MicroSquirt.com read only forum (Jan.15,2018)

Hello-
Has anyone ever seen a fuel pressure gauge that is referenced to the manifold pressure-so that is shows the pressure that the injectors are seeing? I was considering building a display that would warn when the fuel system pressure was abnormal, but obviously, setting a lower limit in pressure without that reference would cause false low pressure alarms during periods of high manifold vacuum.
-Allen

No. But, you could just use absolute pressure, if it is lower than a set minimum you have a problem. If you car is like mine the FP does not change too terribly much. Of course, if you have an adjustable regulator it changes a lot with MAP, and you need what you describe.

I imagine there is some kind of relative pressure gauge with two connections you could use.

You need a differential pressure gage. These have two ports, one for the pressure measurement and one for the ambient measurement. The ambient port would get piped to your manifold. The gage would then be referenced to the manifold pressure, not atmospheric and will provide the reading I believe you are looking for.

jack

 >  If you car is like mine the FP does not change too terribly much. Of course, if you have an adjustable regulator it changes a lot with MAP, and you need what you describe. 
 
What's specific about yours? - Your fuel pressure regulator should be referenced to vacuum and/or boost - so the injectors always see the same pressure difference.
I.e When you're running 10psi of boost, your injectors will receive and extra 10 psi of fuel pressure. Same when in high vacuum, the pressure on the injectors goes down. I  think mine goes down to about 25-30 psi at idle (from 42psi) 


Posted by email.

Jack wrote:You need a differential pressure gage. These have two ports, one for the pressure measurement and one for the ambient measurement. The ambient port would get piped to your manifold. The gage would then be referenced to the manifold pressure, not atmospheric and will provide the reading I believe you are looking for.

jack

I just wanted to add: Differential pressure gauges are pretty rare in the automotive aftermarket, but many industrial supply shops like McMaster-Carr sell them.

Or you could take a fuel pressure gauge and mount it in a sealed box that connects to the intake manifold. It would definitely raise a few eyebrows at a car show, but it'll work.

Why not use a electric oil pressure gauge and use it for fuel instead of oil?

I know that in the miata community, this is seems fairly commun.