Won't boost above 12psi...

[daveforber]

I suppose the first answer is "maybe you shouldn't be trying"... but I am

I have a V40 2.0T (the one with the 12T turbo), and have had an MBC forcing 12psi for the last year. Recently set up an AFR gauge and thought to push it further, but no matter what I do it won't go above 12psi.

The MBC is screwed fully in now, and it's still 12psi.

I'm not exactly at my wits end, but it is annoying (I wouldn't have spent money on getting the AFR gauge set up if it wasn't possible!). Current suspects in my mind would be the recirc valve and/or the wastegate ... but the wastegate is surely controlled by the MBC?

There doesn't seem to be a boost leak as such, it just won't boost higher than 12. How do I check the recirc valve/wastegate operation, or am I barking up the wrong tree?

Thanks, as always, in advance.

[2-jaffacake-tone]

actuator not strong enough to hold boost? you could try removing the vacume pipe off the actuator and seeing what boost it makes carfully lol.

[Enigma666]

12psi on an lpt.....hmmm that would be about the limits I would push it to anyway I think.
The 12T is not a great turbo to tune with, get yourself a 14T instead, run an adjustable fuel pressure regulator (get yourself a 2.0 NA fuel return line from the breakers) then tune your car according to AFR
That or get the wastegate from a 14T and see what happens

[CONDYBOY]

I don't know what your limits are on the 2.0t but my 1.9d is at over 30psi
get a turbo from one of these babies and fill yer boots! whahey!

[Enigma666]

Over 2 bar on a diesel are you crazy?
That thing will go bang for sure mate

[CONDYBOY]

This is how it is, It was at peak boost 27psi when the pedal is floored in third or fouth gear, And over 30psi after the remap, I must point out that this is peak boost which drops to around 23psi quite quickly. Normal driving i.e. cruising at 50-70 mph the boost sits below 10psi.

[hamish]

CB,

27psi = 1.8 bar which is Spot On for a tuned Diesel. Enjoy.

Regards,
Hamish.

[CONDYBOY]

Cheers hamish, I am going off my boost guage which may not be accurate, but gives an idea of what is going on! as the diesel works differently to a petrol engine I had to plumb in the boost guage direct to the intake pipes and not to the CV system so I don't get any vac readings at all.

Any body wanting to fit a boost guage to a diesel? Here's a link to how I did it!
http://www.vpcuk.org/forums/showthread.php?t=15707

[daveforber]

actuator not strong enough to hold boost? you could try removing the vacume pipe off the actuator and seeing what boost it makes carfully lol.

Diesels? Pah!

Will give that a go (gently). Assuming it still doesn't go above 12psi, then am I looking at replacing the turbo/wastegate, or are they tweakable?

And if it does goes above 12psi, then presumably the MBC is at fault?

[2-jaffacake-tone]

if it still wont go over 12psi could be a weak actuator.

the actuator keeps the wastgate closed untill target boost is reached..

[daveforber]

2.5 turns on the actuator rod and it's a new car. Boosting to 14psi with acceptable AFRs, and spooling a hell of a lot quicker.

Thanks for pointing me in the right direction.