Hi everyone, so the problem drives me crazy

The engine seems cant hold the fuel pressure, after i turn the motor off, fuel pressure drops to zero in 3-5 mins.

So i get a new fuel pressure regulator changed with pressure gauge, pressure still drops. Then i pull out all four injectors, get them tested and professional cleaned, no leaks. But they put on new orings for the injectors, i plug them back, and turn the key to ON position( Didnt start the car) to just let the fuel pump pumps fuel, suprisely, the fuel pressure holds pretty well around 40psi, i checked the pressure the day after, it was still held at 30psi. So I thought i ruled out the problem, but when i started the car and let it run for a while, then turn it off and check the pressure, the same problem came back, fuel pressure drops in mins. I pulled out injectors again, the orings they changed seem a little bigger than OEM ones, so i ordered OEM orings and insulators(two small orings at top and bottom of the injector) from toyotapartszone, i put OEM orings on, lubricated with engine oil, plugged them back in and turned the key to ON ( same as above), the pressure held pretty well again, then i started the car and turn it off, checked the pressure, it cant be held any more.

I really have no idea what the real problem is, FPR, injectors, orings, fuel lines are all good with certain, could this be fuel pump check valve? If its check valve, wouldnt the pressure be off all the time? Does the check valve keep closed when just truning the key to ON position? Please give me some help, i am so confused, anything will be helpful,thank you so much everyone!!

Fuel pump has a check valve (one-way valve) on the discharge side. Its
job is to hold pressure in the line and prevent drainback to the tank when
the pump turns off. Valve opens when the pumps runs, and closes when it stops.



Sounds like yours might be having trouble to shut off tight every time.
End of the day it is not such a big deal. Worst case if you get drainback,
it could take the pump a couple of seconds to prime the rail. Since your
pump is wired to run when you turn the key ON, that should not be a huge
problem unless you like to do a Le Mans start on cold mornings

Cheers... jondee86

Thank you jondee86, i wish it is check valve then i can finally end this. If its really the check valve, i have no idea why it closed tightly and hold pressure every time after i put injectors in with new orings, but after i started the car, the pressure bleeds off fast.

SOME pumps have a check valve, not all.

It's not necessary, does nothing useful but save a second or less at most and is not the cause of any problem/s you may have, unless it was stuck closed & restricting flow.

allencr wrote:SOME pumps have a check valve, not all.

It's not necessary, does nothing useful but save a second or less at most and is not the cause of any problem/s you may have, unless it was stuck closed & restricting flow.

I am still suspecting the injector lower orings, the upper ones should be good, i cant see and feel any leak at the top of injectors, but if the lower orings dont seal well, fuel may leak from there to throttle body, make the motor run rich.