I have a 2003 E350 7.3L. After starting up, will run ok for about 20-30 minutes of driving, then will lose almost all power, shuddering. If I stop for 10-20 minutes, then restart, will run sorta ok for a little, then same problem again. Has been to mechanic 4 times, and they are clueless.

It really feels like it is fuel-starved, like it's simply not getting enough fuel.

-No check engine light
-Checked fuel tank for sediment/blockage, is fine
-replaced fuel filter
-replaced 2 fuel injectors that they said weren't functioning properly
-has aftermarket fuel pump

This seriously sprang up out of nowhere...I was out of town for 2 weeks, and it drove fine before that, then came home and have had problems ever since.
Please help, my mechanic has no idea (or maybe just wants to nickle and dime me).

NOTE:
Not sure if it is relevent, but I also have a second tank which uses SVO (straight vegetable oil). Last time I drove it, I tried switching to the SVO tank, and it pretty much ran fine...then back to the diesel tank and lousy again. Tried switching twice more and same results...so maybe problem is in the diesel line?

Also, ever since this problem started, has been shifting kinda weird...not sure if a related problem.

 

I dont know much about powerstrokes but check your MAP sensor connection one of the wires corroded on my truck and without the map sensor it only provides fuel for 0 psi and has no power maybe yours is just loose.

 

There may be more fuel filters hiding out somewhere- I think someone on here said there were three on these rigs - the screen in the tank, one on the frame rail , and the one on the engine.

 

I heard of vegetable oil clogging up systems before, wouldn't recommend it. If you are looking to save at the pump build yourself an HHO powerplant and get and extra alternator on your beast. But yes replace all filters, you are going to need to check out your fuel system very closely. Check the pump and be sure to put the ford filters on it. Would recommend going to powerstrokehelp.com and watching the video of the biodeisel truck that had a clogged system. Also look into meth/water injection for fuel saving too. Old trick used in Europe. Water injection was used to compensate for the heat and timing advancement needed in the extremely high psi motors. Would actually recommend on every car, it became illegal because they were really turning up the power with their cars and after a lot of them blew up (from the pressure) water injection became illegal cause somehow the water was to blame..

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And yes one in tank, one big one under cab and a small one on top of the motor, looks like the oil filter with the black cap and whatnot just smaller

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Could be MAP too good call but i think this one is caused by the fuel. There is a product out there for cleaning lines out. Not sure what its called for that im sorry but yeah look for the foam cleanser works well.

 

How cold is it outside? there should be a screen on the inlet to your fuel pump, the one on top of the motor, and the screen in the tank. im assuming you drain your water/fuel seperator? run any additives?

your transmission acting weird is most likely a result of the engine not putting out what it should, so in turn the trans does what it can in relation to engine power.

also, check the fuel tank switching valve. sometimes when they start to go bad they wont completely switch from one position to the other, they'll kind of get stuck more towards one side causing a restriction and fuel starvation. try to bypass the switching valve with the diesel tank, see if it makes a difference.

and yes check your MAP sensor. although this seems completely fuel related, doesnt hurt to look

also, how old is the diesel in that one tank? red or green?