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Fuel pressure

3K views 27 replies 12 participants last post by  slammin86 
#1 · (Edited)
Last weekend I had the car out for a little while and I noticed that when I sprayed it that the fuel pressure took a drastic drop but then gained right back. It usually sits right around 58psi but the needle dropped to about 30 and then right back up. Is this normal or just a fault in the gauge? the car felt like it was running fine and I didn't have any problems with it.

I do have a walbro 255 pump and fast fuel rails the only thing still stock with the fuel system is the injectors and the gauge that is reading it is a speedhut (same a team scss).
 
#3 ·
100 wet shot through a plate.
 
#4 ·
Anyone?
 
#5 ·
Is your car tuned for the Nitrous? Running that much fuel starvation (58 down to 30psi) is horrible for your engine. I doubt it's the gauge to be honest
 
#6 ·
The car is tuned for nitrous, that is what the entire build revolved around.
 
#8 ·
Then yea, you need to do whay noyz1 says. Get a wideband A/F in there and see what your car is doing. Or get someone you know around you who has one to hook one up, take it for a spin and see for yourself when you spray
 
#9 ·
Fuel pressure should never drop to 30psi, that is way to low and you will hurt something.....first thing I would is double check all your fuel lines and connections as well as your fuel pump, what does it do when you WOT it on N/A? it sounds like you have some sort of pressure problem, it's not a gauge, do not spray it until you find your problem.
 
#10 ·
Yea it wont be getting sprayed until I get it figured out, NA it doesn't move at all. The bitch of all of this is, I have a wideband but it didn't come with the sensor to go into the mid so I have that on order. I will be at modern muscle on Saturday ordering some tings so I will talk to them then.
 
#11 ·
You are probably draining the fuel rail of fuel when the nitrous hits, hence the drop in fuel pressure.

Since the Gto runs the regulator in the tank it does not see the huge draw of fuel when the nirous solenoid opens. Think of the fuel in the rail as water backed up to a dam, when you open the solenoid all the fuel rushes out and the regulator, since its in the tank takes a second or two to realize what just happened and increase the pressure.
 
#13 ·
That is with the bottle.
 
#15 ·
It is instantaneous. Takes about a second or two.
 
#17 ·
I have similar setup I think. Walbro 255 and a 100 shot on the plate. Fuel pressure is steady at 62psi under normal conditions. Drops to 60 floored all motor. Drops to 58 under the 100 shot.

I just had the pump replaced. The old one did what yours did without the nitrous after warming up. This started after about 1000 miles on the walbro pump and just kept getting worse. Now I am back to what is described above.
 
#18 ·
It's the internal regulator in the tank that causes that problem.
It takes a sec for the relay to increase fuel pressure when it sense's a
increase in demand


remove the Ground wire from the pressure regulator in the tank.
It is used to lower voltage to the pump at high bypass levels..
and delays full pressure at WOT

 
#21 ·
look at it before you coment.... there is still a ground just not a resistor
 
#22 ·
Yea, I figure I will just talk to the guys at Modern Muscle. Justin has never led me wrong before.
 
#23 ·
I also have the Walbro upgrade and high-flow fuel rails and mine did not keep up either. I then bought the dedicated fuel system from Nitrous Outlet that I keep filled with 110 octane race gas and I haven't had a problem since. Pics are in my sig.
 
#25 ·
see here - "the regulator, since its in the tank takes a second or two to realize what just happened and increase the pressure."


and here - "It's the internal regulator in the tank that causes that problem.
It takes a sec for the relay to increase fuel pressure when it sense's a
increase in demand"


Might be your issue......
I solved it by using a dedicated fuel system. If i had seen how hardcore did it I probably would have done it that way. Good luck figuring it out.
 
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