What conditions will stop N75 operation?

[kingfishers2]

I have just completed a 20v turbo conversion for a friend and the car will not boost past 0.5 bar.
I have sofar replaced the DV, Boost leak test (OK), VAGCOM (no codes) and checked all fuses plugs ect.

I am assuming the N75 is not getting a signal from the ecu to change state, there is 12v at the plug when the car is running but it doesnt change state when the throttle is opened.
Which sort of explains the 0.5 bar as it will bypass straight to the lower chamber of the wastegate.
Will the ecu stop the N75 if there are problems elsewhere? im pretty stuck with this really as mentioned before there are no fault codes....??

[andy10v]

3B or ABY?

3B will limit boost due to water temp, faulty MFTS, faulty/corroded MFTS plug/wiring. (and throw no codes)

Martin had an issue with boost due to the altitude sensor on his ABY90q IIRC. (car thought it was a XXXX altitude)

[FITZY]

MFTS can cause this, I can speak from experience

[UrS4boy]

0.5 Bar = Wastegate Spring Pressure.

You have to have the ECU MAP sensor connected to the intake manifold via the hard green plastic line. If the MAP sensor doesn't see the boost signal, it can't/doesn't control the WGFV. Typically there is moisture trap (fuel condenser) between the intake manifold and the MAP sensor.

Moisture Trap info:

http://forums.quattroworld.com/s4s6/msgs/20401.phtml

MAP sensor info:

http://forums.quattroworld.com/s4s6/msgs/20417.phtml

N75 WGFV info:

http://forums.quattroworld.com/s4s6/msgs/20987.phtml

AAN boost signal hose in lime green:


3B/ABY/ADU boost signal hose in lime green:

[Kieron20V]

It may well be getting 12v at one pin, but the ecu controls the valve by pwm on the ground side of the valve.
Have you buzzed out the n75 plug to the motronic connector pin to make sure its intact?

[driftin jo]

If you have a problem/ wiring problem with the MAF sensor the ECU will turn off
boost control as will various other sensor malfunctions as mentioned, as you have no codes my guess is a dead N75, have you tried a different one ? Is it connected correctly ?

[kingfishers2]

3B or ABY?

3B will limit boost due to water temp, faulty MFTS, faulty/corroded MFTS plug/wiring. (and throw no codes)

Martin had an issue with boost due to the altitude sensor on his ABY90q IIRC. (car thought it was a XXXX altitude)

Its an ABY so that will rule out the MFTS its not interfaced on the ABY if im correct?
Will Vagcom show up the altitude sensor readings?
Cheers

[kingfishers2]

0.5 Bar = Wastegate Spring Pressure.

You have to have the ECU MAP sensor connected to the intake manifold via the hard green plastic line. If the MAP sensor doesn't see the boost signal, it can't/doesn't control the WGFV. Typically there is moisture trap (fuel condenser) between the intake manifold and the MAP sensor.

Moisture Trap info:

http://forums.quattroworld.com/s4s6/msgs/20401.phtml

MAP sensor info:

http://forums.quattroworld.com/s4s6/msgs/20417.phtml

N75 WGFV info:

http://forums.quattroworld.com/s4s6/msgs/20987.phtml

AAN boost signal hose in lime green:


3B/ABY/ADU boost signal hose in lime green:

I have a direct link from the intake manifold to the ecu at the moment so im sure the map sensor is seeing boost.

[kingfishers2]

It may well be getting 12v at one pin, but the ecu controls the valve by pwm on the ground side of the valve.
Have you buzzed out the n75 plug to the motronic connector pin to make sure its intact?

I ran out of light today but im planning on checking continuity on the loom tomorow, the solenoid clicks if you plug it in whilst the cars running so it must have a +12/GND to energise the coil, i think its more the actual operation that is the problem.

[kingfishers2]

If you have a problem/ wiring problem with the MAF sensor the ECU will turn off
boost control as will various other sensor malfunctions as mentioned, as you have no codes my guess is a dead N75, have you tried a different one ? Is it connected correctly ?

Its definatly connected correctly long port to intake hose i have 3x N75s so that rules that out!

[UrS4boy]

I have a direct link from the intake manifold to the ecu at the moment so im sure the map sensor is seeing boost.

But are you sure that the "direct link" doesn't have split or has come off the brass tube going into the ECU?

[newsh]

But are you sure that the "direct link" doesn't have split or has come off the brass tube going into the ECU?

That would make a massive whistling noise in the car

Have you tried the output test from vagcom?

[kingfishers2]

100% sure its a brand new conversion all the vac pipes are new and secure.

[UrS4boy]

That would make a massive whistling noise in the car

Not if the split or loose clamp was in the engine bay.

[UrS4boy]

I have a direct link from the intake manifold to the ecu at the moment so im sure the map sensor is seeing boost.

Just so you know, that moisture trap/fuel condenser is there for a reason and it helps to protect the MAP sensor from fuel vapours or worse (e.g. a failed fuel pressure regulator diaphragm will pump fuel directly at the MAP sensor, at least the moisture trap will slow that down).