FUEL PUMP FAILURE

wotwot · Unread post by **wotwot** » 03 Jul 2011, 13:11

I have another post on going at the moment (dispatch fuel pump),
and just out of wanting to know what stops pumps from pumping when they DIE.
Now I dont mean the immobiliser or stop solenoid, I mean the solenoid has its plunger and spring removed and refitted.
So no electrics to the pump at all and assuming the timing is correct.
If I take an injector feed pipe off the back of the pump and crank it over and no fuel comes out WHY.
Would something inside the pump be so badly worn that it wont push any fuel out.
Please ask questions if this sounds strange my grammer is not the best,it sounds right when reading through the post.
MY TINY BRAIN HAS TO KNOW

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Unread post by **Peter.N.** » 03 Jul 2011, 14:05

Possible but very unlikely. Are you sure you have a good feed of fuel into the pump? Does it have a throttle lever or is it fly by wire?

Peter

wotwot · Unread post by **wotwot** » 03 Jul 2011, 16:16

Hi peter and thanks for the reply,
I am refering to manual bosch pumps with no electric supply whatsoever,so cable operated
and fuel is being sucked in to the pump.
This was a general question about all pumps really,although mine is DEAD.
I have heard people discuss pumps becoming weaker and not pumping enough,this I assume comes over a period of time.
Can anything fail inside the pump itself.Again not break as such but wear out.

Unread post by **Peter.N.** » 03 Jul 2011, 17:44

I can only speak from experience and I have never had a Bosch pump fail and one of my cars has done nearly 300,000 miles. If you operate the primer can you hear the fuel flowing through the pump?

Peter

wotwot · Unread post by **wotwot** » 03 Jul 2011, 19:44

Yes when pumping by hand you can even see the fuel going into the pump as it has a clear tube onto the banjo.
But as said it was more of a general question regards to bosch pumps,and if parts inside wear to an extent where fuel does not come back out of the pump.And which bits would stop it working.
On my other post I said on there that I had spent an hour drip filling the pump till it would not fill anymore just to see if the pump needed priming.
This post is more of a investigation than a fault finding post.

Unread post by **CitroJim** » 03 Jul 2011, 19:56

Apart from a catastrophic mechanical failure inside, there is very little that'll stop a Bosch pump from basically functioning.

One potential cause may be broken plunger springs but even then it might just manage to fire and run roughly with a bit of din.

About the only thing that'll really suddenly stop them dead is a failure of the stop solenoid. Did you try Andy's suggestion of taking the plunger out of the stop solenoid and trying it with no stop solenoid in place?

When did the engine last run and when last run, was it OK?

Generally Bosch pumps don't suddenly die, they just fade away...

wotwot · Unread post by **wotwot** » 03 Jul 2011, 21:07

Thanks Citrojim yes taken solenoid out and removed spring and plunger,
but still no fuel.
So even if parts inside are worn fuel would still come out. When
I know there is a seal kit for pumps but is there a service kit for them,and would it be economical to get one or better to just get a known good pump.
reconditioned pumps seem very pricey do they replace much inside them.

Unread post by **CitroJim** » 03 Jul 2011, 21:21

That's odd. It's just possible the HP pumping element has broken. It's made of very brittle material but it's a rare failure. That's about all that would stop it dead in its tracks.

A properly reconditioned pump will have many new parts inside but mainly the cost is in the expertise of the builder and the test/calibration. Both are expensive, the first from a wages point of view and the second from the cost of the test bench on which the calibration and testing takes place. We're talking of a price that looks more like a telephone number...

Pumps can be successfully resealed without all the calibration palaver but not on a commercial basis as the work cannot be warranted.

Unread post by **Peter.N.** » 03 Jul 2011, 21:22

the only thing I can think of trying is to temporaraly blank of the return pipe so as to build some pressure up in the pump and see if that has any effect.

Peter

wotwot · Unread post by **wotwot** » 03 Jul 2011, 21:42

Thanks for that guys.
what does the HP pumping element look like now we have the pump off, we were thinking of having a peek inside to see if we could learn anything from it.
After all we're thinking it is dead anyway so maybe we can find the cause of the failure.
We had thought of that peter but what would that achieve,if it did start pumping fuel out what would be the fault within the pump.

Unread post by **CitroJim** » 03 Jul 2011, 21:46

Have a look here. It shows the HP pumping element quite clearly... It's the rod that goes into the distributor head. It pumps with a reciprocating motion. In those pictures you can see the big plunger springs.

These pages show how to dismantle some other aspects of the pump.

wotwot · Unread post by **wotwot** » 03 Jul 2011, 21:52

Thanks for the links will have a look tommorow when i gat the pump on the bench.

wotwot · Unread post by **wotwot** » 04 Jul 2011, 08:20

Nicely described and laid out photos of a bosch pump.
Cant wait to get to grips with the strip down and investigation on why the pump has failed,if it has???.
still dont understand how they fail so will be good to get stuck in.

http://gnarlodious.com/Vanagon/Bosch_Pump/-Rebuild#84

Edit does anyone know of a good source for the seal kits,I live in essex so if the supplier is close enough I could pick up would be even better.

thorter · Unread post by **thorter** » 04 Jul 2011, 10:18

As the pump works in suck mode, failed pump = no fuel. A way to check if it is a failed pump might be to fix up a temporary feed from a can or similar about a foot above the pump. If it starts - fault identified, but there’s no guarantee it can’t fail blocked!

Fred

wotwot · Unread post by **wotwot** » 04 Jul 2011, 11:26

Cheers fred we did spend an hour feeding fuel in by hand drip by drip to see if it needed pre priming,in this respect I think something is amiss inside the pump.
When i strip it I will come back and report my findings be they good or bad.
I'm in the mind of Well what can go wrong if nothing is physically broken inside.
Should be an interesting fact finding mission.