i have a 03 f150 kingranch supercrew with a 5.4 in it..... i was accelerating to get on the interstate and out of nowhere the engine starts a heavy miss. i pull over and turn the truck off and crank it back up and the miss is not as bad but still there. i notice the a/c is no longer working.. after getting home i run the codes and get a code for miss on cylinder 3.... seeing that im used to faulty cop's i change the cop and plug. this doesnt solve the problem so i changed the tps sensor thinking it may be sensing wot and kicking the ac off and causing other problems... i was wrong.... so i did some studying and have checked the melted wire theory and even cleaned my maf sensor.... still no luck...... anybody have any ideas?

 

A TPS won't be the cause of a dropped cylinder or the A/C issue.
If you still have a cylinder 3 code, what is the code telling you specifically in it's definition or give the code you have for interpetation.
Good luck.

 

the first time i pulled codes i got po353 ignition coil c primary secondart circuit malfunction.... after changing the cop and clearing codes i drove it and it gave me the same code plus a random miss on cylinder 3 and bank rich i believe....

 

I thought you may have this code after replacing the coil.
Try to follow this;
The coil is fired from the PCM by grounding it's lead in the PCM with a program controlled solid state switch.
If that switch goes open or shorted as a fault, it cannot fire the coil.
The harness is the only thing between the PCM and the coil.
The test is to see if the ground is being extended to the coil while the motor is running.
If not, you are in for possible replacement of the PCM.
The rich code is obviously the raw gas being passed by that cylinder (assumes the injector is working).
A replacement PCM involves reprogramming as well as doing the PATS with your two ignition keys.
Do not keep driving the truck with a cylinder out because it may take the cats for that bank out from overheating and add to the possible total cost which if this all happens you will not be a happy camper , as they say.
What looks like a single cylinder issue can become very costly when you need dealer service.
Let us know how it all turns out.
Good luck.

 

im lucky i have this truck and also a full time work truck that i have been driving while the ford has been out of commission. so bluegrass can you go into detail on how i need to check the pcm.... also does anybody have any harness electrical diagrams for my truck.?

 

You need to get a voltmeter accross the coil lead to see it pulse as the PCM grounds the lead to the coil as the motor idles or cranks over.
Another way to test for an open or a ground is to cut a coil connector off a coil and solder leads on the cut side so a meter can be connected and plugged into the coil connector.
Then look at the resistance looking back at the PCM switch.
If it's shorted you will see resistance from near zero to less than 2000 ohms.
If open, nothing.
If good should see in the 10,000 ohm range+/-.
The design is made this way so a dealer can look at it in about the same way and tell an open from a short.
Good luck.

 

ok i wont lie i dont know alot about voltage and checking everything so sorry if i did something wrong... please work with me... i set my multimeter to 20k with the horseshoe symbol. a friend told me thats what i would set it to check ohms resistance.......?????
i did this and checked the plug for said coil as i had somebody turn the engine over.. it read in 750 range i checked 2 other coils and got numbers in the 550s and 600s.... please advise????????

 

ok i just got a wild hair and took a led tester and decided to check the harness for the coils.... with the motor running at idle all working coils had a constant positive and a strong blinking negative..... when testing the missing cylinder it had a strong constant positive but the negative is also constant but the light is very dim........ thought this may help diagnose the problem

 

You are seeing the problem by compairison.
The computer can't pulse the coil.

....What is supposed to happen is the ground from the computer allows current to flow through the coil winding from positive to negitive ground.
....This saturates the core's magnetic storage ability, the coil is wound on.
....When the ground is 'removed' , the magnetic field colapse acts on the coils self inductance stepup ratio and causes voltage step up from 14 volts to many thousands of volts causeing the spark to appear at the output to the spark plug.
....Try this as a last check.
Plug in a known good coil with a spark plug pushed into the boot and laying the body on a grounded surface.
Have some one crank the motor and observe for spark.
If you see little to no spark, your seeing the trouble.
Then look at other coil connectors on good cylinders to see what the resistance is looking back at the PCM switch.
Recheck cylinder 3 for compairison again.
From this you can decide if the PCM switch for cylinder 3 is faulty or even the big connector on the PCM may have a high resistance contact for that cylinder.
If the PCM, it has to be replaced, reprogrammed and Pats and 2 keys reprogrammed.
I think your at a point now that dealer service is needed to vairify the condition and the repair action taken.
I explained the above because many people will be looking at this and some will have the same kind of issue to deal with in chasing a dead cylinder.


>>>>I might add to remove fuel injector plugs on any cylinder you have spark plugs removed from to prevent a fire from fuel being injected into that cylinder and being pushed out the plug hole causing it to ignite from any spark your testing for or coils connected and laying close by.
Good luck.

 

thanks man big help im gonna probably take it to a dealer in a couple weeks