Fuel pump questions.

So Ive almost narrowed it down to the fuel pump, is the fuel pump supposed to prime when you turn the key on? And i put a gauge coming right off the pump and 0psi when they key is turned on, when cranking it goes up to 35 psi and right back down to 0 when we stop cranking. So it holds no prime. 2002 Tacoma 2.7l

 

@TnShooter

 

I believe it doesnt prime the fuel unless its on the ON position

 

The pump will not come on until the engine cranks.
The ECM only allows the pump to run when it sees a crank signal.

Best I remember 41-43 psi is normal.

 

I have people telling me both, it doesn’t hold pressure after it cranks, I put a gauge on the tank and it will jump to 35 psi and go right back down to 0 when you stop cranking, is it supposed to hold psi?

 

It needs to hold 21 psi or more for 5 mins.

 

The 2.7 ECM allows the pump when cranking (start signal) and/or when it sees a "cam position signal", crank position on the 5vz.
The system should hold pressure, for a while.
Below, substitute camshaft for crankshaft in the lower right (NE signal).
It's a bit misleading in that the ECM will allow the pump with either input signal, it does not need both.

 

So whats going on with your truck? Im assuming it doesnt start up?

 

The Denso fuel pump has a integral check valve when it fails pressure back bleeds to the tank, symptoms are long hard starts after sitting for long periods or even overnight, I changed mine for this very reason, and yes the pump will only turn on when there is a crank signal (engine rotation) at ecu… as others have mentioned.
R/

 

So in the early mornings after sitting all night it will start up no problem, run it for a little bit and let it set for 20/30 minutes and it takes 2 or 3 times before it will crank. Also when driving if you want to really give it gas and pass someone it will bog down when you have it on the floor but half throttle it will go.

 

This is the only engine code it has p0171

 

have you replaced the fuel filter?

 

Toyoda213 I have not, it has been relocated to right under the intake/fuel rail, so I’m assuming it has been changed, it doesn’t look all that old

 

Changing the fuel filter is good advice, yeah i know not fun on the 2.7 but worth the effort and piece of mind, next sounds crazy but there is a connector under the drivers seat, inspect it for corrosion and good condition.
R/