Backfiring = LEAN
Running fine most times and then struggles when under load = LACK OF FUEL
There have been a few people now in this thread suggest a weak fuel pump, that is how they fixed their 5.0 explorers when they acted similar
I have been around these 5.0's "just a little bit"
It really sounds like a failing fuel pump
I have seen this many times before, I have fixed it many times before. The 98-01 5.0 with the returnless fuel system DOES THIS ALL THE TIME when the pump gets weak
Timing? bent valve? Not if it runs perfectly fine until he puts it under load
Clogged converter, this truck does not have them
New cam sensor may not have been installed perfectly, it could be a tooth off, it could also be a bad part right out of the box. But typically it would not run perfectly smooth at idle if the CPS was a tooth off or out 180
The codes you are getting point to a problem with the cam sensor
Now the codes:
If the truck was in my shop I would take a half an hour and checkout the cam sensor you installed, make sure cyl #1 was at TDC compression stroke when you dropped it in and make SURE it is aligned on the correct tooth on the cam
Then I would check the wiring to the sensor, make sure the pins are clean and seated, harness looks good. A quick continuity check of the wires through the 42 pin plug and to the correct pins on the PCM connector can rule out a problem there.
Check the firing order
Check all wiring, vacuum lines, overall visual inspection of the engine bay
Any coolant seepage around heads?
Visual inspection of the plug wires
How do the spark plugs look? pull a couple and have a look
MAS sensor clean or dirty on the sensor wires
Any leaks in the intake? signs of leaks around the rubber hoses and lines
Signs of leaks around the intake base gaskets, build up of soot, grease dirt
How quickly does the 5.0 start? long crank? points to weak fuel pressure
A properly tuned and running 5.0 should fire immediately on the bump of the starter, yes even with 290K miles
Check fuel pressure cold, then get truck up to temp and drive it monitor fuel pressure when the problem occurs......
60 psi on a cold pump is within spec, I bet you find the fuel pressure is lower when its hot......... My $$$ is still on a weak fuel pump or problem in the fuel system causing the LEAN CONDITION
This is the internet, the truck is not in the shop in front of us....so we all have to guess.
Put your BEST guess out here based on the facts in the thread and experience with these engines
He has been chasing this problem, runs fine until warm and then no acceleration under load
He has replaced the crank sensor, no change (a bad crank sensor the truck wont start, no reason to change this)
cam sensor and cam synchronizer, no change
TPS, no change (why would you change the TPS? just test it!)
Cleared codes, they come right back ONCE the problem occurs
Checked fuel pressure cold, 60 psi which IMO is a little WEAK for one of these truck. In spec yes, but when I see 58-60 psi on my gauge, cold truck, on a returnless 5.0 explorer I start to suspect the fuel pump it should be more like 62-68 psi in my experience