D2 A8 Quattro no starter – Fuel pump relay wont energise.

[re2500]

Hi Fellas, sorry ive not been around lately, I hope you can help me with one of my current projects.
Ive acquired (don’t ask) a non runner D2 A8 quattro Sport. Ive tried a few things to get it going but my current hurdle is the fact that the Fuel Pump Relay -J17 (372 relay) won’t energise. The relay itself seems to be fine and if I bridge the relay I get 12v at the pump. I’m just not getting 12v to the pins that energise the relay.
Obviously this is controlled by the ECU, so my question is, what signals does the ECU require before triggering this relay?
VSS? Cam position? Etc
I believe (read hope) it’s not the ecu, due to the fact I have had it running for a few seconds at a time, at one point it was happily idling for a few minutes before randomly dying off.
I’ve already changed the fuel pump and fuel filter as a matter of course.

[UrS4boy]

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

If it is anything like the AAN (or ABY or ADU), the J17 fuel pump relay is energized by the ECU *ONLY* when the ECU gets a signal from the the G28 engine speed sensor that tells the ECU that the engine is spinning (or at starting, being spun) at greater than 25 RPM (or 13 RPM according to Paul N. here). This means that if the battery is weak and unable to spin the engine on the starter fast enough, the engine WILL NOT start because the fuel pump relay is not energized. Since the fuel pump relay also powers a bunch of other engine stuff, you can not just provide power to the fuel pump and hope the engine will start. However, as a test ONLY, you could try removing the cover on the fuel pump relay and jamming it engaged to see if the engine will start (assuming that the battery is still marginal but enough to spin the engine). Once the engine is spinning, the ECU in a AAN/ABY/ADU still needs good cam sensor and crank sensor signals to complete the starting process.

Read this for more J17 info: http://forums.quattroworld.com/s4s6/msgs/22583.phtml

[maxiice]

Hi
You should run a diagnose and check for errors, The ecu need signal from trigger and cam.

[Ryss]

Just in case we have a miss diagnosis of the problem.

I believe that the D2 has a horrible arrangement of the tank, where fuel is lifted from one side of tank via a venturi effect into a bowl from which the pump delivers fuel. Or something like that.

If this plastic confusion of pipes and venturies cracks no fuel will be delivered to the engine when fuel level drops below half, even if the pump is running.

Something to watch out for! And maybe some one with a bit more knowledge of this problem, can add some light.

[re2500]

Ok, so there is a possibility it could be a bad g28 engine speed sensor , cam sensor or trigger sensor (crank I assume). The battery is fully charged and turning the engine over quickly. Just no 12v to energise the the pump relay. If I hard wire the pump then I get fuel flow. Thanks chaps