Why Won’t My 1998 7.3 Start After Sitting?

Seeking Help
1

I’m learning to work on engines, so I’d really appreciate clear advice.

Here’s what’s relevant:

  • Van sat for 2 years without starting.
  • Installed two brand-new batteries yesterday.
  • Dropped the fuel tank and disconnected fuel lines.

The Issue:

After hooking up the new batteries, the van started and ran for a bit. Then it began misfiring, followed by knocking, so I shut it down immediately. I checked the oil (no gas smell), confirmed the fuel tank was 3/4 full, checked transmission fluid, and emptied the water separator. Now, the engine cranks but won’t start.

Any advice is welcome! I’ll keep updating as I work through suggestions.

2

Sounds like air got in the fuel lines when you dropped the tank. That could explain the rough running. Did you replace the fuel in the tank, or just empty the separator? Old diesel can get water in it after sitting for years, which might be why it’s not starting now.

3

@Pax
I only emptied the separator. Could air in the lines stop it from starting? I thought these systems purged air automatically. Also, if there’s water in the fuel, would draining the tank and refilling it fix it? I’ve been using the diesel in this tank to run other accessories without problems.

4

@Thayer
Yes, air in the lines could cause this. The system should purge, but it can take time. For water in the fuel, you’ll need to pump it out and refill. Running accessories doesn’t rule out water buildup—it might not be enough to stop them but could affect the engine.

5

@Pax
I’ll check for fuel flow at the bowl. Should I expect fuel to flow automatically during the wait-to-start cycle? If not, is there a way to force air or water out?

6

Thayer said:
@Pax
I’ll check for fuel flow at the bowl. Should I expect fuel to flow automatically during the wait-to-start cycle? If not, is there a way to force air or water out?

Yes, the wait-to-start light primes the pump. Open the drain on the fuel bowl to check for fuel flow. Capture some in a pan—it might help to see if water or sludge separates out.

7

@Pax
I swapped the fuel filter today. The bowl might have been empty, but I refilled it with fresh diesel. Unfortunately, the engine still doesn’t fire up. I suspect the batteries are too drained to crank properly, so I’m recharging them overnight.

8

@Thayer
Did the WTS light come on? Do you hear the fuel pump or starter clicking? What did the old filter look like—clean or clogged?

9

Pax said:
@Thayer
Did the WTS light come on? Do you hear the fuel pump or starter clicking? What did the old filter look like—clean or clogged?

The WTS light is strong. I didn’t pay much attention to pump or starter sounds. The old filter looked fine, but I replaced it as a precaution.

10

@Thayer
Could glow plugs be an issue? But if it ran yesterday, that’s less likely.

11

Pax said:
@Thayer
Could glow plugs be an issue? But if it ran yesterday, that’s less likely.

I’m in SoCal, so it’s warm—about 70°F today. Cold start issues shouldn’t apply here.

12

Thayer said:

Pax said:
@Thayer
Could glow plugs be an issue? But if it ran yesterday, that’s less likely.

I’m in SoCal, so it’s warm—about 70°F today. Cold start issues shouldn’t apply here.

Maybe your batteries just weren’t charged enough. Diesel engines need a strong crank to fire.

13

Air in the fuel system explains the rough running. Once you get it started again, it should clear itself out.

14

Micah said:
Air in the fuel system explains the rough running. Once you get it started again, it should clear itself out.

Getting it running is the hard part right now. Once it’s running, I’ll let it sort itself out.

15

Air or a blockage in the fuel system could cause this. Also, check oil pressure with an OBD reader—it might not be high enough to start. Replace the fuel filter if you haven’t yet.

16

Mckinley said:
Air or a blockage in the fuel system could cause this. Also, check oil pressure with an OBD reader—it might not be high enough to start. Replace the fuel filter if you haven’t yet.

Thanks! I replaced the filter and added fresh fuel to the bowl. I’ll grab an OBD reader to check oil pressure next.

17

Open the fuel bowl to see what’s inside. Replace the filter, add fresh diesel, and charge the batteries. If the bowl keeps emptying, your lift pump might be bad.

18

Keegan said:
Open the fuel bowl to see what’s inside. Replace the filter, add fresh diesel, and charge the batteries. If the bowl keeps emptying, your lift pump might be bad.

Already filled the bowl with fresh fuel and charged the batteries. I’ll know tomorrow if that fixes anything.

19

Get a code reader and check fuel pressure. If it’s low, the lift pump could be bad. Does the tach move while cranking? If not, check the CPS wiring. Also test the glow plug relay and glow plugs.