Al Gietzen wrote:

BTW; Grand Rapids Technologies EIS now includes the option for differential
flow for fuel injected systems.

[N.B.: the URL for Grand Rapids Technologies is
http://www.hometown.aol.com/enginfosys
--R.Kent ]

James Phillips replied:

Ok Al, I give.... can you explain this for the FI ignorant? James

Al Gietzen responded:

Generally in a carburated engine you have fuel going only one way; so you
put a flow meter in the line and measure flow rate, total fuel burned etc.
In the case of Fuel Injection the pressure at the fuel rail is maintained by
bypassing excess fuel back to the tank, or sump, or the line before the
pump.  Generally we like to have it go back to the tank, where it can mix
with the cool fuel.

If it's not possible (or convenient) to measure the flow where there is a
single flow path; we have to measure the flow going to the engine; and the
flow coming back, and subtract one from the other to get net flow to the
engine; differential flow.

Grand Rapids Technologies makes a nice engine monitoring unit (EIS, for
engine information system) at a reasonable price.  It reads out fuel flow,
total fuel used, etc.  Until recently their unit worked only with one flow
meter, so it didn't work on systems that returned fuel upstream from the
flow meter.  But now they do; and it costs $300 more, of course.

How'd I do?

I have recently been to their website, which is quite well done; but I am
now not able to find it, and neither do the seach engines. Don't know what's
up, but as soon as I find it (or someone else does sooner) I'll post it.

Russell Kent wrote:

Al,
I've looked over the website and see the stuff on fuel flow measuring (down to 0.1
gph which is the best accuracy I've seen so far).  What I don't see is:

  1. any indication that the fuel flow sensing is differential, or
  2. any prices for fuel flow sensors (on the price list that has all the probes,
     etc.).

I did find fuel *pressure* sensors, but we all know those aren't the same things.

Grand Rapids' web page calls the option a "FloScan flow sending unit."

Al, where did you get your information?

Russell Kent

I might point out that this is kind of academic as a computerized fuel injection 
system like Tracy's knows exactly how much fuel is actually being injected. Tracy's 
entire EFI system cost little more than most flow meter based measuring systems.

Paul Lamar
 
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