Troubleshooting fuel issues on my 7.3—need help

I recently replaced all 8 injector cups, got the truck running, and bled out what I could before driving it. It was running great after the initial fuel knock went away.

I drove it around the block, planning to fill up the tank since I live on a hill. It made it about 3/4 of a mile, just shy of the gas station, and then it suddenly lost power. I had to keep the throttle floored just to limp it along (barely 5 mph). It struggled to hit 30 mph even downhill.

I managed to get to the gas station (I had a little over 1/4 tank) and added $40 worth of fuel. It idled roughly but enough to give me hope I could make it home. However, it stalled on the first hill—the driveway leaving the gas station—and wouldn’t start again.

Here’s what I’ve noticed:

  1. The more I prime the fuel system, the longer it will idle properly.
  2. After changing the fuel bowl filter, it’s still acting worse—barely tries to start now. Temps were in the 30s, if that matters.

I’m at a loss. I can provide a video if anyone knowledgeable wants to take a look.

When you changed the fuel filter, was the fuel bowl full? Have you done the hutch mod? With less than 1/4 tank, you might have sucked in air.

Nova said:
When you changed the fuel filter, was the fuel bowl full? Have you done the hutch mod? With less than 1/4 tank, you might have sucked in air.

Yes, the fuel bowl was full.

@Vance
Hmm, sounds like you might’ve just sucked in some air. Look into the hutch mod; it explains this issue. Honestly, this might just be a coincidence with the injector cup job.

Nova said:
@Vance
Hmm, sounds like you might’ve just sucked in some air. Look into the hutch mod; it explains this issue. Honestly, this might just be a coincidence with the injector cup job.

I hear a pump from the middle of the truck, but nothing from the tank at the back. Shouldn’t I hear it if there’s one in there? I’ve only had this truck for two months, so I’m still learning.

@Vance
If it’s a late ‘99 or newer, it only has one pump on the frame rail. Nothing inside the tank.

Nova said:
@Vance
If it’s a late ‘99 or newer, it only has one pump on the frame rail. Nothing inside the tank.

Yep, it’s a 2000 model.

Vance said:

Nova said:
@Vance
If it’s a late ‘99 or newer, it only has one pump on the frame rail. Nothing inside the tank.

Yep, it’s a 2000 model.

Gotcha. If the injector cups were installed correctly, my guess is the 1/4 tank issue. Once you get fuel above that, it should start running better pretty quickly.

@Nova
I filled it up to 3/4 of a tank after limping to the station. How long should it take to run right again?

Vance said:
@Nova
I filled it up to 3/4 of a tank after limping to the station. How long should it take to run right again?

It shouldn’t take long. It might stumble a bit as it clears air out of the system. Also, check for air in the oil system—sometimes that can cause issues too. I haven’t done injectors yet, but I know with cups, you need to get all the oil and coolant out of the cylinders before starting.

Nova said:
When you changed the fuel filter, was the fuel bowl full? Have you done the hutch mod? With less than 1/4 tank, you might have sucked in air.

Yes, it was completely full, but I couldn’t get it to drain until I pressurized it again.

I had a similar issue on a truck after a big motor job. The owner drove it fine until it hit 1/4 tank, and then it died. It sounded like it was running on half the engine. We had to pressurize the tank to prime the pump, and it started again. Turns out, the foot on the sending unit had fallen off.

Other possible causes:

  1. A UVCH short (cracked wire insulation).
  2. IDM failure (the valve harness tested fine but the truck ran terribly). Both were frustrating to troubleshoot.

While it’s running rough, unplug each UVCH to see if it makes a difference. That’s how I found cracked wires on mine.

@Teegan
I’ve got brand-new UVCHs on both sides. What are the odds of them being bad already?

Vance said:
@Teegan
I’ve got brand-new UVCHs on both sides. What are the odds of them being bad already?

Not sure, but some folks report issues with the Dorman ones. You could try running a buzz test with a cheap scanner like Veepeak and Forscan. It might help identify wiring problems or throw error codes.

@Teegan
Do you have to pressurize the fuel tank? When I changed the filter, the bowl was full, but I couldn’t get it to drain.

Vance said:
@Teegan
Do you have to pressurize the fuel tank? When I changed the filter, the bowl was full, but I couldn’t get it to drain.

Yes, we used a shop vacuum in reverse (like a leaf blower) to pressurize the tank while cycling the key forward. If your drain line is clogged, try running a wire up from the bottom to clear it. Alternatively, disconnect the flexline at the back of the fuel bowl and blow it out with compressed air.