How to test fuel pump relay (Page 1/1)
kingkitesurf AUG 11, 05:51 PM
I had a look everywhere here on the forum, google etc. All kinds of info on Fuel pump relays. But nowhere can I find how to test this Fiero V6 Fuel Pump Relay for proper functioning.
Normally a relay has a schematic embossed on there so you can test. The one that is in the engine compartment on the firewall driver side next to the A/C relay does not have that.
I have a 12v source and a multi meter.... Does anybody know how to test it?

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Job 86 Fiero GT 2.8 V6 with Lambo Countach body

fierosound AUG 14, 12:33 PM
Follow the power.
The ECM closes the relay for 3 seconds when key is turned on to prime/pressurize fuel system.
The once engine is running, the ECM receives a reference signal from distributor and then keeps replay closed.
The oil pressure switch is a backup in case relay fails.
It provides power to fuel pump once oil pressure builds up during cranking (and running).



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My World of Wheels Winners (Click on links below)

3.4L Supercharged 87 GT and Super Duty 4 Indy #163

[This message has been edited by fierosound (edited 08-14-2020).]

Rexgirl AUG 14, 04:48 PM
An easy place to start is to look for battery voltage on the Tan/White wire in the ALDL connector. That is the wire from the relay to the fuel pump .The ALDL connector is behind the cigarette lighter plate.
Patrick AUG 14, 04:53 PM

quote
Originally posted by Rexgirl:

An easy place to start is to look for battery voltage on the Tan/White wire in the ALDL connector. That is the wire from the relay to the fuel pump.



Interesting. I've used that terminal many times, but not in that manner. If I've wanted to test a non-functioning fuel pump, I've applied 12v to that terminal to bypass the fuel pump relay.
Blacktree AUG 14, 07:37 PM
The relay energizes that wire, also. So if the fuel pump relay is working, that wire should have 12VDC any time the fuel pump is supposed to be running.

The schematic is posted above. But just to be thorough, here's a testing procedure you can use.

- Make sure the black wire has a good ground
- Apply 12V to the green/white wire. The relay should click (if it has a good ground)
- Make sure the orange / black wire has power (hot at all times)
- Check for power on the beige/white wire when you turn the key

Side note: I've also seen the relay sockets deteriorate, and make it seem like the relay is bad.

[This message has been edited by Blacktree (edited 08-14-2020).]

fierosound AUG 14, 11:16 PM

quote
Originally posted by Patrick:

Interesting. I've used that terminal many times, but not in that manner. If I've wanted to test a non-functioning fuel pump, I've applied 12v to that terminal to bypass the fuel pump relay.



It's also handy when you need to empty the fuel tank (if pump works)


Patrick AUG 14, 11:27 PM

quote
Originally posted by fierosound:

It's also handy when you need to empty the fuel tank (if pump works)



Of course, the need to empty the tank is usually to lessen its weight prior to dropping it... to investigate why a fuel pump isn't pumping. Yeah, been there done that.
fierosound AUG 15, 08:29 PM

quote
Of course, the need to empty the tank is usually to lessen its weight prior to dropping it... to investigate why a fuel pump isn't pumping. Yeah, been there done that.



But handy to know about the ALDL fuel pump connection...

There are people driving around with a bad fuel pump relay and don't know it.
Their only complaint is, "I have to crank for half minute or longer before it starts".
It's the Oil Pressure Sender powering up the fuel pump once oil pressure has built up from cranking engine.

Now... if their Oil Pressure Sender ALSO fails, they are hooped because the fuel pump isn't getting power from anywhere.
Unless they know they can "hotwire" the fuel pump through the ALDL port to power it up.

altownsend OCT 17, 11:46 PM
1986 Fiero, 4-speed manual, V-6

Fuel Pump Relay:

My prime circuit was not working, causing me to get the il pressure up, so that the fuel relay would power the fuel pump. So, I cut the green/white stripe wire coming from the ECM, and spliced it between a 12 VDC power source (keyed), and a toggle switch to power the pump at first start-up.

Two days ago, October 15, the toggle switch circuit stopped working.

Troubleshooting:

I jumped the wires for the fuel pump at the OBT port, and the pump did not activate.
I checked the fuse (Fuse position 2, 10A), fuse okay
I removed the fuel relay and attached an electrical load - lamp-using the brown striped fuel pump wire and green/white wire at the fuel relay plug to test 12VDC at the plug. With my switch, I confirmed 12 VDC at the fuel relay plug.

I purchased new fuel relay and put it in, and neither of the new relays activated the fuel pump. The fuel pump will no longer activate with the switch. I confirmed that the switched circuit is sending 12 VDC to the fuel relay plug. Does anyone know what my problem?

New relays, no fuel pump. The engine will still start and run using the oil pressure switch.
dwilsonfl JUL 08, 09:20 PM
Did you find out what was causing the issue?