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Pavlin Koev
Pavlin Koev, CERTIFIED TECHNICIAN
Category: Ford
Satisfied Customers: 3485
Experience:  17 YEARS HANDS ON EXPERIENCE, TRUCK&COACH TECHNICIAN LICENCE
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2004 F-150 FX4: misfire..cylinder..the coil, injector

This answer was rated:

I have a 2004 F-150 FX4, I just had a shop replace the spark plugs( do to them breaking ). After the shop put ti back together the computer showed a misfire on #5 cylinder. They have replaced the coil, injector and tried a different spark plug. Note the old plug came out clean as one piece. Could it be a wire shorting or something totally different? tired of wasting money on this issue.

Pavlin Koev :

Hi and Welcome to Just Answer! My name is XXXXX XXXXX I will do my best to help.

Pavlin Koev :

engine computer has individual drivers for each ignition coil.

Pavlin Koev :

if wiring is not shorted to ground or to power, then it is blown power transistor inside computer.

Customer:

So could it be maybe the wire has been pulled out of the connector or is the computer just bad now?

Pavlin Koev :

it can be either

Pavlin Koev :

you must check ontrol circuit

Pavlin Koev :

if you are planning to do it yourself, I can send you wiring

Customer:

ok that would be great

Customer:

It just all of a sudden it started, all because of the junk plugs

Pavlin Koev :

yes, bad spark plug can damage computer

Pavlin Koev :

increased resistance will blow power transistor that controls the circuit

Customer:

Well if you can send that diagram I can probably figure it out from there, thanks

Pavlin Koev :

i will, you must have pulsating ground on that wire

Pavlin Koev :

I will point it to you

Customer:

ok

Customer:

Do you need my e-mail address?

Pavlin Koev :

just few minutes to prepair it

Customer:

ok

Pavlin Koev :

no will send it here, will do it in printable file

Customer:

ok

Pavlin Koev :

click HERE to see

Pavlin Koev :

#5 will have light green wire with yellow stripe

Customer:

got it

Pavlin Koev :

going to computer pin #10

Customer:

pulsating ground on that wire? what happens if that is good?

Pavlin Koev :

power from fuse travels through coil windings and it is grounded by computer.

Customer:

Say wiring is all good and computer is good what else would cause imisfire or is that the last resort?

Pavlin Koev :

if wiring and computer are good, then it will be low compression or bad valve lifters on this cylinder

Customer:

ok Checked compression and that was good. Thank you for helping find another possible solution

Pavlin Koev :

no

Pavlin Koev :

but do you have spark on that cylinder or not?

Customer:

Yes have spark,

Pavlin Koev :

on #5

Customer:

tried coil , injector, new and old plugs . all on #5

Customer:

Just trying to figure it out

Pavlin Koev :

compair to other cylinders what compression you have?

Customer:

could not tell you because I didn't do the check. I am getting my truck back tomorrow with the misfire. Tired of spending money at the shop

Pavlin Koev :

so you only know what they are telling you

Customer:

Yes Sir

Pavlin Koev :

any codes ?

Pavlin Koev :

p0355?

Customer:

The shop says there is but what I don't know. They say it says #5 is misfiring

Customer:

I was told that it gets better idiling but driving you can feel it

Customer:

Should I have replaced all coils with plugs?

Pavlin Koev :

it sounds like coil problem, but coil is driven by computer.

Pavlin Koev :

you check this wiring first

Customer:

I will tomorrow

Pavlin Koev :

when checking wire from one end to the other it must not be more than 0.6 to 1.0 ohm resistance

Customer:

ok

Pavlin Koev :

if computer detects problem with the circuit it will switch it off

Customer:

Well I will check all wiring tomorrow, so thanks for the diagram and the info

Pavlin Koev :

you are Welcome!

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