Andy A

Not sure why I decided to check the fuel pressure regulator, but the other day I decided to hook up the mityvac to it and pull a vacuum on it. It pulls vacuum but immediately starts dropping to 0, it will not hold a vacuum. Is this normal or a sign of a bad fuel pressure regulator? I tested a couple of other fuel pressure regulators I have lying around and if a vacuum is pulled on them it holds until I pop the release lever on the mityvac.
3vz engine

dubbsbetty

iTrader: (2)

Not too sure what the good book says about puling a vacuum on the regulator but if yours doesn't hold a vacuum and the others will id say that's a great place to begin. There's a spring loaded diaphragm inside that vessel along with a valve that opens. When fuel pressure becomes to high that valve opens via engine vacuum and allows fuel to return to the fuel tank. Hope that helps or that I am near accurate.

scope103

There's a little more to it than that; the purpose of the FPR is to keep the same pressure across the injectors, regardless of the position of the throttle plate.

But it is a closed system; if it won't hold a vacuum for more than a few seconds you might have a leak in the FPR, and it isn't going to fix itself. The fuel pressure will be too high, you'll be wasting gas, and eventually throw a code 26.

BUT: are you sure you did the test correctly? If the hose from the mityvac fails to get a perfect seal at any point, that could be what you're seeing. Since you don't have a code 26 now, I would re-do your test very carefully.

Andy A

Thanks dubbsbetty & scope103
Scope just got the mityvac awhile ago and was playing with it and that is basically why I decided to try the FP regulator. So far this is the second time I have tried it on the FP regulator and got the same results. It just does not hold a vacuum, starts dropping immediately. I know that some of the adjustable type FP regulators are designed to leak down but the ones on the 3.0 are closed. I basically just pulled the vac line attached to the fuel pressue regulator, attached the mityvac to the FP regulator vacuum port and went from there. I will try it again tomorrow. Right now I have bigger issue, went to vac bleed the brakes and the LSPV is leaking like crazy so it is off the road till I order a new one and get it installed. I have been getting a code 71 here lately but that is egr so that is something else I have to work on.

Andy

Andy A

Scope tested it again this morning when I got in from work, same results, drops like a rock, also noticed just a little bit of fluid this time, tried to see if it smelled like gas but inconclusive as my sniffer does not work to well at times. Definitely getting a good seal.

The only other things to do that I can think of are to test one from an auto parts store or if someone on the site can test theirs.

PS it is the original and has approx 223000 miles on it.

Andy

Punchy

[QUOTE=scope103;52080639]There's a little more to it than that; the purpose of the FPR is to keep the same pressure across the injectors, regardless of the position of the throttle plate. QUOTE]

There is more to it then that for the Toyota FPR, During throttle up vacuum decreases on the FPR and the fuel pressure increases.
I don't remember what the manual says but mine runs 40PSI idle and up to 55PSI throttled up.
This broadens the range of the injectors.

If the red VSV is bad or connected wrong it can make the fuel pressure very evenly up and down depending on the vacuum in the manifold instead of spiking high and low during accel and decal.

scope103

That's because "during throttle up" the pressure in the intake manifold increases (or, put another way, the vacuum decreases). The pressure across the injectors is constant. http://www.autoshop101.com/forms/h22.pdf p8. It doesn't "spike" during accel or deccel, unless you have a very heavy foot.

The FPU (Fuel Pressure Up) Vacuum Switching Valve (mounted on the left apron in a V6) increases the pressure in the rail during cranking of a hot engine, to avoid vapor lock. If that Valve is "bad" it will hold the fuel rail pressure high all the time; it won't vary with the vacuum in the manifold (varying evenly is what it is supposed to do).

The spec fuel pressure at idle (maximum vacuum) is 33-37psi, at engine off (minimum vacuum) is 38-44psi. http://personal.utulsa.edu/~nathan-b...87fuelpump.pdf The maximum difference you could possibly get between idle and throttle up is 14.7psi (the difference between a perfect vacuum and no vacuum at all), so if you're getting 40 and 55 it's probably just inaccuracy in your gauging.