Chasing misfire

Dennis Owner/Technician Plymouth, Michigan Posted   Latest   Edited  
2012 Ford Expedition XLT 5.4L (5) 6-spd (6R80)

Misfire at idle and light acceleration​.​No misfire felt during cruise​.​Plugs,coils and injector have been swapped​.​Vacum gauge reads steady between at idle and 1600 rpm​.​Compression is 240 on first 3 cylinders bank one​.​Tested injector pulse with noid light is good​.​Coil is firing​.​Plug looks normal compare to two plugs after it .Gap was excessive​.​Regapped and swapped plugs.I'm thinking its mechanical but would data to prove it before tear down.I have to be missing something​.​Staring to think spring valve or follower on one of the intakes is the issue​.​Wondering if it not showing becuase the other valve is working fine.

Vehicle is 2012 ford expedtion xlt 5.4 3v sorry keeps deleting the info when i post.

Eric Owner/Technician
Peoria, Illinois
Eric Default

Is the valve timing advanced? Compression seems off be me. What are the fuel trims at idle, 2000 rpm no load and 2500 rpm load? What are the rear O2 voltages when misfiring. I would recommend a relative compression with ign sync and cranking vac. test with a scope.

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Bruce Owner/Technician
New Brighton, Pennsylvania
Bruce Default

Misfire at idle like a weak cylinder? Goes away raising rpms? Need fuel trim, short and long, Fuel trim positive on idle and normalizes with rpms raised = vacuum leak and can effect the cylinder nearest. Mechanical problems like a burnt valve. Slightest leak on a exhaust will do this. Oscilloscope with first look pressure tester in exhaust and then intake would help. Relative compression…

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Jared Diagnostician
Essex, Maryland
Jared Default

Try using fords powerbalance feature on your scantool. Mode 6 miss counts? One cylinder or random/multiple?

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Michael Mobile Technician
Clinton, Utah
Michael Default

Hi Dennis, Try disconnecting the cam sensor on the drivers side. Chain stretch or improper timing can cause this issue. -Mike

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Eric Owner/Technician
Grand Rapids, Michigan
Eric Default

I'm with Eric, that compression is too high, but what is the compression on the rest of the cylinders? Do you have access to an in cylinder pressure transducer? A relative compression test at the very least would help. If you are lacking a scope and a few of the essential accessories, time to pony up. These will be invaluable in accurately diagnosing this exact type of issue.

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Larry Owner/Technician
Ham Lake, Minnesota
Larry Default

The compression seems way to high​.​fuel trims would help . If you are questioning valve sealing set your scope up for a 10 second capture and watch cranking psi for variations

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Chris Technical Support Specialist
Commack, New York
Chris Default

The cam timing can be verified with live data as long as it runs and is not grossly out of time. Look for VCT error pids in the data stream. The error pids will calculate how far from desired position the actual advance is. VCT error should read close to 0° when under steady loads, there may be some lag when actuating. Check error pids at idle and off idle, then monitor under load and steady…

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George Diagnostician
Burnaby, British Columbia
George Default

I'm with Bruce need more information but does sound like valve seat problem

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James Owner
Lavalette, West Virginia
James Default

I’m gonna say cam phasers or solenoids check oil pressure at idle

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Dennis Owner/Technician
Plymouth, Michigan
Dennis Default

The 240 psi cranking was with a 3 second crank wot. 2 second crank is 185​.​Unfortunitely customer declined further diag.

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