280z owners-What is this for?

[JEFF]

What is the BCDD ( boost controled deceleration device ) for?

Emitions during throttle let off?

I put a '78 N47 head on my 240 block ( F.I. Electronic ign. - the whole 9 yards ) The BCDD is mounted to the bottom of the throtle chamber. It has one wire coming out of it. That wire was hooked into a plugblock near the speedo but it dead ended there - the '78 Z ran good before I pulled the head and wireing. Now that the head is on the 240 block ........

When I start it up (first piston to the top fires right up) it idles good at about 700 rpm and will stay that way untill I rev the motor once. That's when it will stay idleing at about 2700 - 2900 RPM untill I turn the ignition off. Is this related to the BCDD? Or do I have some thing else wrong? ANY suggestions would be nice!

- Jeff

[JEFF]

Anyone??

Keeping the post current.

- Jeff

[2ManyZs]

Yup, it is an emmissions thing. It supplies air to the maniflod when coasting to compensate for manifold vacuum changes....

On a 280, there is a wire that runs to the speedo that has a diode of some type that controls the idle. It registers the speed when coming to a stop (at a light for example) and will cause the idle to not drop to a full idle if it is bad. My 75 did that once, when coming to a stop the idle would not drop to idle for a mintue (sometimes not at all), all I had to do was change to a different speedo.... Since you say the wire was connected to the BCDD, all I can think of is it may be supplying too much air to the intake and thereby messing up the idle by supplying extra vaccum to the intake when it shouldn't (?)

Best guess? Put the 280 speedo in and see what happens as the 240 speedo has no way of controlling it...

[JEFF]

I no longer have the 280 speedo - could I remove the BCDD and block off the opening? I have removed all the other smog stuff, would one more hurt/or majorly effect its running? It was a dead end wire on the 280Z - I thought that it was possibly used for automatic trans cars but due to mass production purposes only some were conected. Not the case??

Two mistakes when getting rid of the parts car : I did not take the dash (even though it was in my lap) & I left the 280 block in it.

I did take almost everything else including all the glass and all the rubber plugs/gromets that i could find.

- Jeff

[2ManyZs]

See no reason you can't take it off, but if blocking it off doesn't solve the idle problem.. hmmmmm:ermm:

[JEFF]

My thought about taking it off was that it was/is making a intake leak that goes under the throttle chamber and not through it. If that is what is happening then the TPS is not sending the right signal for the "true" amount of air going through the throttle chamber. Wouldn't that cause a lean high idle? That BCDD does have air passages in it , or at least one. Maybe that the BCDD doesn't have the wire hooked to anything makes that passage open. What do you think?

- Jeff