AAZ probs - injection pump from JX?

[dekhelia]

Finally got my AAZ lump in, but suffering a few teething troubles. Would be very grateful for any thoughts!

Firstly, I don't think I'm getting any diesel though the injector pump. I've actually manually filled up the pump on the IN side, till it dribbles out the RETURN side. So there's fuel in there. But after cranking, if I crack one of the injector pipes, they're dry. Also, there seems to be a pool of diesel collecting under the pump and dripping down the block. So there may be a problem with a leak, although nothing obvious stands out as a source.

The engine itself was always a bit of an unknown, as it came with a van that I bought in Germany as a spare that they guy always intended to put in, but he didn't know if it worked either. Anyway, blah blah - I know the engine works because I've had it running on Easy Start for a few seconds, and it sounds fine.

The injection pump on my knackered JX is a known working pump - can I just put this pump on, or are there significant differences of size, set-up, belt lengths, calibration etc?

Likje I say, any input will be appreciatively received.

[colinthefox]

The injection pump consists of two pumps really. There is a low pressure vane type which sucks fuel up from the tank and fills the pump body, and a high pressure pump which takes fuel from the pump body and squirts it at very high pressure to the injectors. The vane pump has to be completely full of fuel, or it won't suck fuel, and won't pump fuel to the high pressure side of the pump. Then the high pressure pump and the injector pipes have to be completely full of fuel, or it won't pump to the injectors.

First you have to fill pump body by any means possible. It sounds like you have done that. Then you have to make sure all air is driven out of the low pressure pump body so the high pressure pump has a supply of fuel. (I don't know about the AAZ pump, but there is usually an air bleed screw on the side of the pump to do this). Crank the engine till fuel without bubbles comes out of the bleed screw. Once you are sure the pump body is completely full, you slacken all the injector unions at the same time and crank the engine till fuel squirts out of all the slackened unions. Once every bit is completely full of fuel, the engine will start providing compression and glowplugs are OK.

Injection pumps are very long lived, and rarely knackered. It can be very frustrating bleeding an empty pump until you know what is going on inside. Having said that, it sometimes happens that a pump which has been standing empty gets sticky vanes in the low pressure bit, and the engine will idle but not rev. That's a different problem, which may cure itself if you leave it idling for long enough.

Another problem can be leaks. Firstly check the back leakage pipes (they are the braided rubber pipes which go between the injectors, and the rubber cap on the last injector). If you have a leak in those, or anywhere else, all the fuel can leak back intothe tank as fast as you suck it up. If in doubt get new back leakage pipes from any motor accessory shop. Check all other joins for even the slightest leak.


Forgive me if I'm telling you stuff you know alrerady. I have assumed scanty knowledge.
Oh and if you fit the old JX pump, it will only give the same power as the old JX, cos it's only pumping the same amount of fuel, give or take a bit. And you'll have the same problem bleeding that pump too!

[dekhelia]

That's very helpful, thanks. Pretty much all of what you've said is enlightening, as my knowledge in this area is almost nil (much more used to petrol engines).

Given what you've said about the difficulty of getting the pump/pipes et al full of diesel, do you think it would help to tow the van off, and let the system prime that way?

I really don't want to have to change pumps if it's at all avoidable [suicide smiley thing]

[colinthefox]

I really don't know about towing to prime the system. It's straightforward to do once you understand what's going on. But last time I did my tractor I got it wrong first time!

[mm289]

Easiest way to prime is to put a vacuum on the return pipe side of the pump. I use my auto brake bleed setup, but any vacuum will do, even a manual "bulb" type pump primer.

This will suck diesel right through the pump and then your good to crank until you see the fuel at the cracked off injectors as per colins post.

If you search on here/brickyard for pump problems you will find a couple of posts discussing pumps that have been standing for a while refusing to prime/pump. IIRC it was to do with the vanes seizing on the pump from standing (especially if not full of diesel and damp gets in), then the low pressure side doesn't draw fuel through.

Cheers,

MM

[dekhelia]

That's useful to know, thanks. I have a solo brake bleeder kit so I shall try that next.

Do I need to crack the injectors before turning the engine over?