Fuel Pressure Subaru Turbo motor

[Cookie]

I know without going on a dyno, it is hard to know the fuel pressure under load, but I have a basic question. So here is the situation.

Subaru 2.5 turbo motor (450hp), just got back from shop and dyno (not at Outfront). Cart was not even drivable. Motor runs bad, we check plugs, wires, all new Fuel filters as well. Engine seems to sputter, pull a plug wire and it won't idle on 3 cylinders.

So we pull off my Engine Fuel pressure gauge and put on the Subie. At idle it is at 45lbs, to me that seems very low. We increase the fuel pressure to 65lbs at idle, now it runs and idles smoothly. We were able to run it all weekend, but I still think that is low, it still has a sputter when you first hit the gas but clears out and runs. I think my turbo Honda at idle is more at 80lbs, will confirm when I get new gauge. What do you think it should be at idle?

Another question, engine builder said it was good to go after a $1200 dyno tune, but it came out of the trailer running like crap. What would cause a recent drop in Fuel pressure? Before all of this, all E85 was removed from tank and all new Fuel filters were installed as well.

 

[John@Outfront]

there is no "base fuel pressure" it can be what ever you want it to be and tune from there. typical Subaru regulators are 3 bar (43.5psi with no vacuum hose connected) fuel pressure can be adjusted up or down just like you can pick smaller and bigger injectors. if you have too small of injectors for the HP goals you can cheat a little and raise the fuel pressure without buying larger injectors. the opposite is true too, you could have too big of injectors for your hp goals and can then lower fuel pressure a bit to again..... "not buy injectors" We never go below 3 bar of pressure but just adjusting it higher is not the answer, even if it runs better--you have issues

what kind of ecu? show pics of the injectors

now i don't know who tuned your car and took $1200 but i sure wish i could do that.......in 20 years of tuning the most i have ever charged is 2 hours ($650)ever to tune a Subaru. if someone took $1200 from you then something else is wrong and they wasted their time trying to fix it through a tune and it doesn't sound like that was the answer either

or i suppose the $1200 was not for the dyno alone but included other services......

 

[Jtmoney714]

My Honda fuel pressure was about 48 and would rise with boost.

 

[daveH]

there is no way your base fuel pressure (the pressure at idle with the Vacuum line open to atmosphere) should be that high. you will kill your fuel pump in short order or smoke the wiring. the vacuum line to the regulator also see's boost, and then raises pressure 1:1. so your 65psi base would be 80psi at 15lbs of boost. your pump will have to work wayto hard at that pressure unless you have a REALLY good fuel pump.

more than likely you have a different issue.

almost always a car that is tuned properly but acts like it is starving for fuel (turning up your base PSI kinda proved that) look for issues with fuel delivery.....such as pump failing, bad filter, clogged injectors etc. a faulty MAP sensor would be suspect.