Help needed with troubleshooting saftey switch

[RickKlem]

When I turn my key to the On position my fuel pump begins to run. From what I understand the pump should not run until the starter has been engaged or if the air plate is lifted up. I am trying to figure out why mine is not reacting as expected. Where do I begin troubleshooting? Could the switch on the air plate be bad or out of adjustment? If so, how do you get to it and how do you test it?
I’m looking for step by step things to check for.
Thanks
Rick

[75 911s]

On my 75 the fuel pump turns on when the ignition switch is turned to "on" as well. I think this is a midyear design. I thought they changed it in 77 but things were changing mid production year as well. I thought they changed this when they went with the front fuel pump in 76. But I'm not sure. Was your 77 converted or is it one of the 77 3.0 cars? Where is the fuel pump?

[proporsche]

hi..have you had your 911 in some kind of service place?
if this happens it could be that you safety plug on your sensor plate is disconnected .this a safety device in case you turn the car on roof .It will stop the fuel pump.So when the plug is off the pump will run with the key on...
here different model of 911 but location same--check it..to start with..
ivan

[RickKlem]

Originally Posted by 75 911s

On my 75 the fuel pump turns on when the ignition switch is turned to "on" as well. I think this is a midyear design. I thought they changed it in 77 but things were changing mid production year as well. I thought they changed this when they went with the front fuel pump in 76. But I'm not sure. Was your 77 converted or is it one of the 77 3.0 cars? Where is the fuel pump?

It is a 77 that had a 2.7 and I installed a 81 3.0 in it. From what I understand the the 76 and later had a saftey switch on the air plate and it would shut the fuel pump of when it is in the rest postion. The power would come from the starter until the plate was lifted by air intake. Mine is acting like the switch is engaged or the plate is up and that is why i want to test it to see if that is my issue.


Thanks
Rick

[RickKlem]

Originally Posted by proporsche

hi..have you had your 911 in some kind of service place?
if this happens it could be that you safety plug on your sensor plate is disconnected .this a safety device in case you turn the car on roof .It will stop the fuel pump.So when the plug is off the pump will run with the key on...
here different model of 911 but location same--check it..to start with..
ivan

The green plug is plugged into it. It appears to be two wires in the plug, where do they go to?

[proporsche]

You plug is plugged in as you are saying and with the key on the fuel pump runs?

[RickKlem]

Originally Posted by proporsche

You plug is plugged in as you are saying and with the key on the fuel pump runs?

Yes

[proporsche]

ok i see you open another thread regarding the car was sitting for a while.What else did you do on it.
Any works on wiring?I would start with the basics fuel pump fuse and relay...
Ivan

[boyt911sc]

Originally Posted by RickKlem

When I turn my key to the On position my fuel pump begins to run. From what I understand the pump should not run until the starter has been engaged or if the air plate is lifted up. I am trying to figure out why mine is not reacting as expected. Where do I begin troubleshooting? Could the switch on the air plate be bad or out of adjustment? If so, how do you get to it and how do you test it?
I’m looking for step by step things to check for.
Thanks
Rick

Rick,

Check if the AFS electrical plug is connected at the backside of the AFM (air flow meter). You could find out if the electrical plug is connected by using your fingers to feel it or use a small mirror. If it is connected then you could do the following test.

a). Remove the FP relay and locate terminal #85 on the relay socket. You could test terminal #85 either using continuity test between #85 and the sensor plate. Or use a 12-volt TL (test light). I find the TL more convenient and practical for this kind of test.

Terminal #85 is a ground connection for the FP relay that goes to the driver-side terminal or pin of the AF switch. The passenger side terminal of the AFS switch is connected to the AFM body and the wire (brown) goes to D- (alternator).

If you decide to use a 12-volt TL which I strongly recommend, use terminal#85 (FP relay socket) as your ground source. Connect the alligator clip of the TL to a known 12-volt source or use the positive pole of the battery. With the TL connected to a 12-volt source, place the tip of the TL to any known good ground for test. Then test terminal #85. It should not lit up (NORMAL). If it does lit up, you got a PROBLEM.

Either the electrical plug is disconnected or the switch is defective.

b). AFS switch test and adjustment. Will do this later after you have done the above test.

Keep us posted.

Tony

Correction/edit:

The highlighted text above should read as: "It should lit up (NORMAL). If it does not lit up, you got a problem".

[RickKlem]

Originally Posted by boyt911sc

Rick,

Check if the AFS electrical plug is connected at the backside of the AFM (air flow meter). You could find out if the electrical plug is connected by using your fingers to feel it or use a small mirror. If it is connected then you could do the following test.

a). Remove the FP relay and locate terminal #85 on the relay socket. You could test terminal #85 either using continuity test between #85 and the sensor plate. Or use a 12-volt TL (test light). I find the TL more convenient and practical for this kind of test.

Terminal #85 is a ground connection for the FP relay that goes to the driver-side terminal or pin of the AF switch. The passenger side terminal of the AFS switch is connected to the AFM body and the wire (brown) goes to D- (alternator).

If you decide to use a 12-volt TL which I strongly recommend, use terminal#85 (FP relay socket) as your ground source. Connect the alligator clip of the TL to a known 12-volt source or use the positive pole of the battery. With the TL connected to a 12-volt source, place the tip of the TL to any known good ground for test. Then test terminal #85. It should not lit up (NORMAL). If it does lit up, you got a PROBLEM.

Either the electrical plug is disconnected or the switch is defective.

b). AFS switch test and adjustment. Will do this later after you have done the above test.

Keep us posted.

Tony

I tested 85 and it did not light up. So what is next step?

Thanks
Rick

[boyt911sc]

Originally Posted by RickKlem

I tested 85 and it did not light up. So what is next step?

Thanks
Rick

Rick,

The TL should light up. Make sure you have tested the TL using a known good ground source before using terminal #85. If terminal #85 is not grounded;
a). The electrical plug to the AFS (air flow sensor) switch could be unplugged or defective.
b). The brown wire between terminal #85 and the driver-side pin at the plug or connector is open.
c). You need to test the continuity between terminal #85 and the AFS switch.
d). The sensor plate is misaligned and not coming in contact with the ground contact.
e). Everything OK except the passenger side terminal (AFS) is not grounded.

These are the conditions you have to test and verify. One step at a time. Have you checked if the electrical plug to the AFS switch is connected or not? You did not mention anything about it. Keep us posted.

Tony

[RickKlem]

Originally Posted by boyt911sc

Rick,

The TL should light up. Make sure you have tested the TL using a known good ground source before using terminal #85. If terminal #85 is not grounded;
a). The electrical plug to the AFS (air flow sensor) switch could be unplugged or defective.
b). The brown wire between terminal #85 and the driver-side pin at the plug or connector is open.
c). You need to test the continuity between terminal #85 and the AFS switch.
d). The sensor plate is misaligned and not coming in contact with the ground contact.
e). Everything OK except the passenger side terminal (AFS) is not grounded.

These are the conditions you have to test and verify. One step at a time. Have you checked if the electrical plug to the AFS switch is connected or not? You did not mention anything about it. Keep us posted.

Tony

The switch is plugged in as I replied in post 7. In your first post you mentioned that it should not lite up, and if it did then I have a problem. That might have been a typo. I will check the rest of your suggestions and report back . I am doing this with the key in the off position, is that correct? By the way , I checked all of the other ports and they all lite up.

Rick

[timmy2]

When you installed the '81 which engine harness did you use?
The air flow switch is wired differently in the '77 than the '81.
The '77 has a brown with black single plug below the 14 pin connector at the fuse panel that is for the safety switch. The single wire female plug that goes to it, comes off the '77 engine harness just before the female 14 pin connector.
The safety switch wire in the '81 normally goes to the 2 wire "T" connector by the CDI box.

[boyt911sc]

Originally Posted by boyt911sc

Rick,

...............

If you decide to use a 12-volt TL which I strongly recommend, use terminal#85 (FP relay socket) as your ground source. Connect the alligator clip of the TL to a known 12-volt source or use the positive pole of the battery. With the TL connected to a 12-volt source, place the tip of the TL to any known good ground for test. Then test terminal #85. It should not lit up (NORMAL). If it does lit up, you got a PROBLEM.

Tony

Rick,

There were mistakes (typo) in the last 2 sentences above (post #9). It should read as:

"It should lit up (NORMAL). If it does not lit up, you got a problem"

My wife was calling me for dinner and quickly posted it. I had it backward. My mistake.

To recap it, the reason the FP is running with the ignition switch @ ON position could be caused by:

a). A defective FP relay.
b). Terminal #85 is not grounded.

Your test has shown that terminal #85 is not grounded. This is the problem. It should be grounded. The culprit could be one of the following:

a). Terminal #85 has a loose or open connection to the AFS (driver-side) pin or terminal. A continuity test has to be done.
b). The AFS switch is misaligned and not getting a good contact with the sensor plate.
c). The connection from the passenger side of the AFS terminal (plug/connector) going to D- (alternator) is loose or open.

Any of the above condition will cause terminal #85 to loose ground contact.

Tony

[timmy2]

Tony, unless he swapped the wires on the body or harness going from a '77 to an '81 engine harness, the safety switch won't work.
OP hasn't replied to my post as to how the wiring was adapted.

[boyt911sc]

Originally Posted by timmy2

Tony, unless he swapped the wires on the body or harness going from a '77 to an '81 engine harness, the safety switch won't work.
OP hasn't replied to my post as to how the wiring was adapted.

Rick,

The SC engine wire harness has a white 2-wire connector close to the 6-pin CDI plug. Take a look if this white connector is connected to the chassis wire harness. One is red coming from the ignition switch and the other brown/black or brown. This brown wire from the chassis wire harness is connected to terminal #85 (FP relay socket).

The other side (brown) for the engine harness goes to the AFS connector (driver side 1-2-3). If you post a picture of the engine wire harness with the white connector will be very helpful. Thanks.

Tony

[timmy2]

Brown/black on '77 body harness comes out below the rear 14 pin connector.
Tach and CDI power are in the "T" connector for '77
Refer to my earlier posts.
Need to know how the engine swap wiring was done.

Find the single brown/black wire below the 14 pin connector, ground it and see if the fuel pump stops.

[boyt911sc]

Originally Posted by timmy2

Brown/black on '77 body harness comes out below the rear 14 pin connector.
Tach and CDI power are in the "T" connector for '77
Refer to my earlier posts.
Need to know how the engine swap wiring was done.

Find the single brown/black wire below the 14 pin connector, ground it and see if the fuel pump stops.

Dennis,

I don't understand why you said that the white plug connection for the AFS switch is different from '77 to those of the SC's? I will take another look at the white connector from the '77S chassis and inspect the wires. Here is the picture of the engine wire harness on the '77S:



Below is the picture of the white connector from the engine harness that I got from you.


Shouldn't this be just a direct plug in to work? You are the harness guy and got all the experience about these harnesses. I just took the picture this morning and have not really look deeply into the details. Please advise. Thanks.

Tony

[timmy2]

Tony, look at your first photo. The wires going to the T plug are red and purple/black. They are CDI power and tach signal.
The 78 and newer body harnesses have red and brown/black (or brown/red) for CDI power and safety switch.
The '76 and '77 have the safety switch Brown/black wire as a single plug below the 14 pin connector.

[timmy2]

Take a good look at the schematics for the '77.
https://www.dropbox.com/sh/jxno8o6qae3roun/AADW1qBcRc53LoEG0TPbRwFva?dl=0