Audible Fuel Pump click but Fuel Pump is not running 1983 911SC

[xiaoman]

Hello To All,

I have read multiple posts about this problem and can’t quite find the solution, so I find myself asking it on the Forum with the hope I can find a solution.

My car is a 1983 911SC, it would not start and I did not hear the fuel pump making the usual sound/s.
I replaced the pump with one from our host and I “STILL” hear only a click when the key is turned to the on position. The same sound I heard from the previous one I replaced, indicating to me perhaps the older pump was/is fine.

1. With a test light in hand, I had the key in the on position, connected it to the positive side of the FP, but “NO” light signal from the tester…..however, I did hear/feel the click from the pump, same as before.
I assume the click means it’s getting "SOME” power….am I correct, if so why not enough to power the test light, does the click indicate something to test for?

BTW, The wires on the FP are correct, black to positive etc.

2 .I then jumped terminals 67a and 30, turned the key to on and the pump started to run normally, not just click once.

3. I swapped the red relay with a known working “black” one…..no change to FP, still not running/priming with the key in the on position.

4. Checked fuses and connections at the fuse box, all seem good.

If/since the pump has an audible click it seems to be getting some power but not enough to run…..what else to test?

Best, Ben

Same issue:
https://forums.pelicanparts.com/porsche-911-technical-forum/767660-fuel-relay-clicks-fuel-pump-no-power.html

[porschedude996]

Pump should not come on unless there is air flow over the Air-Flow Sensor. There is a switch connection on the forward side of the sendor.

[boyt911sc]

Originally Posted by xiaoman

Hello To All,

I have read multiple posts about this problem and can’t quite find the solution, so I find myself asking it on the Forum with the hope I can find a solution.

My car is a 1983 911SC, it would not start and I did not hear the fuel pump making the usual sound/s.
I replaced the pump with one from our host and I “STILL” hear only a click when the key is turned to the on position. The same sound I heard from the previous one I replaced, indicating to me perhaps the older pump was/is fine.

1. With a test light in hand, I had the key in the on position, connected it to the positive side of the FP, but “NO” light signal from the tester…..however, I did hear/feel the click from the pump, same as before.
I assume the click means it’s getting "SOME” power….am I correct, if so why not enough to power the test light, does the click indicate something to test for?

BTW, The wires on the FP are correct, black to positive etc.

2 .I then jumped terminals 67a and 30, turned the key to on and the pump started to run normally, not just click once.

3. I swapped the red relay with a known working “black” one…..no change to FP, still not running/priming with the key in the on position.

4. Checked fuses and connections at the fuse box, all seem good.

If/since the pump has an audible click it seems to be getting some power but not enough to run…..what else to test?

Best, Ben

Same issue:
https://forums.pelicanparts.com/porsche-911-technical-forum/767660-fuel-relay-clicks-fuel-pump-no-power.html

Ben,

In item #2 above, maybe you meant 87a and 30? There is no 67A terminal in the FP Relay. If you want to fix this problem, I strongly recommend that you read DKLever48’s thread about testing the different FP Relay Terminals. Everything you need to know about the subject was well covered in the thread. Good luck.

Tony

[xiaoman]

Originally Posted by boyt911sc

Ben,

In item #2 above, maybe you meant 87a and 30? There is no 67A terminal in the FP Relay. If you want to fix this problem, I strongly recommend that you read DKLever48’s thread about testing the different FP Relay Terminals. Everything you need to know about the subject was well covered in the thread. Good luck.

Tony

Tony,
You are correct about the typo.....87A, not 67A.
I would like to take a look at the thread you are suggesting, can you provide the link or tell me how to go about finding it, there are so many threads on the forum finding a specific one for me seems a bit daunting.
Hopefully the read will answer my questions about the why/what etc.
Otherwise I will be back on this thread asking a few more questions.

Best, Ben

[wazzz]

FP should not receive power until you crank the engine, and then of course it keeps getting power once the engine is running, but from a slightly different circuit. You shouldn't hear any click at the pump itself when you switch ignition on. The click you are hearing probably comes from the FP relay tripping, and this is normal.
You should check that the airflow sensor contact at the airflow meter sensor plate opens as soon as the plate moves. If not that would explain the no start.

See this well made animation for an explanation of how it works.
https://nineelevenheaven.wordpress.com/the-protection-circuit-of-the-fuel-pump/

[xiaoman]

Originally Posted by wazzz

FP should not receive power until you crank the engine, and then of course it keeps getting power once the engine is running, but from a slightly different circuit. You shouldn't hear any click at the pump itself when you switch ignition on. The click you are hearing probably comes from the FP relay tripping, and this is normal.
You should check that the airflow sensor contact at the airflow meter sensor plate opens as soon as the plate moves. If not that would explain the no start.

See this well made animation for an explanation of how it works.
https://nineelevenheaven.wordpress.com/the-protection-circuit-of-the-fuel-pump/

wazzz,
Thanks for the diagram and your explanation/clarification about how this part of the fuel system works, I have a much better understanding of the system.
I will continue to do my testing......maybe air flow sensor is the next item to check.
Best, Ben

[boyt911sc]

Originally Posted by xiaoman

Tony,
You are correct about the typo.....87A, not 67A.
I would like to take a look at the thread you are suggesting, can you provide the link or tell me how to go about finding it, there are so many threads on the forum finding a specific one for me seems a bit daunting.
Hopefully the read will answer my questions about the why/what etc.
Otherwise I will be back on this thread asking a few more questions.

Best, Ben

Ben,

On top of the technical forum page (this page) you will see the Blue Banner and go to “Search”, select “Advanced Search”, enter the User’s name (DKLlever48), then select “Find Thread Posted by User”. All the threads started by DKLever48 will appear. Open the thread “Fuel Pump Relay Testing”.

Start reading how to test the five (5) terminals of the FP relay namely:
87A
87
86
85
30

You will be very familiar with FP relay after reading the discussions.

Tony

[xiaoman]

Tony,
Will do!
Many Thanks, Ben

[xiaoman]

I got finally got the SC to start this morning, but it would die after a very short time.....it still seemed like a no gas situation.

I checked the pump again and the probe would light up while using the start position on the key.

The jumpers back on 87A and 30 and the car would start and run alright.....is there any danger to the wiring to leave the relay on for a prolonged time while trying to diagnoses the problem? (no driving, just driveway running)

I did notice that the tach was not responding, showing no revs etc.any red flags here?

Thanks, Ben

[boyt911sc]

Originally Posted by xiaoman

I got finally got the SC to start this morning, but it would die after a very short time.....it still seemed like a no gas situation.

I checked the pump again and the probe would light up while using the start position on the key.

The jumpers back on 87A and 30 and the car would start and run alright.....is there any danger to the wiring to leave the relay on for a prolonged time while trying to diagnoses the problem? (no driving, just driveway running)

I did notice that the tach was not responding, showing no revs etc.any red flags here?

Thanks, Ben

Ben,

Instead of jumpering terminals 87A and 30 to run the FP, try disconnecting the AFS plug and start the motor. Removing the AFS plug would keep terminals 87A and 30 connected (closed) with a good working FP relay. Try this trick and keep us posted.

Tony

[xiaoman]

Hi Tony,

Thanks for staying with me on this........I have read a lot of your posts and appreciate the assistance to me as well as your dedication to all of the members on the forum.
The car will run but seems slow to respond/not peppy .....timing is correct
Some questions before I start to disconnect things.

1. Since the tach has stopped working does that indicate anything to you regarding my start only with jumpers on, or is it unrelated?

2.Will running the motor with the jumpers on (no driving) for. an extended period cause any issues?
I'd like to keep it running to burn off the oil that's accumulated on the exchangers to stop the smoking.

3. When disconnecting the AFS switch does the pump run by itself when moving the key to the start position......and will it continue to run after it is started?

4. What does bypassing the AFS accomplish and tell us?

I know all this seems "old" hat for you and a lot of members here.....Again, Many Thanks for all your effort as well as others chiming in on the thread.

Best, Ben

Clarify comment for me.....see post 11 on this thread.....concerned about removal etc.
https://forums.pelicanparts.com/porsche-911-technical-forum/988110-79-sc-location-air-flow-sensor.html

[PeteKz]

Ben:
1. The tach receives its signal from the CDI box. Since it does run, it seems to me that the tach problem is independent. Do you have the stock Bosch CDI box? Does it make a high-pitched whine when you turn the key to Ignition? It should.
2. Running the engine with the jumpers attached will not hurt anything.
3. When you disconnect the AFS switch, the fuel pump should run when the key is in the Ignition position, whether the engine is running or not.
4. The AFS is a safety feature that stops the fuel pump when the engine is not sucking air through the intake. It stops the FP by interrupting the FP relay. Disconnecting the AFS will help us verify FP relay function.

[xiaoman]

Originally Posted by PeteKz

Ben:
1. The tach receives its signal from the CDI box. Since it does run, it seems to me that the tach problem is independent. Do you have the stock Bosch CDI box? Does it make a high-pitched whine when you turn the key to Ignition? It should.
2. Running the engine with the jumpers attached will not hurt anything.
3. When you disconnect the AFS switch, the fuel pump should run when the key is in the Ignition position, whether the engine is running or not.
4. The AFS is a safety feature that stops the fuel pump when the engine is not sucking air through the intake. It stops the FP by interrupting the FP relay. Disconnecting the AFS will help us verify FP relay function.

Hi Pete,
Thanks for the clarification about runtime and the AFS switch, it was very helpful.
To answer a few of your questions.......
Yes, the CDI Box was rebuilt by Bob Ashlock, who did an incredible job with a fast turnaround.....the dead box was the reason for the layup on my SC...so yes whine and great spark present.
Funny thing about the tach, is that in the beginning when cranking the motor with a no start, I could see the tack needle moving but after the start no revolutions showing.
I need to get to work so the SC will need to wait for a few days....

Best, Ben

[PeteKz]

If Bob A rebuilt your CDI box, then it's most likely the tach that isn't working correctly. But ask Bob anyway. If the tach moves when cranking, then the wire connection to the tach most likely is okay.

[xiaoman]

Tony,
I am back after reading the posts on Dklever48 journey:Hoping to limit this thread to much less than Dklever's.

I did the following tests and it seems that I need to disconnect the AFS plug as you suggested.....

BTW, I did switch the relays, no change

Originally Posted by boyt911sc

Ben,

Instead of jumpering terminals 87A and 30 to run the FP, try disconnecting the AFS plug and start the motor. Removing the AFS plug would keep terminals 87A and 30 connected (closed) with a good working FP relay. Try this trick and keep us posted.

Tony

Here is the basic test for the FP and relay circuitry:
1). Pull out the FP relay and do the test (ignition switch @ OFF position) for the individual terminal at the socket: A simple 12-volt self-powered test light will work well for this test or a regular non-powered test light, or a volt meter.

87...........no power check
87a.........no power check
86...........no power (87a 86 are bridged) check
85...........no power (should be grounded at this point) check
30...........no power (has ground contact?) check

2). Turn ignition switch @ ON position (not start):

87............no power check
87a..........has power check
86...........has power check
85...........no power, presence of ground contact (?) check I assume you mean because there is no power there is ground etc........
30...........no power, presence of ground contact (?) check

3). Next, insert the FP relay into the socket and turn the ignition SW @ ON position (not start):

87...........no power check
87a........ has power check
86……….. has power check
85...........should have ground contact (?) no power
30...........no power but exhibit ground contact. (?) no power

4). To test terminals #30 and #85, follow test #3 and do the following:
a). Remove the air filter cover and filter.
b). Lift the AFS (air flow sensor) very briefly (no more than a few seconds) Three (3) seconds are too long for this test. The FP should run and deliver fuel to the injectors. No Fuel Delivery

All the above is for a NORMAL operating FP and relay circuitry. Any deviation for these conditions will identify the culprit/s. The FP is good and out of the equation. If you have any question/s, just ask. Keep us posted.

Tony

From ossiblue

Try one more test, if you will (you may need an assistant.) Listen closely to the pump relay as someone turns on the ignition. Do you hear (feel) the relay “click?" check

With the ignition still on, have your helper gently lift the air flow plunger, does the relay "click" again? No click



I read an earlier post that says there is a wire/connector near the front of the engine that may interrupt the AFS without removing the cap on the TB....is this true, any pictures of the location? Is there another way to bypass the AFS switch?

My concern about the boot because of its location, is breaking any the hoses or their connectors as well as the clip on the AFS....if that's the only way then I will attempt it

Best, Ben

[xiaoman]

Originally Posted by boyt911sc

Ben,

Instead of jumpering terminals 87A and 30 to run the FP, try disconnecting the AFS plug and start the motor. Removing the AFS plug would keep terminals 87A and 30 connected (closed) with a good working FP relay. Try this trick and keep us posted.

Tony

Tony, I found the post I was mentioning and you were on the thread.....starting at post 2

Question, can I use this connector to bypass the switch?

Thread mentioned"
https://forums.pelicanparts.com/porsche-911-technical-forum/957179-wiring-where-does-air-flow-switch-wire-go.html

Best, Ben

[xiaoman]

I am continuing to do some tests and ran across a thread that mentioned testing terminal 85 on the FP relay with a test light.........

I Performed the test and the TL did not light suggesting no ground. The only thing done recently was to change the FP and to install a re-built CDI box......as mentioned earlier, the tach is now not working now.(related issue?)

I know I need to disconnect the AFS switch, for various reasons, I would like to do it at the harness near the CDI....but I don't know which wire OR if it can be done that way, without causing more issues...suggestions?
Best, Ben

BTW, is there any problem keeping the jumper wires on 87A and 30 while driving the car? Does the rely need to be put back into the board or is it alright to leave it out?

[boyt911sc]

Ben,

Based from your testing (item #4), I suspect there is an anomaly at terminal #85. Do this test to confirm:
1). Connect a CIS pressure gauge to check for cold control fuel pressure.
2). Turn the ignition switch to ON/Run position (not START).
3). Use a test light to confirm terminal #85 is GROUNDED. Keep the TL LIT during the test.
4). Disconnect the AFS plug from the backside of AFM (air flow meter).

The FP should run and the TL should turned OFF. For normal condition, these two (2) conditions should be present. If NOT, terminal #85 is the CULPRIT. Keep us posted.

Tony