This has been going on 3-4 weeks.

Miss / judder is usually on gentle acceleration after maybe 20mph. I can ease off the throttle a little and the miss goes away, or push harder and then it also goes away.

Once up to speed - cruises smoothly at 50-55 on the flat. A little uphill grade or good headwind and there it goes again.

There was no CEL until a couple of days ago when it started flashing on long grades...but no code. Then yesterday it threw 0307 on the way home.

Today I fitted new coil and plug on 7, and since I was working all the way back there, on 8 as well. No change in behavior, except I didn't get the CEL to even flash on a 20 mile drive this evening.

The only other things I tried are fuel filter and a couple of tanks with injector gumout.

Dealer diagnosis was inconclusive - it was 'all over the place' on the dyno and at that time it had not thrown the 0307 code. They just wanted to swap stuff out on trial and error basis....Anybody got a better clue please?

I'm in MI so heat has nothing to do with it, and I notice no difference whether engine is cold or hot.

 

I have the same exact problem on my 98 which has been going on for a while. Today I finally got the CEL to blink on at highway speed in overdrive under same conditions you describe. Went home and got my scanner because CEL flashes only during misfire then goes out. Hooked up scanner and drove same stretch of road and came up with P0308. So far I pulled the coil pack and compared resistance with brand new coil pack: primary/secondary old: .7 ohms, 8200 ohms; new .7 ohms, 4260 ohms. Not sure if the resistance differences are sufficient to cause the problem. Too late to find an auto parts store with Motorcraft plugs. Any chance that you know what the correct Motorcraft plug # is? Are certain brands of coil packs better than others?

Last year I had similar problem and that time I had the repair work done. At that time it turned out to be the #4 cylinder coilpack

 

The emissions label under the hood will tell you the spark plug and gap. When it come to electrical parts go with original equipment. I've heard of too many bad experiences with aftermarket.

 

Thanks - so I could be on the right lines at least. What is the procedure for
testing coil? (including anything you think is obvious, like do I need
to remove for testing?) I'm quite new to these COP things.

TIA - Lynn.

 

Switch it with another cylinder and see if the code changes to the other cylinder

 

lynnr,

The cop has to be tested off the vehicle. Take a multimeter and measure the resistance of the two contact pins on the cop that the connector plugs into. This will give you the primary resistance which should be about .55 ohms, then look on the cop housing and you will see a + mark near one of those two contact pins. For the secondary resistance measurement, measure between the + pin and inside the boot. I stuck a 1/4"socket extension into the boot and held the test leadsw against that and the + pin. The resistance on the secondary side should be around 55oo ohms. In my case the resitance of the old cop was almost twice as much as the new one which now leads me to believe that only half the current will get to the plug assuming voltage stays the same. I think this could cause the misfire under load.

 

Thanks 98expeditionXLT - Well explained. I'll be right on it...

 

Check the boots on the cop for signs of spliting or arching. Altough the cop is replaced most of the time, I have heard the boots can be the cause for misfire and not the coil itself. I saw a TSB Ford issued giving specific instructions to dealers for cop testing because over 50% of the coils submitted for warranty claims were good.

 

I checked the boot on the old cop very carefully and I do not see any cracks or splits. Does anyone know if it is possible to get a copy of the TSB mentioned by slc10844? Since I can let the EXP sit for the next few days, I would rather be absolutely certain that the COP is bad.

 

...and it was a COP - the last one I got to, #3.

As I tested that last one though, I really thought I was on the wrong track. They ALL checked out on the multimeter to the same values as described by 98expeditionXLT which is the same value as a new one. So, testing resistance isn't (in my limited experience here) necessarily a reliable method.

I had started with #7 since the OBD pointed to it, and changed #8 at the same time while I was back there. The CEL never flashed again but the miss stayed.

So I purchased another new COP and as well as testing, circulated it around....so swapping out is a reliable method ;-) Oh, and they go back in much easier with dielectric grease.

I learned that if you drop something on this job (the plastic schrader cap off the pressure release on the fuel line, you need to pick it up right away, however inaccessible, or it will fall down the plug hole immediately you remove the COP. Then I learned that a 1/2" plastic hose duct-taped into the shop vac provides just enough lift to pull it out. (That was on #7) - you can't even *see* the hole ;-(

If you're thinking of changing out plugs / COPs and have doubts, then take heart. If I can do it, anyone can. I've probably shelled out over a grand including the 100k service and for COP changes (when failure was clear on OBD) in the 4 years I had the vehicle, and I just figured it was time to try. I have a total 6 fingers, and the remaining ones are curled and crooked. Google 'dupuytrens'. If you got a full set of good digits it'll be a breeze ;-)

Thanks for the guidance guys...great all round forum.

 

So what resistance values did you get for the #3 cop?

I finished with my #8 last night. I had some doubt about the accuracy of my multimeter at home so I brought the new and old cops to work where I had one of the electronic techs check the resistances with a high end multimeter. His results were identical to mine. After installing the new cop and a new spark plug, I test drove my Expedition on the same stretch of road as I did previously and no shudder or misfire this time. No I am ready to change the rest of the plugs and at the same time I plan to test each cop.

 

Where you said .55 ohms, all of mine including #3 showed .5 ohms, and all gave the same 5500 ohms between the plug side and both + and - pins.
Outwardly they looked in good condition as did the boots. I could only figure the fault can be stress-related... ??

 

I have read other posts on this forum where one had to start with a good cop and and keep swapping cops until finding the bad one. That is an awful lot of work, but I guess it may be the only true method to locating the problem. I hate to guess what a dealership or garage would charge for that process when the #4 cop replacement cost me almost $300.

 

Exactly - and with the fuel rail pushed to one side #4 takes 5 minutes. I paid $300 for one COP replacement when I lived in NH - they changed the plug too. Then I moved to MI (too far to complain) and the plug blew out. It had only been screwed partway in. $400 to replace, and that was my lucky day - most of the thread was intact.

I read somewhere to use anti-sieze and hand turn the plug with a piece of tube pushed over the top - don't start it with socket. That advice worked fine on my #7 and 8 - the only plugs I changed this time around.

 

[QUOTE=98expeditionXLT]Does anyone know if it is possible to get a copy of the TSB mentioned by slc10844? QUOTE]

The test involved diagnostic equipment used by Ford dealers and a special test kit for testing the coils. It didn't appear to be the type of equipment the average garage would carry. The kit is purchased through Rotundra, a supplier of Ford approve equipment. TSB 04-16-1 is the bulletin number. The fact that Ford put out the TSB is an indication even the factory trained technicians have problems diagnosing defective cops. If half of the coils sent in for warranty claims are good, and assuming replacing the coils have corrected the problem, could part of the problem be the boots?

Without test equipment, the best way is to purchase a coil and swap it around until the misfire is gone. If you have two or more bad coils it can be a bit of a challange.