2013 Sierra p0307 mystery intermittent misfire

Shane Owner/Technician Arkansas Posted   Latest  
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2013 GMC Sierra 1500 SLE 5.3L (7 LC9) 6-spd (6L80) — 3GTP2VE7XDG135662
P0307 — Cylinder 7 Misfire Detected
Intermittent Misfire
Flashing Cel

diagnostics, testing and inspection - scanned all systems, found multiple cylinder misfire, evap system large leak, fuel trim cylinder imbalance bank 1, and throttle closed position performance dtcs set in ecm; viewed live data found no current misfires but all cylinders having history misfires; cleared all dtcs, verified no current misfires on any cylinders, road tested found running lean, viewed fuel trim data found fuel trims seem normal, normal ethanol content; road tested vehicle found as evap system starts purging fuel trims begin to change, smoke tested evap system and found o ring on fuel pump module leaking profusely, advise replace fuel pump/sender module o ring and re test; upon bringing vehicle into shop for repairs, noted CEL was flashing; and engine was misfiring, documented cylinder 7 misfire tested for ignition found spark present removed fuel injectors performed fuel injector flow test on fuel injector bench machine could not note any inconsistencies in the flow rate of injectors performed pinpoint test checking for continuity from PCM to fuel injector connector proper continuity was present swapped ignition coils from Left Bank to right Bank swapped spark plugs from cylinder 7 to cylinder one misfire stuck with cylinder 7 and intermittently cylinder 5 check for cylinder compression on cylinder number 7 noted static compression at 150 running compression 75 tested compression on right Bank cylinder number 2 found compression static 150 running over 100 noting a 25 psi difference from bank to bank recommend removal of valve cover to inspect for damage and valve drain; removed valve cover, was unable to see any visible damage, performed leakdown test and found exhaust valve burned and leaking, advise remove cylinder head and have valve job done at machine shop; customer approved repairs and requests DOD delete; performed repairs and services, after head removal sublet to machine shop for head repairs, replaced head gaskets and bolts, replaced lifters with non dod lifters and special lifter trays for dod delete, installed non dod camshaft, re assembled, installed dod delete valley plate along with oil pressure sensor relocation kit; performed calibration update for dod delete and found system has already been disabled in tune; road tested to verify repairs, found after second test drive cel flashing and cylinder 7 misfire reset, cleared dtcs and symptom immediately stops indicating no mechanical failures; performed all tests again found valves sealing properly now, swapped coils and road tested, found misfire intermittently resets cylinder 7; swapped injectors, found misfire intermittently resets cylinder 7; tested for spark, checked compression, checked harness, found no issues, and misfire will not set until being road tested; installed used pcm, programmed via acdelco sps to verify correct calibrations, then performed dod delete calibrations in hp tuners, found service number for pcm incorrect so unable to calibrate with hp tuners; repeated process with another pcm with same result; advise next step is to install OEM new pcm, program and calibrate for dod delete then retest; installed new PCM from chevrolet dealer, programmed via acdelco techlineconnect/sps with latest calibrations, then performed dod delete calibration in hp tuners, road tested found misfire did not return on initial or second test drive, upon third test drive vehicle began intermittently exhibiting flashing CEL and misfire graphic showed misfires on cylinder 7; checked ground circuit on each ignition coil connector and verified continuity, found no issues; repeated compression test and compared cranking/running compression of 130/70 and 135/65 on cylinders 1 and 7 respectively, unable to find any issues at this time;

Need some help here, if anyone had time to read all that. Ghost misfire that comes and goes, and everything has been done shy of replacing an engine harness.

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Interesting
Saul Diagnostician
Texas
Saul
 

Could it be something with the crankshaft reluctor wheel, or maybe the crankshaft position sensor. Have you scoped the crankshaft position sensor?

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Shane Owner/Technician
Arkansas
Shane
 

I have not. Do you think that would be something that would show up all the time? Sometimes this vehicle can make several good trips before it even counts a single misfire

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Saul Diagnostician
Texas
Saul
 

I haven't seen this particular problem on one of these trucks, but was just throwing it out there as an idea. Bernie Thompson has a really good video on YouTube about a Honda I believe, that was getting misfire codes because a bad reluctor wheel.

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Jesse Engineer
Missouri
Jesse
 

I had a '99 GMC Sierra do something similar. Was running great in town. Went to drive it on a long trip and didnt make it 2 miles before it started cutting out and misfiring like mad. Drove a couple of more miles hoping it would clear up. It didn't so I limped back home. Ended up with misfires on #5 & #7. Installed new plugs, was better for a couple of miles but it came right back. Pulled…

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Paul Mechanic
Illinois
Paul
 

Have you verified correct cylinder misfire call-out? Firstlook in tailpipe with scope? Are you feeling misfire? Did you do case relearn?( I assume you did case with all the PCM swaps). Two things you may want to check, but doesn't explain the intermittent cycle if it's mechanical. Piston height of that cylinder as you readings seem to indicate number 7 is always lower than the rest, bent…

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