If you have a D-Jetronic setup with the decel valve, try this for me. While out of gear and idling with brake on, pull the end of the hose to the decel valve that's connected to the air cleaner box (the big connector on the end of the decel valve, not the one on the side, and not the skinny one). Put your thumb over the open end of the hose and open the throttle to 4000 rpm. Now, as quickly as possible, let it snap shut. Did you feel a strong vacuum with your thumb? Let me know, thanks.

I believe this is referred to as black box testing.

C'mon - can someone try this for me? Thanks...

Ok, I gave this a shot and here's what I come up with.

At first I tried it and was getting about 5 inches of vacuum but when I came back in to report I noticed that according to DD's EFI hose diagram on Pelican that I had the hoses mixed up.

I swapped the side and end hoses so they're correct according to his diagram and now I get no vacuum on the air cleaner hose (to the end of the decel valve).

So,

- hoses hooked up correctly is 0 vacuum

- hoses hooked up backwards is 5 inches of vacuum.

Now, there's no telling if my decel valve is working correctly to start with so these results may be bogus.

If you need me to try anything else let me know.

What size is that dual port elbow supposed to be where it connects to the intake? 9mm or 12mm?

There are two ports on the side of the intake, 9mm and 12mm, which should the elbow be attached too? (it would seem to me the 9mm port since the 12mm port should be connected to the PCV valve which is also 12mm).

The nipple sizes are shown on my diagram below, not sure which nipple is referenced.

Jeff, your diagram and DD's differ slightly. On Dave's diagram both of the ports on the dual-port elbow go to the decel valve, which isn't really possible due to hose sizes.

I was just double checking my house routing to make sure I wasn't giving Brad incorrect info for his test.

I think Daves diagram and mine are identical with regard to the decel valve hoses. What am I missing, what looks different?

They're different. Here's how;

On Dave's diagram follow the two (red & blue) lines from the decel valve back to the manifold. Dave has both of these connecting to the dual-port elbow. Yours has the smaller decel valve line and the PCV valve connecting to the dual-port elbow. The extra line from the decel valve connects directly to the manifold next to the dual-port elbow.

Yours matches the way my car was routed and my spare motor.

Interesting Joel, thanks for opiting that out...I never realized the difference. I wonder if it does make an operational difference?

I noticed the difference in the two diagrams, too.

So, looks like Joel got the same result I did, interesting. Jeff, you've got two cars, can you give it a try and let me know what you get? If you do get a strong vacuum, do one more thing for me. Put your hand vacuum pump (I know you've got one!) on the control port of the decel valve and tell me what vacuum level opens the valve (check by blowing through it). Mine's at about 18-19 inHg right now and it acts like Joel's, it doesn't open on overrun.

I have to agree with Jeff's diagram. That's how my car was plumbed (when it had a decel valve). And it doesn't make too much sense for the two ports of the decel valve to be joined together in the dual port elbow.

Demick

I'm not sure about operational differences but we're dealing with 3 different size hoses and 2 different sized nipples on the manifold, it all only goes together one way. I think that it may be an error in Dave's diagram (but I'm not 100% positive).

This had me really confused this afternoon trying to sort it out -- until I saw your diagram Jeff. Then it made sense, and was the same on both my engines before I started tinkering.

It would not be the first error in my drawings... Probably not the last in that particular drawing, even!

On my car, the oil breather connects to an elbow on the more-forward fiting on the right-front of the air cleaner. The Decel Valve hooks up to both parts of the "stacked elbow". That's the way it was when I got it; I assumed the DV was non-directional and never really bothered to mess with it.

Hmm, I'll have to see if I can dig up some software that will let me change the diagram if it's wrong!!

--DD

Hey, everybody's allowed one error per year

I tried your diagram Dave but the PCV valve is 12mm and the front-most nipple on my manifold is only 9mm (same as the hose from the decel valve).

The dual-port elbow has a 12mm inlet and a 12mm and 7mm outlet. The 12mm outlet has a small piece of pipe (about an inch long) to connect the 12mm hose from the elbow to the PCV valve.

The elbow fits on the nipple just right of the 9mm nipple and is 12mm.

Confusing, eh?

It's worse on my car. When I got the engine 20 years ago, it came with a plenum that has a 9 mm port in the front, and a 7 mm port in the rear, no kidding. So, I've got the control line to the decel valve hooked up to the 7 mm port, then I've got a short length of hose coming out of the 9 mm port, going into a tee connector that branches off to the PCV valve on one side, and the decel valve "side connector" on the other, nice and kludgy.

Of course, when I got the motor recently rebuilt, I completely forgot that I had picked up the "correct" plenum a couple of years ago, and it was sitting in my parts box. Now, I'd need to get it powder coated and checked for integrity, then rip nearly everything off the top of the motor (which is in the car, now) to swap it out. I think not, at least until the next time the motor is out of the car.