fuel pressure regulator

centralcoaster · Post by **centralcoaster** » Sun Dec 04, 2016 3:48 pm

I've been trying to get my 78 530 back on the road. I have solved most of the elecrical problems with some wise advice from this forum. Now on to the fuel side. My previous fuel pressure regulator would come up to 32 psi when at idle but drop all of the pressure almost immed. when I turn the car off. I just installed a new one and noticed the pressure does drop off to nearly zero, but it takes some a minute or so . I clamped off the return line and still had the pressure drop off. then I clamped off the supply side. I know there could be pressure lost throught the injectors, but they were tested individuallly before reinstalling them recently.

so, my questions
Should pressure remain around 30 lbs with the engine off. and if so is there some check valve in the supply line to prevent leakage back to the tank:?

RonDwyer · Post by **RonDwyer** » Sun Dec 04, 2016 6:14 pm

I do believe there is a check valve on the discharge side of the fuel pump.

centralcoaster · Post by **centralcoaster** » Sun Dec 04, 2016 7:19 pm

thanks for the reply, should i have operating fuel pressure remaining after power is shut off?

RandyM · Post by **RandyM** » Sun Dec 04, 2016 10:14 pm

Pressure should stay up. 32 psi is low, should be about 44 psi iirc. Did the new regulator fix that? Where are you measuring pressure? Are you sure gauge is accurate? Clamping technique might be less secure than u think. You didn't give result of clamping supply side in your post. Have you checked ALL hose connections? That old rubber may have given up after nearly 40 years. And it appears that check valves in pumps do fail.

Also see here: http://www.bimmerforums.com/forum/showt ... e-Resolved

centralcoaster · Post by **centralcoaster** » Mon Dec 05, 2016 1:41 am

I am measuring the pressure at the cold start injector. I have replaced all of the hoses in the lines and to the injectors. Earlier this year I hasd stripped off the plenum and intake tubes , and removed all of the injectors. I tested each for a good spray pattern while doing so, I put each of the injectors under pressure and activated them with voltage to the connection. None appeared to be leaking.
the new puel pressure regulator was just installed. the pressure without any vacuum does go up over 40 pounds. when the fule pump is turned off the pressure does go down to 20 lps or less, whether I crimp the supply side or the return line hoses. I was going to purssure the system , turn off the pump and crimp bothe fuel hoses to see if theree saw a pressure drop due to the injectors, but had to quit for the day . I haven't put the intake tubes back in place as the # 3 and 4 tubes are harder to get at and thought I may need to get a different regulator if this new one should hold pressure.
I hope thqt answers some of the questions asked.

RonDwyer · Post by **RonDwyer** » Wed Dec 07, 2016 11:20 pm

The regulator shows availability, likely not for long.

http://www.realoem.com/bmw/enUS/part?id ... 3531260789

When it goes NLA an alternative is an adjustable unit from possibly Summit Racing.

centralcoaster · Post by **centralcoaster** » Sun Dec 11, 2016 7:05 pm

I was able to get a new regulator, It is insalled, that is the one that i still have questions about. should it hold the 40 + pressure when the ignition is off? I am getting leakage of pressure on the return and supply side. I ordered a check valve to put on the supply side, and will install it soon. but if the return side leaks then does that mean the regulator is no gooe?

fyi this regulator is also used if a nissan model, so maybe that will keep it available for a while

RandyM · Post by **RandyM** » Sun Dec 11, 2016 8:27 pm

The return side is non pressurized; just acts as an open drain line from FPR to tank. Sounds like the check valve in your pump is not functioning. Maybe that's also related to your pressure previously being below spec. Try
tapping on the pump while off and then while running. That miraculously cured my pump from a low volume condition once.

centralcoaster · Post by **centralcoaster** » Fri Dec 16, 2016 10:10 pm

thanks for the tip on the fuel pump. I will give it a try. I am sitill not sure if the regulator is supposed to hold full pressure once the fuel pump is turned off?
does anyone know ?

RandyM · Post by **RandyM** » Sat Dec 17, 2016 1:52 am

This topic page 2
http://www.firstfives.org/bboard/viewto ... hlight=fpr

And here:
http://workshopmanuals.com/bmw/5_series ... pressure)/

I think you need a new engine…a search engine that is! There's one at the top of the page.