The Decel Valve Hose Diagram for the 2.0L Djet is Wrong, It doesn't work unless it's hooked up differently Options

[orange914]

Why not put a direct link to the diagram in the "Info" section,
since posts about hose routing pop up every now and then.

--- bill

after searching info section i found this vaccuum diagram here. i second that it would find good use in the info. section (IMG:style_emoticons/default/beerchug.gif)

mike

[arvcube]

OK, here's what I think the guts of this thing look like, open and closed - if you want to see the picture more clearly, click on it to open it in a separate window:

I think this diagram explains it all...Here's my take:
The Control Port is hooked up to the intake manifold (past the TB)
The End port is hooked up to the intake manifold (past the TB)
The Side port is hooked up to the air box or atmosphere.
P2 is completely sealed from P1
The End port is normally closed by some valve or plunger or whatever because of the spring pressure acted on it on the P2 side of the diaphragm.
When there is high manifold vacuum (overrun situation) the same amount of vacuum is applied to both the Control port and the End port (because they share the same source). Because the "valve" is sealing the End port (based on larger spring pressure), the End port is somewhat sealed or "plugged". Only when the manifold vacuum is high enough to overcome the spring pressure from the larger spring in the P2 area does the diaphragm deflect, thus opening the seal (valve, which is assisted by the smaller spring) from the End port, allowing fresh air to enter from side port to the manifold.
Extra air in the manifold during this overrun condition leans out the mixture and usually results in exhaust "popping." I think this would help to decrease exhaust emissions...

[McMark]

It doesn't lean out the mixture as much as you're thinking because D-Jet is vacuum based. So this 'controlled air leak' will lower the vacuum from really-high-overrun-vacuum to somewhat-normal-idle-vacuum.

I wonder if disabling the deceleration valve would cause high overrun vacuum to hit the MPS and cause the MPS to fail prematurely... (IMG:style_emoticons/default/idea.gif)

[JeffBowlsby]

I wonder if disabling the deceleration valve would cause high overrun vacuum to hit the MPS and cause the MPS to fail prematurely... (IMG:style_emoticons/default/idea.gif)

Uh huh...yeppers.

The vacuum hose diagrams on my site including the decel valve are correct now.

http://members.rennlist.com/914_collectibles/RareDocs.htm

[arvcube]

It doesn't lean out the mixture as much as you're thinking because D-Jet is vacuum based. So this 'controlled air leak' will lower the vacuum from really-high-overrun-vacuum to somewhat-normal-idle-vacuum.

I wonder if disabling the deceleration valve would cause high overrun vacuum to hit the MPS and cause the MPS to fail prematurely... (IMG:style_emoticons/default/idea.gif)

That makes sense...I think the functionality of the decel valve only applies to a limited range, dependent on how the spring pressure is set. So if the MPS measures manifold pressure, then high vacuum (idle or overrun situation, throttle closed) would cause the MPS to signal a leaner condition, while low to zero vacuum (WOT)would signal a richer condition...? if that's the case then maybe the decel valve was used as an additional way to lean out the exhaust emissions during these high vacuum situations even though the MPS and the "ecu" already does most of that....? (IMG:style_emoticons/default/wacko.gif)

[roadster fan]

And that, sir, is why you’re the king of D-Jet.

Thank you for all your efforts to expand the knowledge base of D-jet EFI. Without your research I would have never attempted to revive my 71 D-jet system.

The decel valve appears to be the perfect device to protect the MPS and would explain why early cars do not have one and later cars do. (IMG:style_emoticons/default/idea.gif) should I add one to my early car? hmmm?

Thanks again for making the complicated more understandable,

Jim