Hello, I have maybe a year on my isspro gauges and my fuel pressure gauge seems to be acting up. Is the sender an often replaced item? I have a needle valve, snubber, fuel hose plumbed to my sender. My hose is 6 ft long to my sender. At idle it is fluctuating from 11 psi and at idle revving to 2k it is at 18 psi.  Just trouble shooting on where to start. 

On a mechanical fuel pump higher pressure while revving the engine would be normal and lower pressure at idle would be normal. On an electric pump like mine it is the opposite. So I am not sure you have a problem.

25 minutes ago, dripley said:

On a mechanical fuel pump higher pressure while revving the engine would be normal and lower pressure at idle would be normal. On an electric pump like mine it is the opposite. So I am not sure you have a problem.

I agree that at idle the pressure would be lower but my normal idle pressure is 16, versus 11. In normal conditions my psi fluctuates from 16-19:idle-driving. Right now it is dropping while under acceleration when normally it would be increasing. 

I'd be looking at the fuel pressure regulator, filters/strainers, drive belt, etc. Of course checking with a mechanical gauge or other known gauge would be a good idea, too.

 

Your sender seems VERY well protected. My ISSPRO sender doesn't have it that safe, with 60k miles on it. How many miles are on yours?

17 minutes ago, LorenS said:

I'd be looking at the fuel pressure regulator, filters/strainers, drive belt, etc. Of course checking with a mechanical gauge or other known gauge would be a good idea, too.

 

Your sender seems VERY well protected. My ISSPRO sender doesn't have it that safe, with 60k miles on it. How many miles are on yours?

Maybe 10k max. I did change the stock filter as well, and it has a new return line strainer as well. I went through 3 isspro mechanical gauges that were protected in the same fashion, and they all would start sweeping while driving, going bad. How far open does everybody have their needle valve? On my return line it has a check valve that allows you to raise or lower the fuel pressure. I have pulled it twice and checked for debris, however it was clean. 

Mine runs barely open, no snubber on about 4' of line to the mechanical gauge. Same as I set it up about 10 years ago. 

27 minutes ago, dripley said:

Mine runs barely open, no snubber on about 4' of line to the mechanical gauge. Same as I set it up about 10 years ago. 

I guess I might be looking at getting a new needle valve and redoing my gauge inlet side of things. I just recently have a new lift pump and fuel sending unit. I am honestly tired of fuel related issues! The only other thing I might try is getting a new check valve from glacier diesel as that is the cheaper part compared to the sender. I don’t think my sender should be bad this quickly. My current needle valve is 1/8 open. 

Mine is just cracked open.  Takes a couple seconds to show full pressure. If I open more the needle jumps to full pressure almost immediately. It is getting harder to do on mine, Kind of feels like the valve seat has gotten hard over the years. 

Mine is just open a crack. I think 1/8 of a turn is too far and will likely destroy sender over time if I understand correctly. 

On my previous mechanical gauges, they would come up to 16 psi within 4 seconds. On my electric gauge it takes roughly 10 seconds to come up to 16 psi. I guess my sender could be hammered to death. I feel my sender is protected very well with the needle valve and snubber, guess I could be wrong. 

You could check it with a test gauge just to be sure. I have to agree that you have protected pretty well.

10 minutes ago, dripley said:

You could check it with a test gauge just to be sure. I have to agree that you have protected pretty well.

I can’t recall if my new vp has a test Schrader valve or not, will check.  I might be fighting the inevitable in getting a new sender. I don’t have an older gauge to test with otherwise. I wonder if a feed line could be found that has a Schrader valve and an outlet to my sender? 

I don't even have a needle valve, just the Geno's snubber.

 

Is the wiring/ground for your gauge in good shape?

2 hours ago, LorenS said:

I don't even have a needle valve, just the Geno's snubber.

 

Is the wiring/ground for your gauge in good shape?

I read online that the isspro boost gauge could have issues sharing the same ground as the other two gauges. I will separate each ground and see if that helps, my boost gauge is flaky as well. All the wiring is new (year old), my gauges are daisy chained together currently so may need to do some new wiring. I think the daisy chain was just for power/illumination. I am going to have to look it over again. 

I looked over my wiring and as my gauges are daisy chained, they all share the same ground wire. I will change this so all of my gauges has its own single ground wire versus sharing. See if that helps. 

I checked my single ground for my 3 gauges, it’s clean and the metal has been scuffed to bare metal. Not 100% sure if this is the right direction, but I am going to get a new sender first, and barely crack my needle valve. See what happens, then go from there. Unless anybody has any other ideas. 

If the problem could be the boost, I'd unhook the boost gauge and go for a drive before I dropped coin on a sending unit.

6 minutes ago, LorenS said:

If the problem could be the boost, I'd unhook the boost gauge and go for a drive before I dropped coin on a sending unit.

I will give it a shot, see if anything changes. Could be the sender, the check valve, or mechanical pump. It has all new filters currently. My only other thought is possibly air in the system but it is running just fine. 

All of my gauges share the same ground. In both the 2002 and 2006 trucks.

I feel pretty confident it isn’t a ground issue. I have checked all my wiring and it all looks just fine. I have unplugged all gauges and they come back on just fine. Just low fuel pressure. Pretty sure I am going to need to spend some coin to isolate the issue. Dang it! 

Personally, I would start with verifying fuel pressure with a test gauge and go from their, before replacing parts, 

1 hour ago, 01cummins4ever said:

Personally, I would start with verifying fuel pressure with a test gauge and go from their, before replacing parts, 

Where would I hook up the test gauge. I don’t have a Schrader valve on the back on my filter. Is there an alternate test port location? I assume I could unscrew my sender and use that location to hook up a fuel pressure test gauge.