.. Put the key forward to ignition and the fuel pump comes on for a second and shuts off. It happens maybe once a month and has only been starting to happen for the last 4 months.

From my knowledge, the fuel pump should only come on when the AFM says to, or the key is in the start position. I have noticed the check engine light goes out when it does this. Car is strong and runs well, so I am baffled by this.

The reason I bring it up is because it isnt supposed to happen, but at the same time, it isnt causing any issues.

 

I've heard from other posters that S5's will do this although I have no proof of this. If it's not normal then the ECU might be suspect as it is the ECU's job to provide a ground to the circuit opening relay when the key is turned to the on position but engine running. The ground would activate the relay to flow voltage through the fuel pump circuit w/key to on. If it's not normal then the Brown wire at the circuit opening relay can be checked. W/key to on and engine off the wire should have 12 volts and not a ground (very low voltage).

 

It rarely does it so I doubt I'd ever be able to test. I guess I'll have to either wait until it becomes an issue or just live with it if it doesn't.

 

I wonder if it is the signs of a sticky Afm?

 

I thought the same thing too, but ruled it out because in the event my car does this the fuel pump only runs for a second and then shuts down. I wouldn't figure the afm would magically unstick itself. Correct me if I am wrong, but if the AFM where sticking slightly the fuel pump would never shut off if the key was forward in the ignition.

99% of the time issues with my car are really freak problems which defy any sort normal automotive diagnosis. For example, when my engine was intermittently running on one rotor because of an intermittently failing injector. It wasn't the plug, it was the ******* injector itself.

 

S4 AFM has the fuel switch inside that places the ground on the Brown wire of the circuit opening relay. S5 AFM does not have this feature as the ECU is responsible for placing the ground on the Brown wire.

 

I just had a bingo moment!

I have been digging through the wiring diagrams for the last hour to help myself and that other poster with the CAS issue.

The S5 ecu is wanting an RPM signal to turn the fuel pump on. Since my remote start (i am an installer for a living) requires an rpm trigger signal, it is piggy backed off the leading coils rpm bullet connector. This wire runs through the driver side grommet to the remote start brain. Here is the bingo moment...

Since this wire is not shielded, it picks up an inductive "blip" from the main relay when I put the ignition forward. This inductive blip erroneously tells the ECU the engine is running for a split second.

 

Good deal!

 

I take that as you agree?

 

Not to go off topic jj, but someone told me you might know a thing or two about convertible headrest speaker wiring and troubleshooting?

 

Yesir, whats up?