Troubleshooting Help Wanted.

Simon Clowes

Mar 25, 2021
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1999 Expy 175000 miles on clock. 5.4l V8.
1) Sudden need to use extra RPM to maintain speed on slopes that did not previously need it, often causing a downshift.

2) Slight drop in overall mpg - approx 2.5 mpg.

3) High pitched whistle that only seems to be there on acceleration.

4) Intermittent loss of oil but no visible sign of leak. I can several weeks (approx 300 mile per week) with no loss then next couple of weeks go thru a quart a week then back to no loss.

I am aware these may well be separate issues but they all showed at about the same time.

I have checked transmission fluid - good level and colour. confirmed is switching into OD. Inspected for oil leaks both engine off and running. No observe burnt oil in exhaust.

At this stage I am head scratching


Active Member
Jun 25, 2017
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This is going to sound a bit strange, but has the throttle body every been cleaned?
The reason I ask is that a dirty throttle body will 'mimic' other types of issues. I don't know if the throttle body of first generations are electronic or not. When the electronic throttle bodies become caked with carbon, especially on the 'backside' which cannot be seen nor cleaned well without removing. The PCM receives incorrect data on the position of the butterfly and CAN make all kinds of weird adjustments, including transmission shift points.

Again, not sure on first generations, but there is sometimes a 'bypass' that allows air into the intake manifold. If the butterfly is malfunctioning, the whistling noise could be air flowing through the bypass.

As for loss of oil with no visible leak(s) part of the function of the EGR is to 'reburn' emission gases, from exhaust and the crank case. The EGR routes those gases into the throttle body. Its POSSIBLE that excessive oil is making its way through the PCV and into the throttle body.

My first step would be to remove, inspect and clean the throttle body. Once cleaned and reinstalled, I'd clear the PCM of the data for throttle position and shift points. This can be achieved the hardway with a scan tool such as ForScan or shorting out the capacitors via grounding the positive battery terminal. There are several videos on YouTube detailing how to do this. Basically remove the negative terminal from the battery and cover the negative post with a rag. The negative battery cable CANNOT come in contact with the battery during this procedure. Take a piece of wire and run it from the positive battery cable to the ground CABLE, not ground battery post. Leave in contact for about a minute to allow the capacitors to drain. This will 'delete' the memory. Hook the battery back up correctly and start the truck. Allow the truck to reach operating temperature and drive 'normally' for 20 minutes or so. The PCM will 'relearn' the throttle body positions and the shift points.

Robert A

May 2, 2012
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Corpus Christi, Texas
Check to see if your PCV valve is gummed up, then check how soft the PCV hose is...might be collapsing under vacuum.
this is spot on after months of struggling with COPs, plug change and 1 fuel injector replacing the PCV and cleaning the throttle body again took care of intermittent sputtering and loss of acceleration.

2000 Expedition XLT 4.6 aka "Big Red"

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