Check engine light came on. Can easily hear and feel a miss. Stopped by my local parts store and they hooked up their diagnostic computer.
Display showed Number 6 Cylinder Misfire. Going to remove the coil and test ohms with a VOM.
What numbers would I be looking at for resistance, both bad and good? I am hoping it is only a bad coil and will be an easy swap. Thanks

 

While I can't answer your question, one way to figure it out is to swap the bad COP to a different cylinder and retest. If the code follows the COP, you have your answer.

Although getting an answer to your question would also give you a good idea if its your COP or the COP boot.

Stewart

 

I too have no idea on what resistance to look for, but Stewart's method will tell you quickly if it's that COP that has died.
Denso is the OEM manufacturer for Motorcraft COPS and can be bought (Rockauto) for half the price of MC labeled coils. Denso part#673-6000
The new COP will come with a boot but if you don't know for sure when the last plug/boot change was then now is a great time to freshen things up.
New set of 10 boots (they degrade over time and will bleed voltage leading to more misses) Denso part# 671-0001, use a dab of dielectric grease on each end of the boot springs at the contact points.
Plugs are the Motorcraft SP-479. I use just a touch of anti-sieze on the plug threads and over torque the plugs (compared to the factory specs). '00/'03 spec calls for 11 ft/lbs and '03/'05 is 17 ft/lbs, I have an '05 and used 32 ft/lbs. Many owners of the earliry build trucks (like yours) with the fewer threads have had good luck with 26/28 ft/lbs.
To make plug access a bit easier the Gearwrench part# 80546 5/8"X6" swivel plug socket is a winner.
Once you have the COPs and boots removed it's a good idea to blow out the plug wells with compressed air to remove any sand or dirt to keep it from falling into the cylinder or fouling the threads on new plug installation.

 

Ohmmeter checks of COPs is usually a waste of time. The typical failure mode won't change the resistance enough to be distinguishable.

Just swap (or replace) the COP and its spark plug.

 

Yep just replace the coil.... I had an Expedition that went through coils all the time. Also check the boot if it is cracked or torn at the bottom replace or it will misfire through the crack(s)

 

Thanks, I may give that a try if I can get back to the parts store.

 

Thanks for all the numbers info. It's much appreciated!

 

Thank you for the info.

 

I watched a video after posting this and they talked about that. Thanks for the info.

 

Thanks for all the help.

I am going to talk to the previous owner to see if he remembers when and if the plugs and coils were ever changed. He had a complete history of work done to this vehicle before he traded it in to a dealer. When I bought it, he told me to ask the dealer about the history and maintenance records. The salesman told me it was misplaced when the old sales manager quit and they went through his office and chucked things out. It may have wound up in the garbage. I let the salesman know I was pissed about that. The rig is super clean inside and out and doesn't even look close to having 168k on it.

 

In light of that info, if it were me, I'd just buy 10 new replacement boots, install them on all the COP's, and clear any and all codes. Then I'd move the previously identified "bad" COP to a good cylinder (obviously one easily accessed ) and after driving for a few days, check for any newly set codes. This will tell you if you have a bad COP that needs replacing, or if replacing the COP boot on the "bad" COP solved the issue.

Replacing the old COP boots with new ones isn't very expensive and it's a great preventive maintenance job that...one could argue...has perfect timing!

Stewart

 

I'm thinking I might do that along with replacing plugs to start out.

Tinkered with it today, and it may not be a coil.
I pulled the electrical connectors from each COP one at a time with the engine running, and there was a noticeable drop in the idle and ran much rougher after disconnecting each one, including the number six cylinder, which was the one that showed as a misfire on the computer when I had it tested last weekend. Basically it ran worse pulling each connector, compared to the normal miss that I'm dealing with.
Also when I put it in gear, and the idle drops, it starts running more rough. And when backing out of the driveway, it died. Pulling up into the driveway, it died again. It would restart fine but as soon as I put it in gear, the miss would get worse and then die as I gave it gas.
I have checked for any loose connectors and lines all over the engine.
I see mention of cleaning the mass airflow sensor. Would this cause a miss if dirty?

 

Dirty MAF wont cause a miss, but will contribute to poor running condition compounded by any other weak links like old plugs or failing boots.


I would throw 10 new plugs and boots on it and see how that improves the miss issue, sounds like it may be due for them anyway. I just installed new plugs in my brother's Caliber Friday night, it started missing badly on the way to my house (about a 90 mile drive from his place). The factory plugs I pulled out (at 147K miles!) had .075 gap compared to the factory spec of .040 gap on the platinum plugs I installed. He is amazed at how much smoother and snappier it is running now.
Just be sure to carefully follow the proper plug installation procedures to help prevent plug blowouts.

 

Thanks Tom.
Stewart also says replace the boots to start with. I will take the advice given here by all and start with that, along with changing plugs. That is the least expensive route.
I have read the procedure on changing plugs. Should have no problem. When wrenching on anything, my motorcycles and guns included, I do it all by feel and never get western on anything with a tool. I know how to use some finesse.

 

Will post the outcome as soon as I get the plugs and boots changed.
I appreciate everyone's help.