Engine/Transmission (1994 - 1998) question for 12v guys with fuel pressure gauges

[WDixon27]

i have about 3k miles on my new lift pump and during that time i have had very little needle bounce, maybe a pound or two at idle and nothing at speed and in the last week it's gotten so bad i disconnected my gauge and plugged it on the side of the road so it wouldn't get killed, i just replaced the 7k mile fuel filter incase it was restricted and causing the problem and reconnected the gauge it's still crap, at idle it probably swings 15-20 psi and in the highway it's buzzing so bad you can't really see the pointer, it's a 60# isspro with a isolator, valve in the lift pump took a dump or it's broken in now and acting normal? seems kinda sudden to change so much in a week, the truck doesn't seem to act any different

 

[SEmerson]

My guage has rattled from the start. I just snubbed it with a needle valve when I put it in.

 

[Signal73]

i have about 3k miles on my new lift pump and during that time i have had very little needle bounce, maybe a pound or two at idle and nothing at speed and in the last week it's gotten so bad i disconnected my gauge and plugged it on the side of the road so it wouldn't get killed, i just replaced the 7k mile fuel filter incase it was restricted and causing the problem and reconnected the gauge it's still crap, at idle it probably swings 15-20 psi and in the highway it's buzzing so bad you can't really see the pointer, it's a 60# isspro with a isolator, valve in the lift pump took a dump or it's broken in now and acting normal? seems kinda sudden to change so much in a week, the truck doesn't seem to act any different

My temporary one I install in the banjo does the same thing yours is now doing. Its normal I suppose due to the pulsations of fuel the pump sends out. Not sure why yours didnt do it in the beginning, maybe if you have a sender inline, the pulsations have damaged it???

 

[EKlem]

I installed my pressure gauge when I put in a new lift pump and like you, had very little bounce initially. It slowly got to be more like 4-5 psi of pulsation over the course of 5k miles. Eventually, when I would pop the hood, the lines from the fuel pressure tap to the isolator and from the isolator to the gauge would be jumping a couple of inches with every pulse to the point that I thought something was going to give way. I added the snubber that isspro makes and it has worked great since. It did give me a little scare the first time I fired it up with the snubber and it took 5 minutes for the pressure gauge to get up to normal pressure but it has gotten quicker as the snubber has broken in. Many people on this forum have made a needle valve out of hardware store parts and had good luck with that as well.

 

[Matthug]

Yes you must run some kind of snubber. It's possible that the gauge might also be damaged but it might be OK though.

I ran a line directly in the cab (no isolator) because I do not leave it hooked up all the time. I also have the 60 PSI isspro FP gauge. I used a 1/2 micron snubber, the smallest there is and it STILL pulses 1-2 PSI and slightly vibrates enough to rattle. My bro uses a 1 micron snubber in his 24 valve, but it's way too small on his truck the fuel pressure gauge takes 20 seconds to go up to what PSI it's running and is extremely slow reacting. I guess these P7100's really pulse, the isolator apparently helps but you still need a snubber so you don't damage the isolator and/pr the gauge.

 

[WDixon27]

i got the isspro snubber when i got the 60# gauge to replace the 30 pounder i started with and removed it after i discovered it took 10 minutes or more on the interstate to get up to pressure, (sort of annoying to have it hold pressure several minutes after shut off too) i may try to find a better element to use in it but i will probably just find a valve and adjust it manually

 

[Matthug]

I believe isspro's snubber is a 1 micron. You can get a 2-5 micron snubber from Mcmaster-Carr for about $7, get the porous disc type.

How did you hook your sending unit up? Didn't you drill and tap the banjo bolt going into the injection pump? Like I said I have a direct line going in and a 1/2 micron isn't enough to dampen all the pulses, but and isolator must take out some of that apparently. Try either a 2-5 micron or a 10 micron snubber, if your 1 micron takes literally that long to make the gauge react perhaps even the 10 micron would be good enough just the dampen the initial major pulses of the pump then the isolator can take care of the rest.

 

[WDixon27]

drilled and tapped the banjo on the output side of the filter, i may try that snubber if i can't find a valve in town

 

[EKlem]

The snubber from isspro seems to loosen up after a bit. Mine is now much faster reacting than when I first got it but there is no pulsing. The thing that seems odd to me is that when I first start up, it takes a little while for the gauge to get to 10 psi(like 45 seconds) then it is much quicker reacting after that.

 

[WDixon27]

i ran mine for a week before i had a chance to look into it and it didn't change, i just picked up a needle valve on the way home from work and will install it tomorrow

The snubber from isspro seems to loosen up after a bit. Mine is now much faster reacting than when I first got it but there is no pulsing. The thing that seems odd to me is that when I first start up, it takes a little while for the gauge to get to 10 psi(like 45 seconds) then it is much quicker reacting after that.

 

[EKlem]

i ran mine for a week before i had a chance to look into it and it didn't change, i just picked up a needle valve on the way home from work and will install it tomorrow

I hope that it works well for you.

 

[SEmerson]

I use a needle valve for snubbing. That way you can ajust it as needed.

 

[WDixon27]

that's what i ended up with, few bucks worth of stuff from the local ace hardwear and it's good ta go

I use a needle valve for snubbing. That way you can ajust it as needed.