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Steve
Steve, Ford Technician
Category: Ford
Satisfied Customers: 6833
Experience:  25 years working for Ford dealer. Ford Master tech.
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F150: Ive been experiencing an intermittent miss in my 03

Customer Question

I've been experiencing an intermittent miss in my '03 F150 5.4L. Yesterday, it started missing in conjunction with the THEFT light flashing and the CEL came on. It is still intermittent but happens much more frequently now. Plugs and coils were replaced about 16 months/14k miles ago. Any suggestions as to root cause?
Submitted: 9 months ago.
Category: Ford
Expert:  Steve replied 9 months ago.

Steve :

Hi, my name isXXXXX be helping you today. Please give me a moment to review your question before we start the consultation.

Steve :

Have you had a chance to see what the engine code is for the cel light coming on yet?

Customer:

No, I tried to scan it but the diagnostic port wouldn't power it. That is a separate issue that I need to address tomorrow.

Steve :

The reason is because the fuse is blown to pin 16 It uses the cigar lighter fuse replace it and check for codes.

Steve :

You are going to find a missfire code

Steve :

What happens is one of the coil on plugs is backfeeding to the computer. Replace the coil on plug in the cylinder the missfire is in.

Customer:

I was afraid of that. I replaced plugs and coils in 9/12 and it was a PITA.

Steve :

What happens is one of the coil on plugs is back feeding to the computer. Replace the coil on plug in the cylinder the misfire is in.

Customer:

Even though it had the occasional misfire it ran great and just yesterday started running really bad and the THEFT light thing started. It is probably just a coincidence but it started when it got really cold out (< 20 degrees).

Customer:

It seems the coils on these things are a real problem.

Steve :

The spark plugs should be ok, you have a bad coil on plug back feeding to the computer causes all those concerns. If you bought the coils from a parts store instead of the Ford ones, this happens.

Steve :

What happens is one of the coil on plugs is back feeding to the computer. Replace the coil on plug in the cylinder the misfire is in.

Customer:

I purchased Motorcraft coils. Hopefully, it will be one that is easy to get to.

Customer:

Thank you for your help and for the tip on the blown fuse.

Steve :

They are warranted for 12 months or 12 k miles take it back and get a new one for free.

Steve :

You are very welcome

Steve, Ford Technician
Category: Ford
Satisfied Customers: 6833
Experience: 25 years working for Ford dealer. Ford Master tech.
Steve and 7 other Ford Specialists are ready to help you
Customer: replied 8 months ago.

What is the best way to determine which cylinder is causing the problem? There are no trouble codes.

Expert:  Steve replied 8 months ago.
James,

You will need an advanced scanner that can go into mode 6 and it will give you the misfire count and which cylinder is misfiring.

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