Hi Guys,
I am new here and hopefully you can answer my question. just so you know, I have an evo x gsr 2011, tune by Chag. all is fine and car has a lot of HPs. my fuel pressure was at 43.5 with vacuum line disconnected. until now all good. but since I installed the surge tank, the fuel pressure now is at 70psi and cannot adjust it that much. +/- 2psi.
can you help me on what I have done wrong please? any of you had experienced this before? all is connected as per instructions.
hop you can help
thank you for your time all
stephane
What fuel pump are you using in the gas tank?
So, when you have a surge tank, the pump that draws fuel from the main gas tank is essentially flowing at 100%. Because this pump is not required to supply any pressure at all, even the stock X pump is more than adequate to supply almost all surge tank configurations. So flow rate is quite high for the "lift pump"
When you mod the OEM pump hangar to use a Walbro 450, you have to drill out the return venturi. I'm sure you have seen this information before. The venturi "pump" has such a small hole in it that it creates a restriction in the return system, so much that it will artificially increase your fuel pressure at idle. So, most people drill the venturi out, and call it a day. That modification works for a 450 using the OEM hangar, as the pump must supply both volume and pressure. As pressure increases, volume decreases.
So, now you've installed a surge tank. In order to follow this, think of the "lift pump" system and the "main pump" (surge tank) system as separate components. When the pump in the surge is activated, the
only thing it is doing is pressurizing and recirculating the fuel that is
already inside the surge tank. So, it will not add or subtract pressure (unless you're using a massive pump, something larger than a hellcat pump) When the lift pump is turned on, it is
only supplying fuel to the surge tank. Once the surge is full, all that fuel gets dumped back into your main gas tank under the seat...
HOWEVER....the lift pump is flowing at
MAX flow rate. Because it is flowing so much fuel, it will
also cause an artificial increase in pressure, because it flows so much fuel that the venturi pump on the pump hangar gets overwhelmed and causes a restriction.
Try this.... Take your car, pull the back seat off, and unplug the fuel pump from the main hangar. Start the car. The surge tank has a minimum of half a liter of fuel in it when full, you should be fine to idle for an hour or more with that much fuel. Check fuel pressure with only the surge running, and report back. If pressure is now down to an acceptable level, then consider changing out the lift pump for something smaller, or connect the lift pump to a fuel pump controller, to variate speed at idle/ cruise.
