem gm part, still getting bouncing fuel pressure at idle around 50-54psi, 52 psi with key on engine not running. I also already replaced cylinder #7 fuel injector with a new one and cleaned other injectors and blew out the fuel rail with compressed air, no change. I swapped all the coils from one of my personal vehicles that runs fine and still getting misfire. Also pulled the passenger side valve cover and no signs of bent pushrods, broken valve springs and rocker are torqued to spec. Vacuum at idle is 20psi, I removed the vacuum line from the regulator and no change in idle speed or run quality. I did have a weird issue with the car idling the fuel pressure regulator would make a squeak nose once in a while would that be a sign of a clogged fuel filter or bad fuel pump? Engine is also only 2 years old, friend had another mechanic look over this vehicle before me for the same issue and recommended a new rebuilt engine, which didn't fix the problem. Thanks for any help with this as I am starting to run out of ideas on what is causing this. Also tried to do a crank relearn and my scanner isn't communicating with the computer.
