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Clicking fuel pump relays

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Car is an '84 930. I noticed before that occasionally I get a loud clicking from the car it idle speed. Blip the throttle and it goes away. I put it down to a noisy tappet or something similar, was going to drop it off at the dealer for a look.

I discovered today that it's the fuel pump relays in the front - they are both clicking rapidly (~10-15hz) and getting warm. I know thats not right!

I dont have a wiring diagram for the 930 but I wonder if its a tachiometric relay similar to the ones they used in K-jet VW Golf GTIs back in the day - where the relay only kicks in when engine speed is above a certain low limit. Could it be that when the idle speed is low the relay will start to disengage then click back again as the next cylinder fires?

Anyone seen this before? I recently had a fuel pump relay fail and I guess that extended periods of toggling like this will seriously 'life' the component.
 
Your not alone, mine does exactly the same. I believe the air flow sensor switches the relays, as the sensor opens with the air flow into the engine the fuel pump relays are switch on. I think your right, at idle the air flow sensor is switching the relays on and off as the air pulses past. I don't think mine is clicking quite as rapidly as yours though.

Stu
 
If you think that is the problem, that is easy to test. Simply disconnect the electrical plug that goes to the CIS metering plate (flapper valve). If the problem still persists then you know that is not the problem.

The purpose of the switch you are bypassing by disconnecting it is to prevent the engine getting flooded by leaving the ignition on. The other purpose is if you were involved in an accident and the engine cut out then the fuel pumps would be turned off too!
 
Right, will give that a go and see what happens.
If that stops the relays clicking, then is it at fault? Or it is just because the idle speed is too low and inlet pulses cause it to flutter?
 
ORIGINAL: nathan 1981 930 G50

If you think that is the problem, that is easy to test. Simply disconnect the electrical plug that goes to the CIS metering plate (flapper valve). If the problem still persists then you know that is not the problem.

The purpose of the switch you are bypassing by disconnecting it is to prevent the engine getting flooded by leaving the ignition on. The other purpose is if you were involved in an accident and the engine cut out then the fuel pumps would be turned off too!
Click to expand...
Nathan,
The connector on the metering head, do I need to move the airbox out of the way to get to it or is it in plain view?
I had the relays clicking again today (for the first time in ages) and when I popped the lid I couldnt see the connector you mentioned.
 
AFAIK the connection you need to get at is on the left hand side of CIS fuel head and to the right of the flap metering system. The airbox should not be in the way providing you can get your hands behind there!
I have never needed to unplug mine on the car as I never had the need.
The whole assembly though is currently on the bench though while I am doing 'upgrades'[:D]
1799190505_2b09aa2fcd_o.jpg

 
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