Can someone explain this?

[MattS2]

My car has sat outside idle over the Xmas period
I tried to start it the other day but it would not fire up, just turning over.


I decided I would have a little look today and plugged in Vagcom, getting the crank position fault (0513?) and also an intermittent cam position sensor G40 fault (0515?).

I don't normally touch the S2, preferring to leave it to my trusted mechanic, but on this occasion I had a fiddle.

I pulled the small pipe off the fuel regulator to see if there was fuel present on turning over. - There was no fuel.

I manually activated the fuel pump relay. - I could hear fuel flowing through the pipe work but still no fuel through the small pipe.

I then tried to start the car after reconnecting the pipe to the regulator. It fired up almost immediately.

All Vagcom faults cleared.



So my questions are,

A - What does the small pipe do coming off the fuel regulator?

B - What did I do that made the car start?

C - Should I get the G40 sensor replaced?


Cheers


Matt

[newsh]

The small pipe from the FPR is the vacuum hose which feeds the vacuum or boost pressure to the FPR.

Maybe you disturbed the G40 sensor connector?

[Error404]

1. Small pipe is the vacuum line - it doesn't flow fuel but supplies vacuum/boost to the regulator.
2. IIRC the ECU needs to see the cam sensor input in order to activate the fuel pump relay. Sounds like the G40 is lazy/one the way out to me.
3. Yes I would change it


EDIT: beaten to it by John

[driftin jo]

Intermittent cam position sensor G40 fault is why your car wouldn't start, the small pipe is manifold pressure ref to the reg. The rest is a coincidence. Check the contacts for water ingress on the g40 connector, leaving it at this time of year may have caused condensation water ingress, if it does it again after cleaning contacts and applying a little WD40 to keep the water out then replace it.

[UrS4boy]

Fuel Pressure Regulator Info

So my questions are,
A - What does the small pipe do coming off the fuel regulator?

As already answered, that is a vacuum line, as shown in the diagram below. More FPR in the link:

http://forums.quattroworld.com/s4s6/msgs/21108.phtml

[UrS4boy]

I decided I would have a little look today and plugged in Vagcom, getting the crank position fault (0513?) and also an intermittent cam position sensor G40 fault (0515?).

Crank position sensor fault will *ALWAYS* show up when the codes are pulled on an engine that is NOT running. That was a false positive.

The G40 cam sensor intermittent fault might be real:

http://forums.quattroworld.com/s4s6/msgs/139944.phtml

General G40 info:

http://forums.quattroworld.com/s4s6/msgs/22580.phtml

[europeanme]

is there enough power in the battery to run everything?.....mine gets very temperamental if I don't run it for a while and a fresh charge seems to sort it out...just a thought

I've still got your injectors

[UrS4boy]

J17 Fuel Pump Relay and why it is important to an UrS

2. IIRC the ECU needs to see the cam sensor input in order to activate the fuel pump relay. Sounds like the G40 is lazy/one the way out to me.

The ECU does require the G40 cam sensor and G4 crank sensor inputs to actually start the car. However, only the G28 engine speed sensor is needed to provide the signal, i.e. > 13 RPM, to trigger the J17 Fuel Pump Relay.

More J17 FPR info: http://forums.quattroworld.com/s4s6/msgs/22583.phtml

[UrS4boy]

is there enough power in the battery to run everything?.....mine gets very temperamental if I don't run it for a while and a fresh charge seems to sort it out...just a thought

If the battery is too weak to power the starter enough to spin the engine at > 13 RPM, the engine will not start because the J17 Fuel Pump Relay will not be activated.

http://forums.quattroworld.com/s4s6/msgs/22583.phtml

[MattS2]

Thank you for the replies

I don't think I disturbed any connectors but I will be sure to check them and I understand the crank sensor fault being false.


The links giving details on the G40 sensor are great but I don't think I'll be swapping it myself

Mike - No rush with the injectors bud

Matt.

[S2central.net]

I have a G40 tester that plugs right in if you want to try. Without good G40 signal the ecu has no clue what phase the engine is on for cylinder 1 and beyond. You can lash up a tester with a 5v led if you have one.

[MattS2]

I have a G40 tester that plugs right in if you want to try.

Thats a very kind offer thank you Paul.
I will keep it in mind.


Matt

[europeanme]

If the battery is too weak to power the starter enough to spin the engine at > 13 RPM, the engine will not start because the J17 Fuel Pump Relay will not be activated.

http://forums.quattroworld.com/s4s6/msgs/22583.phtml

it was just an idea Dave as mine just turns over and there is the distinct lack of drone from the fuel pump but once the battery gets some more juice in it, it starts no problem...

[UrS4boy]

My car has sat outside idle over the Xmas period
I tried to start it the other day but it would not fire up, just turning over.Matt

I should have just linked you to this (previously posted here):

Reasons why your AAN (or ABY or ADU) isn't starting:

http://forums.quattroworld.com/s4s6/msgs/210191.phtml