My fuel pressure has been doing weird things. Running 8psi cold (42*) and gradually gets higher as outside temp and engine temps come up. But overall it's been falling. Running 15psi warm. I kicked up the pressure to 15 cold and now goes up to 22psi warm. A better range. But a month ago it was low consistent and I raised it back up. Sound like a raptor issue?

I also have a vibration/buzz coming through my cab gauge. Isspro with snubber from vulcan. It quiets down if I pull it out a half inch or so. The gauge has a vibration that you can feel if you pull it clear out of the pillar. I don't have a test gauge. I'll check with a few locals to see if they have one.

If the buzz increases and decreases with engine RPM then I would think that it is the snubber not working correctly. You might try switching it out for a needle valve. Either the snubber isnt working right or the gauge is starting to die on you. Sorry to say.. The pressure swings do kind of sound like the raptor issues with the adjustable regulator. Very common for pressure swings like that.

I stopped off at the auto parts store and got a tester gauge. Seems that my gauge or isolator is faulty. Gauge said 15 tester said 35. So I've been turning up the pressure to compensate for the pilar gauge. Throttled it back to 20 psi on the tester. Seems pretty consistent with tester.

How do I figure out which direction to go now ? Gauge or isolator? Maybe I should do the needle valve mod and run diesel into the gauge on the pillar? When you need to bleed the system do you close the needle vavle entirely to keep from getting air into the tubing to the gauge?

Honestly you can't go wrong with a mechanical gauge. The whole deal of fuel rupturing in the cab is way overdrawn. The only way fuel will ever rupture in the cab is if the line gets cut or rubbed through or a fitting works itself loose. Wrap your line where it goes through the firewall and tighten your compression fittings and you will have zero worries. I hear of horror stories on the interweb but the problems are 99% of the time the end users fault. My uncles have both been running mechanical gauges in their rigs for decades and have never had any problems.

I have a mechanical gauge. I'll read the archives for brake line as I recal as the preferred cab line.

I use 1/4" tubing to my mechanical gauge in the cab and have had a problem with any of it. I have a lot of it if you need some just let me know.

It's the fittings that cost. I'm set up for 1/8". All I need is the needle valve and tubing. Thanks anyway mike.

I think I have 1/4" straight fittings also. I know I don't have a needle valve but I think the smallest one if have seen is 1/4"

Vulcan Performance carries an 1/8" needle valve. Some folks have gotten them at NAPA also.

I have a 1/8 needle valve that I got from napa. Moparman knows the part number for it. I would just try running the needle valve and see what you get. Snubbers and isolators ave been known to cause pressure reading problems and it is not very common that a mechanical gauge will have problems unless it was run unprotected from the VP.

WH6820 from an earlier thread written by Michael?

That sounds right. Should be 1/8in pipe threads to 1/8in tubing. Works great. Been using one for over a year with no issues and they are fairly cheap too.

The original symptoms sound like an isolator that needs to be refilled.  Here are the instructions for doing that:

Remove the line and fitting from the "gauge" side of the isolator.  Using a skinny but not sharp rod (like the eraser side of a wooden pencil, or a chopstick), push into the isolator from the now-open side, to push the piston completely to the other side.  If the isolator is mounted such that the gauge side port is not pointing straight up, temporarily remove the mounting hardware and hold it with that port pointing up.  In this orientation, fill the gauge side of the isolator with antifreeze (using a turkey baster or syringe), then replace the fitting and tube.  Remove the other end of the tube from the back of the gauge, and fill it with antifreeze (using the turkey baster or syringe).  If you have someone helping you, it helps to have them loosen the tube at the isolator (while still holding it with the fitting pointing up), to let air out of that end while you force the fluid in from the gauge end.  Re-install the tube to the back of the gauge, tighten everything up, and check for leaks.

 

The rattle in the gauge could be due to that, or it could be the gearing just getting more loosened up with age and the pulsations that come from a VP44.  If you send me your mailing address at michael at isspro dot com, I can have a replacement smaller orfice sent to you.  It threads into the back of the gauge, just remove the fittings from the back of the gauge and use a small flat blade screwdriver to remove the old one and install the new one.

 

Regards,

Michael Pliska

Wow, everyone is here! Thanks!

I put my test gauge at fire up this morning. Generally reading low in the morning. Test gauge showed 20# at fire up. So the good news is that my fuel pump is not the problem.

I think that I'll eliminate the isolator and run diesel to the cab. Is it not necessary to purge air from the line going to the cab? Air does compress more than liquids.

No need to purge air, it will just compress as necessary and allow the gauge to read.  The problem with air is when using an isolator, as it runs out of diaphragm travel if it has too much air to compress.