MillenniumFalcon

I'm still digging through all the shade tree fixes done to my car over the years...trying to get things right again.

My car has the wires for the fuel pump safety switch disconnected and taped off... the fuel pump comes on and stays on where you turn on the key. I did a continuity check on the safety switch on the back side of the airflow sensor- when the airflow sensor is resting on it's stop, there is continuity. Raise the airflow sensor, and there is no continuity...

It seems backwards to me- is this the way the switch is supposed to work? If so, why do you think somebody would have disconnected it and taped off the wires?

Thanks,

Dave

1975 911S

theiceman

I seem to remember researching this once before. This is correct the return for the circuit is completed when the metal plate falls and grounds the switch. A very simple design makes the air flow plate the actual switch. If the engine stops that plate will absolutely fall and kill the fuel pump. Well, assuming the car is the right way up,
I would even bet porsche designed it to ground when it is upside down too

theiceman

Okay think I got it
When the switch is closed normally it allows the pump to be run when the key is in the start position
When the car is started the circuit deenergizes and the relay contact goes to its rest position which completes the circuit for fuel pump for continuous running.
If the plate falls and completes the circuit again and energizes the relay. This pulls the contact off the rest position and breaks the circuit for fuel pump running. And puts it back to running on key start only
You really should get a Bentley if you can for that car.
Even if you borrow someone's sc book this piece is the same.

Lorenfb

"When the switch is closed normally it allows the pump to be run when the key is in the start position"

That is correct, i.e. When starting the engine the sensor plate switch is
essentially bypassed to allow the FP to run. Once the ignition switch
is off the start position, the FP operation relies on the position of the
sensor plate.

MillenniumFalcon

Thanks guys- I didn't consider the Bentley manual because it said it didn't cover my year car (1975). I have downloaded a bunch of stuff off the web that is generic CIS stuff, which has helped, but I cannot even find the fuel pump relay anywhere in the car....

Then I went to adjust the microswitch on the throttle body, only to discover that it's either missing or my car didn't come with one... the Haynes manual gives the procedure for adjusting it, but does not discuss what the microswitch does...! So, i have no idea whether my car is missing the part, or whether some cars were made without a microswitch on the throttle body. This is when I discovered that the throttle butterfly plate was only opening 1/2 way at full throttle, because the linkage that passes through the firewall had broken at some point, and somebody took what was left of it and curled it around the bellcrank, effectively shortening the linkage by a substantial amount. Waiting on a linkage from Germany now.....

My other post about the WUR- early cars had a return line made from flexible hose with regular clamps. Later cars have the hard plastic return line coming off the WUR with a banjo fitting, and the entire return line assembly (4 lines and a junction block) are one part number... wonder why they went to hard platic line in the later cars??

I really appreciate your input! I don't have access to any other cars to look at- just my Haynes manual, the internet and you guys.

theiceman

The switch is not a micro switch and it's not on the throttle body hour car I am sure has one because I have a 75 air plate I think and it has it. If someone doesn't post a pic I will post one later. It's a real pita to get to however as it's kind of behind the fuel distributor.

MillenniumFalcon

Iceman, it's really tough, because the car is old, it's been in the hands of many before me, and I can't be sure everything that is supposed to be on the CIS system is there.... it is a California car that had the smog system removed a long time ago. The engine number is a late 1975 build.

The WUR that is installed on the motor is the later type (the one with the banjo fitting for the return fuel line)- every diagram I read says this type of WUR belongs on a 1977 and later car. According to the diagram, a 1975 should have the earlier style WUR that has a clamped line for the fuel return line. My car also appears to have the correct return line system for a 1977 system (all plastic hoses, except that the WUR line that should be a plastic line, is missing and has been replaced by a clamped line). If I do have the wrong WUR installed, then I should probably have a microswitch on the throttle body, because then it is set-up like a 1975 should be set up??

I have no microswitch or microswitch support installed, and I cannot find any wires dangling that shoudl be connected to it (but they could have been cut and re-taped a long time ago, jsut like my fuel pump safety switch has been disconnected and taped back).

My rubber intake boot is the early style (pre-'77), without the extra elbow for the additional air pipe.

I do not have an Auxiliary Air Regulator or Additional Air Valve in the system, both of which would be found on a '77 and later CIS system.

So, it seems that I really should have a throttle microswitch on my CIS system.

The Big Question: I understand that the microswitch controls something both off-idle and at WOT.... BUT WHAT is it controlling??? Where do the wires from the microswitch go????

Everything I have read (and I have read a lot at this point) on line about CIS systems tells me that the CIS system evolved/changed quite a bit over the years.... they do mention that the throttle switch is there and that it has a function, but they never say what that function is. If I could find out exactly where the current from that switch goes, perhaps I could trace it to another component to see why it is missing.

At this point, I can assume nothing- This car has obviously had a lot of cheap, strange things done to it to keep it running on a budget, and all kinds of things could have been swapped out of it, or have been removed and some kind of work-around employed. The engine runs, and it seems to run not so badly, but I want the system to set up correctly- and I don't care whether it's for a 1975, 1976 or 1977 engine- as long as it's all there and doing what it is supposed to do!

I appreciate your help- thank you.

David

1975 911S California Car

theiceman

Once again I don't think there is any micro switch on the throttle body. But there is a swich (the safety switch ) on the air plate asm ( the blue thing. ) This is not really a "micro switch" at all but a safety cut off.

MillenniumFalcon

Thanks for posting the picture.. I am clear on the difference between the safety switch on the airflow meter and the microswitch that may/may not be on the throttle body (depending on what year CIS you have) Hmmmm...yours has the Additional Air Valve and the extra pipe going into the rubber boot on the throttle body (slide #2)

The parts diagrams that I am looking at show it set up one of two ways: either you have it set-up like yours (1977 and later) and no microswitch on the throttle body, or you have it set up like the earlier version, without the Additional Air Valve and associated plumbing, but you do have a microswitch on the throttle body.

See first slide below- this is supposedly the early set up (pre- 1977). This is exactly what I have on my car, sans the micro switch (item #10 on the first slide)

Second image is 1977 and later.

The microswitch is acted upon by the adjustable stop screw on the throttle body (item # 10 in the first slide), and Haynes manual shows method for adjusting it, but Haynes does not discuss what the switch does. All I know is that it has to be set for off-idle function and WOT function That is what I am thinking should be on my car, and really want to know what it sends current to on the CIS....