I thought about just adding to the other recent misfire thread, but felt I should probably start my own. There's A LOT to read here, so I apologize in advance.

2000 F150 with the 5.4. I bought it about a month ago. Ran 2 full tanks of gas through her, no problem whatsoever. Then, I filled up 2 weeks ago and about 25 miles later, I started to notice a very slight misfire during acceleration of 30-45 MPG. A few days passed and it got noticeably worse; even missing at idle. However, it would only misfire after the engine had warmed up. No CEL or codes (as per AutoZone) are thrown.

I started checking everything I knew how off the top of my head. All fluids were good, EXCEPT for the oil. It didn't even register on the dip stick (why I didn't check the oil while checking for oil leaks before I bought, I don't know, but oh well). I changed it and checked for oil leaks again (found none). No coolant noticed in the oil, no abnormal sludge/deposits noticed. No smoke from the pipes. I believe all is well on that front.

I then started to research the misfire symptoms and came to the conclusion that maybe it was just "bad gas", or excessive water in the tank, since it started happening right after filling up. I put in some HEET and some Injector cleaner (thinking maybe it could also be a clogged jet). I also bought a fuel filter, but didn't install it right away (judging by the date signed on the oil filter of 9/14/09, I figured this truck had been seriously neglected in the past so a fuel filter should be well past due). 15-20 miles and my misfires went away 100%. I thought I had hit the nail on the head. I ran the rest of the tank down over the next week or so and had no problems at all.

Fast forward to today (about a week and a half with NO misfires), and it was time to fill up again. I went to a different gas station this time (first was Shell; this time Exxon). I filled with 89 Octane instead of 87 Octane as well. Remember how I said I thought I hit the nail on the head? Wrong! 10 or 20 miles after filling up, my misfires were back, worse than ever. At lunch, I ran to AutoZone and bought some more HEET and Injector cleaner. Unfortunately, I haven't seen this "cure" the misfires this time. They are also a lot stronger and more noticeable. Still no CEL or codes stored, though. I got home and replaced the fuel filter. Still no change after about 15 miles of driving.

Now, for some more detailed symptoms on the misfires:
- Like I said, it only starts after the engine has warmed up.
-The misfires are unpredictable. I may have very slight misfire at idle, very strong misfire (to where I think it's about to die) at idle, or no misfires at all. Every stop light is a different story!
- The misfires will usually (maybe 90% of the time) go away under high acceleration
- The misfires are completely random. When I want it to misfire (for diagnosis), I can't seem to get it to misfire. When I don't want it to misfire, it misses like crazy
- The misfires do not change regardless of engine load (i.e. no change between having the A/C or heater on/off; same with radio, lights, etc)
- I removed the air intake in the driveway that didn't seem to change the way the truck idled (other than a more throaty "backfire" when letting off the accelerator cable). The sensor inside the intake works just fine (cover it or blow hard on it and the truck dies)
- The vac tube going in just before the intake manifold SEEMS loose (seems like a worm clamp or something should be on it, but there's not). I didn't feel any loss of vac around it, though. Wrapping it up didn't change the idle. If I pulled it out all the way, the truck died
- I have NOT checked for coolant leakage signs around the plugs (call me stupid, but I can't see the plugs on this beast)
- With the dual flowmasters, it's hard to tell, but I can hear a sucking noise when I let off the accelerator. I can hear it in the engine bay when I get on the accelerator cable, but it's inside the intake manifold, and is pretty normal for what I know. It's the sucking sound that I hear inside the cab while driving and letting off the gas that I'm not sure about
- All fuses are good

I've really been avoiding checking the COP, wires, plugs, etc because of the "horror stories" I've read about how hard it is on this engine. I hate to admit it, but I can't even see the plugs, etc. I have a feeling that my problem lies in that, though. I can't deny that the truck very likely needs a full tune-up, and it really couldn't hurt, but I've been trying all of the cheap/quick "fixes" first. Does anyone have any ideas? Oh, and if someone could find/post a picture of the 5.4 engine bay, pointing out the plugs/wires, I would be eternally grateful. =)

 

How many miles are on the thing?
Probably need new plugs. There down inside the head.

 

Let me give you some recent experience I had with my 5.4. First , if you have an idle problem it's usually the IAC valve. My truck was doing the same thing as yours. Only had a misfire around 12-1400 rpms in overdrive,
after reaching operating temp. I did have a cel light for insufficient egr flow though. I didn't think it was related to the skip. Not sure now but , I
finally found my p401 code problem and repaired it. Now , after driving several drive cycles I noticed no more misfire. You might want to keep it in mind as you go along with your repairs. That being said, #4 cop is notorious for going bad. There are heater hoses and a/c lines in that area
that are notorious for causing that cop to become wet. After a while the
cop starts causing your symptoms. ( and yes , it's a little bit of a pain to get to) I know these answers may confuse you but it's more info to work with. Good Luck!

 

how do you check COP;s , i'am getting same miss and no codes, 02 5.4

 

some scanners will show pending codes. Autozone can check them but you have to find the right individual. They don't always show up.
I have found them by putting someone in the cab. Start the truck and put the emergency brake on and put the truck in reverse. Bring rpms up to around 7-8 hundred and unplug each coil one at a time. If you don't here the engine change , that's probably a bad coil. If rpms drop it's okay.

 

We had a warm weekend here in Texas and my misfires were almost unbearable and nearly impossible to drive. I found that the warmer the air and warmer the truck was, the worse the misfires were. Night driving or driving while the engine was dead cold produced ZERO misfires. Like I said, no CEL has ever been tripped and AutoZone scanned it (but I realized yesterday that they didn't turn my key, so I think that girl didn't know how to scan).

Needless to say, I decided it was worth a shot to try and have the codes read again (at a different AutoZone) while my truck was obviously misfiring. Sure enough, this time they picked up a code (and now I have to figure out why the CEL isn't working). I can't remember what the code was specifically, but it was for the IAT. Makes perfect sense with the misfires happening more frequently the warmer the outside air and engine is.

So now that I write this, I'm off to check the resistance of the IAT and replace it if it is out of spec. It's a $15 part, so it's worth a shot.

Oh, and the truck has 135,000 miles. I'm also in luck in having a friend with a 2000 Ford Excursion (or is it Expedition?) with the 5.4L... and he has changed the plugs, COP's, and injectors on it twice. So if this ends up not fixing my troubles, I think I will bite down and do a complete change on these components. I KNOW it needs it, even if that's not the root problem.

Thanks for the help all. I will reply back tomorrow after I've put some miles on the new IAT (if I change it) and go from there.

 

Well, the IAT checked out just fine. The voltage from the plug was also fine. I think I might have a larger problem, though, with my throttle body. Going to make a new post for it.

*edit*
Just a little more info on the IAT. The voltage at the plug was just under 5v (which the manual states is good). Resistance at cold was about 40 (again, fine per the manual). I pulled the sensor and blew on it and saw the resistance fall (which the manual states it should do). I got out the blow dryer and blew it on the sensor. The resistance drastically fell quickly (which again is as it should do). I don't know the temp of the blow dryer, so I can't compare it to the chart specifically, but based on all of this the sensor is fine. I guess I need to have the codes cleared and see if the same code comes back. I'll also get a printout of the code and look at it myself to make sure they looked it up correctly.

Back to square one, and leaning more upon a plug, COP, and injector change. Sigh...

 

Latest update:

- Replaced IAT sensor (even though the other one tested fine) and cleared the code.
- Took off the throttle body and gave it a good cleaning.
- Ran the truck in the dark garage to look for arcing. None notices
- Sprayed a shot of carb cleaner at the vac lines to fine any leak. No change in engine idle with the shots
- Ran 50 miles to bring all the monitors back to READY. During this time, no codes or freeze frames occurred

The misfire still only happens at warmer temperatures. During cold start or cold days, there is absolutely no misfire. Once the engine warms up, or if the outside temperature is warm, the misfires start. The warmer the engine or air, the harder and more frequent the misfires occur. At it's worse, it misfires under light and medium acceleration. If I put the pedal to the floor, it will not misfire. It doesn't always misfire at idle, though, even under the worse scenario. Occasionally, the misfires will go away during the drive. For example, I work an hour away. For the first 5 miles (while the engine is warming up), I have no misfires. Then it slowly starts to misfire until it reaches its worse point. Then on random days, typically around 3/4 of the way through the trip, the misfires will start to slowly diminish and go away for the remainder of the trip.

This problem is really starting to confuse me. I have ZERO misfire codes thrown (and obviously no CEL thrown). My gas mileage is still the same as it was before the problem started. Could it be that the truck isn't even misfiring??? I don't know what else it would be doing, and I can easily feel the loss in power during the problem, but why would it not throw a misfire code? Any ideas?

 

I have the 05 5.4L 3v on my f250, and when I had it scanned the other day, both scans showed misfires on cylinders 3 and 8. I replaced the thermostat, and have ordered new O2 sensors. Once I install the new O2 sensors, I'm going to run it thru again. I replaced the thermostat, because the scanner (not an off the shelf brand, but a Pegasys professional scanner) indicated that my peak water temp was only getting to 180 degrees, but the oil temp was getting up to around 210 where it should be.

One thing that was recommended by the service tech was for me to make replace all these parts, and then bring it back. If that doesn't help, the next steps are:
1) Change out the plug and recheck (I've got 76K on the original plugs)
2) Change out the COPs on cylinders 3 and 8 and check
(Neither of the above are a wasted effort even if it doesn't resolve the problem.)
3) Reflash the ECM/PCM to pick up any new codes over the last 6 years and recheck.

After that, it's time to take it to an Ford ASE mechanic and hope for the best.

 

Yeah, I'm pretty much down to that, I think... plugs, COP's, and likely the injectors. I'm just hoping, I guess, that's it's something more friendly for me to do myself. I get my work bonus the first week of March and I had other plans with that money, but if I can't get the problem resolved by then, it's going straight to the shop. It would be so much easier for me if the dang thing would just throw me a code!

 

I think Ford intentionally omits errors from the flash programming on the ECM/PCM so that you end up taking it back to the dealer. If a cylinder is missing, even occasionally, it should throw one error code or other. Instead, you have to know somebody with a professional reader that knows what he/she is looking at to pinpoint the problems. The Pegasys is real good if you can find somebody with one. A Genesys might be able to detect them, but I'm not certain.