Should I Buy This 1984 F250 6.9L IDI

I found a 1984 F250 with the 6.9L IDI diesel for sale at $650. The seller says it was running fine until it suddenly died on the road. He suspects a solenoid issue, but I want to be sure before pulling the trigger.

I own a pressure washing company, so a 3/4-ton diesel could be useful for carrying large amounts of water. If I don’t use it for work, I’d like to build a rig (maybe for junk hauling) or flip it for a profit.

The truck doesn’t come with a topper, and I’m aware of potential odometer rollback issues with the 5-digit display.

What should I check before buying? Could this be a simple fix, or am I looking at a bigger issue?

Be careful with the 5-digit odometer. My old man sold his with 420k miles, and I saw it listed later with ‘280k miles.’ If it’s in NW Ohio, I’d be suspicious.

Merlin said:
Be careful with the 5-digit odometer. My old man sold his with 420k miles, and I saw it listed later with ‘280k miles.’ If it’s in NW Ohio, I’d be suspicious.

Not in Ohio, and no topper. But yeah, I’ll keep that in mind when checking the odometer history.

If someone says ‘solenoid issue,’ they usually mean the starter or a relay to the starter. If the engine cranks normally, that’s not the issue.

Your problem is more likely fuel-related rather than electrical.

@Hollis
6.9L IDIs are all mechanical, so the only solenoid involved in shutting the truck off is the fuel cutoff solenoid on the injection pump. If it lost power or failed, the engine won’t run. Other possibilities:

  • Clogged fuel filter
  • Injection pump failure (rare but possible)
  • Air intrusion in the fuel system

Quick checks before buying:

  1. Have someone turn the key while you put a finger on the fuel cutoff solenoid. You should feel a ‘click.’
  2. Crack the fuel line on injector #1 and crank the engine. If no fuel comes out, the injection pump isn’t working.
  3. Check the fuel filter and look for air bubbles in the lines.

If all of that checks out and it still won’t start, it could be low compression, which is a bigger issue.

@Darcy
That’s super helpful. I’ll try those before deciding. If I see bubbles in the fuel, does that mean there’s a loose connection somewhere?

Kiran said:
@Darcy
That’s super helpful. I’ll try those before deciding. If I see bubbles in the fuel, does that mean there’s a loose connection somewhere?

Yep. If someone recently worked on the fuel system, a line could be loose or cracked. The engine-driven fuel pump on the passenger side should be pulling diesel, not air.

Check the fuel pump’s output by loosening the outlet line—if no fuel comes out, you’ve got a supply issue. If fuel does come out but nothing reaches the injectors, it’s likely the injection pump.

I’ve had two 6.9 IDIs. They’re reliable but slow as hell without a turbo. I used to tow with one and it was painful. I upgraded to a 7.3 Powerstroke and it was night and day.

But if you’re just hauling water tanks and not in a rush, it’s a solid engine. Just be prepared for some frustration if you’re used to modern diesels.

@Uma
I’d take reliability over power any day. The 6.9 and 7.3 are opposite ends of the spectrum from the nightmare 6.0s.

Merlin said:
@Uma
I’d take reliability over power any day. The 6.9 and 7.3 are opposite ends of the spectrum from the nightmare 6.0s.

I won’t argue with that. Parts are cheap and easy to work on. Just don’t expect to go 70 mph uphill.

You have a lot of money to sink into it? $650 is a ‘get this out of my yard’ price.

The fact that it ‘just died’ on the road sounds suspicious. I never trust sellers who say ‘probably just a fuse.’

Check:

  • Fuel getting to the cylinders?
  • Compression test?
  • Voltage to the solenoid?

People love to offload junk for cheap. Be careful.

@Cass
I have a love/hate relationship with your comment.

On one hand, I want to buy this thing and everyone else is saying it’s probably minor.

On the other hand, you’re making me think twice—which is probably a good thing. JUST LET ME BE IRRESPONSIBLE AND BUY BIG THINGS OKAY?!

@Kiran
Haha, I want to encourage bad decisions, but this is a roll of the dice. If it’s meant to be, it’ll feel right.

Cass said:
@Kiran
Haha, I want to encourage bad decisions, but this is a roll of the dice. If it’s meant to be, it’ll feel right.

I turned it down. If it’s still there in a week, maybe I’ll negotiate lower.

@Kiran
Good call. There’s always another deal around the corner.