Hi guys, This job is a bit of a nightmare being my wifes car. She rang me Thursday morning to say the car wouldnt start, there was plenty of battery just not firing, this occured briefly last Saturday but started after a few goes.
We drove to York, 50 miles, parked up for about six hours and then got back to the car which stsrted first compression which was what it normally did. We then drove home ok and no more bother till Thursday morning.
I brought my laptop home Thursday night and checked out the engine management, there were no codes present and the data looked good showing RPM signal and other varying data from the sensors. it was dark now so decided to wait till Saturday and see what info I could find.
Saturday morning I checked for fuel at the filter, a brief spurt when key on then full flow when cranked, seemed ok. After taking off a few bits I managed to plumb a gauge into the test port on the back of the tandem pump, the data I found specified 3.5 bar at 1500 rpm so we cranked the engine and the pressure rose quite slowly I thought to about 2 bar, it then seemed to stabilize at this point but no firing so I clamped off the return pipe as it was cranking and this brought it up to +3 bar, at this point it started to get fuel and after a few second fired up. Whith the clamp off and engine running the gauge then showed over 3 bar and engine running normally. It seemed to me that the tandem pump had somehow drained of fuel so I fitted a non-return valve in its supply pipe. I ran it around for a while and it seems ok but morning may tell me differently.
Has anyone had a similar problem to this and has anyone got any detailed info on exactly what goes on in the primary fuel supply of these vehicles, there must be a pressure regulater built into the tandem pump I think, anyway thanks in advance for any thoughts on this.
Colin.

Colin
In tank lift pump.
Kev.

Hi Colin,
The pressure you are seeing at the test port on the pump is the cavity pressure in the head and not the pre supply pressure to the pump, thats why the spec you have is stated with the engine running at 1500 Rpm. HTH

Regards Mark

Thanks for your input guys, do we have a spec for primary pump supply pressure and flow because as I said in the post there appears to be a good flow to the tandem pump while craking but I didnt check the pressure at that point and I woul imagine that if the fuel system is full when the motor is turned off it should be ok to start next time. also earlier Passat PD model do not have an in tank pump.

Hello again, just tried an experiment, I unplugged the in-tank pump under the boot floor and then tried to start the car, it started first compression as uaual but only ran for about a minute then died, it then took about fifteen seconds of cranking to restart, its then ok again so it looks as though if there is already fuel primed in the system it doesnt need the in-tank pump to start. I have just found some good info here.
http://www.scribd.com/doc/37094435/pumpe-duse
you can download the pdf version of this which is very interesting.
Thannks for looking.
Colin.

Hi Colin, i done a Caddy not long ago it turned out to be the o ring seals around the injectors VW do a kit for these which includes a new set screw for the injector about £18 per injector.

As Mark said you are checking the cavity pressure not the pre supply pressure the one i done had about 2 bar cranking after about 20 secs of cranking when i replaced the seals it fired up instantly and run about 4 bar

be careful setting the injectors up when you replace the seals there is a procedure to follow
if you don't you could damage the injector

And they are about £400 a pop

hth

Kev Gundry

Thanks for that Kevin I'm starting to think somewhere down that line myself as it seems that the fuel had somehow drained away but there is no sign of any diesel in the engine oil yet and since Saturday it has been no more bother. We will have to wait and see I think.

Hi

Any sign of diesel leak from tandem pump ?

Cheers Aidan

Hi Aidan, no external leak I can see anywhere.
Thanks for looking.
Its been no more bother as yet.
Colin.

Have you tested the presure at the tandem pump? Should pump about 5 - 7 bar to injectors.

Also use a gauge to check for fuel line or filter blockages

Check the colour of the fuel, the tandem pumps also put oil in the fuel turning it black when they fail.

Hope this helps.

Thanks Richard, There was no black in the returning fuel and the pump was making three to four bar at idle. No more bother as yet, it looks like the one-way valve may have helped.
Colin.