Fuel Rail Pressure Gauge options

[chrischrischris]

The Lindsey gauge might be the most obvious option, but the way it sticks off the end of the gauge seems very awkward. Is there a better kit available or am I being too critical of the LR gauge?

[Outlaw944]

When i changed my lines to AN fittings I went with Radium Engineering for my FPR and FD.

[walfreyydo]

You can build your own with a gauge and NPT to metric adapters. The fuel rail I believe is a M12x1.5 thread and you can get an adapter from metric to NPT and attach any pressure gauge you want.

This is what I did. I ran one for a while but the vibration of the engine caused the needle inside the gauge to fail, so I replaced the gauge and now I just keep it in my toolbox so I have a quick and handy way of measuring fuel pressure if needed. It occurred to me that having the gauge attached all the time just isnt needed. When and if the car is running rough, you can quickly re-attach and check.

Here is a thread I put together on Rennlist outlining what I did. Again, my thinking on this has evolved since the below thread (based on some of the feedback people offered) and I have since removed it but keep it handy for diagnosis purposes. Due to the risk of leaks the risk vs benefit just wasnt worth it in my mind:
https://rennlist.com/forums/924-931-944 ... gauge.html

[t36]

Yeah, the actual end of the fuel rail uses a “globeseal” fitting. It essentially requires a female threaded m12x1.5 nut that pulls a ball seated end into it. Much like the round ball that actually seals the fitting normally.

Without that fitting, I would never run a fuel pressure gauge full time. You don’t want to rely solely on threads to seal. A threaded m12x1.5 adapter may be fine for pressure testing on occasion. But it’s not the correct the fitting and would be really dangerous to commit to leaving on the rail.

[dr bob]

I have a spare fuel rail cap, and tapped it to accept my fuel pressure gauge for testing. The original seal is provided by a ball that the cap presses into the flared end of the rail. To allow the gauge to see the actual rail pressure, I use a common brass 1/4" tube compression sleeve, one originally used in a fitting for copper tubing. On fitting the cap on the rail, I hold the fitting in axial alignment with a small screwdriver through the tapped hole as I snug the nut. Snug, not 'tight'; let the soft brass sleeve do the sealing, and Don't Stretch The Threads On The Rail. Once that fitting is in place. the hose to the gauge is screwed in, and the gauge is connected.

There have been a couple well-documented episodes of hard-mounted rail gauges failing catastrophically. Folks decided that the gauge was an interesting bit of eye candy when the hood was opened. The stem of the gauge and the brass tube inside suffer from vibration-induced fatigue failure. If you must have a gauge in the engine bay, mount it off the motor completely, with a piece of rated connecting hose, well supported. Realistically, most of us might check fuel pressure once in a blue moon (or two), and even then only when tuning or when some symptom shows up while driving. Bottom line is that a rail-mounted gauge is an unnecessary liability in my experience.

If you truly have a need to continuously monitor fuel pressure, you'll use a pressure transducer mounted in the engine bay instead of the gauge, and wire that to a dash-mounted gauge and your datalogger.

NEVER use copper or plastic tubing to bring fuel to a gauge or transducer, even more critical if the gauge is in the cabin.

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The overarching reminder is that flame inhalation, while instantly and irreversibly fatal, actually takes seven to ten minutes of suffocation time. Not Fun. For the car, a small leak from a metal fracture generates a nice fog of fuel. In the engine bay, the fog ignites on contact with hot exhaust. Even if you manage to turn the key off in a few seconds, there's still pressure maintained by the accumulator, the regulator and the damper(s), just a few more ounces of fuel fog, and almost immediately more than your small dry chemical extinguisher will contain. ASSuming you have one and can get to it.

I add a thin film of Teflon sealing paste to the threads on the end of the rail, and in the flared end of the rail where the ball seats. Then just snug on the nut is plenty to keep the fuel inside. The Teflon makes for more consistent torque, and you can deduct about 20% of the normal torque for the lubricated threads and still get the same specific pressure to seat the ball in the rail inside.