Mechanical boost far too low

[Dr H]

Ok the saga continues...................

Follwoing on from the 'still got a ****** boost leak thread' I have been testing the mechanical boost on the car. With the WGFV disconnected the car refuses to boost over 0.5 bar. This is even at 4k in 6th doing 90mph up a hill with my foot on the floor

I turned the WG spring down in stages and by the time I'd got to 5 full turns I had only gone from just over 0.4bar to no more than 0.5 bar. Doesn't show any signs of a leak just very slowly makes its way up to 0.5 bar and then stays there.

With the WGFV connected the car boosts to 1.4-1.5 bar (but obviously looses it from an apparent leak).

So the strater for 10 in this round of the quiz is................What is causing my low mechanical boost?

[Doug_RS2]

That sounds like it is leaking - but only above 0.4Bar - so you will need to test it at over that.

Have you changed the diaphragm Leigh? I would get a new one in there anyway. Make sure the thread is not damaged on the shaft - and use loctite - this is just to make sure you get a good seal through the shaft.

A silly question - is the wastgate sitting on the exhaust manifold properly and screwed down right?

I have a spare wastegate but need to swap mine over - I think Paul N has one as well.

[Doug_RS2]

Have you replaced the hose that goes from the wastgate to WGFV?

[S2central.net]

Just thought of this one - I seem to recall testing your WG diaphragm and it was OK, but as your WG was tampered with in a past life, it might be worth checking that the valve moves freely and that its not stuck partially open somehow... Carefully remove the cap feel that the valve moves OK.

You are welcome to try my spare WG if you think its worth a rattle.

[Dr H]

Guys

Have raplaced the hose to the WG. Couldn't find a silicone one at the moment so went for a standard (fuel grade) piece of 8mm hose. Will replace with silicone soon but seems fine at the minute.

Not changed the diaphragm so maybe that it worth a try - how much?

Will go and check the valve now and reprt back.

Cheers

[martinjs]

Leigh, have you changed/tested your dump valve?
you could try taking the pipe off the turbo outlet and plug it somehow then plug your dump valve take off and isv take off then get a pressure tester in the pipe which attaches to the throttle body. Then pressurise the system upto say 2bar and see if it holds, this will test most of your hose joins, x-member and i/c, i'll be doing this when i get my new i/c and pipework fitted this w/end hopefully.

HTH

martin

[Dr H]

Ok, checked valve and it moves up and down fine - can easily do it with your fingers so no sticking at all. Very slight play in it but I guess it needs this to move freely.

Diaphragm looks fine and spring looks OK.

Maybe a new diaphragm and spring is worth a go? Does the diaphragm come as a single piece with the metal base or do you remove the old membrane and put another on?

Will remove the air box this weekend and check all the nuts and bolts on the WG, turbo and manifolds, no reason to believe thay are loose but worth a check.

[Dr H]

Leigh, have you changed/tested your dump valve?
you could try taking the pipe off the turbo outlet and plug it somehow then plug your dump valve take off and isv take off then get a pressure tester in the pipe which attaches to the throttle body. Then pressurise the system upto say 2bar and see if it holds, this will test most of your hose joins, x-member and i/c, i'll be doing this when i get my new i/c and pipework fitted this w/end hopefully.

HTH

martin

I've done this a few times before I fitted the samcos and it didn't show anything obvious. It was loosing a little very slowly but it was suggested that it will loose a little through the turbo seals.

[martinjs]

did you get at least 1.5bar into it leigh? , if its a very small leak is could only start leaking over a certain presure.

i think to remove the WG diaphragm you have to remove the nut in that dish that the spring sits in, but the whole shaft will spin so has to be held somehow.

martin

[audiman]

Mmmmm, when did this start occuring??? Had you replaced anything or fiddled with anything?? Im just wondering if the wastegate valve seat isnt located correctly? Did you take that off when you did your turbo?

[newsh]

Hole in the dump valve diaphagm?

[newsh]

If the WG diaphragm was bad it would boost too much, not too little..

[Dr H]

Mmmmm, when did this start occuring??? Had you replaced anything or fiddled with anything?? Im just wondering if the wastegate valve seat isnt located correctly? Did you take that off when you did your turbo?

I did remove it when I did the turbo but the fault occured some time after that. For a while it was fine then all of a sudden...........

@newsh - new DV fitted and it's just the same

[audiman]

Have you tried using some petrol and some matches

[S2central.net]

Well fook me. My car runs at 1.4bar max with the WGFV connected, but only 0.4bar with it disconnected. Just tested it 2nite to be absolutely certain. I had previously read/heard that the stock WG and spring position (like mine) is good for 0.6 'mechanical boost' but its obviously not the case...

Its actually a very good valet mode stunt with the WGFV disconnected. Looks like Leighs WG is ok from a sanity check against this.