bmwfanatic320

hey all, just joined the forum...but anyway, my buddy has a 1997 f150 w/ the 4.2. it has a waste spark ignition system and when checking the secondary coil resistance i had a 15 kohm reading....auto parts guy is telling me range is from 10k-15k...other people are saying 6.5k-11.5k. before i throw the coil pack on it i wanted some verification on this spec.

p.s. it has a nasty misfire only in gear under load...idle is perfect, cruise is fine, just when accelerating under load in certain gears.

Thanks,
Nick

henry73

I'm having similar issues with my 97 v6. I tested my coil and got a reading of 13.5 kohms and the chilton books says range is 6.5 to 11.5 plus I put on a timing light and attached the pickup lead to each plug wire and number 2 don't light up the light so I guess my coil is bad.

bmwfanatic320

the more i read, the more i think it's the coil. i wish i could get a solid range from a reliable source. AllData and ShopKey both say that the spec was not available at time of release. I definately don't trust Haynes. Is Chilton's a reliable manual?

would any1 with a properly running 4.2 care to check their secondary coil resistance?

henry73

I went ahead and bought a new one and I get a reading of 9.5k on the secondary resistance on the new one.

Try the timing light trick if you have one. Put the pick-up lead to each spark wire while the truck was running and thats how I discovered that #2 wasn't firing at all, and I swapped wires with #1 and it still didn't fire on #2.

bmwfanatic320

thanks alot, that helps me out since i'm already having a hard time telling my friend that owns the truck platinum tipped motorcraft plugs cost $8 a piece...not to mention the plugs cost about $100!!!!!! at least now i can tell him it's definately the coil w/o a doubt.

ken.norwich

how do i check the secondary resistance on my truck with a voltmeter? besides obviously switching it to ohms lol where do i touch the positive and negatives to?