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Join Date: Nov 2013
Location: Zion National Park Utah
Posts: 39
1979 SC Fuel Relay gremlins

I brought a spare fuel relay (cheaper version) to carry with me ... just in case. (from our Hosts)

Anyway to be prudent I tested it and it didn't work - put the old one back in - all fine !

So sent it back ... and ordered the more expensive "Genuine Porsche" (although still made in China !) That just arrived - and guess what - it doesn't work e
.

Is there some test I can do other than plugging it in to see its really bad. Seems by car is good enough test bed !


Last edited by ukinusa; 05-18-2020 at 07:21 AM..
Old 05-18-2020, 06:28 AM
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How tight does it fit in the socket? Sometimes it is the pin alignment in conjunction with usage of the socket. Check to see if the pin alignments are identical in separation and angle between all the relays.
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1978 Targa - 1980 3.0; Carrera intake; Megasquirt 2; EDIS ignition; 22/28 mm torsion bars and late Carrera sway bars; Carrera front brakes. Targa top rebuild in 2017. Suspension rebuild in 2019. Needs new paint and interior carpets.
Old 05-18-2020, 06:39 AM
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Pin85 to ground, pin 86 to 12v, first relay should open.
If you put 12v then on pin 30, you should also see 12v on 87 (given you connected 85 and 86 as described).
To test the second relay (fuel pump) : put pin 85b to ground additionally and you should hear the second relay click. 12V should now also be available on 87b.


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Old 05-18-2020, 06:55 AM
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FP relay tests........

Quote:
Originally Posted by ukinusa View Post
I brought a spare fuel relay (cheaper version) to carry with me ... just in case.

Anyway to be prudent I tested it and it didn't work - put the old one back in - all fine !

So sent it back ... and ordered the more expensive "Genuine Porsche" (although still made in China !) That just arrived - and guess what - it doesn't work .

Is there some test I can do other than plugging it in to see its really bad. Seems by car is good enough test bed !

Steve,

You could bench test the FP relay by using continuity tester or applying 12 volts dc. ‘‘This is how I test it:
  • Terminals #87a & #30 are NC (normally closed)
  • Terminals #87 & #30 are NO (normally open)
  • Terminals #86 & #85 are the terminals for the switch.
  • When you apply 12-volts to #86 and #85 is grounded, the normally closed 87a-30 will switch to 87-30 position.

Imagine the relay is installed in the car. When you turned the ignition switch to ON position (not START), power is applied #86 and if #85 is grounded, the “switch” will be energized from 87a-30 (NC) to 87-30 (NO).
Note: Terminals 87a and 86 are bridged or connected at the FP relay socket.

So disconnecting the AFS plug from the metering unit is removing the ground for #85. And when you turned the ignition switch to ON position and supply power to 86/87a (bridged), the normally closed terminals (87a-30) will remain closed because the ground was disconnected. Thus causing the FP to run every time the ignition switch is activated.

If the relay switch is defective or stuck at either positions, the relay will not be able to work normally and have to be replaced.

Tony

Last edited by boyt911sc; 05-18-2020 at 07:42 AM..
Old 05-18-2020, 07:35 AM
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Thanks guys - will follow these ideas and report back
Steve
Old 05-18-2020, 09:06 AM
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So - before I removed the 12v battery and found suitable test leads and clips I had a brain wave ! Rare I know !! A friend has an almost identical 1980 sc - what better way to test these relays !

Upshot - both my "faulty' relays worked just fine in her car, but when I put them in my car - zilch/nada. So I think the issue lies in the female socket . What is somewhat scary is the relay I have in now works just fine, so maybe one of the pins on this relay is set 'just so' but could loos e contact at any point.

I need to get behind or 'into' that rubber socket and look at all the connections and size of the pin sockets - which I assume means lifting off the fuse panel to get access...

I still want to follow the testing protocols outlined above, but that is less urgent now; clearly these faulty relays are in fact ok - at least on another SC !
Old 05-18-2020, 03:32 PM
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You could try opening up the prongs on the relay to ensure it is making contact when inserting it into the panel.

Lou
Old 05-18-2020, 04:08 PM
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Read DKLever48’s fuel pump relay thread.......

Quote:
Originally Posted by ukinusa View Post
So - before I removed the 12v battery and found suitable test leads and clips I had a brain wave ! Rare I know !! A friend has an almost identical 1980 sc - what better way to test these relays !

Upshot - both my "faulty' relays worked just fine in her car, but when I put them in my car - zilch/nada. So I think the issue lies in the female socket . What is somewhat scary is the relay I have in now works just fine, so maybe one of the pins on this relay is set 'just so' but could loos e contact at any point.

I need to get behind or 'into' that rubber socket and look at all the connections and size of the pin sockets - which I assume means lifting off the fuse panel to get access...

I still want to follow the testing protocols outlined above, but that is less urgent now; clearly these faulty relays are in fact ok - at least on another SC !

Steve,

Search DKLever48’s thread about fuel pump relay socket testing. Everything you need to know about the 5-pin relay socket for the FP relay. By the time you finished reading the 5-page thread, you will knowledgeable in the subject and ready to tackle any problem facing you.

Tony
Old 05-18-2020, 04:29 PM
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Slide a razor blade down the pins on the new relays to see if they work.
The female socket terminals in the relay base can spread over time.
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Old 05-18-2020, 05:58 PM
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My was on the point of failure - It was getting extremely hot and when I wiggled some wires in behind the panel my pump would cut out. I replaced socket from one on a donor harness and problem solved.
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1978 Targa - 1980 3.0; Carrera intake; Megasquirt 2; EDIS ignition; 22/28 mm torsion bars and late Carrera sway bars; Carrera front brakes. Targa top rebuild in 2017. Suspension rebuild in 2019. Needs new paint and interior carpets.
Old 05-18-2020, 07:59 PM
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So I followed all test protocols, and both suspect relays tested good.
I opened the pins slightly with a fine blade - they were a little tight.
Socket 30 was very wide so closed that down with needle nose pliers, to grip pin better.

My assumption of 2 bad relays was based on the not hearing the FP run - I am little deaf I admit. As I couldn't hear the FP why start the car ? ! I have no idea why teh FP went quiet - poor connection at the wide open #30 ?

Moral - test in sequence and VERIFY the failure too...is still real or there in each test cycle - I didn't

Tony (as ever - a huge thank you) . He referred to his test procedures in another thread and there was also a small commentary too from him. In case others stumble here, I will repeat them below.
================================================== =
Credit 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
87a.........no power
86...........no power (87a 86 are bridged)
85...........no power (should be grounded at this point)
30...........no power (has ground contact?)

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

87............no power
87a..........has power
86...........has power
85...........no power, presence of ground contact
30...........no power, presence of ground contact

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

87...........no power
87a.........has power
86...........has power
85...........should have ground contact
30...........no power - but exhibit ground contact.


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.

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.
Terminal 30 is connected to the fuel pump.

87a is connected to the switched ignition.

87 is connected to the starting circuit.

86 is connected to the ignition.

85 is connected to the air flow sensor ("safety switch".)

When you turn on the ignition, power goes to 86 and the relay coil is activated because it is grounded via terminal 85. This moves the relay leg to 87.

As soon as you move the key to "start," current flows through 87 to 30 and the fuel pump runs and the engine fires and runs.

As soon as the engine creates intake vacuum, the air-flow sensor (connected to the plunger in the intake) switches "open" breaking the ground connection to 85 in the relay.

As soon as the ground is broken, the relay coil de-energizes and the switch flips to 87a.

Now, 87a (continuous ignition power) is feeding 30 (fuel pump) and the engine runs until the ignition is switched off.

When you jumped 30 and 87a, you directly connected the fuel pump (30) to a power source (87a) with the ignition on. That's why your pump ran.

From your tests, it appears your relay is bad. Since you know the pump does run, plug in the relay and have someone turn on the ignition. Do you hear the relay "click?" If not, replace the relay.

Even if the relay does click, it may be bad (ie. it clicks because the leg flips to 87, but doesn't switch back.) You have already lifted the sensor plate and the pump did not run. You jumped terminal 30 and 87a and got the pump to run. The only remaining suspect is the relay.
Old 05-19-2020, 07:42 AM
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For good RED relays, go to 914rubber.com

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Old 05-19-2020, 07:49 AM
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