s4bill

In the center of the picture appears to be some type of regulator or valve?

On the right side appears to be some type of connection for a hose?

Just wondering what it is and if I am missing something?

Dean_Fuller

Connects to the botton of the air filter box.

Rob Edwards

It's the diverter valve, which takes air from the air pump and diverts it to the cats to heat them faster at startup. You're missing the hose from the airpump to the valve.


In your picture there is also a white vacuum line which is disconnected, it should attach to the diverter valve's rubber elbow.


There is also a purge valve to the carbon canister- it's buried under the hoses to the reservoir and filler neck. *There's a black vacuum line that runs from under the middle of the intake, over the passenger side valve cover, to the purge valve.

Here's a diagram of S4+ vacuum lines. Annoyingly it doesn't show the diverter valve.....

s4bill

The hose showing just to the left of this valve connects to the air box. I am refering to the valve itself. There appears to be a hose connection on the right side.

Does this connect to the air box as well?

s4bill

What is the implication of this hose missing from the diverter valve?
Is there a reason why the PO might have removed it?

What is the implication of this white vacuum line being disconnected?
Just curious if I will see any difference when I reconnect it.

Thanks for the help

Rob Edwards

Not having the hose from the air pump to the diverter valve is pretty meaningless, unless you live in a state with a visual smog test, but even then it's unlikely a tech would notice.

The uncorked white vacuum line means you have a vacuum leak. What rpm does your car idle at when cold, and when hot? It'll run incrementally better without the vacuum leak.

s4bill

I live in MD and have historic tags so I am exempt from emission testing now.

I hooked the hose back to this elbow on the valve and I didnt really notice anything significantly different. This may seem silly but the car sounds different?

The car idles at the second bar of the tach shortly after it runs for a while. Is that too low?

I think I will take a picture of it as soon as it starts and where it is after it is warm.

What I did notice yesterday and I dont kow if this is related is that warm air is blowing from the vents when I drive. This is with the controls off and driving at highway speeds.

I was playig with the HVAC controls the other day just to see if the heat works. The AC does not work so I was just curious about heat (this is another thread) This could have always been like this and I never put my hands to the vents while I was driving.

WallyP

You probably do not have a functioning air pump. The open connection on the diverter valve should be connected to the pump.

The hot air is not related to the dirverter valve. You probably have one of two problems.
- The heater control valve, located behind the passenger cylinder head under the air cleaner, may be faulty, or may not be getting vacuum due to leaks in the HVAC system.
- The rubber seal on top of the bulkhead behind the engine may be missing. This seal touches the hood to prevent hot air from entering the HVAC inlet on the passenger side.

s4bill

Is there a best approach to check for vacuum leaks?

Does this white vacuum line that connects to the diverter value route inside (closer the engine block) or to the outside of the vertical hose that connecs to the air box?

Running it to inside seems to put less stress on the hose but running it to the outside keeps father from the engine black.

s4bill

"...- The heater control valve, located behind the passenger cylinder head under the air cleaner, may be faulty, or may not be getting vacuum due to leaks in the HVAC system."

How do you test thiis?
Can you manualy close the valve to see if that corrects the problem?

WallyP

Several quick tests:
- Look at the rear of the engine compartment and see if the rubber seal on top of the firewall is missing.
- if the HVAC air is cool when the engine is first started, then gets warmer as the engine warms up, the heater control valve may be faulty or not getting vacuum.
- Remove the air cleaner housing and find the heater valve behind the right cam cover. Set the HVAC controls for full cold air. Watch the heater valve as someone starts the engine. If you have vacuum, and the valve works, you can watch it close.
- Pull the vacuum hose off the valve and check for vacuum with the engine running and the HVAC set for full cold. No vacuum, or very weak vacuum, may be leaking HVAC actuators (common) or problems with the vacuum supply on the power brake booster valve.
- You can manually close the heater valve and hold it closed with a wire tie.

Go to our web site, then tips/links, Wally's World, HVAC, and there is a long detailed paper on the operation, testing and repair of the HVAC system.

michael j wright

Not knowing the 32v motor,I may be wrong on this, but on my 16v the white vac line goes to the heater valve. This may be why you are getting hot.

WallyP

Correct on the 32-valve cars as well.

s4bill

"- Remove the air cleaner housing and find the heater valve behind the right cam cover. Set the HVAC controls for full cold air. Watch the heater valve as someone starts the engine. If you have vacuum, and the valve works, you can watch it close."

I set the controls to the far left for cold. I put the AC to on and changed the switch to blow to vents. I imagine it doesnt matter where you move the bottom control as long as the top control is set to cold?

- Pull the vacuum hose off the valve and check for vacuum with the engine running and the HVAC set for full cold. No vacuum, or very weak vacuum, may be leaking HVAC actuators (common) or problems with the vacuum supply on the power brake booster valve.

There is no vacuum at the valve. I did check vacuum at the diverter valve (with an old vacuum/fuel presser guage) and the reading is 14. Is that too low?

I checked the HVAC write up and it is fantastic. It appears that it would be very helpful or even necessary to get a Mighty VAC? Is MV8500 Silverline Elite Automotive Kit or MV8000 Automotive Tune-up and Brake Bleeding Kit the kit you mention? I will be looking to bleed brakes and possibly flush the brake lines with the new fluid. Does this change what I should buy for this exercise?

Rob Edwards

MityVac is pretty essential if you're going to do any DIY hands-on on your 928. I would splurge for the MV8500 (I have one), the 8000 has a plastic body, lots of negative reviews on Amazon about its quality and lack-of-vacuumitude.