Ok my dads truck has a misfire in cyl 6. It is more noticable in light throttle. I changed the plugs and boots. The coil pack and the injector is getting power. I checked a bunch of coil packs and they all seemed to be with in a tenth of each other. I'm goin to check for heat on the manifold with one of those lazer guns just for shXXs and giggles. Other than maybe switching injectors to another cyl to see if it follows is the only thing i can think off. This thing is pissing me off and it onl has 40000 miles. Thanks for any input.

 

Replace the coil pack. I had the same issue, outlined in another thread here, repaced the coil pack and fixed the problem.

 

Before replacing the coil pack, you could swap it with another one, say number five, and see if the misfire also changes cylinders. Much like swapping fuel injectors, only easier. Just a thought.

Robbie

 

Checking the primary and secondary resistance will identify shorts or opens in coils. Passing one doesn't mean the coil is good. Tunneling is a weaking of the insulation between wraps in the coil, usually caused by an open plug wire (like running with a pulled the plug wire to troubleshoot). It won't show up on a resistance check, only under load.

Seems like most people with COP problems don't really have a problem with the coil, they seem to have a problem with the boot, usually getting wet. Clean, dry, use dielectric grease.

A very good way to check the secondary (only a few inches long in this case) including the plug, the wire, and the boot is to use a spark tester. It has a 3/4" gap which is about as hard to fire as a .050 gap under compression at wide open throttle. If it will fire that, it will fire the plug. Try to position the boot very close to where it would be on the plug.

I'm treading on thin ice here but since it takes more voltage to fire a plug under load (less vacuum, higher pressure, more molecules in the plug gap to ionize) so secondary (high KV) issues get worse under load. Since your problem occurs under light throttle, I wouldn't suspect a coil/wire/boot problem.

Even thinner ice, check for EGR flow.

 

bigbronc, you seem to be the forum's resident mechanic. From your posts, I'll bet you're a Ford Master Tech. On the modular engines (guessing that's what he's got) is there an easy way to ensure there's no EGR flow? Especially assuming he doesn't have a way to cap it off?

If he could, that'd get that possibility out of the way.

 

If the egr is cool to the touch while idling, it is not flowing. If it is hot, that means that it is flowing. If it was flowing when not needed, a dtc will be set. Unless he already has a bad dpfe sensor and it doesn't detect the flow.

Robbie

 

i just started a thread concerning an untrackable missfire..my truck had around 40k when it started it is up to 80 now and i still have not fixed it... not fixed yet mainly due to the money and time i have thrown away and being scared to throw more away trying to track it don again..after reading the threads i am more confident now to search the pcv and the egr and hoses etc...i have heard that a clogged egr valve or bad pcv can show as a coil missfire..there is water getting in the spark plug wells as well...but mine is a 4.6..i read that can happen from the heater hose on a 5.4...mine is definitley not a bad coil pack..but the computers tell you it is. .. i am not a master mechanic but i hope this helps.. well good luck

 

check my post to rokinrandy's thread. it is amazing that 1 problem like a missfire can have so many solutions.

 

Miss- fires can be due to many reasons and not everyones' has the same reason.
1. Bad plug.
2. Moisture in the boot area.
3. Oil in the plug well from a leaking valve cover gasket.
4. Bad coil, COP, wire.
5. Air leak at the intake of the runner for the peticular cylinder.
6. Oil contamination from worn or broken rings.
7. Fuel deposits from a peticular fuel at combustion.
8. Head gasket leak allowing coolant into the cylinder or loss of compression.
9. Valve operation failures/ loss of sealing.
10. Failure to use the proper sealent on the boots.
11. Faulty injector operation.
There can be other and rare reasons.

.
One area that can be peticulerly troublesome to run down is a coil the has increased it's output voltage.

.
This can breakdown the boot, and the plug insulator.
.
Moving that coil around can result in appearing to fix/find the fault over the short term, but causing more faults with other plugs and boots it is used with, and results in great confusion until a point is reached where many or all plugs are changed and the bad coil is elimated out of use as well as quite a bit of money spent to arrive at that point.
Then often it is not known what was actually the original fault that started it all except the code indicating a missfire on one specific cylinder.
The PCM missfire detection process is very very good and will pick up all the above conditions.
That is what it was designed to do, otherwise there would be no good reason to have that ability and not be able to trust it and have still greater problems trying to solve a missfire that sometimes has people thinking parts are defefective that have nothing to do with a missfire, spending even more time and money and on and on it would go..
Print this out and keep it in mind.

 

Hello Everyone,
I'm new to this forum. I was reading this particular post and have a question. I'm not so sharp with a volt / ohm meter but I did check the primary / secondary resistance on my cop's and came up with 0.6 to 0.7 on the primary and 5300 to 5400 on the secondary (5.3 - 5.4 on my meter). The Hayhes Manual says 0.55 Prim. and 5500 on sec. or cop needs to be replaced due to being out of spec.. It doesn't look like there's any room for error. Do these numbers look normal? Any help on this subject would be greatly appreciated.