How to test or tell if 2nd fuel pump is working

langsbr

Captain
Apr 5, 2017
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07 335i 6MT e90
I recently installed a PR Stage 3 LPFP. I did the modular upgrade from the stage 2. I suspect it's not coming on via the pressure switch at 13psi. Is there an easy way to tell if it's running? I can hear the main pump prime fine when the door opens.

Can I simply short the sensor wires to get that pump to engage?

Sorry if this seems like a dumb question, but the pressure sensor (PR says it's not a Hobbs switch) didn't have any information or datasheet with it.
 

langsbr

Captain
Apr 5, 2017
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07 335i 6MT e90
What should I expect at 13psi? Should the lpfp increase? If so, by how much? Should it stay there, or does it get regulated back down to where it needs to be? It seems that if fuel pressure spiked there, it would have a rich condition.

I could go the LED route, but I was less concerned about it while driving, and simply wanted to know if everything was good, basically bench test it.

Apparently I can just jumper the sensor wires and the pump should come on, so I can confirm the pump runs.
 

RuskiRacer

Captain
Jul 17, 2019
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2009 e93 335i
There's really not gonna be any spike. All the fuel flows through the pressure regulator so is getting regulated your most likely not gonna see those spikes. Drop a log and lets see how it looks
 

nyt

Sergeant
Sep 15, 2019
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2010 335xi
hook up a voltmeter to the terminals, make sure they dont short anywhere, enter boost and look at the voltage.
 

langsbr

Captain
Apr 5, 2017
1,266
771
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07 335i 6MT e90
I discovered that the weatherpack connector had pushed out on the pressure sensor harness. Popped it back in and shorted the pins and the fuel pump cut right on. Plugged it back in and LPFP no longer drops anymore. I did keep having a cylinder 6 misfire. Swapped the injector with a spare and good to go!
 

Dumaurier7

Lieutenant
May 19, 2020
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Great that you figured it out! Just for information though, you could have jumpered the pressure switch to start the second pump, start the car and unplug the connector for the main pump, once the engine stays running the pump is good! once the pump is good the problem would be with the pressure switch or harness/relay.