Fuel pressure sending unit

[Munch]

I read somewhere that because the C5 is a non return fuel system that it can be hard on the sending unit of electric fuel pressure gauges. Something about rapid pulsing of the fuel pressure or the like. I don't know if they were talking about cheap sending units or not, I'm using an Auto Meter unit. Anyway, anyone ever hear this before and if so, what's the fix?
It's probably nonsense but I wanted to check.

Thanks.

[Y2Kvert4me]

Troubleshooting a problem you don't yet have, interesting.

It's actually a pretty good question, as most probably don't stop and think about the pulsation in rail pressure as the injectors slam open and closed. There has to be some pulsing, even on a return style system. but the later 99+ cars don't even have that.

The later cars do have a pressure damper on the crossover of the stock rail, so the first obvious question is....Are the people blowing out sending units using aftermarket rails with no return/no damper?

I've never seen this issue discussed before, so I'm curious too, if it indeed is a problem many experience.

[Munch]

I came across a bunch of people having this problem when researching a GlowShift fuel pressure gauge which is a cheap gauge. A lot of people said their sending unit took a crap on non return fuel systems and were recommending some sort of buffer or something for the sending unit. I never saw anything about this problem when researching the autometer sending unit so maybe it was just a pos unit.

[Munch]

Another question. When using a line to remote mount the sensor off of the motor won't there be air trapped in that line and how are you supposed to get it out?

Also, the remote lines are 4an which is a lot smaller than the fuel rail, will that cause a higher than actual pressure reading? Should I use a 4an to 6an expander and run a 6an line to my sending unit?

[Y2Kvert4me]

Originally Posted by Munch

Another question.

I count two.

When using a line to remote mount the sensor off of the motor won't there be air trapped in that line and how are you supposed to get it out?

No, any air in the line will quickly disappear once the engine is started. Unlike a closed hydraulic system like a brake or clutch, the injectors open into a large area of vacuum, so any air within the fuel plumbing will be drawn out first. (ever notice if your car's been parked for more than a couple days it takes a few extra cranks to fire up? The fuel system does bleed down over time).

Also, the remote lines are 4an which is a lot smaller than the fuel rail, will that cause a higher than actual pressure reading? Should I use a 4an to 6an expander and run a 6an line to my sending unit?

No, because it is regulated upstream, pressure will remain a constant regardless of the hose size.

Pascal's law of physics tells us "Pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure ratio (initial difference) remains the same".

This very same principle is what makes a floor jack or hydraulic cylinder such a powerful tool.

[Y2Kvert4me]

And BTW Munch, saw your post on another forum...

The rail is actually threaded 7/16"-20 with a 37° taper, which yes, is the correct AN/JIC flare. (you may wish to correct your 7/16-24 typo )

If you are using a hose, a -4AN female swivel end will thread right on it and seal just fine.
The Autometer sender is 1/8" MNPT (pipe thread). If you are having a hose made, see if you can get the other end made with a 1/8" FNPT end fitting, will save you from needing a -4 to 1/8" adapter.

[Munch]

Thanks, fixed the post on that other place. Good looking out.

Summit has a kit that's a 3' 4an line with some npt adapters that I was looking at for like $30 but I was going to call around on Monday and see if I can get a line like you described made up. Less fittings the better.