Fuel Pumps

[Classik]

Forgot to say that the throttle body adapter test (can't remember the measuring group on VCDS) passed ok.

[Classik]

Oh and I changed the G65 High Pressure sensor, and I'm happy to say it's all back to normal on the HVAC front, so at least there's light at the end of the (long) tunnel..

[Shoppinit]

You sure about pin 2? It appears that it should be 12V from fuel pump relay, vis fuse 34. That feed also feeds a shed load of other sensors, so maybe you should double check the voltage measurement technique. Check between the battery ground and chassis ground for good measure. I *think* the 12V will be used for heating the resistive grid (which is then cooled by the air flow). With VAG, green / yellow is often +12V and black / green is often ground.

Pin 3 looks like ground, but *not necessarily* the same ground as the chassis. It's the ECU 0v for the signal circuit.

Pin 4 should be 5V, I believe. I think this MAF needs 5V for the signal part. Bit like how a 3 wire potentiometer works.

Pin 5 is the signal from the MAF to the ECU. It's a shielded wire and the shield drains to chassis ground. This is (presumably) the voltage that will change with the change in resistance due to different air flow.

What do you get if you measure (MAF disconnected) voltage between:
pins 3 and 4
pins 2 and 3
pins 3 and chassis

I suspect pin 1 is used on some models for intake air temperature. The RS6 has a separate sensor for that.

[Shoppinit]

Crackling doesn't sound right. Could be some gunk inside the throttle. Might need a clean on the butterly valve.

The insides of the throttle body position measurement bit are laughably simple. If anything was crackling inside that then you'd have warning lights all over the place.

If you leave the ignition on without starting the engine for 10 seconds, the ECU will carry out a throttle adaptation (not sure based on what other conditions).

Good news on the AC. That led you on a merry dance.

[Classik]

Alright, so the bad news is that my multimeter is not reliable as far as measuring low resistance is concerned. Now I read 6 ohms between pin 3 and chassis ground as opposed to the moving 30-40 Ohms mentionned before (facepalm emiticon). Sorry about that, in an hour or so I'll have a better multimeter from a friend and I'll redo the impedance measurements...

As far as the voltages are concerned, and I think those can be trusted (confirmed in an hour), I have :

- 1,8V between pins 3&2
- 5V between pins 3&4
- 5mV between pin 3 and chassis ground

Please note that the chassis ground is taken at the little ground hub, just below the brown exhaust gaz temperature sensor controller. Same voltage measurements when ground is taken directly from the intake manifold.

So more later with more reliable tools in an hour or so. Thank you!

[Classik]

Regarding the throttle butterly valve, you seem to say it can be cleaned or shall I consider looking for a replacement (more €€€... )?

[Shoppinit]

Yeah, they can be cleaned fairly easily. Once you’ve got it off of course.

[Shoppinit]

What have you got between pins 2 and chassis ground? And is it on both connectors?

[Classik]

With the borrowed multimeter (definitely need to change mine...) here are the correct figures:

pins 3 and 4 : 4.97V (confirmed with both multimeters)
pins 2 and 3 : 1.71V (confirmed)
pins 3 and chassis : 5mV (confirmed)

And to add to the list, I've redone the former measurements, ground is battery - pole:

Pin 1 : N/A not connected
Pin 2 : +1.75V on both banks (confirmed)
Pin 3: 12mV - Impedance to ground = 7 Ohms on both banks - No more variations thanks to the new multimeter
Pin 4: +4.95V
Pin 5: 12mV - Impedance to ground = 11 kOhms on both banks

Also the resistance between the chassis ground (hub below the brown exhaust gaz temperature sensor controller or intake manifold) is now measured at 4 Ohms compared to the battery ground.

So if I understand correctly, I have 2 issues here:

1/ Pin 2 which sould show 12V! Checked the fuse (OK), need to check the relay. I know there are all below the driving wheel, but do you happen to know which one is that?
2/ Ground between chassis and battery: I'd say 4 Ohms is slightly too much to my taste, what do you reckon?

[Classik]

What have you got between pins 2 and chassis ground? And is it on both connectors?

I read 1.72V on both connectors between Pin 2 and chassis ground, which seems coherent with the above taking into account the resistance between chassis and battery grounds.

[Classik]

Yeah, they can be cleaned fairly easily. Once you’ve got it off of course.

I suppose this should be OK if I take out again the bumper and radiator/condenser?

But still, would the dirt explain the crackling electrical noise?

[Shoppinit]

No, but it's hard to describe a sound. Are you sure it's not coming from somewhere else? A relay somewhere?

Also can you test the voltage at the N80? Both pins wrt chassis ground?

[Classik]

No, but it's hard to describe a sound. Are you sure it's not coming from somewhere else? A relay somewhere?

I'm definite that it comes from the throttle body. Add to that I get no more noises when the connector is disconnected.

Also can you test the voltage at the N80? Both pins wrt chassis ground?

Pin 1: 1.68V vs chassis ground
Pin 2 : 3.44V vs chassis ground

I suppose it's no surprise the difference is 1.76V, the exact same voltage MAFs are receiving on Pin 2? Bad relay then? (crossing fingers on that one!!)

[Shoppinit]

I can't believe anything at all would work if you only had 1.7V at all the sensors / actuators.

[Classik]

As mentionned earlier those measurements were made with key on, engine NOT started. Maybe a stupid thing to do, but that's how these were made. I'll come back asap with same measurements, engine started.