Measuring Fuel Pressure on D-Jet

[pbanders]

Fuel pressure is one of the most critical parameters in the D-Jet system. One thing to be aware of is that many of the typical dial-type fuel pressure gauges are often miscalibrated enough to cause problems in setting the fuel pressure accurately. The spec pressure is 2.0 atm, or 29.4 psig. It should be set to within 1 psig of spec.

I bought a fairly cheap gauge from my FLAPS ($30-40 or so) that I recently used to test two local AZ guys cars, Travis Neff-Hohne and Greg James. On Travis' car, I measured 26 psig, on Greg's, 34 psig.

Then I decided to check my gauge against my Fluke PV350 pressure transducer. This is a NIST-traceable device that has very good accuracy. After I cross-calibrated, I now put Travis' fuel pressure at about 28.5 psig (delta of 2.5 psig). Greg's fuel pressure is actually about 37 psig (delta of 3 psig)! Way too high (and if you're reading this, Greg, yes, we'll work on resetting it).

Moral of the story is to make certain to buy a quality gauge that has a statement of calibration. Otherwise, expect to be chasing FI problems that are due to incorrect fuel pressure setting.

[captjm]

I bought a gauge at a local speed shop for twenty bucks. After reading your post I wonder if I can check my gauge calibration using my air compressor and its gauge. Maybe using a tire air gauge to vote in as well.

[efrenv]

I used a small air compressor and it's gage to check my fuel pressure regulator. Connected the compressor hose to the fuel pressure regulator intake port. Started the compressor at a high pressure .. ie 40, 50 psi. When the air stopped passing through the pressure regulator, read the pressure on the compressor gage. That's the setting of the fuel pressure regulator. Seems to be working fine.

[pbanders]

I have to ask the question - what makes either of you think that your air compressor's gauge is accurate? Most are fairly cheap dial gauges. Just because two gauges agree, doesn't mean they're accurate, unless one of the two gauges has a statement of calibration and some accuracy criteria.

[captjm]

I believe I have a tire gauge that has a statement of calibration. If I can pick the right fittings I think I can use it to test the other gauges for accuracy. No?

[Bleyseng]

I use a gauge that is oil filled and for measuring fluid pressure off a paint sprayer rig I used to have. ( sold the rig without the gauge). It seems to work fine but I dont have the calibration paper work anymore. Using a gauge that measures air pressure, I think isn't very accurate for what we a trying to measure like Brad said.
Geoff

[pbanders]

Originally posted by captjm
I believe I have a tire gauge that has a statement of calibration. If I can pick the right fittings I think I can use it to test the other gauges for accuracy. No?

Depends on the tire gauge. Most I've seen aren't calibrated, except for the pricey ones. I did a cross correlation with my PV350 on one of mine, it was accurate to about 2 psig.