Fuel pressure

[rtalich]

I am trying to track down an issue... My motor is a 2.5L Type IV fuel injected t3/t4 turbo. What fuel pressure should I be running?

Thanks!

[ps2375]

You want to have a FPR that adjusts pressure according to manifold pressure. So you always have the same pressure differential so that the injectors flow the same for a given duty cycle.

[Clonebug]

Depending on what ECU you use it would more than likely be right around 43 psi.

I know the 69 VW squareback I had ran at 28 psi but most modern FI run at 43 psi and some newer ones can run higher.
For FI turbo you would want 43 psi and a boost referenced regulator.
I use a standard German FI stock regulator hooked up just below the throttle body plate so it sees vacuum and boost.

[Piledriver]

The injectors actually determine what pressure you run, but as Clonebug said, most are flow spec'd at 42 PSI and run a regulator with manifold vac/pressure reference.

I have a set on the shelf that are spec'd for 400>2250...and the matching Mazda dumb injector driver box for them. And a suitable PWM controlled fuel pump, just need to figure out how to drive it.

[rtalich]

Thanks guys! It is a Mallory FPR... I can't recall the exact PN but it does have a vacuum/boost port that is connected to my vacuum/boost plenum. ECU is SDSefi.

[ps2375]

You can run almost any fuel pressure you want, the injectors rated flow is usually measured at 3bar. But, once you start tuning, you want the reference pressure to stay the same and rise/lower with manifold pressure.

[miniman82]

I say as long as the ECU has enough tuning room, it really doesn't matter. It's all elementary anyway, since so many numbers can be fudged. Example: if you have small injectors that get maxed out towards the top of the RPM/boost map, you can run more fuel pressure (to a point) to compensate. More base FP has the effect of making an injector look larger to the ECU, all other settings left alone. Be aware there are different types as well, a rising rate regulator will seriously flatten the high load portions of your fuel maps where you would have thought you needed bigger numbers. That's the regulator flowing more fuel through the injectors, not the ECU. Let your wideband be your guide, trust your instruments. If it reads lean on a run, assume you're lean and add more fuel.