Livelink - Oil and Fuel Pressure

[2005redgt]

Guys,

Does anyone know if we can monitor Fuel Pressure and/or Oil Pressure from the ECU ?

Update on Fuel Pressure: I tried "pressure drop across injectors" but it gives me a differnt number from my Autometer gauge that I mounted. The Autometer gauge is about 10 PSI lower at idle than what is datalogged.

Is this our only fuel pressure option ?

-Bryan

 

[07torchgt]

fuel rail pressure yes, oil not sure

 

[Kevin@PMP]

Pressure drop across the injectors should stay right around DeltaP (commanded fuel pressure), actual fuel pressure is equal to DeltaP + manifold pressure. At idle manifold pressure is around -10psi (or 20 in-hg) so 29.5 on your gauge = 39.5 (pressure drop across injectors and DeltaP) - 10psi (manifold pressure).

 

[TexasBlownV8]

Download this file for detailed OBD info and values; it might help:
http://www.motorcraftservice.com/vdirs/diagnostics/pdf/OBDSM507.pdf

Depending on the actual PID value, there is usually some conversion, too, of the raw data value into a reasonable and meaningful value. Many of those conversions are in this document.

And yes, fuel pressure relalive to vacuum or something else can be read from the OBD system, as well as many other values. I think oil pressure is one of them too, but not sure.

FWIW, I use a ELM327 decive to interface real-time to the OBDII/CAN system, using a Palm Tungsten hand-held to convert and display values. Much like a Livewire would do, or simple data logging does.

 

[Charlie Sheen]

Guys,

Does anyone know if we can monitor Fuel Pressure and/or Oil Pressure from the ECU ?...

yes

http://www.s197forum.com/forum/showthread.php?t=7198&highlight=aeroforce

 

[Big Top Gt]

Pressure drop across the injectors should stay right around DeltaP (commanded fuel pressure), actual fuel pressure is equal to DeltaP + manifold pressure. At idle manifold pressure is around -10psi (or 20 in-hg) so 29.5 on your gauge = 39.5 (pressure drop across injectors and DeltaP) - 10psi (manifold pressure).

Ok, so the 29-30 on my gauge is reading correctly and is where it should be?

 

[thump_rrr]

Ok, so the 29-30 on my gauge is reading correctly and is where it should be?

As stated in the other thread http://s197forum.com/forum/showthread.php?t=11054 fuel pressure is constantly in flux and is directly related to manifold vacuum/boot pressure.

Without a vac/boost gauge you cannot determine correct fuel pressure.
The Delta P across the fuel injectors is calculated with the method I outlined in the other post and copied below.

Fuel Pressure Differential should be a constant 39psi.

So to measure the fuel pressure differential in vacuum the formula is Inches of Hg / 2.036 = psi.
Assuming that you have 22" Hg

22 inches Hg / 2.036 = -10.84 psi
so 39 - 10.8= 28.2psi
while in boost you would just add boost pressure to the constant 39psi. so at 10lbs of boost you should have 49psi.

 

[Big Top Gt]

If I need to use vacuum readings to figure out fuel pressure, what's the point of putting a Fuel Pressure gauge in these cars?

It doesn't make sense.

I've got a boost/vacuum gauge in the car. I just walked out to the car and started it. It's showing 29-30 pounds of fuel pressure and roughly 20-22 in (hg?) of vacuum. (per the gauge)

Which falls right into line with your math above. This setup is different than the one in my Cobra. With that fuel setup (return style) you pull the vacuum hose, set it to 39, and reattach the vacuum line. Voila!!! Fuel Pressure is set. With the returnless setup, which is still uncharted territory for me, there's no pulling the line.

Thanks! I appreciate the help.

Oh, and for those of you who are wondering what "Delta P" is; it means Change in pressure, in this case across the injectors. Hope this helps.