I developed a missfire this morning and I am suspecting a bad coil or plug. Everywhere I called wants ~$50 just to hook it up to machine and tell me which cylinder isn't firing.

My question is, can I take off a coil pack, hook an ohm meter to it and tell if it's bad or not? Has anyone else tried this or think it might work?

 

what do you have? CoilOverPlug(cop) or the 4 post coils?...year would help

 

Sorry - it's COP
2000 F150 XLT 4x4 ORP w/ 5.4L

 

just disconnect one at a time until you isolate it or take it to auto Zone..they'll pull it free...get the code(s) and come back here

 

It hasn’t set a code, yet.

Also, I noticed today it doesn’t do it unless the heater has been turned on…
But when I was looking at them yesterday, I didn’t see any evidence of coolant dripping on any of the coil packs to short one out.

Any idea of what the resistance is suppose to be?

 

Are you sure it is caused by the coil? When was the last time the fuel filter was changed? How many miles are on the truck?

Regards

Jean Marc Chartier

 

COP ignition (per the Haynes manual)
primary= .55 ohms
secondary 5,500 ohms


Strange that it only happens after the heater has ben on. Sounds like the famous heater hose leak or it could be some sort of vacuum leak. Not sure how, it just doesn't make sense yet.

 

truck has 46,000 mi

fuel filter has never been changed, but I am planning on replacing it Sat when I replace the plugs and hopefully the bad coil

I forgot to mention it only does it when accelerating - doesn't matter if it's a light load or WOT. It misses out a few times then returns to normal. The longer it runs, the worse it gets. It doesn't miss when it is idling or cruising.

I thought about it being bad gas or the fuel filter, but the problem came on suddenly with about 3/8 of a tank of gas left of a full tank, after I had driven about 6-7 of the 10 miles to work.
On the way home it started doing it after about only a 1/2 mi (heater was still on).
This morning I didn't turn the heater on until I was about 9/10 to the office - and it started missing shortly thereafter.

Also, I cleaned the engine w/ degreaser on Sun and sprayed the engine off. Monday it ran fine. Monday night it rained. Tuedsay morning it started acting up.

 

36fan-
While you've got the coils off replacing the spark plugs, look at the coil boots for signs of arcing. Usually shows as a black spot on the boot its self. Also, look at the old spark plugs for cracks & fouling. A resistance test won't always determine a bad coil. I've seen coils Ohm out OK & still misfire under a load. I think the misfire is probably caused by moisture getting into one of the spark plug wells & a leaking/bad coil boot on that cylinder. Good Luck!