 1975 Porsche 914 1.8 liter, fuel pump |
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| nigolusa |
 Mar 21 2009, 11:58 AM
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#1
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nigolusa  Group: Retired Members Posts: 157 Joined: 10-November 08 From: los angeles Member No.: 9,737 Region Association: Southern California  |
when first turning the key, not all the way, is the fuel pump supposed to be working?
Before installing, tested it and it spun. Now after completing the fuel tank installation, lines etc., I cannot hear it functioning. Is this a relay problem? Or does it spin after the engine starts? (IMG:style_emoticons/default/headbang.gif) |
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| echocanyons |
Mar 21 2009, 12:09 PM
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#2
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Advanced Member Group: Benefactors Posts: 2,115 Joined: 24-December 02 From: Bay Area, CA Member No.: 7 Region Association: Central California 
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It should spin while cranking.
You may also manually move the flapper on the AFM with the key in the on position it should also spin. |
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| Cevan |
Mar 21 2009, 01:23 PM
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#3
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Senior Member Group: Members Posts: 1,079 Joined: 11-December 06 From: Western Massachusetts Member No.: 7,351 |
Answer: no. With the key in the on position, the fuel pump will only run if the flapper on the airflow meter is pushed open (even just a little). When the key is the start position, the dual relay will power the fuel pump. Once the engine starts abd the key returns to the on position, air entering the AFM will keep the flap open and the fuel pump powered.
You can test the pump by turning the key to on and then pushing the flap open. That should make it run. You should hear the dual relay click on also. |
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| nigolusa |
Mar 21 2009, 02:54 PM
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#4
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nigolusa Group: Retired Members Posts: 157 Joined: 10-November 08 From: los angeles Member No.: 9,737 Region Association: Southern California |
QUOTE(Cevan @ Mar 21 2009, 12:23 PM)  Answer: no. With the key in the on position, the fuel pump will only run if the flapper on the airflow meter is pushed open (even just a little). When the key is the start position, the dual relay will power the fuel pump. Once the engine starts abd the key returns to the on position, air entering the AFM will keep the flap open and the fuel pump powered. You can test the pump by turning the key to on and then pushing the flap open. That should make it run. You should hear the dual relay click on also. Thank you Kelly and Chris. I will try and see what happens (IMG:style_emoticons/default/grouphug.gif) |
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| nigolusa |
Mar 21 2009, 03:13 PM
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#5
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nigolusa Group: Retired Members Posts: 157 Joined: 10-November 08 From: los angeles Member No.: 9,737 Region Association: Southern California |
I pushed the flap on the air flow meter, but nothing happened. No click from the dual relay and fuel pump not spinning.
Mind you, I haven't put any gas into the tank yet? What now? |
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| Cevan |
Mar 21 2009, 04:11 PM
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#6
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Senior Member Group: Members Posts: 1,079 Joined: 11-December 06 From: Western Massachusetts Member No.: 7,351 |
QUOTE(nigolusa @ Mar 21 2009, 05:13 PM) I pushed the flap on the air flow meter, but nothing happened. No click from the dual relay and fuel pump not spinning. Mind you, I haven't put any gas into the tank yet? What now? I'm assuming you had the key to the "on" position when you did this? If so, you probably have a bad dual relay. It should be mounted to the battery tray support next to the resistor pack. |
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| nigolusa |
Mar 21 2009, 04:24 PM
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#7
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nigolusa Group: Retired Members Posts: 157 Joined: 10-November 08 From: los angeles Member No.: 9,737 Region Association: Southern California |
QUOTE(Cevan @ Mar 21 2009, 03:11 PM) QUOTE(nigolusa @ Mar 21 2009, 05:13 PM) I pushed the flap on the air flow meter, but nothing happened. No click from the dual relay and fuel pump not spinning. Mind you, I haven't put any gas into the tank yet? What now? I'm assuming you had the key to the "on" position when you did this? If so, you probably have a bad dual relay. It should be mounted to the battery tray support next to the resistor pack. Any way to test the dual relay? |
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| Cevan |
Mar 21 2009, 07:03 PM
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#8
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Senior Member Group: Members Posts: 1,079 Joined: 11-December 06 From: Western Massachusetts Member No.: 7,351 |
Here is a very good explanation of how the dual relay works, including easy to follow diagrams.
You can test the relay and the harness. Unplug the relay and test each side. Put 12 volts to 86c and ground 85. You should hear it click. You should have continuity between 88z and 88a and between 88z and 88b when that side is powered. On the other side, put power to 86a and ground 85. Again you should hear a click. You should have continuity between 88y and 88d and between 88y and 88c. With the relay unplugged, test the relay socket to see if you're getting voltage to the relay. You should have 12 volts at 88z and 88y, even with the key off. Turn the key to on and you should have 12 volts at 86c. In the starting position you should have 12 volts to 86c and 86a. |
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| SirAndy |
Mar 21 2009, 11:28 PM
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#9
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Resident German Group: Admin Posts: 42,469 Joined: 21-January 03 From: Oakland, Kalifornia Member No.: 179 Region Association: Northern California |
QUOTE(nigolusa @ Mar 21 2009, 01:13 PM) Mind you, I haven't put any gas into the tank yet? You really shouldn't run the fuel pump dry. Get some gas in that tank ... (IMG:style_emoticons/default/shades.gif) Andy |
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| nigolusa |
Mar 22 2009, 12:06 AM
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#10
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nigolusa Group: Retired Members Posts: 157 Joined: 10-November 08 From: los angeles Member No.: 9,737 Region Association: Southern California |
QUOTE(Cevan @ Mar 21 2009, 06:03 PM) Here is a very good explanation of how the dual relay works, including easy to follow diagrams. You can test the relay and the harness. Unplug the relay and test each side. Put 12 volts to 86c and ground 85. You should hear it click. You should have continuity between 88z and 88a and between 88z and 88b when that side is powered. On the other side, put power to 86a and ground 85. Again you should hear a click. You should have continuity between 88y and 88d and between 88y and 88c. With the relay unplugged, test the relay socket to see if you're getting voltage to the relay. You should have 12 volts at 88z and 88y, even with the key off. Turn the key to on and you should have 12 volts at 86c. In the starting position you should have 12 volts to 86c and 86a. Relay checks out fine. How do I check the AFM harness is getting current at the ON position? |
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| zonedoubt |
Mar 22 2009, 11:14 AM
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#11
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Canadian Member Group: Members Posts: 668 Joined: 14-May 03 From: Vancouver, BC Member No.: 696 Region Association: Canada |
This a good article on the double relay: http://www.ratwell.com/technical/DoubleRelay.html
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