Mitsubishi Delica Owners Club UK™

[cybersquid]

Hi all.
After changing the seal on the fuel pump (Zexel / Bosch type on a L400) the weekend before last my sump was filling up with diesel!

I've taken the pump off again and checked the seal - there is some evidence of scoring on the rubber and a slight burr on the shaft. I've smoothed the shaft with various fine grades of paper (finished off with a little autosol) ready for the new seal.
I checked the fuel return pipe (the one from the pump to the fuel tank) and it appeared to be blocked. I've now cleared the blockage (with a quick blast of compressed air).

Any other ideas as to why it may have been leaking?

Many thanks.
Tony.

[Google]

[tttonyyy]

Mine had a blocked return pipe for the previous owner.  For him it caused stalling, I don't see how a blocked return would cause the seal to blow by?

Also was there any play on the pump shaft?  I spoke to a pump specialist before doing mine and he told me that sometimes they get those pumps with shaft play so just replacing the seal won't help, the pump would need a recon.

[cybersquid]

Thanks tttonyyy.

No play on the shaft at all!

I assumed that the blocked return pipe would be enough to build up pressure in the pump and cause it to leak out of the front seal. Is this not the case?

Tony.

[strangerover]

forgive the silly question...

have you fitted it the right way round ?

it should look like this....

ready to install



installed


_________________
Regards
Mark

[tttonyyy]

My pump shaft had a groove around it that the top lip of the seal rides in, was that aligned okay?

[cybersquid]

Yup. Definitely the right way around
Yes, also a slight groove in the shaft - didn't line up the the lip of the seal though. Pushed the seal all the way home (using the appropriate deep socket).

Tony.

[delart]

Hi if the shaft has got burr on it, it must be making contact against something hard enough to cause it

[tttonyyy]

Considering that shaft is pretty hard...

How was the old seal removed?

I drilled a 2mm hole in the outer edge of the seal, put in a screw and levered the old seal out by gripping the screw with a pair of pliers and using a screwdriver to lever up between the pump and the jaws of the pliers (actually my missus' idea).  No damage to the pump, seal came out fairly easily.

Strangerover, I notice you have a dimple in your pump where the seal sits, was that from drilling a little too deep?

[cybersquid]

The old seal was removed using the drill and self tapping screw method - pulled clear with the trusty mole grips. Came out easy - no damage done.
There is a wear line on the shaft - presumably from the lip of the old seal (rubber will cause this on a hard steel shaft given enough time). The wear line did have a small burr on it (just enough that you could feel it with a finger nail). The pump shafts are machine finshed (and not polished) I wouldn't have though it would be enougth to damage the seal to any great extent.

Considering it pumped about 4 litres of fuel into the sump in about 20 minutes isn't the problem likely to sit elsewhere?
Does the pump pull up an amount of fuel (based on engine speed), inject a metered amount, and then leak off what isn't used to the tank?
Is the amount of fuel sucked up from the tank regulated by the pump?

Tony.

[tttonyyy]

I don't really know enough about how the pump works.  I know that on the high pressure side the injectors pinch off at 1950 psi and the excess fuel from that stroke comes back down the leak-off pipe from the injectors to the back of the pump and then on to the tank, but I don't know if the lift part of the pump also provides excess fuel and returns the rest to the tank down the same pipe?

[tttonyyy]

The internet knows the answers:

http://www.dieselbombers.com/1st-generation-dodge-cummins-89-93/21942-bosch-ve-pump-operation.html
http://etc.gnarlodious.com/Vanagon/Bosch_Pump/-Rebuild.html

Looks like the lift side does indeed have it's own pressure regulator from the vane pump, returning the excess to the input.  And that's the first thing on the drive shaft.

[cybersquid]

Thanks.
Just found this http://www.htsuk.plus.com/BOSCH_VE_PUMPS.pdf
I will have a read up and find out how the whole thing works. Being a bit of a tight wad I refuse to buy a new pump if it something I can have a go at myself

Tony.

[cybersquid]

Thanks for the great links. Looks like I've got some reading to do tonight

Tony.

[tttonyyy]

I totally subscribe to your way of thinking too Tony   :D

Also going to do some reading, was just skimming through and didn't realise that the cold start mechanism not only pushes on the throttle lever but also advances the injection timing via a cam on an internal advance piston.

Very clever (and complicated!) bits of kit.  

[tttonyyy]

From that PDF you linked:

"The vane-type fuel-supply pump draws fuel from the fuel tank. It delivers a virtually constant flow of fuel per revolution to the interior of the injection pump. A pressure-control valve is fitted to ensure that a defined injection-pump interior pressure is maintained as a function of supply-pump speed. Using this valve, it is possible to set a defined pressure for a given speed. The pump’s interior pressure then increases in proportion to the speed (in other words, the higher the pump speed the higher the pump interior pressure). Some of the fuel flows through the pressure regulating valve and returns to the suction side. Some fuel also flows through the overflow restriction and back to the fuel tank in order to provide cooling and self-venting for the injection pump (Fig. 2). An overflow valve can be fitted instead of the overflow restriction."

[cybersquid]

Cool. Time to get the pump apart and see what's not working
Thanks for your help on this - much appreciated. The Deli has been off the road for over a week and I'm missing it  
Will let you know how it all turns out after another weekend of home mechanics...

Tony.

[tttonyyy]

You sir, are a braver man than I  

[strangerover]

make sure you have a DTI gauge and the special tool to use it

your going to need it if you do a full strip down !
_________________
Regards
Mark

[cybersquid]

Always up for a challenge  

Thanks Mark. I'm sure I can borrow these from somewhere...


Tony.

[cybersquid]

okay, so I bottled it a got a recon pump.  Running like a dream now

Thanks everyone.
Tony.