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Fuel Pump Relay

924nutter

924nutter

PCGB Member
Member
I just just recieved some new, genuine Porsche service supplements and am pleased to let you all know that my hypothethsis about the fuel pump relay was correct. The manual confirms that the electronic section of the fuel pump relay does need pulses from the terminal on the coil to enable it to close, so you can all base diagnoses of fault around that.
 
That'll be to measure the engine speed & cut off the fuel supply if the engine speed is less than 100 rpm won't it ?
 
Dunno. I knows what I knows and that's all I knows. The particular supplement I read made no mention of rpm. I was working on the obviously erronoeous assumption that it was a safety feature, ie ignition on with a stalled engine equals no pulses thus no fuel pressure in the event of an accident and severed fuel lines. 100 rpm works for me. I could just as easily be to prevent flooding or even hydraulic lock.
 
I seem to remember that the fuel pump will only run if the ignition is in the start position, or engine speed is greater than 100 rpm. It is supposed to be a safety device, to prevent fuel continung to be pumped when the engine is not running, as you suggest
 
To be really pedantic, you should call yourself 938 carrera if your car is a rhd car, as the 7 was for lhd cars and the 8 was reserved for the right hand drive models, according to the very informative book by Brian Long.
 
You are right, the relay is laid out this way as a safety feature; in case of a crash you hopefully won't be delivering a pint of fuel every ten seconds to the damaged pipes at the front of the car!!

If you look at the pin numbers on the relay you will find that they are a standard layout, pin 1 goes to coil neg, pin 15 coil pos, pin 30 battery pos, pin 31 battery neg, 87 goes to the pump (and warm-up reg/ aux air device) and some of them have pin 50 which is a cranking signal.

The same setup is used on a load of VWs and also the MK III/IV XR3i.
 
ORIGINAL: 924nutter

To be really pedantic, you should call yourself 938 carrera if your car is a rhd car, as the 7 was for lhd cars and the 8 was reserved for the right hand drive models, according to the very informative book by Brian Long.
Click to expand...

Correct !..........but my road going GT is LHD, while the race car is RHD, but they all had 93ZBN7 chassis numbers , so maybe I can be excused [:D] .

t11ner.... my fuel pump relay knowledge comes from my VW Jetta GLi days, when the market leading workshop manuals said something other than "too difficult, refer to main dealer."
 
Robin,
I thought I could search and find one of these for you very quickly, as I used to be well into these (problematic) relays when I had my 924 2.0 many moons ago... but have realised they seem to be not so generally available AND at exorbitant cost for a relay (£100-ish, for a relay?!) I’m sure you used to be able to get hold of these through: GSF, euro car parts or the like, but doesn’t seem certain now.

I believe the configuration of the relay pins would be as per the image I have posted on here - yours like this?
I used to have quite a few of these(!), but no longer, unfortunately, sorry.
(If not, maybe Charles M might be able to point you in the right direction?)

Good Luck (and Happy Easter to you both anyway [:)])
 
Thanks for the pin layout, that is the same as I am looking for. No one seems to have any stock apart from Design 911 and they have been waiting for a consignment to come in. They have just cancelled my order and returned my money with their apologies after 6 weeks of waiting. The hot wired switch works OK but is obviously not the best way forward.
Happy Easter to you and everyone, Robin.
 
..and also remember, Robin, that while this is directly switched on, you lose the facility on the relay which cuts the electric supply to the car in the event a bad accident (perish the thought!) [;)]

The relay prices are truly crazy!

Paul
 
Im afraid these have been on back order for about 2 years, any stock anyone had has probably been used up by now.
 
I have tried everyone, but it seems that all are out of stock, including one of the manufacturers (Siemens).
Anyone going to the Transxaxle meeting Sunday16th April?

 
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