Boeing 717

Hey Guys this could totally be my imagination but i dont think so.......i drove my car the other day for the first time in a couple of months and it "seemed" like when i lift off the throttle to shift gears it is taking longer than it used to for the revs to come down, like i have to wait longer between shifts (like a really heavy flywheel would keep the engine turning longer). I did notice that my throttle pedal is very sensitive and may be pulling on the cable a little to tight. Could that be the problem or is there a valve or somthing that could be causing this???

Thanks

bogey1

I am so weak on the mechanicals, but a long time ago I had a problem with what i think someone called the decelerator valve? something like that atleast. It was a bronse colored circular piece - its long since gone on my car, but your issue sounds like my problem years ago. Cheap fix as I recall.

Metal Guru

Sounds like the recirculation valve is sticky.
Is it the stock Bosch valve?
I switched mine to a blowoff valve. Revs drop immediately now.

Ag02M5

Really. I have read multiple posts advising against it...specifically from IA.

Metal Guru

I saw Steven's reason and I'm not buying it.
He claims that the engine will go lean for an instant. Fact is, during the event, there's more fuel available than there is air so the engine goes rich for an instant.
How the recirculation valve works and what it does isn't complicated. As long as the pressure is being vented out of the intake between the metering plate and the compressor it won't matter where that air goes.

nathanUK '81 930 G50

Just change the Bosch plastic recirculation valve to an aluminium type recirculation valve. Forge make them and offer different springs and shims so you can tune it how you want. Why waste fuel/energy.

Metal Guru

My Forge recirc valve was very slow to open, especially since it liked to stick and bind.
Guess you get what you pay for.......

nathanUK '81 930 G50

I am not aware of any problems with that part, I've not heard of any problems with them.

Did you try a softer spring?

Metal Guru

Tried everything to no avail.
Ended up buying the Forge hybrid bov. It has a better seal configuration and is much more adjustable than the cheapie.

Boeing 717

OK so that would be this thing here.... right? the black cylinder with the hose coming out of the top??? Is there a way to clean this thing or should i just buy a new one. Are you guys pretty sure thats what is causing this???? Can there be anything else i need to check???



Thanks Guys

Metal Guru

That's it.
Here's the replacement I recommend: http://www.forgemotorsport.com/conte...duct=FMDVSPLTR

nathanUK '81 930 G50

Jerry, it could be a number of faults causing your problem, but this is certainly one of them. The other thing that could happen is for the diaphragm to come out of that Bosch recirc valve and ruin your turbo. I intend to get an aluminium recirc valve when I put my car back together, may run the Bosch one as it's brand new for 6 months or so but not for long term as I don't want to ruin my HFS.

Boeing 717

Ok thanks guys..... i am going to buy one and well see if that fixes it. Can someone explain to me "WHY" this would keep the rpms from falling as fast as they should, im having trouble visualzing how this works.

nathanUK '81 930 G50

Jerry, the small hose on the valve is connected below the throttle plate so air could be sucked in through this small hose if the valve allows it. If the valve was working correctly it wouldn't allow this.

Thinking about it, if you get the problem without boost you could test it by not building any boost & clamping this hose with some mole grips (I think you guys call them vice grips in the US of A ) and see if it feels better.

Don't clamp the pipe and get the turbo spooled though

Metal Guru

The Bosch valve has a diaphragm that a vacuum signal from the engine opens to allows the high pressure air that's trapped between the metering plate and the compressor to vent into the engine, bypassing the throttle plate. This slows the deceleration of the engine which burns unspent fuel and lowers emissions.
Anecdotal evidence suggests that the Bosch valve doesn't last long. The symptoms that you describe sound more like what I was experiencing with the first Forge recirculation valve that I tried.
Problem is that it slows shifting way down and while you are waiting to shift the turbo is slowing down all the time. When you are finally able to shift the turbo is no longer developing any boost.