Another Fuel Relay Question

[Wizardof]

Hi guys,
Yet another person with fuel pump problems. I've got a 3.9 with EFI (14CUX) which was running quite happily until recently. Its developed a problem whereby there doesn't appear to be enough fuel reaching the engine.. but I'm not sure... So, I have been checking all the circuits out. On its own, when given a 12v supply the fuel pump appears to work ok. When I check the fuel pump relay i think it works but this is what I need to check..
The relay has a confirmed 12v supply entering it and it gets a signal feed when the key is turned, but the output of the relay is only around 8v. the signal feed is also around 8v... Is this correct?
Thanks!
Kevin

[stevieturbo]

Normally relays are trigger via an earth, not a positive feed.

Although Im not familiar with this exact application.


Sometimes you can get a bum steer through the coil in the relay if it isnt working, and see a positive voltage, when really the correct items for it to work arent there.

Does the relay click ? If power is getting to the pump itself, then its either the pump, or a blockage in the supply to the pump.

[ramon alban]

Hi guys,
Yet another person with fuel pump problems. I've got a 3.9 with EFI (14CUX) which was running quite happily until recently. Its developed a problem whereby there doesn't appear to be enough fuel reaching the engine.. but I'm not sure... So, I have been checking all the circuits out. On its own, when given a 12v supply the fuel pump appears to work ok. When I check the fuel pump relay i think it works but this is what I need to check..
The relay has a confirmed 12v supply entering it and it gets a signal feed when the key is turned, but the output of the relay is only around 8v. the signal feed is also around 8v... Is this correct?
Thanks!
Kevin

If you are measuring the output of the relay at the pump then you have a four volts idrop due to fuelpump resistor which is normally installed to reduce the voltage to the pump to reduce pump noise (on flapper Efi SD1's that is.) It may not be the same for hotwire.

If the fuel flow and/or pressure are low then you may have faulty pump, blocked filter(s) or damaged fuel pressure regulator.

[Wizardof]

Thanks for the tips guys.. I'll go and check out the fuel lines and pump.. Still intrigued by this relay though!!

cheers
Kevin

[x.l.r.8]

Sounds like it has the wrong configuration relay in the hole, not all 4 pin relays are the same. The relay needs a +ive and a -ive to operate the coil. one need tto be switched to activate the coil and allow current to pass between the other 2 pins be it either a -ive or positive feed. some relays will activate with a lower voltage feed. It sounds like the supply feed is being diverted to the supply which can happen if the wrong relay pin type is being used. They usually are labeled type 'A' or type 'B'.