Recent thread on a members new engine start up got me thinking. (yeah dangerous, I know)

First made up a injector firing/testing harness. Momentary switch, 9 volt & injector connector:



Set up my manifold & injectors. Filled rail with carb cleaner, air pressure set to 40 lbs & got good 4-stream out of each one when activated.



No fluid out of return line, not air or drip, so I put vac pump on regulator at 18-20 then 30 inches vacuum. Nothing.

Why? Is regulator toast?

 

Nobody knows the operation of the regulator well enough to explain this observation?

 

If you had 40psi pressure on the fuel rail and 30 inches of vacuum on the diaphragm and nothing out of the return you have either a stuck FPR or plugged up fuel rail or a bad ruptured diaphragm.

The FPR has a 40 pound spring holding it closed and the vacuum will pull against the spring to open it.



/

 

Thank you for the response.

If the diaphragm was ruptured, the vac pump would not hold vacuum, correct?

Raising the pressure on the supply side above 40 PSI should in theory overcome the spring & allow fluid to pass out the return?

 

Yes that is correct.
Yes that is correct also.

 

I appreciate the feedback. Most FPR discussion is generally if there is gas in the reference tube, change it. Since I hadn't ever run across anything else I thought I ask. I also didn't want to misinterpret results & throw money at a perfectly good part or tear one up trying to test.

So I go back & start raising pressure with no vacuum applied & I get to 46-47 PSI before the return starts to pass air. I cranked in some vacuum with my Mity Vac & I got an increase in flow when I got over 20 inches. I would have to guess that fluid pressure would be a more accurate test over compressed air, but it gives me something.

I also discovered at 60 PSI the fuel rail makes a great air horn. All it needs is a bell & some valves to change pitch. Next trip to the junkyard I'm picking up one for experiments.

Thanks again.