Bcdd

[rcb280z]

Talked about in the past I know but, does anyone know if there are replacement parts for the BCDD? I believe my BCDD has a vacuum leak and am thinking about removing and blocking it off. But I'm not sure what to do about the solenoid. Here's the reason. When I unplug it the idle changes (lowers) and is not as smooth. And when I rev the engine the idle is slow to return to 800. This is while the solenoid is unplugged.

My other concern is emissions. It is hard to pass emissions testing as it is in California. What will it do if its removed? I'm not sure.

I don't want to purchase a used one because it could have the same problems mine has and if it doesn't when will it? There are no new ones that I can tell. I read where people have removed them but no info on emissions results.

The other thing I noticed with my BCDD is when I was standing over the engine just listening (with BCDD solenoid connected) I heard this "click" sound and the engines idle changed. Was not smooth. Acted as if it just became lean. It stayed that way for a few minutes and then I heard another "click" and the idle smoothed out, What?! Not sure whats going on there either. 

[rcb280z]

Update, I think I can say without a doubt there are no parts available to repair these valves. Haven't had too much time to put into solving my issue yet but I am hoping someone has experience with these things. Obviously I do not.  

[Zed Head]

I wonder if your problem isn't actually somewhere else, like maybe at the speedometer.  As I understand the BCDD system, it's supposed to be inactive under something like 10 mph.  You shouldn't be hearing the BCDD clicking, with engine speed changes, at idle.  The AC idle-up solenoid might do that though. The way the BCDD works and a pretty detailed test procedure are described in the Emissions chapter of the FSM.

 

If you just have a blown diaphragm, somebody (one of the Captain's, if I remember right), took theirs apart and replaced the diaphragm with a piece of thin rubber.  It's on here somewhere, they described it.  But your problem doesn't sound like that.

[rcb280z]

Zed Head, I did read that section of the FSM. So if I read everything right there may be an issue with the amplifier on the back of the speedometer correct? Or can this be because the BCDD is out of adjustment? I do believe it is after reading that section in the FSM again. But need your opinion.

 

I decided to unplug the solenoid at the bullet connector near the BCDD and got an unstable idle. Im confused now. Somethings not making sense and I can't put my finger on it. 

[Captain Obvious]

Here's the thread where member sscanf was making his own BCDD diaphragms:

http://www.classiczcars.com/topic/47935-air-flow-meter-fails-some-resistance-checks-repairable/page-2

 

Been a while since I looked at the details in the FSM, but I believe the BCDD is enabled when the solenoid is de-energized. That means that when you disconnect the wire to the BCDD it enables the system.

 

The purpose of the solenoid and the amp on the back of the speedo is that the BCDD is disabled when the speed is very low (below 10mph). In any event, it shouldn't be clicking with the car stationary. Sounds like it's a bad connection somewhere between the BCDD and the speedo stuff...

 

As for emissions... At idle, the BCDD shouldn't do anything to change any emissions even if it's malfunctioning. The BCDD just lets additional air around the throttle plate. There isn't any link between the BCDD and mixture ratios. Your idle speed will bounce around (like you said it is), but it shouldn't change the content out of the tailpipe.

 

The only time the emissions are really impacted by the BCDD is when you're decelerating with your foot off the pedal. That's when the BCDD really does good things for emissions. But at idle? Shouldn't matter if it's working or not.

 

 

[rcb280z]

Ok so I just looked at it a 3rd time. I need to test the amplifier at the back of the speedo. Hope that's not the problem. I have a dash cap and I don't think you can remove the tach or speedo with it in place.

[rcb280z]

Capt. unfortunately here in CA we have "rolling dyno" emissions tests. So, it would benefit me to have mine operating correctly, I believe. What a pain. 

 

There is a 15 mph test and

there is a 25 mph test.

 

So I would assume that on deceleration, without a good functioning BCDD, HC's would load up. 

[Zed Head]

Woohoo, you get to use that funky connector with the rubber plug over it, up by the coil, that we've all wondered about.

 

Could be the old corroded connections problem, or a partial-short across A and B at that connector if the rubber's gone.  Or a gummed up solenoid.  You might check the voltage at the single wire to the solenoid against ground while it's active to see what kind of voltage drop you're getting.  I think a typical solenoid is about 1/3 volt.  SteveJ probably knows for sure.  Get as much easy information about the state-of-the-system as you can before tearing things apart.

[rcb280z]

sscanf has a lazer cutter to make those perfect "cutouts".  Wish I had one. Thanks for the thread.

[rcb280z]

Haha! I know. Hope its a good reading. Im hoping the BCDD just needs to be adjusted but my luck......

Yep, thought about corroded connections already, sorry should have posted that.

Also going to remove solenoid and check that its not all gummed up

[rcb280z]

Hope to do all this tomorrow and post results.

[Captain Obvious]

So I would assume that on deceleration, without a good functioning BCDD, HC's would load up. 

Yes, on deceleration you would have high HC if the BCDD is not functioning properly. I know nothing about the emissions tests in CA (thankfully), but I'd be surprised if they catch that. It won't show up on any static test like idle, 15mph, or 25 mph. The only time it would show up is as a short transient when they took their foot OFF the pedal AFTER running one of the dyno tests. Not sure they'd flag that as a failure, but it's important to have it working regardless.

 

And if that thing is clicking while sitting still at idle, your problems are not simply an adjustment issue at the BCDD. If you got clicking when sitting still, then you've got electrical issues somewhere.