Engine/Transmission (1994 - 1998) Needle Valve & Snubber ?????

[FATCAT]

For the 12 Valve Fuel Pressure gauge installation, everyone says you need a needle valve and/or a snubber.



Does anyone have a picture of what these things look like.



I just installed a copper line from the top of the fuel filter to a guage in the truck and when running the truck I can hear the pulsation in the guage. Also the fiting on the gauge leaked a little (yuck, just a little diesel on the rubber floor mat stinks bad).



I disconnected the line and will need to tighten the connection to the guage more, but I want to put this valve/snubber in the line before I reconnect ... need help visualizing the thing.

 

[QRTRHRS]

FATCAT,



Can't help with the picture but I noticed you said copper tube. I would replace that with stainless. It's been my experiance that copper won't hold up to the vibration.

 

[FATCAT]

Copper is bad?

QRTRHRS, I would think that copper would be good due to its flexability. The leak I had was because I didn't tighten the line enough to the back of the gauge.



Steel huh, now you tell me. It was a pain-in-the-youknowwhat to pull that copper line through the fire wall. TST gave me plastic tubing, but I went with the copper (cheap $$$) to give myself a better feeling.



I would figure that steel tubing would kink easy and would be a nightmare to work with.

 

[Joe G.]

The plastic tubing works fine. I had that on mine for quite a while. I did get a leak because the fitting on the back of the gauge got loose. The tubing never failed.



I have since changed to an electronic gauge from Westach with the same snubber and needle valve that I used with the mechanical gauge to protect the pressure sensor.

 

[illflem]

Plastic lines are the best, they give. Slip the small boost gauge sized tubing though a larger piece of tubing to protect it and prevent kinking. Overtightening a ferrule type compression fitting will only make it leak. If it leaks you will need a new ferrule, best to only use them once. Finger tight plus half a turn with a wrench is plenty.





1/8'' needle valve p/n 6NM31 from Grainger, $3. 38



#ad

 

[FATCAT]

Thanks Illflem for the picture of the needle valve, but is there such thing as a snubber?

 

[illflem]

Here's a gauge snubber, all it is is a coupling filled with sintered bronze to provide a restriction. Problem with snubbers are they are only made with 1/4" thread since most gauges are 1/4''. Most automotive gauges are 1/8'' thread so you need to use a reducer, just more fittings and potential leaks. Another advantage of a needle valve over a snubber is you can shut it all the way down if you have a leak.



#ad

 

[nfox]

Needle valve and snubber

Do i need to use a neddle valve and snubber with a elctronic fuel pressure gauge setup?

 

[Joe G.]

If you don't the pressure spikes from the mechanical lift pump will wreck the sensor and/or the gauge.

 

[nfox]

needle valve and snubber

Where do i install these two pieces when i get them?

 

[illflem]

You only need to use one or the other, like I said the needle valve is better. The closest you can get it to the source of your fuel pressure the better, I attach the needle valve right to the banjo bolt. Install the needle valve fully closed, start your engine then slowly open the valve while someone else watches the gauge, stop when the gauge just starts reading.

 

[Chipstien]

Needle valve here... works like a charm.

 

[Todd T]

needle valve installed just like Ill is telling you to.

 

[QRTRHRS]

Question for illflem or others

Any problem with the air purging out of the line? I hope to finally get mine set up soon.

 

[illflem]

No problem with air at all, it will eventually purge on it's own. Something you may run into with a needle valve is after the air is purged the gauge may pulsate necessitating closing down the valve a little more. Reason is that air creates a damper since it compresses. One trick to use on a temporary gauge instead of a valve or snubber is to install an inline fuel filter in the gauge line so the air dampens the pulses. Fuel will eventually fill the filter though causing pulsations.

 

[David Oxland]

If you want an uptown adjustable one you can check here. I've made a rig for checking exhaust brake backpressure using a #150 and the snubber stops the test gauge from beating itself to death.

David



www.midwestinstrument.com/prodinfo10.htm

 

[FATCAT]

Got it installed ...

Now that I got the new needle valve installed and the guage back up and running, I have these results:



11 - 12 lbs. at idle

22 - 24 lbs. at 2500 rpm.



So, does that sound like the lift pump is going on the truck?

I just recently changed out the Overflow valve.

(approx 151,000 miles on truck).

 

[illflem]

Since the overflow valve is new it has to be the lift pump or one of the three filters is plugged.

 

[FATCAT]

OK Illflem,

I know of the fuel filter and the pre-screen filter above the lift pump ... what is the 3rd filter?



Also, (for the millionth time I'm sure) what are normal fuel pressures at:

idle:

2000 rpm

2500 rpm



at the bleader screw on the fuel filter (where the TST adaptor is attached).

 

[illflem]

There's also a filter in the tank which for the most part is self cleaning due to fuel sloshing in the tank but one bad load of fuel can change that. .

The factory recommended fuel pressure is 22-26 psi though all rpms.

18-34 psi would be fine but anything out of this range would indicate a problem.

Cold fuel and coasting downhill can result in short periods of higher pressure. Hot fuel on a hot day especially after parking on concrete where the sun reflects up at the tank can cause lower than normal pressures.