BlackWrxScooby

I've just fitted a VTA Dump Valve and had very poor running since. does any one know why, it's also started to pop the exhaust which is great but the poor running is terrible. I've checked all the hoses etc, what else can i try

greasemonkey

Yeah, it's because you changed the dumpvalve. The new valve itself might not be set up correctly, you might not have installed it correctly, or fitting it may have exposed a problem your car was already suffering that had previously not been detectable.

Depending on exactly what you mean by "poor running", it could simply be that your car is suffering the problems that VTA valves normally cause on MAF based ECU's.

If it ain't broke, trying to "fix" it rarely does any good. Unless you are running a MAP based ECU, the best sort of dumpvalve to run is either the standard one, or another recirculating design.

It's actually a symptom of the ECU misfuelling due to metered air being vented off to atmosphere instead of recirculated back through the turbo. It's more "bad" than good.

The easiest way to rectify this situation would be to put the standard part back on.

If you must carry on with your purchase, are you sure you blocked the pipe that connected the outlet on the original valve back into the inlet tract? Is the new valve opening too early? Can you shim it, fit different springs, or otherwise adjust its characteristics?

Without knowing exactly what you mean by "poor running", it is difficult to give specific advice.

[Edited by greasemonkey - 1/25/2004 5:17:40 PM]

BlackWrxScooby

cheers, i put the old recirculating one back on and have had no problems. Thing is my newish dump valve came off the same type of car and that had no problems.

the poor running is stalling, juddering as if its mis-firing, i will try and put it on again this weekend.

BlackWrxScooby

and forgot to mention, you can hear air leaking while accelerating then the car start accelerate, do all dump valve do that?

nom

Sounds like it's not set correctly - the spring gubbins isn't doing its job. It should stay sealed until the pressure differential across the throttle plate reaches a certain point, at which point it should 'dump'. Yours appears to leak all the time, making idle almost impossible and also reducing performance.

The standard dump valve is suprisingly good until you start running big boost/flow

greasemonkey

What nom said.

If it's leaking now, and wasn't in its previous car, is it possible that the spring preload has been accidentally altered?

BlackWrxScooby

think i'll stick with the old one but can anyone me me how it works. what does the little hose that connects to the top of the DV do, i suspect its sucks the DV open but what controls the suction? the car is a MY93WRX

greasemonkey

Yeah, little pipe is connected to the inlet manifold.

Idea is that when you close the throttle, a vacuum is created in the inlet manifold, which is used to suck the dumpvalve open.

The stronger the spring that's used, the higher the pressure differential must be to open the valve. If you have too weak a spring, you get the valve opening at idle or slight acceleration, as it sounds like yours was doing.

This causes problems even with a recirculating valve, but it's even more of a pain on a VTA design, as the air that gets dumped to atmosphere has already been measured by the airflow meter, which puts the fuelling all out of whack.

BlackWrxScooby

cheers for your help, will go out and buy a new re-circlating DV next week cause the spring is sticking open which is the reason i got the VTA one.

Thanks again.