Full boost only in 6th gear

[bertman]

The old girl only seems to getting near to 1.4 bar (homefries norm) in 6th gear only. 3rd,4th and 5th gear I am not really seeing anything above a crappy 1.24 bar.
Have tested for boost leaks and none have been found,but surely if it were a leak it wouldn't go up to nearly 1.4 bar
Thinking it must be an electrical gremlin...maybe
Any ideas what could be causing this problemo???

[Rocco]

in my car the maximun full boost always was in the last gear.....

[bertman]

From a previous thread I asked what the in-gear boost figures were for homefries,and the general rule of thumb was that you should see 1.4 bar in all gears except 1st and 2nd

[A80Avant]

lots of things to test.
first fault codes,
then:
MAF,lamda,N75,leaky DV, a leak on the vaccum hoses.

When you pressure tested,what part of the system did you test?

[bertman]

All of the parts are new,pressure tested the boost hoses and found no leaks.Haven't tested the vacuum hoses yet.I take it you take the metal bung out and let the air through the inlet manifold to do that?
A leak would affect the boost in all gears.....wouldn't it

[A80Avant]

if the leak is small it can be very mysterious.High gears produce pressure more easily so that you can actually see the boost you are expecting,but that doesnt happen with the rest of the gears.
vaccum hoses are best visualised,and probably take each end and blow into it.If you just put air in the inlet manifold,air will leak through the cyl.head and you wont know where it is escaping from.
Also you could be loosing air from the intercooler if you havent tested that as well.

[bertman]

That makes sense with the car producing higher boost,but surely with the "fries" it should produce the same amount of boost in the gears mentioned.
Blooming cars

[A80Avant]

yes that is when there are no leaks!
but when there are,its a different story!
do you hear any hissing sound in the car as well?

[bertman]

No obvious hissing sound at least

[Smiley]

Have you done a pressure test on the wastegate (diaphragm)?

[GazzaG60]

id say gate too. or exhaust leak. same thing different places.

6th produces more load and therefore gases so spool should be quicker and boost at its highest attainable.

[bertman]

Have you done a pressure test on the wastegate (diaphragm)?

Erm the answer to that one is ..no I haven't.Could it worth replacing that with funds from my measly christmas bonus.
Would a slightly leaky wastegate diaphram cause these symptons

[newsh]

Erm the answer to that one is ..no I haven't.Could it worth replacing that with funds from my measly christmas bonus.
Would a slightly leaky wastegate diaphram cause these symptons

No, a leaky wastegate diaphragm will likely give more boost not less IMHO. A bad WGFV might be the cause though, worth replaciing if its not that new. I usually leave the inlet tube connected and boost test to about 1 Bar, some pressure will leak past the rings and valves but you'll hear if any of the small hoses are leaking, still need to block off the PCV pipe at the MAF hose though.

[s2_bo]

Go easy on it if your only seeing full boost in top gear.


If you do have a small leak and its only managing to make full boost in 6th then you could be wringing the turbos neck as its trying to make your boost. Might be pushing it up to the equivalent to 2 bar.

my RS2 was like this for a while. Turned out to be a sneaky boost leak and now its fine

Check the Vac lines at the back of the inlet manifold, just blow in then like A80Avant suggested. they should all hold pressure.

Good luck.


P.s. if you do what John suggested you need to have a fully intact PCV system too or air will escape there as soon as you put any pressure past the pistons.

[ryster]

hi there thats the pcv system cheers