Shut off fuel for a compression test

[Charles Moore]

I'm at 280k miles so I'd like to get an idea of the compression on the engine.

Whats the best way to shut off the fuel doing into the cylinders for these engines?

Thanks!

 

[IDIBRONCO]

Unplug the power wire from your injector pump. That way no fuel will be pumped to your injectors.

 

[Charles Moore]

Unplug the power wire from your injector pump. That way no fuel will be pumped to your injectors.

Oh I thought the injection pump was purely mechanical.

Thanks

 

[SlippyRider]

Oh I thought the injection pump was purely mechanical.

Thanks

There's a fuel cut off solenoid that is the kill switch for the engine. It requires 12 volts to hold it open allowing fuel to flow.

You'll notice, looking at your injection pump there are a couple electrical connections. The one closest to the firewall is the shutoff solenoid. The plastic connector things tend to be brittle with age, so don't be surprised if it breaks when you give it a squeeze to disconnect it. It's not a big deal.

 

[Selahdoor]

Actually, there are two connectors, front and back, on the driver's side of the IP.

Front being closest to the radiator. Back, being closest to the firewall.

Front is the fuel shutoff solenoid. Back is the fast idle.

If you didn't bother to do anything at all, you'd just end up with fuel in the cylinders. As, to do the compression test, you have to take out all the glow plugs. No compression can build in any cylinder, so no ignition can take place.

 

[Thewespaul]

The fast idle is the solenoid on the passenger side of the pump that acts on the throttle arm, the rear connector on the IP is for the cold advance

 

[Selahdoor]

You are correct. And you have corrected me on that before. I just keep forgetting the proper nomenclature.

I DO know it advances something! And that it is the front one that shuts off the fuel.

 

[79jasper]

If in question, just unplug the whole engine harness. Real simple, and won't run the glowplugs.
Or you could get a simple remote starter switch....

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[IDIBRONCO]

If in question, just unplug the whole engine harness. Real simple, and won't run the glowplugs.
Or you could get a simple remote starter switch....

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I was thinking of unplugging both plugs on the IP.

 

[79jasper]

A person could. Then we would see threads of "my truck dies when it warms up, and wont restart until it cools off." Lol

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[IDIBRONCO]

Although you can switch them, those wires do lay out to where they're supposed to plug in. Another thing, with all of the advice to "just splice the two glow plug wires together at the main wiring harness plug", it's getting harder to find a truck that you actually can unplug it there.

 

[79jasper]

I only say that because I've seen exactly those posts...

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[Charles Moore]

Cool thanks folks! What compression #'s am I looking for?
94 7.3 IDI non turbo.
Now I've also got to find a compression tester that will work. The one I have doesn't have any connections small enough to fit in the glow plug space...

 

[dgr]

This is the adapter I used on my truck. Tight fit all around but I was able to test all 8 cylinders.

https://www.tooldiscounter.com/product/star-products-diesel-adapter-statu-15-1a