I have had the pressure gage on my system for several months. It has always be fairly steady as far as the pointer goes. All of a sudden it hammers the gage. It fluctuates about five pounds and makes noise at idle coming from the gage. It is hooked up post filter on the '99 from the test port on the filter. Pressures are holding good and the truck seems to run fine. I have run it now for over 2000 miles this way. (in two days) Have I lost some check valve in the VP44 or the bypass valve on the lift pump? Am I losing the VP44? Or have I just lost air trapped in the line and this is normal? It is not an electric gage, but is an Isspro EV.

 

Mine's a 99 too.
I put a needle valve in and run it almost all the way closed to prevent buzzing in my Isspro Fuel mechanical Pressure gauge.
Wild fluctuations could be a sign the the lift pump is on it's last legs.

 

Great, looks like you gave me my answer. The lift pump is new (2200 miles). Still leaves me with the question, why was it smooth before? I can only guess that it had air trapped at a high point and that was absorbing the vibration. Seems like they use something like that for steam heat to stop the hammering in the piping system. Looks like something like that would work here.

 

Gary, that same valve has held up for going on two years on my truck, and Illflem on TDR (who gave me the tip ) has been using it without a failure for longer than that.
I'll keep an eye on it though "Just in case". 8)

Ed

PS This is the one I'm using.
www.grainger.com search for part # 6MN31.

 

The fluctuation is caused by the fuel solenoid in the VP44. WHY that is, I cannot say, but I know it's the solenoid becuse as I turn my PM3 up the bouncing of the needle gets worse.<br><br>Chris

 

[quote author=Shovelhead link=board=13;threadid=15924;start=0#149619 date=1055730277]
Mine's a 99 too.
I put a needle valve in and run it almost all the way closed to prevent buzzing in my Isspro Fuel mechanical Pressure gauge.
Wild fluctuations could be a sign the the lift pump is on it's last legs.[/quote]

Ed,
That's an EXCELLENT idea! I did wonder why you have that valve on there when I saw it, but figured it was for somethign else. I'm gonna look into getting one for mine. The gauge jumping around gets kind of annoying.

Thanks,
Chris

 

Take the harmonics which the VP44 adds to the fuel system. Add this to the fact the lift pump is bolted a hot, vibrating engine with lots of other harmonics involved. Is there any question as to why there are so many lift pump failures?

 

I backtracked and disconnected both ends of the gage feeder tube. Blew out the fuel put it back together and great no more fluctuation solid as a rock. The air cushions the hammer effect of the injection pump.

 

[quote author=Haulin in Dixie link=board=13;threadid=15924;start=0#152101 date=1056313232]<br>I backtracked and disconnected both ends of the gage feeder tube. Blew out the fuel put it back together and great no more fluctuation solid as a rock. The air cushions the hammer effect of the injection pump. <br>[/quote]<br><br>Let me know how that works, specifically the gauge readings. I have always been concerned that the air would make the gauge inaccurate since the air gets comressed a little, and it changes mass when heated. If this theory is correct, you should see lower pressure readings in general, and see them rise as the engine compartment gets hotter.<br>If what you see is negligible, I'll do the same thing to mine, from the filter housing to the isolator. ;D<br><br>Thanks,<br>Chris

 

[quote author=Stamey link=board=13;threadid=15924;start=0#152109 date=1056315384]<br>[quote author=Haulin in Dixie link=board=13;threadid=15924;start=0#152101 date=1056313232]<br>I backtracked and disconnected both ends of the gage feeder tube. Blew out the fuel put it back together and great no more fluctuation solid as a rock. The air cushions the hammer effect of the injection pump. <br>[/quote]<br><br>Let me know how that works, specifically the gauge readings. I have always been concerned that the air would make the gauge inaccurate since the air gets comressed a little, and it changes mass when heated. If this theory is correct, you should see lower pressure readings in general, and see them rise as the engine compartment gets hotter.<br>If what you see is negligible, I'll do the same thing to mine, from the filter housing to the isolator. ;D<br><br>Thanks,<br>Chris<br>[/quote]<br><br>jChris I ran it for a couple of months that way and was surprised that it started hammering. I lost the air from changing the lift pump a couple of times. The only way that air would stay in the line is if there is a loop or part of the line abouve the connection point. The readings shold not change because it is not trapped pressure but is always changing so will read the same as at the filter.

 

The way I have it set up on my 99 is with an isolator at about master cylinder-level before it goes into the truck. I have been through bleeding it in the past, and my needle hammers pretty good. <br>I'm gonna loosen that bleeder screw without the truck running and let a litle air in there to see what happens.<br><br>Thanks,<br>Chris

 

Put a needle valve on that gauge before it blows out the diaphram and puts a goodly amount of fuel in your cab. I have seen more than one fuel pressure gauge blow out on Caterpillar motors at work. There are also snubbers available at grainger or mcmasters. They have very small orafices in them to prevent the pulsations of a lift pump/fuel pump from destroying a fuel pressure gauge.

Good Luck

Don

 

Don you really went back to find this one Its from June. A little followup, since going to the FASS and the 3/8 rubber line there is no more rattle. The tap for the pressure gage is right below the firewall.

 

The type of needle valve from Grainger that many are using is rated compatable for all fuels.

The air cushion method to smooth things out only works for a little while till the line eventually fills with fuel. Old trick is to install an inline fuel filter to provide an air cushion, it only lasts for little while as well.

As for the original post, your sender is going out. I've seen others fail in a way that they "trick" you into thinking your LP is ok. What they do is start reading only zero and the pressure they see most often with no in-between. Some folks have also reported the sender diaphragm failing allowing fuel to follow the wiring into the cab, so much for an electrical gauge preventing that scenario.
After four sender failures in a year I finally gave up and did what I should have in the first place - went with a mechanical, six years now without a problem.