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Power loss under load
My family and I bought a 2001 E350 7.3 PSD, camperized it, and are driving through Mexico right now. I'll try to make the story as short as I can.
About 2 months ago, I started noticing that when I started up a hill at speed, I would get about 5-20 seconds of normal performance - I could hear the turbo spool up and feel the truck accelerate. Then after a few seconds power would drop off and the truck would start to hesitate a shudder a little. Depending on the steepness of the hill, my speed would continue to drop off. I could only manage about 30mph up a hill that I could normally pull at 50-60.
I replaced the fuel filter, but when I cut the old one open it looked clean.
A few weeks later, it got to the point where I could only get it up to 40mph on the flat. No amount of throttle made a difference. I took it to a mechanic who dropped the fuel tank and inspected the fuel pickup thing in the tank for cracks. None were found, and he blew out the fuel lines with compressed air. The next day he and I drove the truck 250 miles without a problem; I pushed it as hard as I could.
We continued on and I still noticed the problem occasionally but it didn't really affect drivability. A few days ago, back in hilly country, and the problem is still there or came back. I can still drive at 65 on the flat, but I only get a few seconds of normal power when I start up a hill. Once over the hill I get back up to speed again. I'll get a few seconds of normal power on the next hill before it happens again.
Googling this leads to turbo-related issues, including wastegate problems, but from what I can find the van doesn't have a wastegate. This morning I removed and cleaned the exhaust back pressure sensor and tube, but it wasn't completely obstructed (I could blow air through it with my mouth) so I'm not hopeful that that fixed the problem.
Before we left home, I had the seemingly common problem of having no power until the engine warms up. I never had that fixed, and I don't experience that problem here (it's warm!). The truck performs normally when driving around town.
Any ideas on what I should check next would be most appreciated.