MBMB

My aftermarket vacuum hose kit came with this diagram. It shows a 34" line going to the EGR Valve (just to the left of the center of the page). But, as far as I know, there is no EGR valve on my GT. I'm puzzled; where does this hose fit?

Thanks.

IcemanG17

Your right about the EGR valve...my guess is it goes to the airpump valve just forward of the airbox...easy to understand how it got labeled an EGR by someone not familiar with the 928 system

worf928

That's a really crappy diagram...

The port on the bottom of the throttle body (TB) feeds vacuum for the air pump valve.
The port on the top of the TB that faces the firewall feeds the fuel regulator and dampeners.
The port on the top of the TB that faces the front of the engine feeds the tank vent valve.

If you mix up the connections, the vacuum to the various items will NOT act like its supposed to and things will get wonky.

ColinB

This is interesting.
I haven't studied it carefully but I don't think my car has the EGR valve either, though as in Mark's it appears on the vacuum diagram. So- if I don't have an EGR v/v how is the breather piping routed? Did it come like this from the factory?

I've always had suspicions about this because I get a lot of oil smoke and very high oil consumption over 6000RPM - allegedly caused by the poorly designed breathing system. It was modified in the GTSs.

Dave, do you have the correct vacuum and breather diagram for the 89GT? Mine has the 7-way vac Tee behind the left cam case (though some are blanked)

Colin. 89GT.

Solid Snake

That's a great diagram! Anyone got one for a '79?

MBMB

Thanks, Dave.

Rob Edwards

Can I make a quick suggestion, having just removed my intake twice? Put a small zip tie around the vacuum elbow connections on the thrrottle body before re-installing the intake. The vacuum lines can get pulled around while re-installing, and you don't want to get it all back together and discover that one of them got pulled off. Most folks probably know this, but it wasn't obvious to me.......

worf928

What's marked on MB's diagram as EGR is the airpump diverter valve. No EGR on 928s - at least in the USA.

Oy. I think we did this once before and your vac system is very different since its RHD. You posted a picture? I seem to recall that you didn't have a port under the throttle body? The only diagrams I have would be from the WSM or CDs. And I don't recall seeing any RHD versions.

On LHD cars there's a 5-way from the throttle body from one port and two additional ports that feed the air pump valve and tank vent vacuum valve.

The tank vent gets its vacuum source from a port just slightly ahead of the throttle plate while the 5-way (and 7-way I assume) gets its juice from the port slightly behind the plate. It's not impossible to get them mixed up because the connection point facing is reversed - the port drawing vacuum from behind the plate points towards the firewall while the port drawing from infront of the plate faces the front of the engine bay. Thus, if you use "elbow' connectors as shown in MB's diagram the natural tendency will be to reverse the connections.

The behavior of vacuum relative to plate opening is totally different for the two ports. I *think* the air pump vacuum source should behave like the 5-way source but I've never measured it comparatively.

So.... If I had to guess on the RHD 7-way...

1 - Fuel Dampener
2 - Fuel Dampener
3 - Fuel Regulator
4 - Off the the Auto Tranny (or blocked on a 5-speed)
5 - Air Pump
6 - ?? Blocked ??
7 - Source from throttle body

* - Tank vent from forward facing port on top of throttle body.

The valve for the flappy, HVAC, Cruise, and storage reservoir get vacuum through the check valve attached to the brake vacuum booster. IIRC you have a really long vacuum line that runs from the booster/check valve across the engine bay to the reservior - and another long one that feeds the flappy.

Post a picture of a RHD engine bay and I'll try to guess about the breather hoses.

Better yet, ask one of the Brits or Kiwis...


EDIT - No vacuum cruise control after '88...

Bill Ball

There's another thing about the routing that is confusing. Both the cannister valve and the air pump diverter valve are close to each other, but one hose routes to the rear and the other toward the front from the throttle housing. The diagram has the routing paths reversed - both the altered and the stock diagram. It doesn't matter except that the stock lines fit better the correct way.

ColinB

Dave

No wonder I couldn't figure out what EGR stands for! So now I presume it's the air pump divertor valve I don't have .

You're quite correct and clearly your memory is better than mine. We did discuss this previously - about two years ago. On that occasion I had just got my car back from the workshop with several of the vacuum lines misrouted. Took a while to figure it out without an accurate diagram, and I still ended up having one line coming from under the intake with nowhere to go. I simply blanked it off and I'm now wondering if this is the one which should have gone to the tank vent. (Instead of which I have the tank vent supplied from the air pump line on the 7-way tee. My air pump is removed.) It seems to work fine like this, just academic interest really. With this exception my 7-way tee is connected as per your guess above.

Your memory is also quite accurate about the flappy vacuum supply. It originates at the 4-way tee at the brake booster, on the right side of the car of course, and runs along the right fuel rail then crosses beneath the upper radiator hoses to the flappy solenoid which is on the left cambelt cover as in LHD cars. The workshop lost this hose altogether.

Thanks for your help.

Colin. 89GT.