2005 5.4 auto 4x4 27,800mi and owned since new. Developed a problem on the way to my FIL funeral (5 hour drive). Transmission seemed to be occaisionally slipping. Upon further inspection, I do not believe the trans is the problem. I think it was some engine management, fuel or ignition problem. This is a meticulously maintained like new SUV. All fluids and filters, etc. are diligently replaced often earlier than required. I last serviced it in April with 25, 500 on the clock. That service was limited to an air filter, fuel filter, tire rotation, oil and filter change and fluids check. It is not and has not ever towed, but on this particular trip it was subjected to hilly, Virginia and West Virginia terrain. I have no CEL on and I personally checked for codes and found none. History showed no misfires and no codes pending. Sitting in park it idles and revs fine. No erratic idle or stumbling...very smooth. It WILL NOT rev past 3,500 rpm. I get differing opinions on computer controlled rev limiting in park or neutral via the computer (some say normal, others not normal). I don't want to take it out to drive and see if it will rev past 3,500 until I have some indication of what the problem might be. I'm currently suspecting a TPS or perhaps a bad COP but don't like throwing parts at a problem. I do have a COMPLETE set of Ford service and emmissions manuals for the car but I'm not sure where to start. If you've had a similar problem I'd like to hear from you. Thanks.

 

A COP issue will usually throw a code pretty easily. If stumbling at fairly low rpm's, check fuel pressure rail, pcv elbow for vacuum leak, and maybe even a plugged cat although pretty unusual for such low mileage.
I bet vacuum leak is the issue.

 

There absolutely is a built-in rev limiter. Once you hit 3-3.5K in either park or neutral the rev limiter kicks in to protect the engine. There is no rev limit when in Drive.

As to the misfire...if you use a scan tool that reads live data and go for a drive, it will give you a readout of how many misfires occurred for each cylinder. Even if a code is not set, by knowing which cylinder has the higher misfire count, you'll have a starting point.

 

Drove it and finally have a code...p0445 (I'm getting old, it may have been p0455) evap emissions leak large. I now have a CEL illuminated as well as a "Check Fuel Cap" on the message center. I've taken out the battery and tray and started inspecting vacuum lines but haven't come across anything obvious. Looking forward to some tips from anyone with further knowledge. Thanks.

 

Maybe someone stole the gas cap? You didn't say your checked?
The line under the battery is probably the rear air supply line if you have air bags, not a vacuum line. Ck next to the a/c condenser for the pcv tee. Most common vacuum failure.

 

Thanks for the response...I forgot to include the gas cap is in place. Still working through possible solutions. I do not have air bag suspension.

 

Even though the gas cap is in place, doesn't mean it is sealing properly.

 

True...but I replaced it with a known "good cap" from a friends 2005 F150 and the problem still presents as of this afternoon. I cannot find any obvious sources of a vacuum leak. I did find 3 open ended vacuum lines, however. 1. A vent line terminated with an open 90 degree white elbow near the fuel filler neck (I don't see any obstructions (mud dauber nest, etc.) 2. What appears to be a very small vacuum line (open ended) clipped to a hard line under the brake M/C. 3. An open small (again, appears to be vacuum) line protruding out of a piece of convoluted tubing which also contains a vacuum line which runs to a small solenoid mounted on the firewall (not fender) directly behind the battery tray. This device is just to the left of the cumputer harness connection when looking from the front toward the rear of the vehicle. Ideas?

 

I don't see the tee near the A/C condenser...can you be more specific?

 

I'm thinking the line (in red, above) may be the line intended for air supply for the models equipped with the air bags. Mine doesn't have them so perhaps this is the case.

 

I had two vacuum related issues that I recently tracked down.

One was a line between the fire wall and the battery, however probably not common due to a battery acid discharge onto that line.

The second might be worth your time. If you remover the engine cover and find the PCV valve the grommet going into the valve cover was worn enough to allow the PCV valve to not seal properly also check the elbow coming off the PCV valve and follow that line to the back of the Intake to check that elbow. Additionally a small line from the PCV valve running in front of the intake goes to a coupling, a tee and a small elbow. That location on mine had extremely worn vacuum couplings.

As you are searching for vacuum leaks there are two "dead ends" I found on mine. One is on the batty side, which I believe you described above. The other is on the other side of the engine. My understanding is that both of those are supposed to be that way.

 

I've been over this thing from the "rooter to the tooter" and can't find anything.

 

Just to kind of recap:
Is the RPM and the speedometer relationship normal. If so, prolly not a tranny issue.

So what are we trying to resolve?

The PCM doesn't think there is a problem.

That is good.

What problem?
What does the complete set of Ford service and emissions manuals suggest?

 

Let's assume it is a P0455 code. This normally wouldn't be caused by a typical vacuum leak. Basically, the PCM is saying that it can't detect a change in pressure in the fuel tank when it goes through its EVAP monitor routine. I would expect you would smell fuel vapors with a large leak.
(Is the symptom that we are chasing is fuel order?)

When the PCM detects a P0455 and you don't notice any vapor fumes, I would look at the EVAP Canister Purge Valve. If it is stuck closed or not opening (i.e., if the electrical connector was not completely connected), there would be no pressure change within the fuel tank.

Likewise, if the Canister Vent Solenoid is stuck open a functioning EVAP Purge valve could not change the fuel tank pressure.

And with a functioning EVAP Purge Valve and a functioning Canister Vent Valve, the PCM would not know if a change in pressure occured if the FTP (Fuel Tank Pressure) senor is malfunctioning.