I was wondering how accurate the resistance test is for ignition coils? I'm going to change my plugs soon and figured to do the coils as well, BUT don't want to throw away good money on something that isn't broke. Can they fall within specs and not be performing at 100%?

 

 

Coils for what?

 

Wasted spark coils are away from the heat and don't see much duty cycle. Probably wasting money if you have the V6.

 

It is coils for my 2000 Lariat with the 4.6L. I'm not having any problems except for a slight miss when I am towing a 4000 lb boat. The only reason I ask about this is my son had a Mustang and one of his buddies worked at the local Ford dealer. He put his car on the computer at the shop and was able to give him a print out of the effectiveness of each coil. For example, coil #1 was 92%......coil #2 was at 86% and so on. This way he was able to see any weak coils. Is there any was to find a weak coil that may miss under the load of pulling a trailer using only my multi meter?

 

Yea COP's very rarely fail completely in this type system unless you use after market knock-offs with no thermal protection and inadequate build magnets. They fail via shorted turns in the winding's. As shorted turns multiply they weaken, eventually failing completely under specific load....specific at first. That load is observed when driving under normal acceleration and at approximately 45mph just before the shift into overdrive. Since the misfire monitor count remains below threshold and doesn't register low-grade misfires, it's unlikely you'll get a MIL (CEL).

Accurate testing can't be done through resistance since a bad coil (low grade) missing under load will ohm out just fine. The theory , -either they work or don't is false with COP ignition systems. Resistance testing only works if the coil is completely shorted therefore compromised 100%.

There's a very affordably way to monitor the misfire count per cylinder which will pinpoint failing coils. Bluetooth adapter (onboard to smartphone), Torque or TorquePro (5 dollar application) and a compatible phone. The app provided live misfire monitor date and with the correct PID will give you Mode 6 = Cylinder history misfire data. Search the apps posted for user info on this site about getting hooked up. Those apps have other uses, this is just one good one.

 

That is some really good info I never knew about. I will have to buy a blue tooth adaptor and download the app. Do you have a reccommendatio on which blue tooth unit to buy?

 

An inductive analyzer can tell you loads, at a glance.
It will show peak secondary spark voltage. You can see if a coil is failing, before it misfires.

if you know how ti interpret graph, it will tell you if cylinder conditions are off too (gap, mixture, etc). Can pick a poor performing cyl out of lineup in a blink of eye.

Theres a reason shops use them.

 

There's a reason why techs use Torque apps.

I was at Ford 2013 and watched a tech use this very app (Torque/Torque Pro) https:https://www.google.com/search?q=torque+pro&ie=utf-8&oe=utf-8&client=firefox-b-1 diagnosing a faulty cylinder () on a gen 10 V10 engine for inspection with the live data function. He mentioned the app was quick. The tech had previously driven the vehicle under load and pin-pointed the misfire. I began passing the word among forums learning that many forum users had already been using these apps...it was new to me back then. Anyway, those apps have grown much more in popularity since that time, user friendly, versatile and has many uses. Give it a try.

 

Not up to date info, ELM327 was popular. Not sure if they bettered that yet.