[5pointslow]

I recentlly installed the Walbro GSS340(255lph high presure)

and now i have a bumpy fuel presure.. it fluxuates from 45-to 50psi and in between.. at idle and just off idle....This cant be normal.. I am running an FMU(12:1 disk) with my vortech blower..
stock 19lb injectors... and what also gets me is, somtimes after i shut the car off, i get a hold presure of 30psi or so... somtimes its 40psi, somtimes its 0psi, like today... what gives?
my stock 95lph fuel pump worked perfect (except under boost)... and didnt give me these fluxuating readings. Also , i can hear the pump from inside the car, and when i prime the pump,(Key on Engine off) i hear it whinning, but the whine is fluxuating also.like tis tryin to sing me a song..lol
... i dont get it. could the sock type filter have fallen off the pump, and cuased it to suck in debri the tank?
im sure i soldered the wires on good,and heat shrinked them, so i know they arent coming off..
I just dont get what could be wrong here.. i installed the thing correctly. now its giving me a fit! and the car is running funny too. i get a bumpy idle and somtimes it wants to stall out on me at red lights..
thanks for the help...

 

[spyder]

fuel pump relay. and fuel pressure regulator seems off.

 

[Tina]

I tell you this much your fuel system is way off. Your 12:1 ratio is to much fuel pressure for 19lb injectors and your intank pump will not support this much pressure. I bet your engine does not make good power at all even though you think it is. Get away from the FMU and install a T-REX pump along with your 255 with correct size fuel injector/matching air meter. These supercharger companys set there systems up so rich protecting customer engines that know nothing about blowers. There is no engineering thought by these companys sqeezing 100psi of fuel through a 19lb injector. Also you have to add more fuel pressure equal to the amount of positive boost. It's normal for intank pumps to have some amount of pressure after shut off. Figure out how much horse power you should have calling around. Take this total horsepower number and multiply it by .6 as this gives you a safe figure for the required amount of pounds per hour of fuel needed then divide by 8 for target injector size. I like to assume only 90% of injectors size and keep fuel pressure at 40psi. Then if you have 7lb of boost you would set fuel regulator to 47 psi. Your car will have so much more power doing all this and even more getting a dynoed chip setting correct fuel curve.

 

[5pointslow]

good info there... well the pump has started to behave now.. guess it just needed to get used to things.
Right now im seeing about 45-47lbs of base fuel presure, and around 85-90lbs at WOT... no pinging,timing at 10*, and the pump seems to be keeping up.. hel,l it keeps up alot better then when i had the stock one in there..
stock pump could only push 60lbs at WOT, and the car just wouldnt pull hard under boost... As soon as i put the walbro pump in, i felt a big diference. As soon as i hit around 3lbs of boost, or above 3500rpms it pulled very hard, and the presure rockets to 85-90lbs.. as soon as the presure hits 85lbs the car just takes off, and dont stop till i hit the rev imilter.. For now the 19lb injectors are working ok.. they are getting the job done, but im sure they are really being pushed at WOT.
ive put over 1000miles on this blower already, without one sign of pinging or any bit of trouble. I also tried swapping over with the 4:1 FMU disk, and that didnt help any, it wouldnt push the presure up to 85lbs, like it needed to.. The car seems to like more fuel presure.. the more i give it, the better it runs..It cant be running too bad, but im sure it has alittle more in it..
In a few weeks, i will be getting the proper injector, matching Mass air, and getting a tune..

 

[Tina]

I don't know what your boost is? Your 12.1 FMU means for every one pound of boost increase your fuel pressure increases 12psi. If you have 10lbs of boost then FMU will increase pressure to 120psi on top of your already stock 41psi (161psi). Believe me your bigger pump is doing better but not keeping up. If you never change intake or heads you would be safe with 30lb injectors. I would use 38lb or 42lb injectors with larger fuel rails for room to grow and use two pumps. Get a 80mm or larger air meter. Your intake 255 pump has a rating of 255lph at 43.5 psi. Any pressure increase above 43.5psi and pump loses flow. The T-REX does not lose flow below 70psi. Your intake pump also loses about 20% volume by the time it reaches fuel rails also. A boost retard would also be good in the future to retard timing as cylinder pressure increases so you can keep your initial timing at 10.