Fuel Pressure Gauge

[rdoimages]

Thanks to the awesome tech article by Stang65fst, I did a fuel heater delete today. Everything went great, didn't even have to pull the filter head off the truck. I decided to use the hole to install a fuel pressure gauge. I tapped the 1/2 npt installed a 1/2 to 1/8 brass bushing and stuck a Marshall 0-15 gauge in it. Truck roared to life, checked for leaks and then saw that the gauge is reading 0. All I really care about is that I've stopped the last visible leak in my fuel system (for now anyhow), but it would be nice if the gauge I paid $20 for did something besides plug the hole!
Am I missing something? Should I pull the gauge and bleed it (I didn't when I installed it) or should I just move on with life?
Thanks for all the great info I've gotten from here, without it I would have sold this thing the same week I bought it.

 

[79jasper]

What does it do if you rev it up?

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[tbrumm]

You may need to vent the gauge to get it to read properly. See the following link:http://www.marshallinstruments.com/FAQs/index.cfm
Go down to the FAQ that says "why isn't my gauge reading properly?" I have a Marshall gauge on my filter head and it generally reads about 3psi at idle and maybe 5-6psi when reved up. This is with a mechanical fuel pump. BUT, unless I vent the gauge prior to reading it, I will get all kinds of strange readings, or it won't register any pressure at all.

 

[rdoimages]

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I tried venting it, no response, so I loosened it while running until I got fuel leaking and tightened it up, now it's bouncing around 2.5 to 3 at idle without any real change when revving it up.
Really it's no harm, no foul, I'm glad it's reading something, at least I'll know my fuel pump is working in a no start situation.


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[tbrumm]

The only other thing I can think of that might make a difference is the fact that the gauge face is pointed upwards. I wouldn't think that would matter, as the gauge is simply reading the pressure of the fluid acting upon. However, I have mine mounted on the fitting for the "restricted filter sensor" and have an elbow on it so the gauge face is vertical and faces to the front so it can be easily read when standing in front of the truck.

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[laserjock]

You are on the wrong circuit. I asked about that a while ago. If you want to check pressure you are better off to do it on the Schrader valve side. Not sure if you will get a meaningful pressure there.

 

[79jasper]

That's what I was wondering.

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[rdoimages]

You are on the wrong circuit. I asked about that a while ago. If you want to check pressure you are better off to do it on the Schrader valve side. Not sure if you will get a meaningful pressure there.

Wouldn't the pressure in the filter head should be the same regardless of where you are in the filter head? Regardless, I am getting 3 lbs reading and I am using the spot I had available easily due to the removal of the fuel heater. I just did the same thing Dieselcrawler did when I read the original tech post.

 

[79jasper]

No. There's pre/post filter.

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[rdoimages]

No. There's pre/post filter.

Ok, maybe I just don't understand fluid dynamics, but unless you introduce a means of regulating pressure into a closed system, the pressure remains relatively constant. In other words, the pressure on one side of the filter should be the same as the pressure on the other side of the filter as long as the input line and the output line are of equal size, or I'm just totally wrong, it could go either way.

 

[laserjock]

The filter is a variable restriction. The IP pulls fuel at a variable flow rate so depending on fuel consumption, pressure may vary greatly post filter and may be pretty steady pre filter.

 

[rdoimages]

The filter is a variable restriction. The IP pulls fuel at a variable flow rate so depending on fuel consumption, pressure may vary greatly post filter and may be pretty steady pre filter.

Good explanation, I'll buy that. Learn something new everyday. Thanks

 

[gandalf]

In your picture, post #4 of this thread, you can see three ports pointing toward the driver's side. The first one, the one toward the front of the truck, is the schraeder valve. A gauge there will give you the pre-filter pressure. The middle port, with the black hose, is the return line. The rear port, the one with the funny fat thing, will give you the post-filter pressure. I think the post-filter pressure is more importane, since that is what is actually going to the IP. That can also give you an indication that you filter is plugged and needs changing.

 

[crash-harris]

In your picture, post #4 of this thread, you can see three ports pointing toward the driver's side. The first one, the one toward the front of the truck, is the schraeder valve. A gauge there will give you the pre-filter pressure. The middle port, with the black hose, is the return line. The rear port, the one with the funny fat thing, will give you the post-filter pressure. I think the post-filter pressure is more importane, since that is what is actually going to the IP. That can also give you an indication that you filter is plugged and needs changing.

This is where I tee'd my electric sender into. Reads between 4-5 psi running warm.

 

[fsmyth]

gandolf is completely correct. Add a tee on the port where the sender is located
and read pressure at that point. The only important reading is what the IP is
getting as working pressure.