I don't know a lot about diesel engines, but my 1999 7.3 is having a hard time starting. When it does start, I can hardly get it above 45mph and when I step on the accelerator, it downshifts, but doesn't accelerate. It seemed to run fine up until yesterday. I did fill the tank with fuel, and it started acting up after about driving 70 miles on the new tank of fuel.
Did I get bad fuel? What can I do?
Thanks

 

Perhaps a bad batch of fuel. Pull the fuel filter and replace with a new one and see how she does after that. Good luck

Cowboy Stev

 

It definitely sounds like bad fuel, stop driving it until you can get the tank dropped and cleaned, or you might ruin the fuel pump. It sounds like your intank filters are clogged, Click for full size image this is what they look like. The filter on the left came from a truck that got bad fuel and had to be towed for a tank cleaning and a pump replacement.

Check out the other pics in my galley and this thread https://www.ford-trucks.com/forums/585717-i-tried-for-a-hutch-but-got-harpooned-have-questions.html for a way to mod your truck so you won't have to drop the tank every time you get some bad fuel.

 

are you showing a water in fuel light on the dash? If no, then add a good quality additive(Stanadyne, Diesel Kleen, etc...) and see if it clears up.

was it dino or Bio diesel. if it was bio and this is your first time running it, the fuel could have loosened some deposits and gunked up your fuel filter. Change fuel filter and use an additive and see it that helps(this is the least expensive route)

when you step on the go pedal and it down shifts do the RPMs go up. could it be your tranny is on the last leg.

 

Unless you ruin the fuel pump and some injectors in the process, and your intank filters will still be clogged anyway!

This is most likely just the PCM initiating a "torque demand downshift" because the engine can't produce enough torque due to low fuel flow!

 

WHen I do step on the go pedal, the truck downshifts, RPMs go up, but it doesn't accelerate. It has a hard time going past 45mph, unless I have miles of road to drive.

 

The safest course of action is to have your tank dropped and cleaned, remove the 2 intank filters and don't install new ones in the tank, but install an external spin-off fuel filter in place of the intank ones to protect the pump, and also replace your regular fuel filter with a new one. Some have gotten temporary relief by blowing compressed air into the fuel line going into the tank to try and reverse flush the intank filters.

The intank filters are 200 micron, and the one in the fuel bowl is 28 microns so they're not perfect for keeping smaller debris out of the injectors. If you do have a tank of dirty fuel (which definitely matches your symptoms) and try to run 30 gal of dirty fuel through the engine, you might wind up with a much more expensive repair bill than paying to get the tank cleaned.

A 99 like yours is probably due for a tank cleaning anyway, and there's a continuing problem with dirty fuel due to the switch over to ULSD which has a higher detergent level and tends to wash up dirt from older supply tanks that have long have been used for LSD, so getting rid of the intank filters is also something you need to do.

Also check out this thread, https://www.ford-trucks.com/forums/617103-bad-fuel-cleaned-out-wont-start-fuel-pump-not-operating.html#post4785365 unfortunately, it looks like OM TOM went to the trouble of dropping and cleaning his tank, but didn't know where to look for the intank filters.