Fuel Pressure Sender Settings

[AbeFM]

Hey! I finally got my fuel pressure gauge in, and before I plumbed it in I wanted to make sure it was right...

EDIT: OH! You're supposed to input in kPa. I get it. Nevermind!


Original post:
In TS, there are three "fuel pressure 1"'s - PSI, KPA, and BAR. I can also get raw "sensor #1".

What are these? None of them agree!
My setup is a 0-5V active gauge, which outputs 0.5V for 0 psi, and 4.5V for 150. So that's 0V = -37.5, and 5V = 168.75 (I had it at 187.5 but that wouldn't cause the issues I was seeing)

Putting in ambiant ~100 kpa, I get -0.2 PSI, -16.4 "sensor 1",
Putting (approximately) 83 psi in there (could be 75, could be 85), I get

Actual Pressure (psi): 0 80
Indicated PSI -2.8 12.3
Indicated RAW -16.4 86.3
Indicated KPA -18.8 84.0
Indicated BAR -0.2 0.8

I'll go tweak the numbers, but right now, it looks like "KPA" and "RAW" are both showing measured pressure in PSI, although the 15 kpa difference between them doesn't make much sense with MAP reading 102.3 right there I don't think that could explain the differnce.

Bar looks like... I don't know. 11.6 psi, covering a total range of 1 bar.

I'm at a loss as to what all these numbers mean. How would I get fuel "gauge pressure"?

-Abe.

[jsmcortina]

Have you configured the fuel pressure settings as per the manual?



James

[AbeFM]

I cowboyed them, James. I cowboyed them good and wrong.

Why ARE there so many different numbers, though - what do they all mean?

[jsmcortina]

You read the manual page - right?
http://www.msextra.com/doc/pdf/html/Meg ... .3-52.html

James

[AbeFM]

Not as much as I should - but in this case, I was wondering, why store all three? It's not a big deal, but I was wondering why the ECU would bother with differing units, it would seem the end user could convert them later. Just out of curiosity.

[jsmcortina]

The ECU doesn't store all three. It stores one for each channel and TunerStudio calculates the other two for each channel:

;fuel pressures
fuel_press1_psi = {fuel_press1 * 0.147 }, "psi"
fuel_press2_psi = {fuel_press2 * 0.147 }, "psi"
fuel_press1_bar = {fuel_press1 / 101.35 }, "bar"
fuel_press2_bar = {fuel_press2 / 101.35 }, "bar"

James

[AbeFM]

Ah! Ok, thanks. Got it all working and relatively well tuned - though I wish there was a way to see fuel pressure without running motor (i.e. to force pump on and have gauge update).

Not a pressing issue. Thanks for the info!

[billr]

One easy way to check fuel pressure without running your engine is to set a "priming pulse", even a very short one so little fuel is actually injected. With a priming pulse the fuel pump is turned on briefly at key-on.

[AbeFM]

Yeah, I messed with the idea of leaving it on a long time... For some reason, my regulator bleeds down really quick! I tried going back and forth (putting it in and out of test mode very quickly seemed to help!) but really, once I was sure I trusted the gauges I just used the raw value Sensor gauge to set things.