Misfiring 5.4L--how to tell which cylinder?
 

Recently bought a 2005 Expedition with 106,000 miles. Soon noticed an intermittent misfire. From a fair amount of online reading, I'm reasonably confident it's one or more coils beginning to fail. It happens at 45 - 55 mph under light acceleration, low RPM, and it's just a smaller "stutter," almost like hitting potholed pavement.

My question is how do I tell which coil to try replacing? AutoZone tells me their scan tools show both set and pending codes, but I've been to two different stores now and they both came up with no codes at all.

Do I just need a more advanced scan tool?

Or do I need to have a scan tool hooked up while driving?

Or do I just wait until it gets more severe and trips the CEL?

I'm semi-handy, but don't have the tools or time to do a "balance check" with vacuum gauges and such.

Thanks very much for any input.

So apparently I need to ask the obvious...what were the codes Autozone found?

No codes at all. That's the issue. I can feel it misfiring, but it's not generating any codes to help me figure which coil(s) to test/replace.

Then you either have to wait until the CEL stays on and get it rescanned, or you have to get your hands on a code reader that reads live data and go for a drive. The live data will display a misfire count per cylinder as you're driving, even if a code doesn't get set.

Great, thanks. That's what I was asking. I just don't know much (anything) about code readers, and I wasn't sure if there was such a thing as a live data reader.

So any recommendations for one? And any ballpark cost estimates? From what I read, it sounds like it might be a wise investment with this engine even if it costs a bit.

It.s not expensive. Google, Torque for Android.

Here is one that will do what you need:

COP's either work or they don't. They don't begin to fail as you note. Maybe a boot that's cracked and starting to ground out.

You say it's studdering at 45-55 mph. Could it be your tranny shifting from 3rd to overdrive? It's a pretty common issue and feels like you're running over "bots dots" that they put down before a stop sign as a warning.

r2millers, I'll try turning off O/D tomorrow to be sure, but I don't think that's it. It's just too inconsistent. From what I've read, in that speed range, cruising along at low RPM with light throttle, the mix gets very lean, which requires more voltage from the coil for ignition. So when a coil isn't producing enough voltage, you get a stutter when you apply a little more throttle.

But then again, I'm only repeating what I've read; I don't know much at all about engines, especially newer ones.

This is the first 5.4L I've driven -- and the first Ford since I was 16 or 17, for that matter -- but I've driven a lot of miles in a lot of other V8 trucks, so I know what torque converters and overdrive shifts feel like and I'm pretty sure this isn't it. In fact, I've really never felt anything exactly like this.

Tell me about the boot you mention if you have a minute. I guess I thought the COP was one whole unit. Is the boot a separate thing, or just the part the slides down over the plug? Would a scan of live data still tell me which cylinder in misfiring (assuming that's what's going on)?

Thanks to all for your help. I really appreciate it.

The boot is what fits onto the COP and slides down over the plug. It can be removed and replaced. If the scanner shows live data it should show how many misfires and what cylinder while you are driving. I have a scanner with live data but unfortunately wouldn't tell me which cylinder was misfiring. Mine was intermittent also so what I did is whenever it started to miss I would hit the gas and run the RPM's up while it was missing. Did that 2 or 3 times and it set off the check engine light to show me which cylinder it was.

Here's another link from a past thread I created. It's pretty clear of the issue with pic's. I tried to just add the pic but the gallery system isn't working.

https://www.ford-trucks.com/forums/1...pak-boots.html

I like my snapon soularis plus but that cost me over ten grand, I't gives you live data and as you drive will show exactly which cylinder is missing

Over 10 grand? I have the AutoXray 6000 that does the same thing and cost me under $300. I guess there really is a sucker born every minute.

How clean is the engine? maybe to dealer pressure washed it and got water past the coil boots. I would not wait until the CEL comes on because every time it skips the cat converter is that much closer to melting down. With 106K on the clock its prob time for a set of plugs.

Good point. Or maybe an intake manifold leak, filling up the plug holes with antifreeze?