2002 Expedition - Won't rev past 2400 rpm in park or driving / won't accelerate

[bryanjtift]

Hello! I have a 2002 expedition that I've been trying to track down an issue with. The vehicle will NOT do any sort of medium to heavy acceleration.

In park, the vehicle will not rev above 2400rpm if you go WOT. If you give it about 50% throttle, it'll climb to redline.
When driving, the vehicle will have hard time accelerating and shifting gears (due to rpms not being able to climb high enough to shift). Slow acceleration is possible but medium to fast acceleration is impossible, engine stops accelerating around 2400-3000rpm.

- replaced the fuel filter
- replaced catalytic converters
- replaced spark plugs and coil plugs
- Replaced MAF (no difference)
- TPS tests fine - goes from 0.9v to 4.8v across full range
- Short term fuel trims are between -2 and 2 indicating no vacuum leak
- Upstream oxygen sensors bounce between 0.1 and 0.9 like they're supposed to
- Transmission fluid level is fine
- No check engine codes or pending codes (checked with Forscan tool)

Air filter is good. There doesn't seem to be any blockage in the intake and the exhaust system, especially with new cats. I checked fuel pressure about a week ago and it was 38psi. I'm going to check again tonight and report back. I'm wondering if my gauge was faulty so I'll be using another fuel gauge

Any ideas here? Anything would be welcome.

My issue seems VERY familiar to this thread but there was never a resolution: https://www.ford-trucks.com/forums/323454-expedition-loss-of-power-at-full-throttle.html
Specifically this: "It down shifted but no acceleration, actually started to slow down. Back out the gas a little and it accelerated. Normal take off from a stop and you won't notice anything is wrong. Full throttle from a dead stop and you take off very slow, full throttle from low speed and the same thing almost dives, it does not sound like it is missing, just no power. Half throttle takes off great."

That quote is exactly my issue. If I lessen the throttle, the engine will kick back up and slowly, slowly accelerate. Apply about half throttle or more and engine falls on its face.

Thanks everyone

 

[Yupster Dog]

@bryanjtift Smoke the intake you might find the culprit.

 

[bryanjtift]

@bryanjtift Smoke the intake you might find the culprit.

I actually just did that and a vacuum test. Smoked it for about 5 minutes but couldn't see where there were any leaks. I ran along the hoses and found no cracks or leaks. That doesn't mean there still isn't a leak, but that it's just hard to see.

Vacuum test resulted in idling at 16inhg which I know is low... Is there any way besides a smoke test to confirm vacuum leak? I already confirmed short term fuels trims were within normal levels which should indicate no vacuum leaks as well.

Thank you

 

[Bigword]

Did you @bryanjtift ever get anywhere on a resolution to this problem? I have a 2002 Expedition EB with 5.4L doing the same thing and I have changed/cleaned almost everything you have done as well, with no results. I guess I will dig into the vacuum lines next.

 

[Junkyard Jack]

Anyone ever get anywhere with this? My truck started doing the same thing yesterday on a trip. I can hear a rattle underneath me when this is happening and that leads me to believe it's a cat issue, but I have not crawled underneath to take a closer look yet.