boosted fuel pressure regulators

danimal · Post by **danimal** » Sat Jul 14, 2001 6:26 pm

>>>my fuel pressure won't go beneath 8.5 psi, and the car was set up to use the dinky-ass stock fuel line as the return line<<<

just like what happened to moggy, when i replaced my fuel return line to the tank with a bigger one, the fuel pressure dropped to ~2.5-3 psi... old cb blow-thru turbo system w/malpasso(?) mechanical fuel pressure regulator.

however, once i put a certain amount of boost to the fuel regulator, it would never go beneath 8.5 psi of fuel pressure... it appeared that the regulator was sticking; the pressure would drop back down to the ~2.5-3 psi level once the car was shut off and restarted... there isn't much to these regulators, it's basically a simple membrane that moves up and down depending on the boost level.

i ended up re-routing the boost pressure line from the cb center manifold section to the port on the dellorto manifold, which is where the boost gauge gets it's reading.

this apparently gave enuf vacuum signal to the fuel pressure regulator that it was able to always drop the fuel pressure all the way down when not on boost... there appears to be no adjustment on these regulators for unboosted fuel pressure levels.

i hope this helps someone else who has the same kind of problems... there is nothing like buying a turbo car that has not been set up correctly; in my case, the p.o. had this vehicle worked on by two performance shops in the area, but apparently it never occurred to either of them to check the fuel pressure, or to install a bigger return line... they just blamed the poor running condition on bad carbs and blow-thru turbocharging in general... when in fact it was excessive fuel pressure on the carbs when they weren't on boost.

of course, i rebuilt the engine completely when i got the vehicle, but that wasn't related to the root cause.

now the problem is that there apparently isn't enuf fuel pressure to stay ahead of the boost... this has always been a problem since i got the car, i can read 15 psi of boost while the fuel rarely hits 12 psi of pressure... i believe that the fuel pressure is supposed to stay about 3 psi ahead of the boost, on a blow-thru carbed system.

the fuel pump looks like one of those bosch rotary units(?), feeding into a 3/8"(?) line that has at least one radical bend in it... the line o.d. doesn't appear to be much bigger than the stock fuel line.

i suppose i'll have to try putting in a bigger feed line.

dan
oceanstreetvideo.com

JohnConnolly · Post by **JohnConnolly** » Sat Jul 14, 2001 6:30 pm

Be careful Dan! If your fuel pressure is lower than the boost pressure in a blow thru system, you are running ONLY on the fuel in the carb's float bowls! It's gonna' go lean. Time to step up to a higher pressure pump and big regulator!

danimal · Post by **danimal** » Sat Jul 14, 2001 9:24 pm

>>>Time to step up to a higher pressure pump and big regulator!<<<

doh! thanks for the feedback, better start pinching pennies somewhere...

i suppose the best fuel supply solution would be one that's kinda "future proof", i.e., max 20 psi now, but maybe 50+ psi capable with fuel injection... all in a boost-sensitive package.

where it starts getting complicated for me is talking about rising rate fuel pressure regulators, which i believe serve as fuel enrichment devices for fuel-injected cars that run boost.

maybe that is something that can be added later.

dan
oceanstreetvideo.com

moggy · Post by **moggy** » Mon Jul 16, 2001 3:51 pm

Where do you take the vacuum line from above or below the carbs?? It should be above.

Also I have a larger fuel line diameter going into the pump than coming out. I havent used stock fuel line anywhere. the return line is he same diamter as the feed line to the regulator. Mine now works fine..

Hope this is helpful.?.

moggy · Post by **moggy** » Mon Jul 16, 2001 3:55 pm

Also just thougt of something else. My regulator has 2 out lines 1 for each carb, I was just wondering if you had 1 line out and then T pieced it to the 2 carbs? If so this might restrict flow if the line diameters aren't right.

danimal · Post by **danimal** » Tue Jul 17, 2001 11:21 pm

>>>Where do you take the vacuum line from above or below the carbs?? It should be above.<<<

hi moggy, the only way i could get the fuel pressure down was to hook up the boost(vacuum) line to the intake manifold, beneath the carb... that is where the wastegate boost sensing line is hooked up.

>>>Also I have a larger fuel line diameter going into the pump than coming out. I havent used stock fuel line anywhere. the return line is he same diamter as the feed line to the regulator. Mine now works fine<<<

my fuel source line from the tank was installed by the p.o., but it's not very big... if replacing that doesn't increase the fuel pressure, i'll have to move up to another fuel suppy system, like john suggested... there are two fuel line ouputs off of the fuel regulator, and the fuel pressure gauge sender is in one of those lines.

dan
oceanstreetvideo.com