'98 F-250 LD, 5.4L w/auto trans - 172,000 miles.

At 164,000 miles a bad missfire developed. At this point, I replaced all 8 plugs and the number 8 coil (no surprise there). Now, after 8,000 miles, the truck is starting to missfire again, but it only seems to be happening when cruising around 40-50 mph. Most apparent around 45mph, when the truck is in OD and I start to climb any size grade, from rolling slope to steep hill. The entire truck starts to shudder. If I manually take it out of OD, or stomp the throttle, it'll kick down, rev up and clean out and go fine again. The only problem I'm having is that it is not posting any codes about engine missfire, or any other thing. From my experience with these trucks, I'm pretty confident that it is either a plug or a COP going bad, but I don't know how to diagnose which one is the problem without the computer giving me a code. Any ideas on this

Also, has anyone used any COPs other than the OEM Motorcraft coils? I've found there are cheaper ones out there, but I don't want to put an inferior coil in, and lose performance or efficiency because of it. Let me know what you guys think

Chris

 

Sure sounds like a bad COP. Mine had the same thing although not quite as bad. Just in the 45-55mph range. I replaced all 8 COPs and plugs and haven't had a problem. I got the Accel COPs from Speed Unlimited off eBay - $222 with 2nd day shipping. I haven't had any problems and I really like the yellow heads sticking up.

I did notice when I pulled mine that two had boots that were really hot (I had driven it within 10 minutes of starting the job - cold night so I didn't mind the heat!). The others were fine, but even after a good while of working on it, the #6 and #7 COP boots were blazing to touch compared with all the others. I threw those two out and kept the other 6 in case I have a failure somewhere else down the line. It's not exact, but it seemed to me that if it was misfiring inside the boot, that might cause the heat. Or, it could be nothing at all!!!

Good luck.

 

hmm, I hadn't thought of looking online yet to find some coils. I suppose thats as good a place as any to buy them, provided its a reputable dealer. I think I'm just gonna bite the bullet and replace them all. One less thing to worry about. I need a vehicle that runs, and runs well without me monkeying around all the time trying to figure out what my problem is now.

 

You have a bad coil. But which one? Best way is to have a dealer stress test all of them and pick out the one that fails because you get no code to tell you.
If you buy all 8 and get one that has low output, your right back into the same thing again and still wondering what the trouble is.
You need to decide to either shotgun the problem and take a chance or get a diagnostic to be sure. May turn out to be cheaper letting a dealer test the coils even if it is just for the hourly or min fee charged.

 

If mjunk1 bought all 8 coils for $222 then it is cheaper to get the coils and not wory about taking it to the dealer and spend another $80 or $100. I'd just buy the plugs and replace them allbut the one he already did. Although. I've replaced plug #8 twice already. As a matter of fact the 2nd time was 2 days ago. Good luck........

 

I've been to a couple of Ford dealerships, and both of them said that there are no ways of testing the coils. They said either they get the code that says which cylinder is bad and replace that coil, or they can hook up the computer to the truck, take it for a test drive and see which cylinder drops off while driving. I've never heard of a 'stress' test. What do they do? What are they looking for?

 

I've heard lots of good things about Global coils from Ebay. Right about $100 shipped with a lifetime warranty. Probably about the same price as getting it diagnosed at the dealer.

That's what I'm going with if I ever get around to ordering them.

Mike

 

They're looking at the output of all the coils and at certain loads a bad coil will drop off, and they're reader can see it and tell them which coil is dropping off. You can chase your tail for hours and hours trying to figure out which one is dropping off, or just go have a test done. At the mileage you're at, you're gonna start having problems with your coils. The Ford oem coils are a quality product, while the jury is still out on the "performance ones". I'd just have the stress test done and replace the weak coil(s).

 

A dealer that doesn't now of stress testing coils is one to stay away from.
Your bad coil has shorted turns which lowers the output below the needed output level.
Since it is not an outright failure and still works at idle and full power it won't set a code.
The reason why it acts the way it does is due to the following.
In cruise running range between 45 and 55 mph and light throttle, the EGR is opened, the fuel reduced and the ignition is advanced.
These conditions result in air to fuel ratios close to 20 to 1.
Under these conditions the plugs require the most voltage to jump the plug gap and start the kernal for combustion.
If one coil is low you feel a stumble/miss on that cylinder under a light application of more throttle until enough throttle is given to close the EGR, richen the fuel and pull the timing back then alls well again until you encounter the same conditions again then it starts all over again.
You now have the full information that your dealer apparently does not know about.
Do as I reccomend and find a dealer to test your coils, replace the bad one and have it all over with.
I have been thru all this and worked the problem out and find few understand this peticular type of issue and many try to even blame a slipping tansmission on a bad coil.
Good luck and come back to tell us how it all went down.

 

I've encountered this problem and went to two different mechanics cuz they were drinking buddies but after a week of watching them chase their tails I took my truck to the dealership and an hour later they called me to tell me they had it fixed after running a stress test and finding a coil that was dropping off under the conditions you listed Bluegrass 7!

 

Well, for anyone interested, I fixed my misfire issue. A mechanic friend of mine suggested putting the vehicle in drive, and having a very trusted friend hold the break. This put a load on the engine making it misfire like crazy and very consistently. He then said to methodically unplug fuel injectors and watch the engine's response on the tachometer. unplugging a good cylinder will decrease the engines rpms (approximately 100rpms) and unplugging the misfiring cylinder results in no change in rpm (or very minimal change)

Going through this routine, I found that the 3rd COP back on the passenger side was the only one i unplugged that made no change in the rpm. I went and bought a new Ford COP (not sure about the aftermarket ones yet) and replaced that one and voila!, fixed my misfire issue.

For safety purposes, make sure to stand off to the side of the truck when doing this sort of test just in case your 'friend' accidently releases the brake.

 

I seem to remember reading somewhere that a hot or scorched boot indicates that a plug may be loose in the head allowing hot combustion gasses to escape past the plug seats. This is a precursor to the infamous ejected plug syndrome in the 5.4L engines. (I would like to hear some other opinions on this.) In the interim, I recommend that you remove those two plugs, inspect them and reinstall them at the proper torque.

 

That is some good advice NKENN! None of the boots should be any warmer than the rest, so make sure those two or three boots that were the plugs are tightened down to specs. I'm glad you fixed your problem lilredwagon! What you did to diagnose the problem is essentially what the Ford garages do, only there's no risk of death or dismemberment with there's lol! Even standing to the side of the truck you would be seriously hurt if the brakes failed (the hood). Anyhow, good to hear you got it fixed!

 

Put it in 2nd gear and do a wide-open throttle pull all the way to the about 4900 RPM. This often puts enough of a load on the engine (especially at lower RPMs) to trigger enough mis-fire to throw a code indicating which cyclinder is causing it. You'll need a good stretch of empty straight road for this.

 

hmm, i'll keep that in mind the next time she starts acting up

Thanks for all the help and information guys. I really appreciate it

Chris