I have a misfire that is causing me a massive headache. 2006 F150 FX4 w/ 5.4L I have had a misfire for 2 months. It is stuck on cyl #4. It has all new motorcraft plugs and coils. The injector has been replaced with a new one. All the wires for that cylinder have been checked and are fine. My buddy (who owns his own shop) and I are at a lost. The dealer is at a lost too.

 

Pull the cam cover and check for a follower off.

 

Bump! Anyone?

 

Any of those who at a loss (What kind of dealer cant figure it out Morons?) Do a compression test? Did you do what Dyonotech suggested? We can only give you suggestions.. if you choose not to listen we cant help you.. There are only a few things that can be wrong Plug, Coil, injector, Wireing for those or internal engine. To eliminate internal engine you need to do a compression test..

 

Compression test is fine. 150lbs+ Follwers are fine. I have tried switching plugs, coils and injectors around. The problem remains on that cylinder. The coil and injector are seeing the right voltage at the connectors.

 

If all is as you say it shouldn't be missing.. I would find another dealer.. Thats the only suggestion I can come up with..

 

The only thing we can come up with is a short in the computer. It only misses under a light load going up hill.

 

I agree with jethat. How many cyls did you perform a compression test on and did you guys make an assumption that the followers are ok because the compression was normal? Are you positive that its only cyl #4?

 

New coils ? All are new ? Then you got a bad new one. Low grade misfires only happen like that with a bad coil. Coils can test good (Ohm/resistance, VREF then PCM sig), but you can't test under a load yourself unless you have a the tools for it. I doubt you have what you need to stress test a low grade or can even bring up your misfire monitors cylinder count history. That's done, ~ @ the dealer = Mode 6, Channel 3 (Red) or WDS w/Rotunda Kit.

You probably swapped coils and the mis happened on another cylinder, but wasn't detected by the monitor. Low grades can be hard to detect and they have to be detected twice within the same drive cycle in order to produce a DTC.

If you started with a misfire on #4 (low grade), That coil needs to be replaced. Swap in one of your old ones. Do this first to confirm determination, and do it twice with a different old coil each time, 3 times if you had more than one misfire on your old set (see what I'm saying),-since you can without any cost.

 

My buddy who is helping owns his on shop with all the tools needed to test everything. After we swap coils, plugs and injectors. We take it for a drive useing his scan tool. It always says Cyl 4 misfire. His scan tool is able to read the codes when the cel is just flashing.

He pulled the cam cover to check the followers. compression was 150lbs+ across all cylinders.

 

Well my $40 scan tool will do that same thing. You have to reboot right after swapping anything. It should be automatic because you have to disconnect the battery before working on anything or you can screw up your PCM fairly easily. You have to erase the KAM when the battery has been disconnected 20 minutes +. So, if your not rebooting properly ..... If your buddy owns a shop , why are you here? Read previous post, I can tell you not listening. Both you and buddy are missing something, check everything that's been posted here, -twice if you have to. You won't get a good portion of this info anywhere else.

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It's either that (above^^^^)or your ignition harness is resting on top of your AC accumulator IMO. That has happened quit a few times in the past. Your can bare a harness wire and cause a major ignition disturbance, actually you don't even need to bare the wire, the mag field alone can create ignition havoc.

Check the wires at that location (above AC accumulator). If harness is relatively close or contacting such, tie them further away. If it was/is the problem, it will disappear immediately after following direction.
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BTW- You really need to check these things and be thorough about it, - your real quick to say "been there done that". Your running out of possibilities.

 

where is the AC accumulator? Is that the evaporator? Having a similar issue and need to look at wiring now

 

Not sure on an 05, - for wire harness locations. Pre 04's - harness looped right above the accumulator back by the firewall close to the battery. That loop would sink over time and come contact. Caused either a bare wire or mag disturbance w/ignition.

 

Here's a ton of reading for you. This is the OBD-II service manual for your truck. I'll assume that you have a Low Data Rate misfire. This is addressed on Pg 9. I'd start at the top of the manual and work my thru the stats eliminating components as you go. This is as easy as hooking up the scanner and reading it to compare values. A lot of these misfires are components that are not directly related to spark, compression, and fuel. Sounds nutz but it works like that- I don't design them, I just have to work around the criteria. Hope you find this helpful.
http://www.motorcraftservice.com/vdi...f/OBDSM608.pdf

 

i think im have a similar problem, i have 97 5.4 it started missing on the #6 so i changed the COP and plug just like the others. well 10 or so miles down the road it came back and strted missing again. so went and got another COP and plug installed and again 10-15 miles latter missing again still sasme cylender.im lost im going to take it to the shop if i cant get it figured. any ideas. i checked compression, its good i dont know what to look for behind the timeing cover? i looked the wire harness over and see no brakes or frays sign or rubbing. so whats next. thank guys.