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Does fuel pump run continuously?

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70

dcarlson12
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dcarlson12

Does fuel pump run continuously?

Post by dcarlson12 » Fri Nov 29, 2019 12:36 pm

Regarding 850's, does the fuel pump run continuously as long as the ignition swithch is in the 'on' position or is there a fuel pressure switch that would cause the pump to cycle 'on' and 'off' depending upon the pressure at the injector fuel rail?

Just trying to figue out when the problem is the fuel pump relay being faulty or if the pump itself is bad.

Thks,
Dwight
94,96 and 97 turbo in the family...



cn90
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cn90

Re: Does fuel pump run continuously?

Post by cn90 » Fri Nov 29, 2019 1:00 pm



2004 V70 2.5T 100K+
2005 XC90 2.5T 110K+

dcarlson12
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dcarlson12

Re: Does fuel pump run continuously?

Post by dcarlson12 » Fri Nov 29, 2019 2:00 pm

Thks for the link.
I still don't know if the pump is supposed to run continuously with the key in the 'on' position (Position II) or does the ECU turn it 'on' and 'off' based upon fuel rail pressure? Or does the pump run continuously and 'excess' fuel passes over a pressure relief valve and return to the tank via a 'return' line?
????
Last edited by dcarlson12 on Fri Nov 29, 2019 2:10 pm, edited 1 time in total.



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Rattnalle
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Re: Does fuel pump run continuously?

Post by Rattnalle » Fri Nov 29, 2019 2:05 pm

IIRC the pump runs continuously while the engine is running with pressure controlled but the regulator letting the right amount back into the tank. However when just turning the ignition on I think the pump only runs a short while to build pressure then stops, at least that's how I've interpreted the sound my 854 made when I'd let the fuel pressure out and needed to refill the fuel rail. Also I needed to turn the key twice to get enough pressure to start if the fuel rail was empty.



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Re: Does fuel pump run continuously?

Post by cn90 » Fri Nov 29, 2019 2:08 pm

1+,

- With key in position II (engine NOT running), fuel cycles for about a few sec to prime the fuel line, then shuts off.
- Of course, when cranking starter motor or when engine is running, the fuel pump runs continuously.
- Pressure is regulated via pressure-regulator.

Later cars (P2 etc.) use the PEM to "modulate" the pressure.


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dcarlson12
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Re: Does fuel pump run continuously?

Post by dcarlson12 » Fri Nov 29, 2019 2:31 pm

Excellent!
So if one jumpers the relay/pump in the relay 'box., the pump will run continuously if the key is in the Position II and won't just run for the one second used to prime the system. Thus one could limp along on the jumper????
Or if the jumper were 'in place' would the pump run even if the key is in the 'off' position?
Thks,
Dwight



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Rattnalle
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Re: Does fuel pump run continuously?

Post by Rattnalle » Fri Nov 29, 2019 2:45 pm

dcarlson12 wrote:
Fri Nov 29, 2019 2:31 pm
Excellent!
So if one jumpers the relay/pump in the relay 'box., the pump will run continuously if the key is in the Position II and won't just run for the one second used to prime the system. Thus one could limp along on the jumper????
Or if the jumper were 'in place' would the pump run even if the key is in the 'off' position?
Thks,
Dwight
Either works but in the latter case you'll just have to remove it after moving the car.



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Re: Does fuel pump run continuously?

Post by abscate » Fri Nov 29, 2019 3:35 pm

The pump will only run with key on, with the fuel pump,relay jumpered


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Re: Does fuel pump run continuously?

Post by wizechatmgr » Fri Nov 29, 2019 8:26 pm

If using a "regular" relay instead of the proper one, it will run as long as the key is on. I've used one intended for Aux lights (aftermarket) when in a jam.


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