76 300D stuck at WOT

[Benz124s]

Hi everyone,
I recently installed a used engine into a 76 300D that I purchased without an engine. Upon starting it for the first time it immediately went to full throttle and refused to stop running even with the key out. Pushing the emergency stop lever did nothing. We finally shut it down by disconnecting the fuel feed line. I checked the throttle linkages and took them apart to clean and lubricate them so everything moves freely. All vacuum lines appear connected. I can't figure out what would make it stick at WOT as it doesn't have a throttle body like the 240D has. I'm guessing the throttle is controlled by the amount of fuel delivered by the injection pump. Any thoughts/ideas? Thanks in advance! I'm afraid to start it again.

[tyl604]

In the SD (mine is a 1981) this is a potential problem when replacing the shutoff valve which is inside the back of the injection pump. If you do not get the new shutoff valve inserted properly, the engine will be a runaway.

Wondering if the 300D also has a shutoff valve in the same place and could be bad.

[Benz124s]

That could be. I'll test the valve with a vacuum pump. Also I noticed it was sucking oil up through the vacuum pump, so the diagram may be bad. It sure was scary not being able to shut it down. Thanks for the reply.

[Sugar Bear]

Create something simple and have it ready to thoroughly block the air intake before attempting another start.

The oil coming from the vacuum pump could create the runaway just like crankcase blowby can.

In the first post the absence of a throttle body was mentioned, that isn't the issue IMO, as mentioned it is the amount of fuel controlling the RPM's.

Be extra careful, a runaway diesel is a dangerous situation that could send shrapnel flying.

[psaboic]

Since you said you were able to shut it down by disconnecting the fuel feed, I'm thinking it is an injection pump issue and not so much caused by oil being sucked through the vacuum pump. That is a concern though but not what I believe is causing the runaway.

[Benz124s]

I pulled the vacuum pump apart this morning but didn't see any visible damage to the diagram and the rubber still feels OK. There was oil on the side of the diagram where the vacuum hoses connect though. The oil dipstick is also quite a bit lower than it was before I first tried to start it. I will definitely have something ready to block the air intake at the next start attempt. When I disconnected the fuel line it took several seconds for it to shut down.

[psaboic]

It took several seconds to shut down because it had to use up all the residual fuel that was in the filters, injection pump and lines. If it was running away on the oil in the engine, it would keep running until it used up all the engine oil or catastrophically failed.......

[resago2000]

stuck rack.

[Benz124s]

Is the rack an internal part of the injection pump? I'm still researching that part.

[engatwork]

Yes, rack is inside ip.