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Old 26-02-2024, 16:08   #1
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Engine fuel shut off solenoid, lubrication, compression test?

I'm looking to do compression testing on my Yanmar motor using a current shunt and oscilloscope.

With this approach I need to cut off the fuel supply to not have the engine start.

Is there any harm holding in the engine fuel cut-off solenoid while I crank the engine over to get my waveforms?

There's a very clear warning in the Yanmar manual to never do this unless in an emergency - which I don't understand as the solenoid is activated each time the engine stops?

I also might have to crank quite a few times to get my setup correct and for the readings to stabilize, I know the diesel pump needs diesel for lubrication

Q: Does the cutoff valve starve the diesel pump pistons/cylinders of lubrication?

Also I prefer to use the fuel cut off valve to cracking open the injector nuts as my partner hates the smell of diesel ( I don;'t mind it ) but it will be practically impossible to clean afterwards.

Big thanks for any advice, suggestions or opinions ..

ChatGPT response was pretty flimsy :
"Manually activating the fuel cutoff valve on a Yanmar diesel engine typically shuts off the fuel supply to the engine, but it shouldn't necessarily starve the diesel pump of lubrication"
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Old 26-02-2024, 17:25   #2
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Re: Engine fuel shut off solenoid, lubrication, compression test?

What model Yanmar do you have? This is important because each model engine has a different injector pump and a different way to cut off the fuel to the injectors and some cut off the fuel to the injector pump itself. Generally speaking I think its ok on inline pumps but rotary pumps are far more fragile. Yanmar uses 2 types of rotary injector pump, bosch VE and the more complex MP2. Hopefully you’re not doing the testing on a common rail engine, thats a little more difficult.
More importantly, if you’re going to be cranking the engine for a long time, shut off the raw water intake to avoid filling the exhaust
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Old 26-02-2024, 18:08   #3
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Re: Engine fuel shut off solenoid, lubrication, compression test?

WOW huge thanks lots of useful information there to google up.

The engine is a 3JH4E with the injector pump Yanmar 729271-51450 (see pic)

Unfortunately there's no general description of the pump in the service manual so I don't know more about it.

Yes; I have forgotten once before to turn the water off during a maintenance task, and had the panic attack that i had flooded the engine; it escaped the lapse.
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Old 26-02-2024, 23:27   #4
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Re: Engine fuel shut off solenoid, lubrication, compression test?

The 3JH4E usually has a Bosch VE rotary pump so yes, there could be a problem if the single rotating plunger was cranked for too long with the fuel shutdown solenoid activated. Normally a compression test takes 3 or 4 revolutions to get a result but you suggested that longer cranking might be needed for your test so why not get some clear plastic hose that will fit neatly over the end of each injector pipe and insert all 3 into a 4 litre container to catch the diesel fuel….then you can crank away more easily with 3 injectors out and not bother with the solenoid and eliminate the remote possibility of damaging the pump plunger.
Oh….. put brake hose pliers on the return line to avoid that inevitable leak.
If for some reason you DON’T have the BoschVE pump on your engine, I’d still go with the 3 clear hoses even though it’s practically impossible to harm an in-line pump while doing an extended bout of dead cranking with the stop activated for a compression test.
Chat GPT actually gave a reasonable response to the question asked.
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