Faulty fuel pump relay

[drnrd]

Does anyone know why the Fuel Pump Relay in my 2000 Explorer 5.0L quit working? All power seems correct according to FCS-12206-99 Diagram 25-1 except circuit 238 DG/YE never becomes hot. I've tried a few different relays and cleaned all connections.

In ACC/Run, the trigger (Pin 2/86, circuit 926, LB/OR) is hot and off otherwise. Pin 1 (Circuit 361 RD) and Pin 3 (Circuit 1059 LB/OG) are also hot as indicated in the diagram.

I think Pin 1/85 is normally ground for such a relay, but the diagram shows it 12v here. That seems to mean there is no ground for the relay, so how could it ever be activated and send power out Pin 5/87 when trigger is on?

 

[Turdle]

Bump. Old thread still works.

Check that the pcm relay is switching the pcm on. Without a lit check engine light with key on, fuel pump will not prime. Pcm must be on for fuel pump to run.

 

[Turdle]

Also check fuel pump cut off inertia switch passenger foot area up under dash

 

[drnrd]

Thanks Turdle. The inertia switch is OK, so I'll check into the PCM in the morning. The Check Engine Light was on as the engine was idling, but I didn't see when it first came on. Could you elaborate just a bit about what I should look for! For example, I imagine that light should be on steady when the key is turned on but before starting the engine, and then it should turn off after the engine starts. Since it stayed on, does that indicate that the fuel pump was being affected badly because the PCM was or was not on at the right time?

 

[410Fortune]

No it means you have a check engine light trouble code in the computer. No need to guess what the cause is just read the codes

The computer does not monitor
Fuel pressure or the fuel pump it simply turns the pump on and off via the relay

 

[J_C]

I think Pin 1/85 is normally ground for such a relay, but the diagram shows it 12v here. That seems to mean there is no ground for the relay, so how could it ever be activated and send power out Pin 5/87 when trigger is on?

Pin 1 and 2 are both sides of the activation coil, either can be hot and the other ground.

In this case, pin 1 hot and pin 2 is grounded by the PCM. You could check continuity of the pin 2 socket contact and the corresponding PCM connector pin (of same wire color?, better to get a pinout of the PCM connector to be certain). Another test would be to run a jumper between that pin, relay installed, and ground to see if the pump comes on... but since there is a check engine light, check the codes first.

Wait a second... you wrote "The Check Engine Light was on as the engine was idling", which means your fuel pump relay is working to some extent including the PCM grounding it. Engine couldn't run otherwise. What was the initial reason to suspect that the relay might not be working? Have you taken a fuel pressure reading?

 

[daivddd]

Pin 1 and 2 are both sides of the activation coil, either can be hot and the other ground.

In this case, pin 1 hot and pin 2 is grounded by the PCM. You could check continuity of the pin 2 socket contact and the corresponding PCM connector pin (of same wire color?, better to get a pinout of the PCM connector to be certain). Another test would be to run a jumper between that pin, relay installed, and ground to see if the pump comes on... but since there is a check engine light, check the codes first.

Wait a second... you wrote "The Check Engine Light was on as the engine was idling", which means your fuel pump relay is working to some extent including the PCM grounding it. Engine couldn't run otherwise. What was the initial reason to suspect that the relay might not be working? Have you taken a fuel pressure reading?

JC, I suspected the relay was not working because all the pins indicate correctly as the diagram I originally posted shows, including no power going to the inertia swith when the trigger is not hot, but there is still no power to that switch when I manually apply voltage to the trigger pin. Simply nothing happens.

I know this is cheap, but since I can't figure out the problem I bypassed the relay altogether. I jumped the relay pin that is hot when the ignition is in run to the wire going to the inertia switch. That turns the pump on when it should be on and I can run the engine.