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Mopar1973Man

Fuel pressure gauges and needle valves

23 posts in this topic

Ok Gang...

I've seen a bunch of you wondering about needle valves... Well here I'm going to explain the reason and why needle valves should be used on all fuel pressure gauges including electric gauges.

Now first thing first is why do we need a needle valve? Well the needle valve is a adjustable damper for the fuel flow. It prevents harsh or water hammer pulses from reaching the gauge or sender.

What is water hammer?

http://en.wikipedia.org/wiki/Water_hammer

Here is what the pulse looks like...

Posted Image

But now figure that is pulse open and close at half the RPM's but for 6 cylinder. This pulsation with eventually wear out or eat the gears out of mechanical gauge or electric senders.

So here is a quick video of proper set needle valve...

http-~~-//www.youtube.com/watch?v=M33ZCc8b-7Q

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appreciate the info. How old is that video or is your truck allways that clean under the hood? Mine has not looked like that since 2004.

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How old is that video or is your truck allways that clean under the hood? Mine has not looked like that since 2004.

That video was shot as of 2 days ago. And yes my truck is always that clean under the hood. When the truck is washed so is the engine...
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Great video, I was looking for just something like that. Mine is open too far I guess.
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I didn't realize that a needle valve was necessary for an electronic guage as well as straight mechanical guage.

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This is what happens to a electric gauge after water hammer has beat it to death... :rolleyes:

The wild swinging up and down is from the water hammer beating the rheostat back and forth till it wears out or damaged the sender so now you get this wild gauge problem... So you must protect both mechanical gauges as well as electric gauge just the same...
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Good info Mike, New guy here, new owner, first post. Came across the thread while searching the forums for info on gauges. Questions:1) When you refer to a needle valve, is this like the needle valve used to tap into my water line in my house for the refrigerator's ice maker? Brass, tee handle, 1/8" NPT male to 1/4" compression fitting.2) Is this a better way to go than using a snubber that is offered by the gauge manufacturer?3) Is it OK to mount the sender directly to the engine, or should it be remotely mounted to the firewall/inner fender?4) Is it recommended to tap the fuel pressure at the fuel filter or would the input banjo at the injector pump be better?Appreciate the help,Joe in St Louis'99 3500 QCLB, DRW, 2WD, Auto, 4.10 Axle, Stock

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Good info Mike, New guy here, new owner, first post. Came across the thread while searching the forums for info on gauges. Questions: 1) When you refer to a needle valve, is this like the needle valve used to tap into my water line in my house for the refrigerator's ice maker? Brass, tee handle, 1/8" NPT male to 1/4" compression fitting. 2) Is this a better way to go than using a snubber that is offered by the gauge manufacturer? 3) Is it OK to mount the sender directly to the engine, or should it be remotely mounted to the firewall/inner fender? 4) Is it recommended to tap the fuel pressure at the fuel filter or would the input banjo at the injector pump be better? Appreciate the help, Joe in St Louis '99 3500 QCLB, DRW, 2WD, Auto, 4.10 Axle, Stock

Yep, same as the one for the fridge. Probably better than a snubber. Firewall is better because of engine vibration. The banjo bolt and fuel filter should be the same pressure if it is the part of the fuel filter that is after filtration. Let me know if you ever need any help, I am in MO too..

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Good info Mike,

New guy here, new owner, first post. Came across the thread while searching the forums for info on gauges.

Questions:

1) When you refer to a needle valve, is this like the needle valve used to tap into my water line in my house for the refrigerator's ice maker? Brass, tee handle, 1/8" NPT male to 1/4" compression fitting.

Needle valve I'm using is a NAPA (Weatherhead) #WH6820 it cost about $8 bucks...

Posted Image

2) Is this a better way to go than using a snubber that is offered by the gauge manufacturer?

I prefer the needle valve it because a snubber is just a fitting with a tiny drilled hole. But a needle valve you can adjust to taste. Also if there is a fuel issue you can just shut the needle valve and keep driving.

3) Is it OK to mount the sender directly to the engine, or should it be remotely mounted to the firewall/inner fender?

Lot of people suggest remote mounts... But is not really needed (In my opinion). Think the oil pressure sensor and all the other senders do well on the engine...

4) Is it recommended to tap the fuel pressure at the fuel filter or would the input banjo at the injector pump be better?

So I would hook in as far from the VP44 as possible to get back from the water hammer but you got to be forward of the filter so at the bottom of the filter is perfect. Because the stock fuel filter always has a head of air in the top of the filter housing and aid in some of the water hammer suppression. Not a good a idea to hook up at the VP44 because that is the source of the water hammer so the wave is the strongest here... (Most damaging effect!) Kind of like stand at ground zero and light a stick of dynamite BOOM! You'll most like be dead... But light a stick of dynamite and throw out a distance from you I'm sure you'll survive the BOOM! and might still feel it...

Posted Image

Appreciate the help,

Joe in St Louis

'99 3500 QCLB, DRW, 2WD, Auto, 4.10 Axle, Stock

My :2cents: in blue... :thumbup2:

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I had mine mounted right at the vp44 but couldn't control it so I added a grease gun hose to get the sensor farther away and she's good now:thumbup2:

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When I had an electric gauge, I used a grease gun hose and mounted it on the firewall. Still went through two sending units. They were GlowShift sending units though so that could have been the issue.

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My :2cents: in blue... :thumbup2:

Hey Michael, question where did you tie the needle valve in to the airdog system? I have an electrical Isspro fuel gauge and need to install a needle valve and stumbled on this old post. I appreciate the info.:thumb1:

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Needle valve is installed right at the point tapping the fuel line. This gives me a shut off point also everything behind the needle valve is protected. So like my needle valve is right in the fuel line between the stock fuel filter and the VP44.

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Anyone know what thread the banjo bolt on the bottom of an 01' fuel filter housing is??? I just recently purchased a isspro guage kit and am wanting to install a needle valve there to feed my isolator.....thanks in advance

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Thanks... Is a 1/8" needle valve sufficient to feed to my isolator?...i went by napa and thats the only size that they could order...now its gonna be next week before i can get my guage installed i watched your needle valve setup video..are you using an isolator??? If so, where did you mount it? thanks in advance

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He has no isolator. I set mine up almost identical to MM's. Needle valve in the line between the fuel filter canister and the vp. Piped straight to the mechanical gauge in the cab. Mike is my hero.post-10340-138698205348_thumb.jpgthere's you some love Mikey.

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Wheres the best place to pick up a switched hot for the guage light?instructions says dimmer sw but there's no where to land a wire.....thanks!

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I have mine tapped into the #5 fuse in the fuse box in the cab. I have this little thingy that after removing the fuse you plug it into the fuse box and replace the fuse. I put it in so long ago I dont remember what you call it. It came with my gauges. The #5 fuse is the illumination circuit for the dash lights and will dim with the dimmer control.

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Thanks..any other options???

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I believe you can tap into the wiring under the dash, but I could not tell you where. I am sure someone else will know.

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I figured it out with a little help....on my truck the brown wire comin out of the dimmer switch dims the factory gaugesi tapped in there! Dripley, you were refering to a tapafuse....napa had them when i went to get some stakons...thanks for all the help

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I have an add a fuse, but this one just fits in the fuse slot and the fuse goes right back in the slot.

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