Florman

I have not generally done any maintenance on my vehicles other than oil changes, so I am not an experienced home mechanic. I have an issue with my 2003 F-150 2WD SuperCrew XLT 4.6L. Over the years I have experienced misfires and had to replace ignition coils with some regularity. I have always had a professional mechanic do this. Usually the check engine light would come on and give a misfire code on a particular cylinder. At around 90,000 miles I replaced all spark plugs. Current mileage is 170,000.

Recently I began experiencing the usual misfire symptoms that signaled the need to replace an ignition coil. The misfire was intermittent, and most often happened when I was accelerating up a hill, usually (but not always) at around 2000 rpm. The check engine light was not on. I took it to a mechanic who had worked on the truck before. He said there were no misfire codes registering and he couldn't get it to misfire while running it in his shop. He said that they checked the plugs and they looked okay. I have some doubt about that, but I'll explain that later below. He said it would be cheaper to just replace three coils, give me the ones he replaced, and see if that fixed the problem. If it still was missing then he said bring it back and I'll switch the new coils to different cylinders with no additional labor charges. The mechanic said this was cheaper than checking individual coils with a current ramping test because that would rack up a lot of labor charges. (I thought he said ramp voltage test, but an internet search of that led me to the term current ramping test, using an oscilliscope. I hope I'm using the right term here.) He said this approach would fix the issue. I paid $400 for this. Parts were $225.75 (plus tax) for 3 coils, labor was $160.

Well, the problem continued. Still no check engine light on. I returned the truck to the mechanic who switched the coils around. I still am experiencing the misfire. I went back to the mechanic yesterday to express my frustration and ask what he could do for me. He said that he probably should have originally told me that the best bet was to replace all spark plugs and ignition coils. He said to replace all spark plugs and 5 more coils would be $600. I asked him why he couldn't just do the current ramping check on the remaining coils. He said that would take too much time and that with the problem being intermittent, this test still might not reveal what coil is bad. I was able to negotiate him down to $400 for replacing the plugs and remaining coils, and he said to bring the truck back in three days when he could start work on it.

However, I am contemplating just buying some inexpensive copper wire coils on eBay and replacing the coils myself. I want to sell this truck and want to stop dumping money into it. But I'm reluctant to sell it as is, because I figure if someone test drives it and notices it missing then they will not buy it.

My questions to everyone out there are these:

1. Does what the mechanic told me about the current ramping test make sense? I could insist he do it for no additional charge (or a minimal one), but is it true that he might not be able to locate the problem coil?
2. I don't fully trust that he checked the spark plugs. Wouldn't he have to remove them all to check them? I don't think I paid enough labor for him to have removed all 8 plugs. Or could he be referring to some quick electronic test that doesn't require removal?
3. If I replace the coils myself (it looks fairly easy) but some plugs are "bad" then will the coils fail right away? How long might they last?

I would appreciate any advice anyone with more knowledge and experience can give me.

Marc D

I've always been taught that once you have a misfire from a plug or coil, you replace all of the coils and the spark plugs at the same time. You know how your truck feels when it misses under a load, so if it's the same as before I'd change all of the coils and plugs. There's not much else that can account for a misfire. Good luck

muncheese

sounds like the mechanic knew to replace everything but knew you would come back to pay for more labor. its hard to argue their labor cost, just ask them exactly what they did and you piece it together. i was charge 200, for labor, to replace my ignition coil and found out it is pretty simple to do, and was charged 160 for the part. man it sucks to get something done that no one has ever taught you. thankfully the internet shares its wide variety of info.

Florman

Thanks for your input, Marc D. Do you know what would happen though if I replace the coils only? I'm nervous about trying the spark plugs myself because I've heard it's is easy to strip the threads when replacing the spark plugs in this engine. I know just replacing the coils may not solve the issue, but I'd like to try it first if it won't instantly ruin the new coils. Any thoughts on the likelihood of that happening?

Florman

Thanks, muncheese. I'm not too worried about trying to change the coils myself for the first time. It's the spark plugs that scare me!

JCR 56

The plugs in your 4.6 are standard one piece plugs and do not break, just torque them to 28ft.lbs. dry, no anti-seize, to prevent blowout. I would use Motorcraft plugs. Stay away from that mechanic, or at least find a mechanic, LOL.