Posts: 425
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Hi all,
I'm sure others have encountered this problem.
I had to change my RPM relay last year as the original was duff.
Anyway the new one does not prime/pressurise the fuel system, this results in a lot of cranking to get the car to start from cold.
I've tried the trick with the ignition key, rocking it from position 1 to 2 etc..., but it still doesn't get it to prime.
Is there an update? or anything that can be done to ensure that the fuel system primes before cranking?
James
One trick (I heard) is to flash the headlights first.
Have you tried to fix the original relay by replacing the 555 timer in it?
Ones I have fixed I just used a DIL socket so if it went again the chip can be changed quickly.
Some say thier cars have never primed when the key turns to position 2 for some reason.
Might be worth doing a survey with vin no. vs relay priming to see if there is a cut off point.
I am using an original (black cased with blue end) relay and mine primes fine.
Ask tho33 or ChrisS about using a solid state type relay as an experiment.
NickT.
Posts: 412
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Joined: Jul 2006
On mine when the RPM relay failed I just installed a normal relay so that when the ignition came on it turned the pump on.
You could actually here the system pressurised as the tone of the pump changed.
I never had a problem starting the car once I did this mod.
Dan
Posts: 569
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Joined: Aug 2006
is the relay from Hervey?
the one i got (with a green case) does not prime the lines on thesecond notch. although it does start the car.
I switched back to my old relay and use Hervey's as spare.
Dave.
Posts: 1,272
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I have a green cased one and an original black one, neither do the prime function. Someone, I can't remember who looked at the circuit and said it can't do a prime, it can only do it because of a voltage spike or sudden drop caused by flicking the key about or flashing lights.
VIN: 6511
I have a green cased one, it does prime but not always which I think could be an earthing problem somewhere.
Al
Posts: 425
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Joined: Jul 2006
bozzzydmc Wrote:I have a spare 'black cased' one and a dark green RPM relay ..Both of these 'prime' in my car ...I will bring these along to Norfolk in June so if anyone cars wont 'prime' you are very welcome to try these relays to see if they do the same in your cars 
Being such an easy part to swap that sounds like a good chance to flick between cars and see if there is a difference between them.
J
Posts: 425
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Joined: Jul 2006
Daniel Shane Wrote:On mine when the RPM relay failed I just installed a normal relay so that when the ignition came on it turned the pump on.
You could actually here the system pressurised as the tone of the pump changed.
I never had a problem starting the car once I did this mod.
Dan
Sounds like the simplest solution, I assume that the RPM relay is designed as a safely feature to cut of the fuel pump in the event of the engine stalling after a crash.
J
Posts: 412
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Joined: Jul 2006
Yeah but if you roll or crash the car the inertia switch should pop and stop the pump as the feed from the RPM relay goes through it.
It required no cutting of wires, I just made an adapter to go from the RPM relay plug to a normal relay base so that I could refit one if I ever wanted. I never did as it worked perfectly for 16000 miles
The one in my Quattro looks the same as the delorean one, but it always primes the system.
Dan
I would have to disagree with you on this one I'm afraid Dan even though I agree with you regarding the inertia switch cutting the fuel supply and the fact the normal relay is a working solution that overcomes the problem.
I believe anything that is designed as a safety feature should not be tampered with or over-ridden. Must be part of my line of work installing/ modifying safety systems on machinery (e-stops, door guard switches, finger guards, PILZ Safety PLC's etc)
If you WANT to over-ride the fuel rpm relay, stick a match in the relay contact to constantly keep it switched on, solder the switched terminals underneath or do the hard wired link by putting wires direct to the fuel pump relay socket. If you do then add an extra link to ensure the CPR has a 12v feed to it too, although you DO THIS AT YOUR OWN RISK.
If the solid state relay incorporates the prime function as a built in feature then this could be a solution to the cars that don't prime.
I think Blimey Ben has ChrisS's solid state one. It would be good to get his feedback on it.
NickT
