Yanmar diesels on 750 & 790... what caused this??

kebo · Jan 13, 2009

I used to have a JD 750 with a Yanmar indirect injection diesel engine in it. Now I have a JD 790 with a direct injection Yanmar engine. On the 750 the only way to turn that engine off was by shutting off the throttle completely. Turning the key off did not turn those engines off. In fact, on that tractor you could remove the key from the ignition and it will still run. Sometimes when you did shut off the throttle, depending on how hard you had ran it, it would diesel right on which was quite annoying.

Now, on my 790 I turn the key off and it shuts off period. No questions asked (so far). I've only had the 790 for about 3 months now, but have not really used it enough to see if it will diesel after I switch the ignition key off. Is there any chance it could diesel on after turning the ignition off??

Is the difference in turning these two engines off because of the indirect injection versus direct injection?

Or is there another reason for that? As you can tell, I'm not very knowledgeable about diesel engines.

Keith

RobS · Jan 13, 2009

I can't speak to the 750 but on my 790 it shuts off with the key every time. I suspect the key controls fuel flow at the pump somehow.

LBrown59 · Jan 13, 2009

RobS said:
I can't speak to the 750 but on my 790 it shuts off with the key every time. I suspect the key controls fuel flow at the pump somehow.

You can't use the key to cut the current off to the spark plugs in a diesel.

Inspector507 · Jan 13, 2009

Key shuts off power to the fuel solenoid is my guess.

Labrat · Jan 13, 2009

There is an electric fuel solenoid on the side of the injection pump that shuts the fuel supply off when you turn the key off. This is common on both the DI and IDI engines now.

kennyd · Jan 13, 2009

Inspector507 said:
Key shuts off power to the fuel solenoid is my guess.

Labrat said:
There is an electric fuel solenoid on the side of the injection pump that shuts the fuel supply off when you turn the key off. This is common on both the DI and IDI engines now.

^^^^^^^
What they said.

kebo · Jan 13, 2009

Labrat said:
There is an electric fuel solenoid on the side of the injection pump that shuts the fuel supply off when you turn the key off. This is common on both the DI and IDI engines now.

Ok, so it sounds like the '84 750 didn't have a fuel solenoid on the pump. That would explain why the ignition key had no effect with turning the engine off, and the only way to shut off the engine was to close off the throttle completely, thus cutting off the fuel. Makes sense to me. Thanks!
Keith

sandman2234 · Jan 13, 2009

RobS said:
I can't speak to the 750 but on my 790 it shuts off with the key every time. I suspect the key controls fuel flow at the pump somehow.

You were correct, in that a solenoid is used to stop the flow of fuel at the pump, that closes when power is removed.
David from jax

Muxster · Jan 13, 2009

Its got nothing to do with the type of injection. The 790 integrates the latest safety interlocks which older tractors did not have. These safety features require the engine to stop if the operator falls. The fuel solenoid that stops the flow of fuel in an unsafe condition is also used for the operator to conveniently shut down the engine. Older tractors that didn't require safety features could be manufactured cheaper with out the "ignition" key shutoff.