Ok here's the jest of it; 99 F-150 LX 4.2L V6 5 spd 4x4 has about 194K. I've done a long regiment of repairs on this truck after buying it dirt cheap, but I've run into a snag and out of ideas.
-changed out the cats to Magnaflow 94306 hi flows as the OEM were plugged up.
-plugs changed to Motorcraft
-vacuum leaks repaired -elbow some hoses
-cylinder head temp sensor replaced OEM
-minor other repairs belts idler pulley & other bearings on pulleys
-EGR pressure feedback sensor-checked EGR valve function OK
-upper intake gasket (checked lower for leaks good)cleaned while off.
-replaced the IAC valve OEM
-vacuum hoses replaced (smoke test repaired leaks)
-MAF cleaned also air filter changed OEM
-front crank seal
-plugs changed to OEM Motorcraft

I do have a bad heater on bank1 HO2 sensor but it switches fine after the motor is warmed up. (checked this on the computer-fuel trims are good both short & long term, I going to change both upstream as I have OEM replacements)

Lots of power at low RPM in low range 4x4, but in high range two wheel drive at high RPM it acts as if it's misfiring on at least two cylinders. But no codes are showing and I've driven it for about 100 miles with several start cycles.

Questions:
What codes should it through if the timing has in fact jumped if in fact it does show a code?
If some of you senior 4.2L owners have some ideas chime in here I'm open for a fresh look at this.

By the way I've search this group and several others but haven't found anything I haven't tried so far.

 

If it's missfiring, have you looked at Mode $06 test 53 at the cylinders missfire counts to see if that is happening?
Take a look at the live ignition timeing while running it up but do it safely.
The cam sync setting controls fuel. Is it set correctly?
Are the IMRC opening as the rpm goes up?
Performance is often an expectation.
This being v6, check the gear ratio on the door jamb sticker.
Usually these have a 3.08 or 3.31. Better to have the 3.31.
Good luck.

 

Thanks for a speedy reply Bluegrass...
The diff is a 3.55 according to the tags and the door stickers says the same thing, now I never thought of the cam sync, the IMRC's are ok, although I'm going to double check them and get a buddy to drive it while I watch the laptop and the timing. Food for thought and a few things that I over looked, thanks again.

 

Have you ever changed the plug wires and/or the coil pack?

 

A wild guess, you said the cats were changed because they were bad, Did the shop check the muffler while doing the cat? If the cat broke up then the pieces could lodge in the muffler and clog it up. This can act simular to a clogged cat and effect high end performance, but I don't think it would throw a code.

Just a thought.

 

Update: the muffler was changed at the same time with the cats, but a good call just the same.
The plug wires and coil pack was swapped out but made no difference.
I did change the camshaft sensor and the setting, it was right on the mark, found a crack in the EGR tube replaced it. It has improved, it doesn't feel like it's missing but still doesn't have the power that my buddy has with his identical truck. In fact his truck has more miles on than mine does.

If anyone has any other ideas throw them out there, at least it gives me ideas of something I haven't thought of.

thanks to all those who have made suggestions I appreciate the input.

 

Hoping to do a run on the weekend with a buddy driving, while I watch the timing on the laptop, it doesn't seem to feel like it had jumped on the timing chain now, but still lacking in power. Living in British Columbia among Canadian Rocky Mountains so everything is either up or down hill, not much flat land driving. I'm temped to pull the engine and drop in Cummings new 4.2L diesel, a tad expensive for a project truck, but it would be fun to build and drive being an old trucker, LOL.

 

For the info, I would put a Scanner on your buddies truck and look at the live data with emphisis on ignition timeing under load vs RPM and fuel trim table values.
Then look at yours to see what noteable differences exist under the same driving conditions.
Then you might have something to run with.
If you do this, please post the differences you see.
Good luck.

 

Found the problem thanks to Bluegrass, your suggestion to scan my buddy's truck and compare them worked. The fuel trims were completely different, my truck was running way to lean, so far that I suspected there was a really big vacuum leak somewhere. Out came the mirror and I started looking under everything. Turns out my brand new EGR line had a split about 4-5 inches long after the lines for the DPFE sensor right up to the first bend. It was hidden under the heat shield fabric and the old one had a piece missing from it so I just assumed the new one was good so figured it was something else. After plugging the EGR line off the fuel trims came down and the power went up, it must have been allowing enough unmetered air in that the ECM couldn’t compensate enough to overcome.
I wouldn't have thought the EGR line would have been able to pull that much air in to through the fuel trims off; I would have thought it should have thrown a P0401 code out for a faulty DPFE sensor again. One thing I’ve learned about Fords, never assume anything and suspect even new parts,at least from now on anyway.
And I want to thank Bluegrass, glc and jgger for your input, it gave me a different view and approach to this problem; you are a credit as to why this site is so successful.

 

Just to rap up with a comment, the system is way more sensitive than most can imagine.
The OX sensors are just that, sensors that detect oxygen levels in hot combustion gases and report to the PCM so fuel control can be done.
It's a loop type situation.
It chases it's own tail until it can't do any more and come to the limits then you feel drivability is not what it should be.
Wonderfull to hear the 'stare and compair' was the lead needed.
When you have insturments to look inside the system, the truth becomes known.
Good luck.