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Disablement of fuel injection during diesel compression test

Old 01-10-2015, 05:07 PM
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Default Disablement of fuel injection during diesel compression test

I have recently acquired a 1980 MB 240D (Chassis 123.123, engine 616.912) through inheritance. I want to run a compression test of each of the four cylinders. The fuel pump is "purely mechanical" ... cannot be shut off electrically... and I want to make sure it does not squirt fuel all over the place ... because I have been instructed (Plan A) to remove the injectors for the purpose of performing compression test... while the engine rotates and activates cams that drive fuel pump. My hunch is that merely keeping ignition switch off will help... assuming vacuum exists (doubtful) to suppress fuel delivery. But depression of emergency shut-off lever ... by some other helpful person... is the best way to suppress fuel delivery.

Any experienced suggestions will be greatly appreciated.

I have a CDROM pertinent to this car's service techniques and specifications. It will help to know the proper torque specifications, for re-assembly of injectors, to engine, etc.!

The manual speaks in generalities...across many automobile model types... and says to access the cylinder by either glow plug hole OR injection nozzles. Obviously, the glow-plug hole access method is vastly more simple. Any objections, to that approach? I have a generous collection of adapters, to handle the "plumbing."

Last edited by John_Peter; 01-10-2015 at 06:01 PM.
Old 01-21-2015, 11:33 AM
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Follow up: I completed my engine compression test, although I could not scrupulously follow the rules offered in my MB repair manual (on CDROM). To wit, I performed the test without heating the engine up to normal operating temperature. The engine was probably at 65deg F... ambient for my driveway in southern California.
I used adapters provided with my new Harbor Freight diesel compression testing kit, to access cylinders through the glow plug holes. This was not easy.. but at least I didn't have to mess with the injector ports.
I presume the fuel injectors forced some amount of fuel into the cylinders, while I cranked the engine... over the period of a couple hours. Atomized vapor shot out of the open holes (three cylinders lacking anything in the glow plug holes).

Compression was reasonably consistent, at 400 psi., over the four cylinders.

I expect to have a "valve job" performed on this car, rather than a "full engine job."
Old 01-22-2015, 10:26 AM
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The engine consumes a lot of oil... 40-weight oil, no less. I now believe... "hope" ... that this obnoxious problem lies with worn valve guide seals. The oil can be sucked into the intake chambers on the "intake stroke" with subsequent combustion... and smoke. Also I get tail-pipe slop... black, gasoline soluble.. non-combusted oil. This likely comes from the seepage of oil into the exhaust manifold, at the exhaust valve stem... though I am groping for the logic that explains the pressure differential that would push oil INTO the exhaust manifold.

I have been told that all diesel engine experience severe blackening of oil. Is this true? My oil certainly is black black black. Do new diesel engines suffer blackening of oil?

WHen this car belonged to my Dad... (for over 30 years)... he didn't have the oil drained. He just kept adding oil! This thing uses a lot of oil.
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