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Posted by: 2xs performance Apr 1 2012, 02:09 PM

Stock '74 2.0

How much pressure does the injector need to work properly?
I know the fuel reg is set about 29 psi.

Posted by: vsg914 Apr 1 2012, 02:23 PM

Hmmm, not sure, but since the specified pressure is 29 lbs, I'm gonna guess thats because thats what they need to operate properly?

Posted by: 2xs performance Apr 1 2012, 02:35 PM

The regulator lets fuel by and keeps system at least 29 psi.
My question is does anyone know at what pressure the pump kicks on?

I never got my fuel pump to run right so I'm just making my own stand alone system. The pump has power whenever the key is on. But to keep the pump from running full time and circulating fuel which would heat the fuel I'm going to install a pressure switch to kick the pump off after pressure is reached. I can get any psi switch I want for about $25.

I'm thinking maybe 25psi might be good. I want enough pressure that the motor will get all the fuel it needs but want my pump to have a rest and cool off when not needed like at idle.

Posted by: type47 Apr 1 2012, 03:25 PM

I'm not sure about the idea that the "pump kicks on" at any particular pressure as I thought it ran continuously (other than starting cycle) and the pressure regulator "bled off" pressure by "controlled leaking" gas back to the tank. Injectors open when the ECU sends a voltage signal to the injector and the time-duration of the signal determines the time open and therefore the amount of fuel injected. I would guess that an injector will work at any pressure since it's basically a solenoid (914 D-Jet injector we're talking about, not MFI injector). 'Course you wouldn't get the right charge unless the pressure was set correctly (~29psi). I do have a question about how you think the fuel is heated and creates a problem. I've never seen any thing about temp of fuel and the factory set up having a problem.

Posted by: vsg914 Apr 1 2012, 03:30 PM

What Jim said. The pump runs for a half second when the key is turned on. Once the engine runs the ecu triggers constant power to the pump. Pressure has nothing to do with it.


"The pump has power whenever the key is on." Not correct.

Posted by: Dave_Darling Apr 1 2012, 03:31 PM

That's correct, the pump just runs continuously the whole time the engine is turning over.

--DD

Posted by: 2xs performance Apr 1 2012, 03:56 PM

Thats what I needed to know. My factory wire doesn't have power anymore. I ran a new wire from the fuse panel that is hot when the key is on. Being as the pump turns on, then off when you first turn the key on I thought the computer was controlling the pump and turning it on and off "as needed". If it is suppose to run all the time I'll just leave it as it is.
I guess I was more worried about wearing the pump out early and the constant fuel flowing all the time but if it's normally that way anyways....

Thanks for the help

Posted by: brant Apr 1 2012, 04:33 PM

Thats why the factory has a return line...
make sure you do also

can't you just trace your factory wire back to the point of the problem?

Posted by: Tom Apr 1 2012, 06:42 PM

The fuel pump shood turn off if the engine dies. That is why the ECU controls the ground to the fuel pump relay. It turns the fuel pump on at three times
1- upon initial key to on, for about 1.5 seconds
2 whenever the starter is engaged - key switch to start.
3- when the engine is exceeding X RPM's
The design is for the fuel pump to shut off if the engine stops for some reason.
Be careful here as an engine problem due to leaking fuel lines will cause the engine to run poorly or stop. You don't want the fuel pump running if there is a leak.
Tom

Posted by: 2xs performance Apr 1 2012, 06:47 PM

return line works fine.

The factory wires are still there. Just need the car to run right now. I'll try and trace down the problem with the factory wires as soon as I get a chance. You make a good point if anything every happens theres no "auto" shut off unless I am able to turn the key off.

Posted by: orange914 Apr 1 2012, 08:50 PM

curculating acually cools the fuel