MD6B some more clues to problem

C

crown28owner

.
Jul 23, 2005
16
When cranking with the starter motor (or by hand for that matter)
for the first few revolutions the fuel is ejected out of the
injection pump, as soon as it reaches a certain rpm after cranking
for 3 or 4 seconds with starter and right when the engine wants to
start the diesel stops coming out of injection pump ?

When I disconnect the lines off the injectors I can see this clearly
everthing fine and then just stops after a few rotations, interestly
if I leave the compression lever open and then crank there seems to
be no problem the fuel keeps coming as you'd expect, slam shut the
compression lever and the fuel stops, next attempt same thing no
hand priming or anything required.

This does not seem to be an problem of not enough fuel getting to
the injection pump, lots of fuel at the feed line on the pump. Could
she be sucking air downstram of pump and only becomes a problem
after a certain RPM ? Is there something in the pump that could
kick out at a certain RPM.

Anybody over here on the west coast of Canada ?

Kevin
 
C

claudiomty

.
Oct 31, 2019
40
Hi Kevin
Disconnect the feed line from the injection pump. Put a piece of rubber
fuel line on it and deposit it down into the bottom of a clear soda bottle
of your choice. Now crank her a bit, After the initial purge of air from the
hose you should get fuel steadily filling the bottle. Mine will fill a
16oz/450ml in about a minute with the starter. Even if you only get 25% of
that it still far mor ethan the engine can burn.

What your looking for is bubbles or foam. If you get any the problem will
be between your primary lift pump and the tank. Our pumps will tolerate no
air or foam. I causes the high pressure side of the injection pump to fall
off in pressure as soon as the foam starts. If you stop and wait, or hand
crank and the pump turns slowly the air bubbles will move up and out through
the return line. If the pump is spinning at speed the bubbles get "swirled"
around with the fuel in the pump, makes foam, bye bye goes the pop pressure.
Stop and wait and it accumulates at the top of the pump, hand crank it gets
purged, starter cranking and it foams.again.

Let us know how it goes.
Claude
V1460
 
S

stevebirch2002

.
Nov 8, 2001
1,818
Hi

When the Brits sailed to Holland in 2000 for the IFR we had a similar
problem with Jenavive, the difference was she kept stopping every 4 - 8
minutes. Turned out to be the pipe inside the keel tank had a very small
pinhole at the top and was sucking air that accumalted and every 4 - 8
minutes tehre was enough to stop the engine (It was a Beta but the fuel
system was the same). Have a look or feed your Volvo from a jerry can
above the engine direct to the lift pump.

Cheers

Steve Birch (Technical)
 
C

crown28owner

.
Jul 23, 2005
16
Hi & thanks everybody for the ideas...I doubt anybody can make much
sense of this but I'll give it a go

Firstly I hooked up a jerry with fresh fuel right into the injection
pump intake (gravity fed), this made no difference, fuel stopped
after a few rotations, I then disconnected the line from the fuel
return on the injection pump and feed into a jar, this did not help
either, fed thru a couple quarts of fuel this way.

I made a bit of a discovery, I normally just disconnnect the line off
the front injector to see if the fuel is pumping but I decided to
disconnect both injectors and the fuel kept coming, while still
cranking if I reconnect either one of the fuel lines back to the
injector then the fuel stops on the other disconnected line and
presumably both lines.

Just for something to do I pulled the injectors and had the same
result they pop and spray fine all day long when turning very fast by
hand but just for the first few rotations on the starter. After
putting it all back together I took the lines off the front of the
pump cranked and let her spray out making a nice mess for 30 seconds,
lots of force and shoots out 2 or 3 feet non stop.

Now that I'm back home I'm thinking (after a couple pints)...air gets
into injection pump right at the fuel intake connection, pump still
works pumping out air and fuel out the injector lines ...this is all
good till I connect one injector and bubbles get into injector, this
gas prevents the injector from popping and puts some sort of back
pressure on the pump shutting down both sides ?

Maybe I still have a bubble problem.

Kevin
 
B

bbach1949

.
Apr 30, 2000
197
I'd take the pump off and have it tested or find a way to test the pressure
in place. Sounds like it's not developing full pressure to work against the
compression of the engine. This would take less time than you've spent so
far. Bill Bach V1071 (Yanmar 2GMF)
 
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