best way to test fuel pressure regulator?

[moondog52]

Well, I spent 2 days trying to get my '89 240SX running again and came up short

It's been sitting in the Phoenix heat for 3 years ... I parked it after the injectors started leaking badly and it was starting to run like cr*p. You don't ever want to leave your 240SX parked for that long ...

So here's what I've done ...

- Replaced fore and aft fuel filters- Replaced the frozen fuel pump- Verified that there is good gas flow to the fuel pressure regulator.- Installed 4 rebuilt Python fuel injectors.- Installed new battery.

She cranks over nice and fine ... I can hear the fuel pump working and there is healthy pressure when I removed the regulator to check it out, but the engine will not start. No gas seems to be getting past the regulator. Starting fluid will make it start for a second or two then it dies again (no gas!).

It seems like a simple device. It holds vacuum when I suck on that connection, but it sure seems like it would take a tremendous amount of vacuum for it to open (it seems completely closed if you try to blow thru the fuel intake).

Can someone please explain how it is supposed to work? If the vacuum line were off (or not working) would the fuel supply be shut off? Or should it still be open and passing fuel to the injectors before the engine is even turning? How is the vaccum supplied to it? It looks like the vacuum line goes to another electronic device on the back of the engine, apparently what is known as the Pressure Regulator Control Valve. Could the regulator be ok but the PRCV is bad and not allowing any vacuum?

Finally ... I have not done anything with the O2 sensor yet. If that were bad, could it keep the engine from starting?

What steps can I take to figure this out?

Thanks!

Brad

[Q45tech]

Are you referring to the input pressure [pulse] damper [also differential vacuum controlled from in front of TB] vs the FPR which is at the end of rail......[spring loaded diaphram set at 34 psi and engine vacuum adds 9-10 psi to 43 psi [when engine vacuum drops to 1-2' HG [as measured in plenum].

Measuring the fuel pressure after the filter and before damper should be constant, the pulse damper tries to maintain a constant pressure as each injector opens -------v--------v----------v-----------v----------vs the fuel pressure regulator which is/acts like an accelerator pump........sudden tip in of accelerator equals sudden vacuum drop equals sudden increase in fuel pressure.

43.4/34= 1.27647 take square root=13% more fuel flow for same exact injector open time.....before ecu has time to think about opening injectors longer...........helps sudden acceleration, avoid stumble, in the first 0.5-1.0 second of any acceleration.

[moondog52]

Yes, I am talking about the vacuum operated fuel pressure regulator at the rear end of the injector rail. I don't know where the damper you refered to is located. On my 240sx the fuel line in the front engine compartment goes to a filter then to the regulator ... where would this "damper" be?

Anyway, from what you are telling me about a vacuum drop resulting in the regulator allowing more gas to flow, it would seem to me that the question I asked before would be answered that there should be gas flow when there is little or NO vacuum. There is no flow of gas thru this one ... you cannot blow thru it when it's off of the car ... so is it bad?

Can you blow thru a new one when it's off the car? Is it in a "normally closed" position when the engine is not running and there is no vacuum present?

[moondog52]

Another user in the tech forum suggested that I have the fuel delivery hooked up to the regulator when the return line should actually go there. I believe he's right ... but I won't be able to try it out until the weekend.

Thanks for thse that took the time to reply!

[Q45tech]

The regulator must close off when there is no pressure otherwise when you turn engine off the fuel would drain from the rail via the return line. Most pumps have a anti drain back valve for the same reason.........to keep the rail pressurized CLOSE to correct pressure even after a week.The regulator won't open until 30-34 psi or so![depends on what idle fuel pressure is supposed to be].

Many have had BAD BAD experiences with Python remans leaking......oem new is the way to go, one less worry.

Never looked at the 240 much but all engines other than brand new returnless work the same way ........they may not have an input pressure damper however as this is an extra feature on many designs.

Your FSM has detailed explanation.

[moondog52]

The user in the tech forum hit the nail .. I had the fuel ines hooked up backwards. THE RETURN LINE GOES TO THE Fuel Pressure Regulator.

Simple mistake that I'm sure has happened often.