Fuel pump doesn't turn on

[cometcyclonemk]

Hey everyone,

Thanks for the tips with my previous post, got the turbo rebuilt and the Mustang is running better than ever... Was rather...

Went autocrossing last weekend (more like shallow water boating given the weather), and everything ran great. Even averaged 31mpg over a 200 mile round trip and a few runs of the autocross course. Came home, no problems. Went to start the car for a drive the other day, and no familiar whir of the fuel pump kicking on.

Troubleshooting so far just involved looking at the inertia switch, which leads to my question. I'm assuming the little white button on the top is the reset... It doesn't seem to, "click" when pushed, but simply depress a bit and spring back up a little. There is very little resistance to pushing it - as though the spring inside is worn out / broken. Is this normal? Can I simply jump the connector to the switch to see if it is the culprit? I'm assuming it just makes a connection between the two wires of the connector...

If that's not the case, any other likely culprits? The car is an 84, but the dual pumps have been replaced with a single in-tank Walbro unit (with less than 5,000 miles on it).

As was noted in my turbo post, the car had been sitting for about 2 years prior to my pulling it back out. I did however siphon the tank dry before filling it with fresh, and the hose came out clean (no sludge in the bottom of the tank).

Thoughts?

Thanks for the help!

*Note: Autocrossing an SVO in monsoon conditions = white-knuckle exercise in just keeping it going straight(ish), but a lot of fun!

[Meotchh]

If you have access to a multi meter & know how to check resitance...

Unplug the connector for the fuel pump at the rear bumper & check the resistance of the pump. You should see ~4ohms for a standard pump & ~1ohm for a HV pump. If there is no resistance (open) you need to drop the tank & check the pump & connections. If you have the proper resistance check everything else in line.

[cometcyclonemk]

Alrighty, tested the pump. ~1.5 Ohms resistance (thanks Meotchh), and kicks on when supplied 12V (at the connector behind the rear bumper). Checked the feed side of the connection - no 12V.

What would the next likely culprits be?

I'm assuming that a shorted wire isn't the culprit (for now), as it seems (in my likely, simplistic view) unlikely that it would be perfectly fine when parked and then simply not start next go around.

Was the behavior of the inertia switch as described above normal? Can I simply bypass it as a test? Next question: I'm assuming the little square box on a 4 wire connector behind the passenger kick panel is a fuel pump relay (forgive my SVO wiring ignorance). It may not, "click" quite like it used to... (Of course I never really listened all that closely to it until now). Haven't pulled it to test yet - the lead is quite short making it difficult for my fat hands to get in there and disconnect it - just wanted to make sure it's what I thought it was before manhandling it and potentially breaking a brittle connector.

If anyone has a wiring diagram for the fuel system (or the whole car) I'd appreciate it very much! Even just a written explanation would be great.

I'm currently assuming: Ignition switch ---12v--- Fuel pump relay----12v----Inertia Switch---12v---Fuel Pump.... But for all I know the ecu has a role, or there's a fuseable link or some other such thing in the circuit.

Thanks again!

[svopony]

have you tried tapping on the gas tank ? sometimes the pump gets stuck and the taping frees it up. I know it sounds getto, but I have had this happen and it does work.

[cometcyclonemk]

No need, the pump turns on just fine when +12v is supplied to the connector at the rear bumper. The, "hot" side doesn't get juice with the ignition switch on - it's somewhere prior to the connector.

[MikeFleming]

If you search for FUEL and PUMP you will find a thread that describes exactly what you're asking about

Also search on YELLOW WIRE in same threads.

Yes, the EEC plays a very important part in the fuel pump circuit - it provides the ground path for the fuel pump relay.

[cometcyclonemk]

Tried the ground to star plug found here: http://www.svocop.com/forum/showthread.php?1156-85-4e-not-going-anywhere&highlight=fuel+pump. Is that what you were referring to, Mike? I couldn't find anything with both fuel pump and yellow wire...

Alas, with the test harness grounded, still got none of that sweet (fuel) pumping action. Sad.

I'm assuming that test bypasses the relays ground path through the EEC and just takes it straight to battery - telling me that relay grounding is not the issue? Next steps would be to check the relay, the inertia switch, and the wiring between them and the pump?

[MikeFleming]

Here:

http://www.svocop.com/forum/showthread.php?1059-Need-help-from-the-SVO-masters-of-knowledge

[cometcyclonemk]

Looks like I have some readin' / testin' to do. Thanks for the link, Mike!

(And apologies for my apparent failure at properly using the search function...)

*Edit* Who was looking for answers to his electrical issue in the engine section?

<-- This guy!

[MikeFleming]

(And apologies for my apparent failure at properly using the search function...) Banned!! ( until your next post )

[cometcyclonemk]

Alrighty. Tested the coil signal wire (assuming that's the small red one going into the little box that makes a click on key-on) - Key-off = 0V, Key On = 12V constant - it remains high even after 2 seconds. I have an LA3 in it, so perhaps it has something to do with that?

Then tested the big yellow wire - 12V constant, all the time.

Then tested the big red wire (which I presume is the coil out, to the fuel pump) - 0.3V constant, never hits 12V with Key-on, and after a few cycles stays at 0V regardless of key position.

I'm assuming this means my solenoid is bad... Going to pick one up now (unless someone suggests otherwise before I make it there)!

Should I be concerned that the coil signal wire stays at +12V with the key on? The fuel pump previously never stayed on until start - just kicked on for a couple seconds with key-on and went silent until the car was started. Is there some sort of a pressure switch perhaps that's been kicking it off or is this indicative of another failure?

(Phew, glad I was only banned until my next post. That was a close one!)

[cometcyclonemk]

It's alive! Replaced the solenoid, fuel pump turns on for about the specified 2 seconds and fires right up. Should I still be concerned with the coil signal being a constant 12V at key-on (as opposed to a 2 second signal)? Since the pump only runs for a few seconds I'd imagine some other magical box of electrical wonder is causing it to turn off..

Thanks again for all the help guys!

[MikeFleming]

Good to hear it's running again! Party On, Wayne!

Concerned? No. If you follow the schematic you will discover the relay coil has one side to Ignition +12V, the other side of the coil gets it's GROUND through the EEC (which, obviously, requires good grounds to the EEC).