How long should fuel pump run after shutdown ?

[javadave]

Ok gurus, not sure if this is a new problem, or something I haven't noticed before. I've been exhaustively researching fuel pump symptoms since I noticed the other day when I started it up to drive home from the store that the pump seemed a bit louder than it normally was for about 10 to 20 seconds. She has 209000 miles on her now, I've put 55k since I bought her in Aug 2014. I've looked through the 3 inch stack of paperwork I got with her and believe this is the original pump. That being said I'm probably going to replace it before it strands me somewhere.

The reason for the thread topic however is this. Tonight I drove it home from work, a little over an hour at various speeds, roughly 42 miles. Backed into the garage and got out, but very faintly heard the fuel pump humming. I popped the hatch and raised the carpet, as I don't recall hearing it run for that long before. I waited a few minutes, but it remained running. Don't know why, but I popped the gas cap, relieved pressure and it shut off. SO then I started putting the carpet back and the t-top straps and wouldn't you know it, it came back on. Had to release gas tank pressure 3 times before it would stay off and I'm probably going back out there before I go to sleep to check it again. Is this normal and I never noticed it before ? Or could this be a sign of an FPCU going bad as well ?
Thanks in advance for your help guys ~

[macgiver]

mac here ,your 300ZX , similar to my 93 J30 (VG30DE motor too I believe) yet I don't believe the fuel pump supposed to overe-run, AFTER engine Completely off ? Maybe that's the design , but in all my time I've never seen or heard - it's sooooo counterintuitive , that a FUEL pump will still run - eng. off + key out FOR ANY length of time-out but I'll never claim GURU status just an "IDIOTUS GENERALIS" Diploma Seriously I just worked on mine last October and heres how INFINITI / Nissan probably does it in your case too = power from a relay usually @ front of vehicle cotrolled by the ecm (which I believe always disconnects from power when car off - to protect from bad jumps and bad Battery chgr's) .Relay sends power BACK to a "Fuel Control Module" (FCM has "relay power", ECM sig.,FCM OUT to F/pump, lastly a ground connection, note:and pump goes series w/ a HEAVY DUTY "Power Resistor" to gnd. too).ECM sig. turns on pump via module at "right times" but ALSO is responsible for SHUTTING DOWN w/no RPM condition ,other engineered-infault response and obviously eng-Off or after the 5 sec. prime etc.
Unless something like a"Mod" or weird wiring situation/mishap is allowing SOME part of this ckt. to kick in?
Another thing is that if your F/pump is accessable back there in the trunk cmptmt. they're easy to R&R, prett yreliable ,IT IS PUMPING , cheap but messy and sort-a dangerous to mess with gas !, you don't want to go there yet !
Now the power resistor is SO big and kick-AZZZ that unless it smells burnt , and/or looks somewhat fried but most importantly if you can test Ohms w/multimeter ( FSM gives spec. I believe mine was .7 ohm? seven tenths ! ) -- You should now be suspecting that Module and FSM i believe HAS a basic "Field Chk." to try.
Lastly maybe i'm learning something here , but the fact a F/pump OVER-RUNS after - again COMPLETE SHUTDOWN , seems to be the heart of this weird fault . GT 2/22/2018

[amc49]

Pump running after car is shut off is a serious crash hazard, think what happens if you crash, fracture a fuel line and it keeps on running with key off. Absolutely NOT RIGHT. They generally are made to cut off instantly with dead ignition.

I'd be looking for sticking relay(s), but it coming back on by itself after once going off says there's more to it than that. Check all your grounds too, a bad ECM ground can make funny things happen. Wouldn't hurt to check the pump wiring interface for any possible shorting going on. Dunno where that one is located but some get exposed to the elements and exposure can make voltage crossing possible. I always well grease my Ford pump terminals to stop that and pack the connector as well.

[NolimitZ32]

Test your Fuel Pump Controller, thought not often they have been known to fail internally producing the exact symptom you describe.

[javadave]

Ok, so came home today, shut her off and sound again from the rear. This time I timed it, was still going after 7 minutes. I don't think its my fuel pump though. Its coming from the same area, under the spare in the hatch ( 2+2 ). but this time I opened the hood and pulled the fuse for the fuel pump. Sound persisted, but I was unable to start the car with the fuse out. Again, popped the gas cap, relieved pressure, noise gone for a few minutes after re-tightening cap. Noise returned, popped cap again, and once again there was pressure. Now I'm stumped. I'm 99.9% sure an after-market piggyback pump wasn't installed. Power antenna is not being operated either, so what could this noise be that disappears when fuel pressure in the tank is released, and manages to bring tank pressure back up a few times ? Also should note, only code 55. Fuel has been a constant 23 mpg.
~D~

[NolimitZ32]

your carbon canister relief valve is sticking

[amc49]

Any solenoid partially powered has the ability to make noise.

Could be pressure buildup in tank too slowly seeping out to make noise.

[javadave]

Thanks all. I'll dig deeper into it my next day off.

[macgiver]

man if by now we're questioning if it's actually the pump , you gotta get someone with a HAND DIRECTLY on the PUMP Housing whilst all these "suspect" noises occur me thinks . Respect , G 2/24/18