Fuel Pump Relay Testing

[broncogirl]

I am dumb with electronics, following guides for testing, not seeing this scenario: With fuel pump relay out, jumping the relay connector from 3 brown to 4 yellow, runs the pumps - or at least the high pressure pump on frame - WITHOUT the key in at all. All the testing guides I'm finding say to turn the key to ON for this part of testing, and I'm not seeing mention of pump(s) running with no key. I kept it jumped for about 15 seconds, longer than typical prime, and the frame pump sounds strong and doesn't shut off. Did not get back to tank to listen there, and did not try with key on, nor cranking.

• Is it a problem that no key is needed to run pump(s?) when wires 3 and 4 are jumped with no relay in? Does that point to any particular cause of my crank-but-no-start issue? Can't find my fuel pressure gauge at the moment, should I try crank and run it like this?

Red #2 from EEC relay shows 11.6V key on, Yellow #4 12.5V from ignition switch with key on. Then this jump test runs without any key.

• Then, tester light fails to light between #1 Tan/lt grn & battery positive when cranking with relay out. Is that a useless test due to jump running with no key, or does that indicate bad EEC, bad connection to EEC, or bad PIP?

Last test, relay back in, cranking, multimeter grounded at battery does not show battery voltage at the two #3 orange/blue wires. Think that would mean bad relay, but only if above test had not failed.

More info: Can't find my pressure gauge at moment. Key on produces some click but no pump hum. Key to crank turns engine over plenty strong but apparently no fuel. Starter fluid spray gets it running, only while that lasts. Have a nicer newer inertia switch, and bypassed it with no change. Newer battery only now down to 12.7, after many start attempts.

 

[Uncle Gump]

So... the yellow wire goes to a fusible link that is hot at all times. It provides power to the switched side of the fuel pump relay at all times. So if you were to jump from yellow to orange/lt blue... the pumps should run.

The EEC relay provides power to the control side of the relay with key on via the red wire. Once key is on... the ECM grounds the tan/lt grn wire to energize the fuel pump relay.

Reading your symptom above... it sure seems like you have a bad fuel pump relay.

 

[broncogirl]

Thanks so much! So, this test, with the relay out, doesn't indicate bad PIP, bad connection to the actual EEC, nor bad EEC: Relay removed, test light on battery positive and connector's wire #1 tan/lt grn (diagram shows straight to EEC's #22 pin), key to cranking, tester fails to light?

 

[Uncle Gump]

Thanks so much! So, this test, with the relay out, doesn't indicate bad PIP, bad connection to the actual EEC, nor bad EEC: Relay removed, test light on battery positive and connector's wire #1 tan/lt grn (diagram shows straight to EEC's #22 pin), key to cranking, tester fails to light?

I'll expand on my above post.

The tan/lr grn wire is grounded by the ECM... WHEN... there are two different senerios...

1. The ignition key is first placed in the ON position for about 2 or 3 seconds. This allows the fuel system to prime for start up.

2. Once the ECM sees engine speed via PIP signal above about 500 rpm... it will then ground the fuel pump relay to run the engine.

 

[Uncle Gump]

So test tan/lt grn as follows.

Remove fuel pump relay.

Test light between B+ and tan/ lt grn wire.

Watch the light... turn key to ON position. Test light should illuminate for approx 2 or 3 seconds and go out.

Note... it will not illuminate again the key cycle until engine RPM goes above approx. 500 RPM. Starter alone will not crank the engine that fast.

 

[bronco_d]

Good job so far Broncogirl! Hope you figure it out soon.