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Fuel pumps constantly on - relays? 700

posted by Will740turbo on Sat Apr 28 02:47 CST 2012
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last visit: Wed Oct 22 16:09 CST 2014

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My fuel pumps run constantly. It's irritating and probably a bit unsafe.

Is it possible that the fuel pump relays don't work properly? Or am I looking at something else?

Cheers
Will

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Fuel pumps constantly on - relays? 700

posted by boxvolvo on Sat Apr 28 05:29 CST 2012
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last visit: Fri Oct 24 04:28 CST 2014

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When you day "constantly" do you mean even when the engine is stopped and the key is in your pocket? Or constantly when the key is in the on position?
Or do you mean that the pumps run constantly when the engine is running?

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Fuel pumps constantly on - relays? 700

posted by Will740turbo on Sun Apr 29 14:48 CST 2012
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last visit: Wed Oct 22 16:09 CST 2014

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Constantly with the key in KP2. Not in my pocket, yes while the car is running. :)

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Fuel pumps constantly on - relays? 700

posted by boxvolvo on Mon Apr 30 05:02 CST 2012
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last visit: Fri Oct 24 04:28 CST 2014

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The fuel pumps are supposed to run constantly. Any fuel not used by the injectors is re-circulated back to the fuel tank.

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Fuel pumps constantly on - relays? 700

posted by Will740turbo on Mon May 7 02:14 CST 2012
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last visit: Wed Oct 22 16:09 CST 2014

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I'm talking about the safety feature where the pumps are supposed to be running only for 3 seconds when the key is first turned to prime the pumps, and when the engine is turning. Otherwise, they're supposed to be off.
It's referenced here: http://www.brickboard.com/FAQ/700-900/EngineFuelinjection.htm#FuelPumpandFIRelayDiagnosticTests And I don't think it was in the FAQ the last time I looked, so I'll be checking for that shorted relay connection.

Cheers!
--
740T and 244DL - Frank the Tank @287K mi. and The Polished Turd @237K mi.

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Fuel pumps constantly on - relays? 700

posted by boxvolvo on Mon May 7 05:19 CST 2012
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last visit: Fri Oct 24 04:28 CST 2014

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Now I understand.

Check pin 86-2 in the relay.

From the FAQs

Why Does My Fuel Pump Relay Have a Soldered Ground from Bent 86-2 Terminal? [Bruce Young] This is a known hack and was done my a mechanic as a cheap fix to compensate for a Bosch 595 or 556 ECU failure. The ECU is supposed to ground that 86-2 terminal when it knows the Ignition system is working. This controlled ground is what normally energizes the fuel injection relay. Right now your Fuel pump will run as soon and as long as the ignition key is on. And it will keep on running in case of an accident, like upside down in a ditch with driver unconscious. The Bosch circuit intent was to prevent pumping fuel to a dead engine as a safety precaution.

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