FStorm150

Replaced my spark plugs 26k miles ago with the suggested Motorcraft SP515 plugs. Before I did, I was experiencing a shutter when going up hill and an extreme loss in power. Was at 90K miles then. Anyway after they were changed the shutter went away and all was good. Now at 116k miles it's doing the same exact thing again. Should I look to change the plugs again or look for a bad coil? I find it hard to believe the plugs went bad after 26k miles. Check engine light has not gone on either. Thoughts?

screamineagle

I would change both plugs and coils. Just my opinion

jamie930

Did you change the COP boots and springs when you did the plugs?

I didn't when I changed my plugs. Had the same problem. Changed the boots and springs problem went away.

Order these from Rock Auto set of 8 STANDARD MOTOR PRODUCTS Part # CPBK240 $22

lewissa81

^^^ What they said. Also try taking a paper style finger nail file, cut it length wise in halves or quarters, and get the corrosion out of the COP where it meets with the boot spring. Blow it out with some air and put some dielectric grease on the springs. I picked up that trick on this forum, but I forget from who (maybe MGD). It saved me from buying a few new coils, at least for now. With 192k miles, I'm sure they don't have too much time left.

FStorm150

Wouldn't my check engine light be on if a coil were bad though? Or not necessarily?

corey_lax

I misfired for weeks without a check engine light. And I'm not talking a little stumble. We were bucking down the highway like a rodeo and it still wouldn't give me a CEL haha. The misfires are supposed to be a certain amount of times per minute and then it will give you a CEL. I guess I didn't get enough misfires....

commando24

I would replace coil. Has happened to me 3 times in the past year and every time was a coil.

FStorm150

Looking to change coils sometime soon. Is there a way to diagnose them individually first and finding the one (or two or three) that are bad rather than changing them all?

effects4

Primary resistance should be less than 0.9 ohms, secondary resistance should be about 5,750 ohms.

Connect an ohmmeter across the primary terminal and the negative terminal of the COP to see if its close to .9ohms. Then recheck at the secondary terminal, fits over the spark plug. Resistance should be around 4,910 - 5,400 ohms.

Pull the boot off the COP and spray battery cleaner inside and let it sit for five minutes. Then clean and clear the corrosion off the metal post, dry and put some dielectric grease in there before putting it all back together.

I plan on doing this to mine as I have a slight miss and sometimes it seems as if the motor is really laboring. I believe it's best to check on a warm engine but not sure.

lewissa81

A word of caution when bench testing coils. While you may find the primary and secondary resistances to be acceptable, there may be deformations within the windings that only show when the coil is firing for a while. These can't be found with an average multimeter. While a bench test can tell you if a coil is definitely bad, it may not tell you if it is good.