Non starter help needed!

[UrS4boy]

There has been lots of discussion about Pin 37 in the ECU (Paul N, Dmitri, me, others). Bottomline: Prior to cranking, the injectors and MAF receive 12V *FROM* the ECU Pin 37 via the Holding Relay (powered via the switched power of Pin 18). Once the engine speed during cranking has exceeded 13 RPM, the J17 fuel pump relay is energized by the ECU via Pin 3. Then the power to the injectors and MAF comes from the FP relay via a fuse (S72 for the AAN). After the engine is shut off, the holding relay powers the MAF to burn-off the residue on the air flow meter wire.

If you turn the ignition on and you have power coming into the ECU on pin 37, you need to connect the T55 to the ECU and check for power on the black/red wires at the injectors (= holding relay is working).

Holding relay info: http://forums.quattroworld.com/s4s6/msgs/102009.phtml

J17 Fuel pump relay info: http://forums.quattroworld.com/s4s6/msgs/22583.phtml

Injector wiring info: http://forums.quattroworld.com/s4s6/msgs/90802.phtml

[andyg plym]

As ever thanks dave

I tested pin 37 again tonight and it appeared to have no power but I will try again once the battery is fully charged. Loom wise in theory it's unlikely to be the problem as its tucked away etc the common denominator is ecu end or the unit itself, it's been off a couple of times recently when chips have been swapped and now I'm sure the ecu plug is fully connecting

Final question is say pin 55 was broken so no power to obd port would this be any way connected to a non start ?

[UrS4boy]

As ever thanks dave. tested pin 37 again tonight and it appeared to have no power but I will try again once the battery is fully charged. Loom wise in theory it's unlikely to be the problem as its tucked away etc the common denominator is ecu end or the unit itself, it's been off a couple of times recently when chips have been swapped and now I'm sure the ecu plug is fully connecting.
Final question is say pin 55 was broken so no power to obd port would this be any way connected to a non start ?

You need to have 12V coming OUT of Pin 18 on the T55 connector with the ignition OFF. You need to have 12V coming out of Pin 27 with the ignition turned to ON (not START). Those are the only two pertinent pins that you can test with the T55 disconnected from the ECU.

You can not test Pin 37 with a DMM probe. It is an output FROM the ECU, not an input. You need to connect the T55 to the ECU and turn the ignition switch to ON (not START) and go under the bonnet and pull an injector connector and check for 12 V in the connector pin that is fed by the Black wire with the red stripe. If you have 12 V (or there abouts), you know the Holding relay appears to be working. If you have 0 V on the injector, but you did have 12 V FROM the T55 at Pin 27 with the ignition ON, then you have internal ECU issues.

Pin 55 is not stopping the engine from starting.

[andyg plym]

Well at present the car runs, I checked all the voltage to ecu plug, all is well, also to injectors, maf and fuse box

Earlier today it wouldn't fire up, it would stink of fuel but refuse to fire up. I opened up the ecu and inspected the internal holding relay, gave it a gentle tap put the ecu back together and it starts.

Now I can wiggle the ecu and wires as much as I like and it still runs.

Other things I did today were to change pin 37 and also I noticed one other obvious fault that was overlooked, the ecu housing that you remove each time- it had a slight dent in it that's been there for ages. When I gently pressed the dent it would cause the engine to cut out, must be the housing making contact with the circuit board and shorting, perhaps I had 2 faults ?

So regarding the holding relay.... Does it just go ? Or breakdown over a period of time ?

[UrS4boy]

Well good news. The dint in the Motronic cover might have been the issue. When you wiggled the T55 connector it might have just resulted in internal contact between the dint and a PCB or board component.

[Christophski]

Well done boy bout time!

[andyg plym]

Thanks guys just paranoid il go to start it in the morning and it will be dead

Be nice to drive it again !