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Arench, Master Technician
Category: Ford
Satisfied Customers: 1490
Experience:  30-years experience auto and truck repair.
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2003 ford explorer 4.6 missfire cyl. P0306 P0316 new coil

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2003 ford explorer 4.6 missfire cyl. P0306 P0316 new coil , injector plugs, crank compression 160 running 75 problem felt at idle never on acceleration have signal to coil and injector. dont understand if clear code with scanner missfire counter builds and light comes on, disconnect battery I can still feel rough but do not record missfires this problem at times is very noticeable at times runs good did timing chain all tensioners guides engine is clean valve covers timing cover no sign of age never any other cylinder missfire no smoke plug clean can i have a PCM problem only 1 cylinder
Greetings from Mikey at Just Answer!

Expand your basic tune up to all cylinders with 8 plugs and 8 coil boots. The computer will sometimes identify the wrong cylinder misfire. Most of the time this is a bad spark plug, or coil boot.

Check for intake vacuum leaks with a smoke machine.

Possible dirty or stuck egr valve creating lean mixture at idle.

Customer: replied 8 years ago.
all coils are new motorcraft as well as plugs already smoked replace egr valve
Do a running compression test at idle engine warm. Get comparison between troubled cylinder and good cylinders. Looking for bad valve guide.
Customer: replied 8 years ago.
already replaced all coils and plugs and egr valve smoked engine tried everything it is my vehicle

Next thing is get a running compression test at hot idle. What you are looking for is a comparison between the problem cylinder and good ones.


I would also try swaping the fuel injector to another cylinder and see if the problem follows the injector.

Customer: replied 8 years ago.
did a running compression 70-75 cranking 160 injector is new I have tried everything I can think of am wondering if pcm has a seperate driver for each cylinder. If I clear code with scanner light come back on in a couple of key cycles but I disconnected battery last week and no light yet and monitors are ready not recording and missfires in scanner I can still feel rough and at times it is barely noticable and at times much more so

One thing I always do is replace the fuel pump and PCM power relays before looking at the PCM. If the power supply gets "fuzzy" unexplainable things can happen.


Make sure there is no corrosion at the pcm connector and visually inspect the connector for backed out pins.


Yes, each coil has its own wire to and driver in the PCM.


I would be interested in knowing the short and long term fuel trim numbers at cruise and idle in drive.

Arench and other Ford Specialists are ready to help you
Customer: replied 8 years ago.
this info did not lead to solution already checked trims and sensors problem is cyl. 6 only and signal is present at coil and injector could i have a problem
Customer: replied 8 years ago.
can the injector or coil signal timing be off can a ford shop be better equiped to find problem with snap on scan tool i cannot read live missfire data only mode 6 recorded data

An osillisope would be the only tool that would be usefull to compare waveforms of different injectors and the ignition primary. A different scan tool is not going to tell you anything more than you already know. It sounds to me like you know what your doing.


If I had this truck I would change the PCM and fuel pump relays and put another set of plugs. If that did not get me anywhere I would change the PCM.


I would rather spend my money on parts then diagnosis.