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
-has aftermarket fuel pump

 

what oil are you using in it?

you could have a foaming issue allowing air to get entrapped in the oil and causing the injectors to misfire.

 

Series 3000 heavy duty diesel oil. I changed it about 1000 miles ago.

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Series 3000 heavy duty diesel oil. I changed it about 1000 miles ago. What oil do u recommend?

 

when I had my 7.3 PSD I used the Motorcraft Brand 10W30 Super Duty Diesel Oil.

it has the proper additives to eliminate the foaming in the oil that plagues the PSD platform. also verify that you put in the proper amount of oil and that it reads full on the dip stick. remember that the injectors in these trucks are fired off of oil pressure. when oil foams it allows air to get entrapped in the oil. when the oil/foam is compressed, the air bubbles compress and does not build pressure that pure oil w/o entrapped air will, therefore not firing the injectors.

just because it says it is "heavy duty diesel oil" don't mean it will work properly in the PSD engine.

other than that, IF you think it is a fuel issue, install a fuel gauge and watch it.

 

Yeah, you should check the fuel pressure to eliminate that as an issue. I have used a few different oils in the powerstrokes I own and never had an issue. Rotella, Motorcraft, Delo, etc... Ive been thinking about trying out the NAPA brand CJ-4 oil because its always on sale and they say it is just a rebranded version of some other major brand of diesel truck oil.

 

You should blow out the lines.