Have a 2003 XLT 4.6L Expedition (160,000mi) that has been awesome, but recently began loosing power at speeds over 45mph (rpms >3000) when towing boat up hill in GA (overdrive off). Runs & shifts smooth w/ no miss fires. Large EGR vacuum line blows off when I floor the gas, but no codes to go by. Researched most forums and can't find answers. I hope you can help.

Here are my readings at idle (and with ACTRON scanner):
EGR line pressure ~ 2PSI (this seems normal back pressure at idle)
idle vacuum test 19psi, increases with higher rpms (no vacuum leaks).
Oxygen Bank 1: 02S11 0.4V, 02S12 0.8V
Oxygen Bank 2: 02S21 0.3V, 02S22 0.7
MAF flow 4.6, Coolant temp: 179 F,
FUEL system 1 closed loop: ST FTRM 3.9%, LTFTRM 7.8%

I ordered an ELMSCAN 5 OBD reader to test engine more before replacing catalytic converters.

Q1) I suspected catalytic converter after it gets hot but how do I test it, what should I look for? When cool the back pressure appears normal.

Q2) How do I find out factory specs on oxygen sensors? they seem ok.

Q3) Does the 2003 Expy have baby cat-convertors or normal ones? I heard baby cats send different signals to computer than normal ones (can't find factory specs).

 

Did you ever figure your issue out? I have the same problem with power loss when pulling my boat up boat launch ramps. Thanks!

 

This sounds like a failing cat to me, typically whenever you blow that hose it's a backpressure problem (or a failed egr). 2PSI seems high to me for an idle line pressure, you want to be closer to 1 if I remember correctly, at least under 1.5psi. 2 For most vehicles indicates restriction.

OEM (and OEM like replacements from companies like magnaflow) are dual section and mount both oxygen sensors. I highly recommend these units to the universal ones. But it's also more expensive. A universal is like 250$ per side, the OEM like one is about 700$.

 

Thanks for the suggestion. Wouldn't a failing cat have reduced power, but not complete power loss? I'm having complete power loss, and then full power suddenly returns after a bunch (maybe 5 or 8) attempts to get back up the launch ramp.

 

Full power loss is indicative of a plugged cat, normally a cat where the honeycomb has broken apart inside a formed a plug due to the high temps. You may be getting power by melting the plug slightly with the high revs. Normally by that point though you'll throw error codes. Have you had the engine scanned?

 

I think I may have a different issue than the original poster. My Navigator will pull the boat up the launch ramp a few feet, and then I have complete loss of power. No revving of the engine...it just idles normally while I'm pressing the gas (and taking my foot off the "everyday" brake. Finally, after a number of attempts (maybe 5 or 7 of them), it'll successfully pull the boat up the ramp. I've had the vehicle at the Forder dealership and no codes are showing.

 

To me that sounds like a bad accelerator pedal assembly. The throttle is electronic, so if the switch is going faulty it will register intermittent moments on the accelerator. Here' info from another section of the forums, I don't know if the 08 uses the same IVS setup though. One user mentions same as you, having to "pump" the go pedal before finally it works.

https://www.ford-trucks.com/forums/9...ce-w-pics.html