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2003 ford f-150: my truck..light came..misfire..Put new plug in #2…

Customer Question
my truck is a 2003...
my truck is a 2003 ford f-150 with a 4.6 liter engine. The light came on and machine at Auto Zone showed a misfire on #2. Put new plug in #2 and run good for a week, started the same thing. Put on machine again and this time it was the #6, put all new plugs and still same thing. Put on machine again and still showd misfire on #6, put new ignition coil on #6 and is a little better but still runs rough and light stays on. Airconditioner also quit working at the same time I put new ignition coil on, dont know if thats related. Have searched to find an answer, but come up short. Need Help.....
Submitted: 8 years ago.Category: Ford
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Answered in 4 hours by:
6/22/2010
Ford Mechanic: Kenny Z., Ford Senior Master Tech replied 8 years ago
Kenny Z.
Kenny Z., Ford Senior Master Tech
Category: Ford
Satisfied Customers: 6,083
Experience: Auto Trans, Drivability and Electrical Specialist
Verified

HiCustomer Thank you for asking your question on JustAnswer.

 

It sounds like you are having coil issues. These coils are known to give off large amounts of RF causing misfires of other coils that are not picked up by the computer. Ford has a test for these coils called a stress test. This test identifies the coils that are emitting the RF. Rather then guessing at which coil is bad, you could have the stress test performed for less than the price of a coil.

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Customer reply replied 8 years ago

Hey Kenny, I want to make sure that we are on the same page.

 

When I took the truck to Auto Zone thier machine picked up on the #2 cylinder right away. I bought all new plugs but only replaced the #2 and the problem was solved. Before I had time to replace the rest of the plugs, same problem started again (which was several weeks).

I took it back and had it checked again to make sure that the plugs were the problem, this time it showed the #6 cylinder, so I replaced all the plugs, thinking it would fix the problem and when it didnt, I went ahead and bought and installed a new ignition coil on #6, still had the same problem.

When I had it put on the machine it showed the code PO356 with definition of "Ignition coil primary circuit condition--coil #6". The explanation said the "ignition coil primary circuit is monitored for errors". Probable cause "Driver circuit fault--ignition modlue or PCM" , the other two causes I had already done. The ford site says the code PO356 is "a ignition coil primary circuit malfunction" and to check for bad connection or fault in the ignition module or PCM driver circuit, depending on how the ignition system is configured.

Im not questioning your answer, I wanted to tell you a little more in detail about what happened. My question that i sent was very short and a little incomplete. Let me know what you think.....

Ford Mechanic: Kenny Z., Ford Senior Master Tech replied 8 years ago
RF from coils can trip primary codes. you can check the ground driver for the coils in question by attaching a test lamp to battery positive and probing the ground wire on the coil. with the engine running it should flash steady. I have also seen coils with high RF take out ground drivers in the PCM. I still recommend a stress test on all of the coils.
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Customer reply replied 8 years ago
Hey Kenny, what is RF? and if the PCM goes bad would that have anything to do with the ac compressor. I noticed the wiring travels to the compressor and the reason I ask is that the ac compressor stoped working right after I put the new ignition coil on. Just trying to find out what the problem is. Thanks............
Ford Mechanic: Kenny Z., Ford Senior Master Tech replied 8 years ago

RF is radio frequency interference. The A/C question needs to be asked in a different question. I don't see how it can be related. We are only allowed to address one problem per question.

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Customer reply replied 8 years ago

Hello Kenny, Please dont think that I'm crazy, but I have to tell ya one more thing before I can wrap this up...........

 

I left the cable off of my hot post on my battery all night until this morning. Before I was to take my truck to the Ford house I had to go about five miles away from house to check on my cattle. The light was not on and the truck was running smooth, there was a little lurge as I first took off but no miss. When I got back home I noticed it was still running smooth, I turned the A/C on and it was still the same until I moved the air thermostate switch up about quarter of inch and heard the compressor come on and it started cooling. No light, No miss and the A/C was cooling. Drove out drive and about 200 yards down the road and A/C stoped cooling and truck started with the slight miss as it has been doing but the light never did come back on.

Every since the miss started, the compressor quit coming on and the ac termostate switch made a clicking type noise when it was set to as cool as it goes and would quit if you move it up about a quarter inch. Does the PCM or some other module put out to the ignition and cooling system or is all of this just coincidence. This is driving me crazy but I promise this will wrap up my driving you crazy with all this information. Thanks.......................

Ford Mechanic: Kenny Z., Ford Senior Master Tech replied 8 years ago

The clicking when you move the temp control sounds like it could be coming from the temp blend door actuator, thats how they sound when they are failing. The A/C compressor clutch could possibly be drawing too much current causing a voltage drop in the electrical system making the PCM have problems from lack of voltage. This is definitely going to be a hands on diagnosis. Too much to cover in a web environment. Don't feel you have to accept as I don't feel I really answered your questions to the point of your truck being fixed.

 

Good luck and take care,

 

Kenny

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