In need of Fuel Pump Control Relay

[hester_prynne]

Does anyone have a Fuel Pump Control Relay for sale? I can't seem to find one. My car is a '78 280z.

Thanks,

_Tony

[Wade Nelson]

Tony -

Forget about the OEM relay. Get a standard relay, $10, at NAPA. HAve someone who understands electrical show you how to properly wire it in. Have a schematic printed out and ready for them. Buy also a wired socket (comes with pigtails) so the relay can be replaced easily down the road.

Chasing extinct parts is pointless, expensive, and even if you found a used one, the contacts are probably well worn. There's simply no benefit other than how fast you can plug it in and be done.

See my other thread on HVAC / Intermittent fan if you want to see a picture of a 30 year old relay with burnt contacts.

Alternately, you may be able to repair the one you've got. Have you opened it up? Does the coil have continuity?

All relays are basically the same, it's only the packaging and arrangement of terminals that makes one OEM and another generic. Sure, some are single pole and others are double, but a general purpose relay, like the Bosch, can generally be wired to achieve exactly the same electrical result as the OEM one.

I'll sometimes remove the top off a failed relay, gut it, and re-use the bottom (the part that holds and arranges the terminals) so it's plug-and-play, and wire the new relay socket pigtails to the old bottom.

The attached picture will give you a "Relays 101" understanding:

The relay on the left is a Toyota relay $75. It functions no differently than the relay on the right, a $10 generic relay. The MAIN difference is the larger plastic shell, which comes down and protects the terminals from water getting on them from the top. People pay an extra $65 for .02 worth of plastic.

The two relays on the right are ALMOST identical, one has two output terminals, the other only one. Sometimes one terminal is normally open, and the other normally closed.

Now look at the fancy FORD relay. It's not just a relay. It's got an IC "chip" in it, a capacitor, and a resistor. Probably some sort of TIMER, where the relay stays open or closed for X seconds after power goes on or off. Kind of like the timer that runs the cooling fan for the injectors on the 280ZX.

If I hadn't cut the case open, I would have never known there was more going on in there. Sometimes relays contain a small diode, especially when they're used to drive an inductive load, like a motor. The diode prevents arcing when the contacts open, making them last a LOT longer. It's good practice to "protect" a relay in this manner.

Picture 2 shows the BACK of the generic relay package, showing you what connections go where, how the pins are wired. This is a "headlight" relay, with two output pins, to drive two (head)lamps.

Edited August 2, 2012 by Wade Nelson

[Zed Head]

I think that he's looking for the multifunctional relay that has the alternator circuit and the oil pump switch circuit running through it to control the fuel pump power. The one that they used from 1978 on. Probably still work-aroundable, just not a simple circuit.

[Wade Nelson]

My assumption was the ECM had a fuel pump output that controlled the fuel pump relay, but your post suggests otherwise:

Let's figure out the logic if it's all done the "hard way..."

1) The alternator provides power to run the fuel pump while engine is spinning, quits pumping fuel if the engine stops.

2) Oil pressure provides a failsafe to cut off the fuel pump if oil pressure is lost.

3) The CRANK signal provides power to run the fuel pump BEFORE oil pressure comes up.

4) Ideally you'd want the fuel pump to run for 5-10 seconds @ ignition on to prime it, but that would get complex

The oem relay/circuit may "allow" the FP to run for 5-10 seconds @ ignition on UNTIL it looks to see if it has oil pressure.

Duplicating ALL of that would indeed be complex, but a simpler circuit would work fine for most drivers. At most 2 diodes and 2 relays. $25.

If these relays are truly extinct maybe I should start manufacturing a plugNplay replacement, or at least sketch out a circuit for those who need one. I'd need an old one to cut apart & play with. And someone begging or bribing me to do so...

Edited August 2, 2012 by Wade Nelson

[hester_prynne]

I took the cover off of the Fuel Pump Control Relay today and everything looks fine. I'm just trying to eliminate things that could be causing my electrical problem (I believe it is electrical).

Recently my fuel pump stopped priming when the key was turned to the ON position. Now the car idles very low and wants to die until I have driven it for 10 minutes or so, after which it idles like normal. I have replaced the fuel pump with a new unit and I also inspected the Fuel Pump Relay it appeared to be OK.

I can jump the two WHITE w/BLACK Stripe wires on the Fuel Pump Control Relay plug and the pump with prime with the key in the ON position. Any one have an idea of what else I could look at for the problem?

Thanks for the help with how to create a new relay by the way. I may break down and build one just to be sure the old relay is not the problem.

_Tony