I installed a Walbro 255 and Aeromotive about 200 miles ago. I noticed that FP at idle with the vaccum line attached is right around 30psi, but after driving for a while I checked it again and its down to 20psi. I got the opinion from a local performance shop owner and he seems to think that my Walbro could be heating up and therefore not pumping as much fuel. I have heard of Walbros doing this before.
Fuel Pressure Drop after driving.
- Thread starter aye mate
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if you pull vacuum reference from FPR at idle does it drop -7psi or so?
did you do the 12v fuel pump mod? (stock resistor will flux)
Also maybe your wiring?
did you do the 12v fuel pump mod? (stock resistor will flux)
Also maybe your wiring?
I'd definately do the 12v mod, it will make tuning easier as well. If you cut the yellow wire to the FP relay, it takes care of it. From there you can remove the FP resistor pack.
I did it the old way of jumpering the wires to the resistor, but the wires were burnt up, leaving me stranded. Cutting the yellow wire is easier anyways.
I did it the old way of jumpering the wires to the resistor, but the wires were burnt up, leaving me stranded. Cutting the yellow wire is easier anyways.
Or you could do it the right way 
#10 wire pos & gnd from battery to 30 amp Bosch relay to pump. I would run a dedicated ground for the pump. Use the stock wiring to switch the relay on (Red/Black iirc)...remove the stock resistor & relay all together.
ECU will turn the pump on via the Bosch relay just like stock, but you won't have 20 ft of wire to complete the high amp circuit to the pump. The heavier gauge wire will provide a very good current supply and minimize voltage drop.
#10 wire pos & gnd from battery to 30 amp Bosch relay to pump. I would run a dedicated ground for the pump. Use the stock wiring to switch the relay on (Red/Black iirc)...remove the stock resistor & relay all together.
ECU will turn the pump on via the Bosch relay just like stock, but you won't have 20 ft of wire to complete the high amp circuit to the pump. The heavier gauge wire will provide a very good current supply and minimize voltage drop.
If this is a mechanical FP guage, then they get inaccurate when hot. Look at your guage instructions or call the manufacture.
Thanks guys! I do have the 12v mod done, but just the jumpered version. Jdub's version sounds like the way to go, sorry Scott, haha. The fuel filter is like a year old. I'll have to dig the papers that came with the AFPR out to see what they say about the gauge. I kind of don't think thats the problem though, be cause when I shut the car off the FP goes back up to the original pressure setting.
What i am doing with mine is removeing both the fuel pump resistor and relay in the engine bay and keeping only the one thats in the kick panel of the supra. Because there is two relays one of them just switches the resistor on or off to lower the fuel pump speed. the one you need is the one in the kick panel inside the car only this one turns the fuel pump on or off controlled by the (ecu) and (afm or ignition) uses two coils to fully turn it on.
this cleans up the engine bay a lot you could stow the connectors in the fender when done doing this right.
do this by removing both the relay and the resistor on the plug going to them you will see a black/red going to both the resistor & the fuel pump solder that wire to the blue/black wire going to the coil of the fuel pump relay then your car will run off the inside one also.
you have to do a J-tube mod thing also there is a restriction to the return there also.
refer to this thread please http://www.supramania.com/forums/showthread.php?t=34548
this cleans up the engine bay a lot you could stow the connectors in the fender when done doing this right.
do this by removing both the relay and the resistor on the plug going to them you will see a black/red going to both the resistor & the fuel pump solder that wire to the blue/black wire going to the coil of the fuel pump relay then your car will run off the inside one also.
you have to do a J-tube mod thing also there is a restriction to the return there also.
refer to this thread please http://www.supramania.com/forums/showthread.php?t=34548
By removing the relay and resistor this way, you are essentially doing the same thing as the 12 volt mod. The difference is you do clean up the engine bay a bit, but you still have the 15-20 year old wiring supplying power to the pump.
The best way is to replace the stock wires w/ heavier gauge to minimize resistance and voltage drop to the pump...plus you are running direct from a battery source. I would also use a 30 amp fuse on the new wires where you connect it to the battery.
The best way is to replace the stock wires w/ heavier gauge to minimize resistance and voltage drop to the pump...plus you are running direct from a battery source. I would also use a 30 amp fuse on the new wires where you connect it to the battery.
You guys are referring to the heavier gauge Black/Red stripe wire and the Blue/Black stripe wire going to the Relay itself correct? Just wanted to be sure before I go hacking wires up and thanks a lot! I'm doing a 2JZ swap soon and want to paint my engine bay and leave the cluster fuck out of the equation!
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jdub said:
exactly. i can't tell you how many old cars i've worked on that drop fuel press @ high RPM thanks to OLD wiring and V drop....