Reasons an injection pump can loose its prime overnight?

[Thezorn]

This I happenning to me. Very hard starts happend 2 days ago morining. Excessing cranking with now smoke, after a few minutes traces of white smoke once pump being to fill with fuel again, more and more smoke, then finally fires up.

Replaced the fuel filter and crappy plastic Tee yesterday. The fuel lines have always had the seldom air bubble coming from between fuel filter and tank, and equal as miuch from the filter to the pump never with any problems.

Im thinking about putting 2 shut off switches between the pump and the filter, one on the supply and one on the return to try and see wether the pump is leaking or there is a larger leak somwhere down the line.
There is no visible signs of a leaky pump as of today and no spilt fuel in the driveway.

Any ideas of what I should check or test to find my problem?

[745 turbogreasel]

an electric lift pump and clear return line  can show you a lot.

[410]

If you're sure that you're losing prime then air is getting in somewhere and allowing the fuel to go back to the tank.  Possible areas are loose hose clamps, or even a cracked line, that stupid tee which sounds like you changed already.  One spot people tend to forget about is the front pump seal.  You won't see a leak because it's not on the pressure side of the pump unless you have a lift pump.

[Thezorn]

One of the hard lines that went through the frame horn under the car had a crack, just big enough that I could barely feel the air pushing out when I blew into it, replace the whole thing with rubber 5/16's fuel line.
Im hoping this was the culprit.

In the back of my mind I was sorta wishing it was a leaky pump, would give me a good enough reason to finally send it to get built by giles

[bbob203]

get rid of the fuel pre heater. get a spin on filter housing or a filter with out the preheater. replace your in and out lines with transparent polyurethane. get rid of your water seperator.

[damac]

I found one of my hard plastic lines was fractured on my car where it was run up into the engine bay.  Wierd thing is I found it on level ground with the car off, it would leave a puddle.

Also I wonder if this can be caused by an old and used and abused governor shaft that is pressed into the ip lid?  I ask because I had a couple reseal projects and would run it from a can and different filters to start fresh with some issues I was having and my pumps did this.  I didn't see fuel dripping from that area and my pump seemed dry but I would see the same thing.  Next morning during a cold start the car would purge the air and make the car run rough for a tad at idle until it cleared out and all of a sudden ran ok on its own.  Very annoying.

The only reason I never replaced that part on my pumps is because I was stuck and the local bosch shop was far away.  That is something I must do in the future with the pumps I am putting back into service.

[Thezorn]

get rid of the fuel pre heater. get a spin on filter housing or a filter with out the preheater. replace your in and out lines with transparent polyurethane. get rid of your water seperator.

No water separator on the early AAZ's as far as I know, hasn't had a preheater on it since I got it, if not ever.

[745 turbogreasel]

Mine is leaking externally to the tune of a pool of fuel a foot long when I park, and a steady drip at idle
It still starts fine if cold, badly if parked 20-40 minutes, then all good again.
Luckily, the pump is off the car, and I have a seal kit in my hand.  too bad the shop is  so cold and wet.

[Baron VonZeppelin]

hasn't had a preheater on it since I got it, if not ever.

That T on the fuel filter - thats the preheat fuel filter set-up.
An 85-87 Jetta/Golf Diesel fuel filter eliminates that T.
Or maybe thats what you did ?

The simplest and most common things i find are the injector jumper hoses having a compromise - and/or the end cap plug on #1 injector.
About $5 puts it all back new.

After that -
Transparent fuel lines before and after filter, and the fuel return line, along with a MityVac tool - you can always pinpoint what area is compromised.

A small low psi diesel rated fuel pusher pump near tank can overcome most prime problems when all else fails. $15-25 on eBay. Also can extend the life or improve operation of a dying Inj Pump.

[R.O.R-2.0]

the advance o-ring, advance assembly, return lines from the injectors, and a few other things are usually overlooked by most, as air leak issues..

i dont use that crappy braided fuel hose for my injector return lines.. i use import vacuum lines, they fit tighter, and up to this point, are diesel safe.. ive been running vacuum line as my injector returns for YEARS now, and all its done, is gotten a little bit harder. its still way flexible, and seals up good tho..

[Thezorn]

hasn't had a preheater on it since I got it, if not ever.

That T on the fuel filter - thats the preheat fuel filter set-up.
An 85-87 Jetta/Golf Diesel fuel filter eliminates that T.
Or maybe thats what you did ?The simplest and most common things i find are the injector jumper hoses having a compromise - and/or the end cap plug on #1 injector.
About $5 puts it all back new.

After that -
Transparent fuel lines before and after filter, and the fuel return line, along with a MityVac tool - you can always pinpoint what area is compromised.

A small low psi diesel rated fuel pusher pump near tank can overcome most prime problems when all else fails. $15-25 on eBay. Also can extend the life or improve operation of a dying Inj Pump.

How does that Tee preheat? there is no externall power going to it?

I am starting to lean towards the pump having a leak somewhere. This morning I put 2 fuel shut-offs in the lines and had the return and supply both turned off all day while I was at College, it sat from about 8:30 until about 3:00pm, when I went to start it I turned the shut-off both open and still had the same problem as before.
I just dont understand where the fuel is going if I have the lines both blocked?

[bbob203]

How does that Tee preheat? there is no externall power going to it?

excess fuel from a warm ip on its way back to the tank opens a little valve in that t that allows it to drip warm fuel into the filter.

[Baron VonZeppelin]

I just dont understand where the fuel is going if I have the lines both blocked?

Your line(s) are draining back to the tank.
Means you have suction leaks - they don't always leave a wet spot.

Get new transparent hose before filter, after filter, return from pump.
New injector jumpers and end cap.

Then watch for suspicious activity from there.
Before restarts and while restarting, and while running.

[billybobf]

I picked up a car for $75 bucks, had the local pro shop shop, all they worked on was imports, the put an inline pump between the filter and the IP fixed the problem... for a while, slowly got worse as far as running went, told him he needed a new IP and the fortune it would cost him. I bought it, I pulled inline pump and replaced with clear line from filter to IP... BUBBLES, replaced the section of line from hardline to filter, no more bubbles. clear line is the most simple diagnostic tool IMO. put some on, let us know what you see

[bbob203]

another quick solution might be a check valve between ip and fuel filter.