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My 01 Super Crew 5.4l is missing at light throttle. Cruise control on flat hwy, no miss, slight incline, starts missing. Put my foot into it and either it stops missing or it covers it up where I don't notice it. No codes set at this point. It's got about 135k on it and for all I know it may have had the original plugs in it so I figured I'd change them. Changed the plugs, still misses. Shortly a code set, something about the EGR sensor (it's got another name but I forget what it is at 1:30am). I found I had broken a hose while changing plugs, fixed it, no more code, still misses. When i sent my GF up to get the non-existent codes checked the parts guy sold her some Lucas fuel system cleaner. I'm figuring a COP going out but the cleaner pretty much completely fixed the miss, till that tank of gas was gone. Few tanks later and it's back again as bad as ever. I bought some seafoam as I've had good luck with that in the past. It almost completely fixes the miss but I get a rare 'bump'. What do I need to look at next? Can it be the fuel filter? I'd think no because I'd figure it'd be even worse at greater throttle opening. Injector? How do I check them? I also posted another thread on a weird fuel economy observation I had. I mention it here as maybe they're related issues. Not sure how to post a link to the other thread so just take a quick look for it.
The missing under the driving conditions you discribe is likely one coil.
It is not a hard fault so will not set a code because the PCM cancels the fault's short term 'miss' count history.
The coil likely has intermittant turns shorting causing low output voltage to the plug.
The missfire is caused by a very lean mixture under cruise conditions when the EGR is called to open.
Under these conditions, the voltage required to fire rises sharply and fails..
Since no code is set to tell you what cylinder is at fault, you need to either sub one coil position at a time, have all the coils stress tested or use a good scanner to trap the fault when it ocurrs during a drive cycle or possibly look at each cylinder's history with a high end scanner (not a reader) looking for an indication.
There you have it. Not an easy way to solve the issue but you know what is involved and what can be done.
Cleaner is not "fixing" a coil.
It will however change the air/fuel ratio by vertue of it's effects within the gasoline mix.
Other things that happen is the PCM can re-adjust the fuel amount as a reaction of the OX sensors to the addition of the cleaner to the gas.
If the coil is at all temperature sensitive, then anything can happen in any sequence at anytime.
Just don't make the mistake of jumping on circumstantial evidence of what appears as a link to the trouble.
Many owners in simular trouble as you, change plugs that seemed to clear the issue only to have it come back again after several hundred miles, then really get confused over a faulty coil.
What happens in that case is the new plugs are easier to fire when new but quickly fall back to the old level of operation the original coil fault cannot fire again. Missing returns.
The original problem was just a coil as indicated by the specific conditions under which the miss shows up.
Complicated isn't it?
Napa, Autovalue(Canada), online at rpm, they have some performance ones, if you're running any other engine mods. Just about any decent autoparts shop will sell them or just go online, or buy from dealer, maybe easier that way.
Easist way I have found (although this will sound wierd) is to drive the truck and force the misfire consistently enough for the code to set. Get it into a lug mode with the misfire and hold it there. Truck will buck and act like crazy and you think this can't be good. But it will continue the misfire long enough for the computer to set the code. P030x will be the code. x is the cylinder number. Numbers are 1 - passenger front. 4 - passenger rear. 5 - drivers front. 8 - drivers rear. One COP will cost you about $40.00 or so at the local parts store.
Sorry to revive a dead thread but I'm having this exact same problem with 2007 5.4 triton. Started with knock sensor. Had it and plugs done. Could be noted one of the plugs was bad and it took us awhile to figure that out. Put a new set of Accel coil packs on after that bc one was bad. Immediately had a sulfur/gas type smell through the AC vents. It got worse, then truck started missing. Took Accels off and put stock back on. Evened out, except for previous miss, and the smell instantly went away. I brought the Accels back and ordered a set of COPs online for cheaper. Installed them and fixed the miss for about a week. Then it came back. It's at low idle, just like OP. It's still present, but more RPMs I guess it's just less noticeable. Like I said, it ran fine for a week, and I'm curious if something can be causing the COPs to go bad, or do I just have bad luck? I was thinking injectors, but with no code, that's a pretty expensive shot in the dark. Maybe I will take one of the originals and start swapping to see if it goes away. My luck, I will grab the bad one.
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