one for turbo experts

[Darran]

This is a boost run graph from a 1.8t ,is it n75 or wastegate sticking? any help appreciated plz

 

[DrStrange]

Hi Darran mate, long time!

I wouldnt know but definitely post this up on the A3 (8L) section of this website and watch the responses fly in!

 

[Darran]

Morning doc, ive already cured the problem,it was going to be one of my learning tuturiols but no one responded so i will keep the secret! Lol, nice to speak to you though

 

[DrStrange]

Morning doc, ive already cured the problem,it was going to be one of my learning tuturiols but no one responded so i will keep the secret! Lol, nice to speak to you though

Good to hear Sir.

Oh do share the secret. I think its just that us A4 B6 owners tend to be in the 'non tuners' bracket so anything to do with boost issues / Turbo / pipping are extensively covered by the A3 lads.

No doubt I will be asking a few questions your way as I think you still have the cabbie?!

 

[Darran]

Hi Doc,
Its n75 not working and bov faulty, causing massive boost!

Note to the wise,
NEVER presume a bov and dump valve do the same job, in theory they do in practice they operate very differently!

 

[DrStrange]

Hi Doc,
Its n75 not working and bov faulty, causing massive boost!

Note to the wise,
NEVER presume a bov and dump valve do the same job, in theory they do in practice they operate very differently!

Hi Darran,
Thanks for the tip and debugging.

To be honest, i did think they were the same.

 

[QuattroCalum]

Hi Doc,
Its n75 not working and bov faulty, causing massive boost!

Note to the wise,
NEVER presume a bov and dump valve do the same job, in theory they do in practice they operate very differently!

Don't you mean dump valve and recirculation valve? As far as I'm aware blow off valve and dump valve simply dump to atmosphere, but the recirculation valve is recirculated to the inlet system.

 

[Bradderz_1988]

Diverter valve - recirculates the metered air back to the intake so the fuel for the measured air that the MAF sensor has read to be calculated by the ECU doesnt run rich.

Dump valve - basically puts measured air to atmosphere hence if used on our cars will get a rich spot after throttle let off and gear changes as the MAF will have read the amount of air and the ECU has calculated the amount of fuel that needs to be injected for that air.

 

[QuattroCalum]

Diverter valve - recirculates the metered air back to the intake so the fuel for the measured air that the MAF sensor has read to be calculated by the ECU doesnt run rich.

Dump valve - basically puts measured air to atmosphere hence if used on our cars will get a rich spot after throttle let off and gear changes as the MAF will have read the amount of air and the ECU has calculated the amount of fuel that needs to be injected for that air.

Yeah, I know how it works, I was just pointing out that you had posted "NEVER presume a bov and dump valve do the same job" when essentially they are the same, a blow off / dump valve differ from a recirculating valve.
The N75 only controls the boost curve not the amount of boost.

 

[Bradderz_1988]

Yeah i didnt say that it was darran and wasn't getting at your post was just saying how each one works.

The N75 does control boost as it is controlled by the ecu which bleeds off boost pressure away from the wastegate which will have a cracking pressure of around 4psi so to up the boost it stops the wastegate opening at that said pressure till it see's the boost it wants to for 20psi the the N75 valve diverters the pressure at the wastegate thus opening it and keeping the boost at its desired pressure.

 

[QuattroCalum]

Yeah i didnt say that it was darran and wasn't getting at your post was just saying how each one works.

The N75 does control boost as it is controlled by the ecu which bleeds off boost pressure away from the wastegate which will have a cracking pressure of around 4psi so to up the boost it stops the wastegate opening at that said pressure till it see's the boost it wants to for 20psi the the N75 valve diverters the pressure at the wastegate thus opening it and keeping the boost at its desired pressure.

I was wrong, I got mixed up with the N249 solenoid, which wasn't even mentioned , N75 does indeed control boost via Ecu, sorry mate.

 

[Bradderz_1988]

No worrys we all read a little too quickly on here i think lol

 

[QuattroCalum]

It wasn't even there to read, my bad. I'm not usually guilty of that