I am new to owning a diesel having just purchased a 90 F250 7.3L 5 spd. I finally confirmed that I am not imagining things and found some driveability issues today.

I had my suspicions before, but today, when driving from the rear tank all of the sudden it felt like the truck had lots more power than before. I had been driving the same hills yesterday having to downshift to go up them and was unable to accelerate going up hill. Today after a normal start and initial driving it was like a turbo or something kicked in and it had much more power: same hills with no down shift and I was even able to accelerate up them.

After enjoying this for about 20 miles I was cruising at around 50mph, and then there was no power, couldn't accelerate or even maintain speed. I switched to the front tank and it ran normally again. When I stopped for fuel I was only able to squeeze 10 gal. in the rear tank so it should have had plenty of fuel left.

Oh, forgot to mention that after first few miles today, it would idle very rough. Like it was missing. It would smooth out above 1300rpm, but idle rough. I was parked playing with it and after several revs above 1300rpm it settled back into a normal idle.

After re-filling the rear tank, it started and ran fine from that tank the remaining 30miles back to my house.

Where do I start with this one?
Do I have a fuel tank problem? or is there something else going on here that I need to look at?

I have plenty of experience with gas engines, but this is my first diesel so any help would be appreciated.
Thanks,
Kevin

 

Your problem MAY be a sticky advance piston...... What fuel additive do you use.

Are there any issues with fuel guage indications when selected tank is changed.

Do a pressure and flow test of the fuel pump at the Schrader valve on the filter header (FSS- fuel shutoff solenoid disconnected on IP). Remove the tire valve core and hook a hose and pressure guage on it should see 4-6 psi when starter cranking engine over. Then do a fuel quantity test same place, should see 1/3 pint in 10 seconds of starter engine cranking, route fuel to a suitable container with a hose. When all finished hook up the FSS wire .

If there is a problem with the lift pump and you are changing it, ensure the new pump comes with instructions as to correct installation procedure if it is the newer model pump with the almost straight arm.

 

You may have a problem with the pickup tube in your tank it seems several members here have had them break or rust off usually about a 3rd from the bottom.

 

I haven't used any fuel additive.

Gas gauges don't seem to be very reliable: rear tank reads past full when full, but 1/4-1/8 after using 10 of the 18 gal. front tank never reads past 1/4 tank no matter how much fuel is in it.

Starmilt, can the pickup be replaced, or do I need to replace the entire tank?

 

Your problem could then be the fuel selector valve..... FSV, the senders are known to wear out also. Senders are available from Rockauto and other places. Front tank sender can be removed without dropping the tank I believe........ rear must have tank dropped or bed raised. FSV replacement is doable just clamp of the fuel lines from the tanks first... how do I know don't ask.

Fuel additive I have used recently is Howes diesel treat most truck stops and IH have it....... it makes my engine purr, just do a good dose into both tanks then do as required by the instruction on each fill.

 

don't think i'd change the pickup tubes without checking the sending units to make sure they weren't bad as well. the easiest way to change the sending units out is to remove the bed bolts and jack the bed off of the frame. that way you don't have to loosen and drop the tanks. as an aside, i noticed that just before mine got to the point where the broken pickup tube was running out of reliable fuel, it did the same thing, i.e., got a boost of power. don't know what causes this, but both my tanks would let me run out of fuel with a 1/4 tank showing on the gauges. (which i don't trust anyway.) not a complete answer to your question, but it's what i know.

speedrdr

 

That is how I know I need to switch tanks, or go get some fuel ASAP. My front tank has something missing from the pickup tube. I am only able to use around eight gallons or so before it starts running lean. I regularly use the rear tank, and use the front tank as my backup tank that gets me to the gas station.

 

Had mine do that twice. But couldnt get to the switch quick enough. luckily i was pulling in work.

 

It's the fuel pickup tubes in the tank. Once they fall off, the pickup sucks air/fuel. That's the power increase Your feeling. All of the sudden, no power, is the fuel pickup finally not being able to pick up any fuel. Switch tanks and runs fine. Is the fact that Your getting un-aerated fuel from the front tank.

Don't bother with anything else, until You eliminate this very common problem. Farting around with a properly operating 20 yo FSV will just cause You headaches.

Pull the rear tank pickup, and I'll almost guarantee that the fuel pickup screen is laying on the bottom of the tank.