Need advice with my 1992 F250 7.3 IDI

[Nick382]

Hello everyone, I mentioned in my introduction post that I was working on this truck and it needed injection attention.

The interesting dilemma I have right now is that while trying to perform a compression test (I ended up borrowing a tester) the injection pump is still delivering fuel. The wacky part is that the truck starts perfectly find when cold, and shuts off when you cut the ignition. While compression testing with the fuel shut off solenoid unplugged, it just kept delivering fuel.

Am I missing something simple here?

 

[79jasper]

Probably unplugged the wrong one.

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[Nick382]

Probably unplugged the wrong one.

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I unplugged everything connected to the IP, even the tach



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[79jasper]

Oh. Lol
Maybe a tiny amount of fuel is normal?

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[Nick382]

Oh. Lol
Maybe a tiny amount of fuel is normal?

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It was enough fuel to leave a puddle under the truck and fuel siting on top of the engine. It pooled up on the block


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[79jasper]

Oh... That's probably coming out the return lines?
The lift pump will always pump, long as the engine is turning.

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[Nick382]

I cranked the engine 5 bumps for each cylinder and there was still fuel pumping on number 8.

I thought the shutoff solenoid wouldn't allow fuel to the IP at all without power. It doesn't make sense that the fuel shutoff valve doesn't work while disconnected and cranking the engine when the truck shuts off with the switch.


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[madpogue]

Did you check for a stuck FSS? Does the engine shut down with the key like it should?

 

[Thewespaul]

Fuel will be supplied to the ip but it will not inject fuel with enough pressure to pop open the injectors, if it's a worn ip it might be allowing a small amount of fuel through just not much pressure

 

[Nick382]

Did you check for a stuck FSS? Does the engine shut down with the key like it should?

Yes, shuts down immediately.


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[Nick382]

Fuel will be supplied to the ip but it will not inject fuel with enough pressure to pop open the injectors, if it's a worn ip it might be allowing a small amount of fuel through just not much pressure

In this case my options are cut fuel to the IP or remove it to do a compression test correctly?


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[Thewespaul]

Yep I would pull feed line off the lift pump

 

[Nick382]

Yep I would pull feed line off the lift pump

Thanks; I'll try that out and see what happens.

I'll report back


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[IDIBRONCO]

If you're using a compression tester that goes into the glow plug hole, there shouldn't be any fuel coming out of the return lines. If your tester goes into the injector holes, then your return lines are open. Since the return lines are connected to the fuel filter, then I could see where the lift pump could push fuel through the filter, into the return lines and out on to the engine. This would have nothing at all to do with the injector pump.

 

[Nick382]

Found out the solenoid does in fact shut the engine down when unplugged while running. After that I clamped the fuel supply hose to the lift pump, and ran the truck until it died. Purged the cylinders of the remaining fuel after all the glow plugs came out, and did the compression test. This time, there was no new fuel being pushed into the cylinders, just fuel from the return lines pooling and being misted.

Compression results were better than I expected for a 200K mile motor.

2: 360 ---------- 1: 400
4: 360 ---------- 3: 380
6: 380 ---------- 5: 380
8: 360 ---------- 7: 380​

I'm going to go ahead and take the IP + injectors off to ship to Justin from IDI performance.