Fuel pressure, before vs after the fuel rail.

[Nikzilla]

1998 S13 SR20DET Blacktop

So I have a bit of a custom fuel setup with all the lines converted to AN. I'm running a stock fuel rail that's been converted to -6 AN.

Here is my setup.

fuel tank
fuel filter
T'ee for the glowshift fuel pressure sensor unit that is wired up to the cabin
1ft of hose
fuel rail
1ft of hose
Tomei FPR with a curcuit sport fuel pressure gauge attached
back to fuel tank

Now, my problem is, the sensor before the fuel rail reads 10 psi lower than the one on the FPR. How do I know what value to aim for?

My current setup is (with the FPR on atmosphere), 53 on the FPR, 43 in the cockpit (I'm trying to run it 5psi rich because I'm breaking in my motor).

Is it possible one of the gauges just sucks? They are both pretty meh brands.

[cotbu]

Being rich when breaking in a motor can do more harm than a properly tuned fuel setup.
You set the fuel pressure at the regulator but use that one after the filter, 1 ft of hose is far from the rail., you could add 5psi every foot from the regulator. There is a reason flow matched injectors, or flowed injectors have marks on them, the ones that flows lower at the same psi get put closer to the regulator, because there is a pressure drop.

Is it possible one of the gauges just sucks? They are both pretty meh brands.
yeah!

[Nikzilla]

Ok, so should I just aim for the middle? The fuel rail is pretty much dead in the middle between the 2 sensors. The only reason I'm running a higher PSI, is because when I had the setup with the stock FPR, and the sensor 1 ft from the rail (albeit with a different setup, different Tee's and lines), it was reading 43.5ish at atmosphere. Now, if I set the pressure to be 48.5/38.5 ish, then at idle vacuum my pressure goes below 30, which is a lot lower than the same gauge showed before (but different configuration).

[cotbu]

I would verify by putting the gauge closer to the rail after the filter temporarily if you have to, just to get a good reading then go from there. I wouldn't wanna guess with the fuel system.

Sent from my Highly Tuned Galaxy S3.4!!!

[Nikzilla]

That's kinda hard to do, but if you think it's that important, I'll do it.

[jr_ss]

First of all, you're going to have pressure drops in the fuel system. Fuel hose, bends, 90's all create drag, which will in turn rob some pressure from your overall system. Second of all you have a pressure drop across the fuel rail at each injector, not to mention when they are opening and closing. Disregard what your craptastic gloknob gauge up stream of the injectors reads and go with the FPR reading. Set you base pressure by that gauge. If it's a few psi high, that's ok, it's better than not having enough pressure.

Here's an idea, invest in a set of quality gauges, what's more expensive to you? A gauge or a bottomend?

[cotbu]

That's kinda hard to do, but if you think it's that important, I'll do it.
I do!
You want to make sure your last injector has the correct fuel pressure, that would be the one closest to the filter 43.5psi entering the rail. Take the reading before the rail after the filter on the oem fuel setup.
The real question is, do you trust those gauges?
And what is your wideband reading?

[TheRealSy90]

I just use an oem regulator and have no problems lol.