Thread: Runaway Diesel engines

I had one back in the early eighties when i was a young mechanic.
I took a Mercedes Benz tractor unit on road test after a service.
The apprentice put too much engine oil in the unit and it took off on me......had to stop it on the brakes and cut the motor.
Drain excess and all OK.
Also once i saw a Detroit Diesel run on in the workshop......the guy pulled the engine stop and it wouldn't cut the engine. Everyone ran and hid...noise, smoke,bang.
W

I remember as a apprentice the mechanic I was assigned to helping with a GM diesel.
We had just finished dropping in some injectors after over haul.
It was started in the engine stand for testing..........and the thing ran away.
The emergency stop flap was not fitted.
The fuel rack/ injectors had a problem.
We were too busy hanging onto the big silly lump to do much.
The mechanic ended up putting his large bear gut over the air let and stopped it that way.

Starting motor with vacuum pipe disconnected or it somehow not functioning on diesel motors with pneumatic governors is one possible cause of runaway not so far mentioned. With a pneumatic governor, a very simple and effective device except that slow idle speeds tend to go up and down a bit, all the throttle control does is open or shut a butterfly in the inlet manifold. The vacuum created when the motor revs up and air intake is restricted sucks in a diaphragm controlling fuel delivered by the injector pump. The more the butterfly is opened, the faster the motor will run before diaphragm pulls control rod to reduce fuel delivery.

One example of engines with these governors is the 3.152 Perkins (ie 3 cylinder 152 cubic inch) as fitted to Fordson Dexta tractors. Have Simms inline injector pump and not the more common CAV rotary as used on eg Massey Fergusons. Around 45 years ago, I remember seeing a collection of bits from a disintegrated engine - forget what make/model that was started while the vacuum pipe was disconnected. Unfortunately its breathing capacity limited by valve timing etc allowed it to run faster than some components wee strong enough to take and the throttle was not closed quickly enough if at all to try and stop it.

Originally Posted by rar110

Fuel cut off can't be working. It's a little electric motor on driver side firewall driver side of pedal box,enclosed in a plastic bag. A pull cable runs to the injector pump to cut the fuel.

I got rid of mine and just use a pull cable in the cab.
Pull to stop, same as a series.

Keith

Here’s my temporary solution.

Well my problem is not a runaway motor, just idles away but will not stop when the ignition is turned off.

There have been many valuable suggestions from the forum, and while following various wires and cleaning terminals and earth points,
I have discovered a disconnect wire at the oil pressure switch/ terminal (photo attached)
That switch /wire is on the circuit according to a (Image wiring circuit for edic motor)

I have tried undoing the oil pressure switch with a good size shifting spanner & WD40, no luck at this point, any suggestions
I don't want to brake the housing its screwed into.

Thanks.

Cyril I reckon the problem is connected to the stop control. The thing in the white bag with cable going to fuel pump just below the air intake pipe in your 2nd pick. The oil pressure switch will stop it going from memory. But not stop it shutting down.

YouTube

Very likely a case of high oil dilution as per JLRP00100.