JPI 900 Fuel pressure

[Steve Dawson]

Has anyone installed the FP sensor on a Bravo? I have a question about the two fuel lines and setup. The analyzer works as advertised and I'm happy with it however JPI hasn't been any help with getting their fuel pressure sensor to read the proper pressure.

Thanks 

Steve 

[Aerodon]

Steve,  what is the issue - do you have a straight or differential fuel pressure transducer?

Aerodon

[oregon87]

I'm going to take a shot at this, from an EI perspective.  Hopefully it will help.  Please note, I do not know how JPI handles the following, but maybe it'll be a bread crumb to follow.  Is your fuel pressure reading too high?  If so, it is likely due to upper deck pressure not being taken into account.  The turbo outlet pressure is basically fed to the "top" of the injectors to equalize the pressure, ensuring flow to the engine.  If this pressure was not fed to the injectors, there would a negative pressure at the "top" of the injectors, resulting in the fuel not making it to the engine.  The upper deck pressure needs to be subtracted from the fuel pressure indication.  As such, fuel pump pressure - upper deck pressure = displayed fuel pressure.  I don't know if JPI offers a differential pressure transducer, or if a second pressure transducer needs to be added and that second transducer's signal subtracted from the fuel pressure transducer's signal.  The latter is how we do it.  

[Steve Dawson]

1/  Don I'm pretty sure it's a differential sensor. I've installed it in the same position as the original (Shading I believe) and it will only show 4-5 psi

 

2/ EI (Oregon) Sorry don't know your name. These are good questions and JPI has not been helpful. They've just said this is what we supply and figure it out yourself. 

BTW, I have tried switching wiring without any luck. 

I've attached some pics so hopefully the will help.