ColinB

Thanks to the Rennlisters who directed me to the WSM diagrams I've been able to sort out most of my misrouted vacuum lines with one exception. The diagram doesn't identify the source point for the vac line going to the flappy solenoid on the left cam cover. It simply says "from vacuum reservoir".

The car had an intake-manifold-off job done recently while I was out of town and when I got it back, amongst other faults, the flappy solenoid was supplied with vacuum from some point under the manifold. I'm sure that's not right. The vacuum fluctuates too much with engine speed and the flappy behaves erratically though it is correctly connected to the solenoid and works normally when I apply a suction.

I never noticed previously but the car actually has TWO vacuum sources. One originating under the intake which supplies the 7-way connector on the left side of the MAF, the other supplied from the brake booster via the 4-way connector at the firewall after the blue/black check valve. This one incorporates the vacuum reservoir and mainly serves the HVAC but, I suspect, also the flappy solenoid. Trouble is, all my ports have hoses in them and the original hose is missing from my car so I can't tell how it connects. Something is clearly still amiss here.

Could someone kindly finger-trace the pipe for me and identify the source.

TIA Colin 89GT

worf928

Colin, the vacuum source for the flappy's solenoid is the 4-way connector from the vacuum check valve.

EDIT: On LHD cars the 4-way connects the HVAC system, the reservoir, the flappy, and the brake booster IIRC.

There is a five-way connector that connects the top of the throttle body to the two dampers and regulator and on 5-speed cars the 5th connector is plugged. There is another vacuum connection on the top of the throttle body that provides vacuum to the fuel vent system's valve (runs over the cam cover) and another from underneath the throttle body that connects to the airpump valve (runs behind the head). (Thus there are 7 possible vacuum connections to the throttle body.)

I don't know what might be different on RHD cars.

Hope that helps.

Bill Ball

The source for the flappy is the 4-way by the brake booster. A rigid plastic tube routes from the 4-way along the fuel rail to the front of the motor into a switch mounted on a bracket above the driver side timing belt cover. From there a rigid line goes to the flappy control. Here are some shots. The flappy feed from the switch is plugged since the SC kit removed the manifold. The other shots are pre-SC and accurate.

While I was getting this together Dave answered and he added comments about the other vacuum sources. As he indicated there is a 5-way off one source on the throttle body and another single feed. Since you mention a 7-way, it appears your mechanic blocked one of the sources (or rather I hope he did) and took everything off the other one. WSM 24-216 has a diagram that shows the 5-way and the other source.

check valve from brake booster


4-way


flappy switch over driver side TB cover

IcemanG17

Colin
Bill has it right....the grey/white runs to the solenoid..plugs in the bottom (not top) & the top (black) line goes to the flappy....if the two lines are reversed...then you will always have a vacuum leak and the flappy will stay open too long. I posted a thread about it earlier this month....sometimes the blue-black one way check valve fails (mine did) or the rubber 4 way "T" dries out (mine did that too) & gets too loose...both are cheap and easy to replace.
Brian

https://rennlist.com/forums/showthre...ghlight=flappy

ColinB

Dave, Bill, Brian.
Thanks for the excellent guidance and pics. I'm sure I can figure it out now. Regarding the throttle-body vac source, although the diagram WSM 24-216 shows a 5-way fitting, my car has a factory-looking one-in, six-out rubber connector with one outlet blanked . The others 5 (should) feed the two dampers, the regulator, the tank vent valve and the valve Dave mentions on the air pump piping. (At the moment this last one is wrongly connected into the 4-way fitting where the flappy source should be). Yet another, presumably the redundant one for A/T cars emerges from under the manifold and is blanked near the right cam cover. All I need now is a length of vac hose to reconfigure it correctly.

Thanks again. Colin 89GT.

worf928

Ok. Swapping the flappy source and the air pump line will return the system to normal.

How do you plan to reconfigure it?

This line is weird.

From your first post, you are sure, that that's not the line to the flappy actuator. (Statement, not a question.)

On an LHD car that would be the line running from the top of the throttle body to the tank vent valve. (On LHD there are three vacuum ports on the throttle body that feed the a) 4-way b) air pump c) tank vent. And then a fourth vacuum line (visible but not on the t-body) from the flappy actuator to valve. Thus, since you have a 7-way connector the other two vacuum ports on the throttle body must be - I would think - plugged/blanked (I doubt the casting is different.) But why wouldn't those ports be plugged at the source? Why run a vacuum line out into the engine bay and then plug it? I have to wonder if there's another vacuum operated gizmo on the RHD cars. Doesn't make sense.

AFAIK the plugged/blanked port on the 5-way (7-way in your case) is what feeds the auto transmission.

You must have one really long vacuum line that runs from the booster (one port of the 4-way with check valve) across the engine bay to the vacuum reservior on the left side.

Surely there must be a TSB or similar for the vacuum system on the RHD cars.

IcemanG17

Colin
That sounds odd...there basically are two vacuum systems on the car...on is a fixed vacuum, which comes off the brake booster and is shown in bills pics above...this provides a steady vacuum to the cruise control,flappy and HVAC systems. The second system comes off the intake manifold and is variable with engine load (I think so anyway, but could be wrong) which controls the fuel dampers etc plus adjusts the shifting for automatics! Your one plugged line off the 5 way "T" is probably because your car is a 5 speed? But one thing is certain...your flappy source line should only come off the 4 way "T" by the brake booster....So your flappy probably isn't working right?
Brian

ColinB

Sorry to reply late, I've been travelling. Thanks for the continuing interest.

Dave
I wrote--- "Yet another, presumably the redundant one for A/T cars emerges from under the manifold and is blanked near the right cam cover. All I need now is a length of vac hose to reconfigure it correctly."--- Sorry, this was misleading. I meant to say all I need is to replace my missing original flappy-source hose from the 4-way fitting to the actuator. I intend to leave the blanked one as-is. See below to Brian. If this is not the redundant A/T line AFAIK there are no aother vacuum gizmos on RHD cars but could it be something to do with the disabled headlamp aim system?

I suspected at one time that the vac line now feeding the flappy solenoid was actually the one connected into the 4-way fixed-vac port and had been mistakenly re-routed under the intake. Not so. I blew into one end, no blow at the other. So even after I reinstall the missing hose I will be left with the one presently feeding the actuator from some mysterious source under the intake. I will blank it since I don't want to remove the intake again but I won't know what I'm blanking.

I took some intake-off pics which unfortunately I dont have with me. The shots are unclear but they seem to show the 3 vac ports on the TB as:- a) to 7-way connector, b) to the mystery blank hose c) a hose from TB to idle control device. Ses also Jim Morehouse's post regarding Euro/RHD WSMs. Very rare it seems.

Brian
Correct. Presently the flappy doesn't respond as it should because it's connected to one of the TB ports under the intake where the vacuum is variable. The cruise on my car is all-electric. No vac system involved and possibly that is why there is a spare blanked vac line coming off the intake. However, as Dave notes "Why run a vacuum line out into the engine bay and then plug it? " I don't know either but the blank looks like a factory item.

Colin 89GT

Tails

Colin B,
I have just been working on checking vacuum leaks from the intake manifold on my RH drive 1990 928 S4 Auto, so I maybe able to help you. The drawing shown on page 24-216 is for the 1987 S4 and the later models are connected up a little different.

On top of the throttle valve just after the butterfly flap two outlets are shown, the after most one links into the 7 way rubber connector (not a 5 way connector as shown) and is the main vacuum connection for the fuel system and the automatic transmission. There is no forward connector on top as shown, it is located underneath the throttle valve. This plastic pipe is led out over the RHS camtower cover to the to the Vacuum Valve (F).

The the other six connections on the 7 way connector are as follows:
1. one to the the fuel pressure damper (D)
2. one to the fuel pressure regulator (E)
3. one to the forward fuel presssure damper (not shown) where the cross connection is fitted between the two fuel injector rails
4. one to the automatic transmission (e), in your case with manual transmission this should be balnked off.
5. one is blanked off at the connector
6. one is lead to the air pump control valve on the RHS behind the coil over damper tower.

The other vacuum system which is fed from the brake booster:
1. one is connected to the solenoid valve on the LHS front of the engine and is connected to the resonance valve (flappy valve)
2. one is led to the the heating and airconditioning (HCAC) system
3. one is led to the vacuum reservoir located under the LH side front fender
4. one is led to the heater control valve.

When you have reconnected your induction vacuum system correctly I would suggest that you check the tightness of the system by taking off the inlet filter housing and sealing off the inlet to the MAF and pressurise the the system to a maximum pressure of 0.6 bar and either do a leakage test or listen for leaks. There are numerous post on how to do this. Porsche recommend the manufacture of a cover for the MAF fitted with a tyre valve, a pressure gauge and a rubber seal which is held in by place by 2 bolts and nuts to the MAF.

There various ways to check the actuation of the resonance valve/flap:
1. Suck on the tube connected to the resonacne flap and you will see it operate the valve if you remove the rubber nipple cover, that is if the rubber diaphram is OK.
2. Put a flag on the shaft of the resonance flap (I use a piece of masking tape and make an inverted "T" with the bottom of the "T" the stickey tape and attach it to the shaft. At start up the resonance flap should open and shut.
3. Remove the electrical plug from the selonid valve and bridge in a 12 volt supply to the positive terminal, start the car and ground the negative terminal, the solenoid valve should open and the resonance flap should operate thrugh 90 degrees.
4. You can also activate the resonace flap by removing the LH ECU plug after first disconnecting the battery, bridge out terminals 17 and 21. Connect a lead with a suitable spade connector to terminal 34, reconnect the battery and connect this leads other end to ground (Best ground is the RHS securing stud for the wooden cover of the CE panel. If all is OK the resonance flap will open.
5. Reconnect everything to normal, warm up engine to normal operating temperature, depress the accelerator pedal to the full throttle position suddenly : the flap will open and close, however, this will not happen unless the engine is running at more than 3500 rpm and at not less than one-third of its full power.

Hope that this is helpful.

Tails 1990 928S4 Auto

worf928

Tails may have solved the mystery: On a RHD 5-speed two of the connections on the 7-way are 'blanked.' And thus, Colin, your 'mystery blanked' vacuum line.

But, Tails, your second point #4 about the connection to the heater control valve seem a bit weird. One connection from the four-way should go through the check-valve to the brake booster. If not, on RHD cars how is the brake booster supplied? (IIRC the HCV is fed vacuum from the HVAC distribution system on the other side of the fire wall and is controlled by the HVAC sliders. If the HCV is hooked to the 4-way it will get a constant source of vacuum and always be closed when the lump is spinning.)

Bill Ball

Tails' note should be pasted in the WSM. The undocumented MY changes are a major hurdle to owners when owners of other MYs are trying to help. Sometimes these things are covered in the MY service tech bulletin, included in Jim Morehouse's CD. Didn't check that.

Tails

Worf928,
You picked up my mistake, which was un-intentional, as I was writing up this post mostly from memory and it was around 1am in the morning.

You are correct the hot water vacuum control valve supplying hot water to the heater is connected to the HVAC system. Unfortunately I'm unable to get a good look at my system at the present time, but
when I have more time I will confirm connections and line colours, however, I believe there is sufficient information for ColinB to solve his problem.

Sorry for the confusion.

Tails 1990 928S4 Auto RHD

ColinB

Dave, Tails
Thanks guys but I'm still not quite there. The mystery vac line doesn't come from the 7-way connector, it originates under the manifold and I can still only guess where the 'wrong' vacuum source to the flappy actuator is connected. Does anyone with MY89 or later have the intake off at the moment?

Colin 89GT

worf928

Actually, I think Tails did provide the mystery clue. You Previously wrote "..six-out rubber connector with one outlet blanked . The others 5..."

Tails wrote:

You have one blanked connector. Tails suggests that there should be two blanked connectors on the 7-way.

So, assuming that:
- there are no factual mistakes
- I have had enough coffee this morning
then, logically...

Your mystery connector is the vacuum like that should go over the right-side cam cover to the tank vent valve.

And your 7-way needs another plug.

Since, as you previously posted, your resonance flap will cycle then this line cannot go to the flappy actuator.

I'm not sure I understand your question Colin. The vacuum source for the flappy's solenoid is the 4-way connector.

In any case, if you have my intake article from the OC website, you can see pictures of the vacuum sources on pages 15 and 18. These are of course for a LHD car. One of the three vacuum sources on LHD throttle bodies must not be present on RHD cars.


No worries. I thought that since the booster and reservoir are - on RHD cars - on opposite sides of the engine bay that the plumbing might in fact not be the same as LHD cars.

I think so. Your observations of the 7-way connector are based upon how your '90S4 is plumbed?

worf928

In the USA we don't get the headlamp aiming system. However, all the wiring harnesses connectors to the lights contain the appropriate number of empty pin holes for the terminals. Thus, I believe - but am not sure - that the aiming system is electric and not vacuum based.

On LHD cars there is no vacuum to the idle stabilizer the only connections are a Bosch 2-pole and the actual air hoses that bypass the throttle plate.

If you compare your pictures to the ones in my intake article we may be able to find any RHD vs. LHD differences. I can post larger pictures if those in the article are too small.