I'm sorry if this question sounds a bit noobish, but i'm having trouble figuring out how to connect the MS to the circut opening relay that acts as a fuel pump relay on the s4 NA, as the old ecu connected to the positive side of the coil in the relay and the MS grounds the coil in the relay. and there are two coils for what appers to be a single switch in this relay according to the FSM.

could somone give me an idea how to connect this to the ms?

thanks.

 

I'll have a look at the FSM later and let you know if someone else hasn't beat me to it.

That sounds different from the S5 NA ECU and relay.

 

I was just looking into this a few weeks ago. My setup is S4 turbo and the wiring is similar but not exactly the same. I have not connected a thing yet as I'm still in the planning stage and aquiring all the necessary items. So this advice has NOT been tested on a actual car.

There are three connections you need to know about:

1) ECU Connection 3B--I believe this connection only tells the ECU when the cranking signal is occuring. During cranking this connection should see 10-12v. MS will not need this connection. Just leave it unconnected at the MS but leave the wires and the rest of the harness untouched--they are needed to to activate the circuit opening relay while cranking.

2) ECU Connection 3D--This one is different than the turbo. Just leave this one unconnected at the ECU, again, MS will not need it. [For turbo owners only: On the S4 turbo this is for the fuel pump relay resistor, which is used to modulate the fuel pump speed. I plan to set up a MS output relay to keep this feature.]

3) Lastly, the most important connection, the brown (BR) wire going from the circuit opening relay to the AFM. Basically the MS will replace the AFM flow switch. Since you will not need the AFM any more, just run this brown wire from the circuit opening relay to the DB37 pin 37 for the MS fuel pump relay. Basically MS will provide the ground to keep the relay active. I haven't decided if I want to put another switch in series with the MS, maybe a oil pressure switch to cut the fuel pump when the engine should not be running. Normally MS will do this for you, but a second safety cut-out may be necessary (to each his own).

As always, trust but verify. Hopefully some of the other guys will chime in and let me know if this is wrong, but this is how I plan to hook it up. Maybe they could tell us more about the use of a second safety cut-out switch.

Good luck,

Scott

 

Thanks Rex4life, using the wire going to the afm was what i was thinking of doing but I wasn't sure. thanks for the advice on the other wires.

also i was wondering if connection C to the old ecu would be a good positive 12V source for the MS and if anyone knows which wire is which for the CAS connections (N,P,T,Q) as well as the trailing (X,U,M) the rest luckliy was pretty straight forward.