Mechanical FP Gauge - Air in line?

[romadant]

About to ditch the Glowshift from the previous owner for a ISSPRO mechanical and have a question. When I'm plumbing the new gauge do I just leave the line after the needle valve full of air, or do I need to bleed it somehow so it fills with diesel?

[hex0rz]

Needle valve?I dunno if this will help, but plumbing in a mech. fuel gauge, you are gonna want a chemical cage protector. Plumbs in between the fuel source and the gauge. From the protector to the gauge, you use antifreeze.Also, when you go to hook the line up to the gauge, use a syringe to fill the line with the antifreeze, then hook it to the gauge.

[Mopar1973Man]

Hex most of use moved away from isolators because the in-accurracy that they produce. Not to mention the scare they will give you when the anti-freeze disappears over time. (Low Fuel Pressure) then you got to remove the isolator test the system to relize the fuel pressure is fine but the isolator had lost its anti-freeze or failed. So the needle valve concept stared years ago with direct plumbing. Diesel fuel is not like gasoline where a simple spark are you have fire. So many people direct plumb there gauge in. Like myself I've been direct plumbed for 8 years now. As for the OP question... Even if air is left in the line the air will slowly disappear... You'll notice nice smooth gauge needle sweeps with a bit of air but as the air disappears the gauge needle will get really snappy and you'll be able to hear the water hammer if you open the needle valve to far.

[dripley]

Mine is installed with the needlevalve straight to the gauge in my 3 pod mount. I drilled a very small hole in the low point in the pod with the gauge so if it were to start leaking I could see a drip before it ran down behind the dash. It worked great since I did have a leak right after install.

[hex0rz]

So, I have a cage protector on mine. How should I have mine set up then? I have it plumbed to the OE canister, can I still keep it that way?

[dripley]

Hex, you dont have to change yours if it is working good for you. I have mine connected the way I wanted it. If yours is working good for you leave it. As long as you are getting accurate readings so be it. Not all of us do things the same way here. Thats part of the beauty of this site. Lots of good info to work with. It is up to you to put it to use the way you see fit. I like mine the way it is, but other folks see it differant. No big deal.Just for my education, what is a cage protector? same thing as an isolator?

[hex0rz]

Yea, its the same. I was just going off of what the device identifies itself as. Apparently, whoever bough the gauges, got it included with the fuel pressure gauge.

It looks like this:

The problem is, how 'am I going to know if this is allowing an accurate reading? Then, how do I know if my gauge has suffered from too much water hammer?

Now, I'm thinking about doing a big line plumbed with quick connects from the OE canister to the vp44. Maybe put a T on there and put a needle valve on it for the gauge, like moparman has in his article...

[JAG1]

I just had Source Automotive install a new F/P gauge. It runs fuel thru a needle valve up to an isolator where air then runs up to the gauge and the gauge reads air pressure. I think the air line part is under a preset air pressure tested and adjusted by the manufacturer. Think that's how it is on the new ones now.

[romadant]

As for the OP question... Even if air is left in the line the air will slowly disappear... You'll notice nice smooth gauge needle sweeps with a bit of air but as the air disappears the gauge needle will get really snappy and you'll be able to hear the water hammer if you open the needle valve to far.

Thanks. I won't worry about the air in the line.

[Mopar1973Man]

Thanks. I won't worry about the air in the line.

I've got black polyon line and can't see if there is air in the line or not. Did effect my reading at all...

[JAG1]

I've got black polyon line and can't see if there is air in the line or not. Did effect my reading at all...

Stop that whistling... it sounds like my turbo:)

[2500ctd]

Yea, its the same. I was just going off of what the device identifies itself as. Apparently, whoever bough the gauges, got it included with the fuel pressure gauge.It looks like this:The problem is, how 'am I going to know if this is allowing an accurate reading? Then, how do I know if my gauge has suffered from too much water hammer?Now, I'm thinking about doing a big line plumbed with quick connects from the OE canister to the vp44. Maybe put a T on there and put a needle valve on it for the gauge, like moparman has in his article...

I had that same isolator and it failed. I do have another one. Different style and it has been a while....maybe 6yrs? Got it from vulcan. no issues with it so far. I have also heard of guys running a snubber too. Not sure on its operation but I am guessing it is a small air chamber. The air helps absorb the water hammer, like mike said how the gauge works as the air trapped in the line slowly leaks out. I didnt want to direct plumb it only due to the smell if it leaks. I am redoing my gauges and thinking of going electric but not sure of a sender that cam handle it. Will probably do the same tricks as a mechanical gauge for plumbing in a sender, needle valve and maybe try one of those snubbers. They are cheap.....Gauge snubber

[Mopar1973Man]

Here is the article about air pockets and water hammer... http://www.siouxchief.com/Resource_/ProductMedia/133/Water%20Hammer%20FAQ%204-04.pdf As for the snubber fittings a lot of people buy them but since they are not adjustable gauge failure seems to still occur. http://www.summitracing.com/parts/ATM-3279/ As for the isolators I think part of the failure problem is the isolator is trying translate the water hammer pulse and it phyiscally wears out the isolator till if fails. Another form of isolator failure you won't see but have to check for is the diaphragm/piston leakage where fuel is on both side and the seperation of fuel / anti-freeze is no longer.

[RJC2]

When I installed my gauge last summer I fell for the islolator sales pitch. I was told that they are the only safe way to do the install and that I would basically be a caveman idiot if I didn't. Well, it lasted two weeks and scared the crap out of me when it failed. I thought that being brand new it couldn't have failed that quickly so I assumed it was something else.Well now, meet the Caveman idiot who fell for the salesmans warning (sales pitch) and didn't take the advice of Mopar Mike and the boys. I have a $100 isolator [paper weight] on my work bench as a reminder. I spent way too much extra time and money fooling around trying to figure out what had happened to my fuel pressure.I too ran the black air brake line directly to the gauge and my fuel pressure has been about 3 pounds higher ever since.