HELP!! Can't get fuel prssure down from 50psi

[SHEPP2]

Hi, I have a 1985 GN hot air engine I have the scan master with no codes. The problem I am having is that I just installed a Accufab Billet Fuel Pressure Regulator, aeromotive stealth 340 fuelpump, 36 lb injectors, new turbo tweak chip, I can not get the fuel pressure down past 47-50 psi. I can go up to 65 or higher but not down. I did some research on kinks in the return fuel lines which I checked didn’t see any binds in them. I change the fuel filter to see if that helps nothing. Question on the fuel filter the arrow does point up (right) towards the regulator which the lines goes into. I call Full Throttle to get some help and the guy said I needed bigger return lines?? I’ve been driving my car to work everyday I smell a little gas from the tailpipes every now and again just a little white smoke at start up. I put a fuel gauge on the line to read as I drive and it stands between 47-50 psi. When I turn the car off it hold pressure at 48 psi so any ideals???

 

[Eric Stage I]

Full Throttle is correct.

Most of the time, the 340lph in-tank pumps cannot be used with the stock fuel return line, and still get the base pressure down to 43psi, and then down into the 30's with vacuum line on.

You could try to run higher base pressure and see how it runs, say 52-53psi, then with vacuum it may drop into the upper 40's. Your BLM's will be lower, and it may be rich at WOT, but it might run ok.

If not, you'll need to put a bigger return line in, or change to a 255lph pump.

 

[SHEPP2]

Full Throttle is correct.

Most of the time, the 340lph in-tank pumps cannot be used with the stock fuel return line, and still get the base pressure down to 43psi, and then down into the 30's with vacuum line on.

You could try to run higher base pressure and see how it runs, say 52-53psi, then with vacuum it may drop into the upper 40's. Your BLM's will be lower, and it may be rich at WOT, but it might run ok.

If not, you'll need to put a bigger return line in, or change to a 255lph pump

Thanks for your reply but what do you mean Base Pressure?? At the moment its at 47-50 psi are you saying set it to 52-53 psi. I just got back on my break for lunch and it cut off while driving. I know yesterday I tried to go lower so I bagged the screw out as much as possible guessing I could be in the range of 40-43 psi. I ran with know problem to work this is crazy!!

 

[SHEPP2]

Thanks for your reply but what do you mean Base Pressure?? At the moment its at 47-50 psi are you saying set it to 52-53 psi. I just got back on my break for lunch and it cut off while driving. I know yesterday I tried to go lower so I bagged the screw out as much as possible guessing I could be in the range of 40-43 psi. I ran with know problem to work this is crazy!!

 

[Eric Stage I]

Do not back the screw off all the way, or it won't rise with boost correctly. There must be some preload.

Base pressure is the pressure at idle with the vacuum line disconnected.

 

[SHEPP2]

Question which way does the gas flow?? Isn't it the fuel filter, fuel regulator,fuel rail to injectors, and back to the tank??

Thanks Eric will do?

Which end is the return line?? Is it on the passenger side of the fuel rail or is it under the fuel pressure regulator?

 

[NY Twin Turbo]

The fuel is sucked through the sock, into the pump, pushed through the filter, pressurizes the fuel rail, sprayed by the injector, and what's not used is returned through the regulator, then goes uninterrupted through the return line back to the tank. The regulator increases pressure by "pinching" the return line. It reduces pressure by letting off the "pinch". It knows how much to pinch based on the vacuum line going to it.

When the vacuum line is off the barb, there is no vacuum signal. This is called base fuel pressure. This is when you make your adjustments. Set it to 43-45 psi based on what your chip provider told you.

If fuel pressure is too high, even with the stud turned almost all the way out, the answer is fuel can't be returned fast enough. This is caused by the pump being to big, or the return line being to small, or a kink in the return line, or a too small a regulator, or a malfunctioning regulator.

I would start with the return line. Check it. If it's good.....make a bigger one.

 

[NY Twin Turbo]

The feed is on the passenger side, the return is under the regulator.

 

[SHEPP2]

Thanks I really do apprionate you explaining that because I didn’t know. I am researching on how to install a new #6 braided return line. I am also thinking it may be best to change both lines and be done as I would like to upgrade maybe later down the road. Any other suggestion would be greatly apprionated as well. I found a thread here on the board on (Modifying stock fuel lines?) still researching. Any pointers??

 

[pacecarta]

are you running e85 and a hotair engine?

 

[SHEPP2]

I have a hot air engine...not running e85 but have thought about it. There's know gas station in my area that have it so...

 

[pacecarta]

nevermind i see 36# injectors , wrong pump for the application

 

[NY Twin Turbo]

Thanks I really do apprionate you explaining that because I didn’t know. I am researching on how to install a new #6 braided return line. I am also thinking it may be best to change both lines and be done as I would like to upgrade maybe later down the road. Any other suggestion would be greatly apprionated as well. I found a thread here on the board on (Modifying stock fuel lines?) still researching. Any pointers??

A long time ago we used to swap the supply to the return. And then we added a new braided line as a supply. Don't remember the details but I had mine this way for a while. You should find it in a search.

Good luck.

 

[novaderrik]

does anyone make a box that can lower the voltage to the fuel pump to lower the pressure? i know some late model vehicles do this to control noise in the passenger compartment, and i think there are some aftermarket universal pumps that do this, too.

shouldn't be that hard to design a boost referenced box that dials the voltage back to, say, 9 volts when not under load then gives full power when the vacuum goes away and boost goes up.

 

[pacecarta]

the weldon pump contoller does that but its not cheap option for the application we are discussing

he can run a new -6 feed line (more tha he will ever need )
and use the stock steel feed line on the frame for the return , tie it into the return line at the front of frame and switching it over above the axle

 

[NY Twin Turbo]

does anyone make a box that can lower the voltage to the fuel pump to lower the pressure? i know some late model vehicles do this to control noise in the passenger compartment, and i think there are some aftermarket universal pumps that do this, too.

shouldn't be that hard to design a boost referenced box that dials the voltage back to, say, 9 volts when not under load then gives full power when the vacuum goes away and boost goes up.

Yes. Aeromotive makes a fuel pump controller to be used with their equipment. It may be adaptable to another fuel pump. But NO. You don't need these sorts of gizmos. Too complicated. Don't add all this extra electronic junk you don't need. Just get it to work with an in-tank pump and standard set-up.

The complexities of fabricating a fuel supply and return are a good preliminary course in "Turbo Buick Hot-Rodding 101". Don't look for a way out. Embrace it. You will be taking on much more complicated tasks as you continue to develop your ride to meet your goals.

 

[pacecarta]

or just put a smaller 255lph pump in the tank because reality is that pump you have is too big ,

 

[NY Twin Turbo]

or just put a smaller 255lph pump in the tank because reality is that pump you have is too big ,

I agree. However, If he's in this for the long haul, he might want to keep it and upgrade the lines. With a Hot-Air set-up he might be using E-85 in the near future. I would.

 

[pacecarta]

my first question to him was if it was a hotair motor on e85 ....and he said he doesnt have any e85 available

agree hotair and e85 would allow more boost and make more power while needing more fuel flow but he doesnt have the injectors to see any gain and he doesnt have any source for e85 ....and availability of e85 will probably get worse before it gets better

 

[NY Twin Turbo]

my first question to him was if it was a hotair motor on e85 ....and he said he doesnt have any e85 available

agree hotair and e85 would allow more boost and make more power while needing more fuel flow but he doesnt have the injectors to see any gain and he doesnt have any source for e85 ....and availability of e85 will probably get worse before it gets better

Good points. I just hate the idea of down sizing after the fact. The pump may be too big and it shouldn't have been ordered. But I would work with it. Maybe because I assume he will end up like the rest of us someday. A raging turbo V6 addict.