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A. Penland
A. Penland, Ford Senior Master Technician, ASE
Category: Ford
Satisfied Customers: 6480
Experience:  ASE Master Certified, ASE Advanced Gasoline Engine Performance
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Why is my 1999 f150 5.4 misfiring so bad after I changed the

Customer Question

Why is my 1999 f150 5.4 misfiring so bad after I changed the cylinder head cause it blew a spark plug ?
Submitted: 10 months ago.
Category: Ford
Expert:  A. Penland replied 10 months ago.

Have you checked for trouble codes in the PCM (Engine Computer)?
Have you isolated what cylinder is causing the miss fire?

Customer: replied 10 months ago.
I have, the scanner says there is no codes available ? It's q little rough when the rims are up but runs worse when idling, it smells almost like it's running rich
Expert:  A. Penland replied 10 months ago.

Try this to isolate the cylinder miss firing.

Start the engine and let it idle. Then unplug on coil at a time and see if it makes a difference in the way the engine is running. If the cylinder is not firing, it will not effect the engine. But if the coil is firing, the engine will run a little more rough.

Customer: replied 10 months ago.
Ok I'll try that, I just called o'reilly's, they said it may not have thrown a code cause it may not have run long enough to & also since it hasn't run that long it could be that the computer hasn't relearned the timing
Expert:  A. Penland replied 10 months ago.

That is true. The miss fire may not be bad enough for the PCM to see it. It has to count it to make sure what cylinder it is and set the code.

Customer: replied 10 months ago.
I see, I'll try taking off individual coil packs & see what it does, I appreciate it
Expert:  A. Penland replied 10 months ago.

No problem. Start on the side you did the cylinder head. Also, make sure all the coils click when you plug them in, along with the injector connectors. I can honestly say.."I have done that".. after putting an engine in and had a miss. Loose #8 injector on the drivers side rear.

Customer: replied 10 months ago.
One more question, what if there were some vaccum lines backwards if possible, would there be a code ?
Expert:  A. Penland replied 10 months ago.

They will cause codes after the engine has run a while. Vacuum lines will cause lean codes. Also inspect the PCV hoses.

Customer: replied 10 months ago.
Ok, I appreciate it, if I'm still puzzled after trying this I'll try on here
Expert:  A. Penland replied 10 months ago.

Just reply back on this page.

Customer: replied 10 months ago.
Sounds good, thanks
Expert:  A. Penland replied 10 months ago.

Your welcome.

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