ok...I've recently installed my guage setup. The day I installed it the outside temp was almost 70. That day and evening my fuel pressure read at 8-8.5 PSI. As soon as I started the truck it ran up to this PSI. It didn't drop very much under power...maybe .5 PSI. Anyway the temp here has dropped a bit over the past few days. We had one sub-freezing night...right now it's about 55-60 outside. Now when I start my truck the fuel pressure stays down around 0 or 1 PSI and then slowly builds as I drive to a high of around 6 PSI. It has never reached what it was when I installed it.

Should I be concerned? At what PSI should I get nervous about the lift pump dying? I have noticed no difference in how the truck drives so far since the drop in PSI. My pressure source is one of the replacement fuel filter caps from Geno's that has the 1/8 port in it.

Thanks.

 

There's something not right somewhere. I'm no expert on lift pump's and such, so I can't help you there. How ever, I think you my have a leak in a line. I would double check all fitting's. Are you using an isolator. If so, did you put antifreeze in the top section.

 

With the slow rise and fall in pressure I'm thinking you have something pinched/kinked/smahed or over tightened.
Your gauge should jump up upon starting.

You should have closer to 15 psi at idle (or atleast I do) you are on a stock pump, right.

And the .5psi difference? That sounds fishy too, but is making me wonder if it isn't in your gauge plumbing.
But, if you haven't seen over 8PSI, you are now in the market for a lift pump.

 

My Bad, I thought the newer ones were still a bit higher than that.

 

I do have an isolator inline with antifreeze in it. I have checked all of the plumbing and found no leaks of any kind. There is never any diesel under my truck or anything.

On the drive home today from work the fuel PSI when I started the truck was at 0 for a bit. I drove a few minutes and it climbed slowly to a steady 7 PSI under normal driving and dropped to 6 PSI with my foot in it. Temp outside was about 66 during the drive home.

Any other suggestions?

 

Mine usually runs around 6 psi. It does come up as soon as I start it. On cold days it runs about 1 psi lower. A few of my budies say this is normal psi on a 3rd gen. but my next mod will be a fass or something similar, I'm not comfortable with that psi and I can pull it down to 0 at will.

 

Is the ISSPRO fuel pressure gauge electric or mechanical? What pressure range do you have on the face? If you have a large scale 0 -100 it will not be very accurate at below 20 psi. Ideal gauge scale is to operate in the middle third of the gauge, i.e. 15 psi of pressure a 0 -30 scale would be good as the 15 is between 10 -20 psi or the middle of the gauge.

If you have a mechanical gauge you could have a pinched hose or your hose from the isolator to the gauge may not be full of fluid. If you have an electrical gauge, you could have a loose connection at the sending unit or the gauge, a poor ground, the 12 VDC power line is not a full 12 volts, or a nick in the wiring insulation where it passes next to a metal edge.

I have an 03 QC HO CTD with an Autometer electric gague range 0 - 30 psi. It runs about 9+ psi @ idle and it drops to about 3 to 4 psi @ WOT with the quad box set to the 140 hp level. I see 7 to 8 psi cruising @ 70 mph with the box set to 60 hp.

Good luck,...........dogger

 

That's about what mine runs as well - ususally between 6 and 8 PSI, and it drops a small bit as it gets colder.

 

I just installed an Isspro FP pressure gauge w/ an isolator. I went through all the instruction procedures and at first everything looked great then I started getting irregular readings. What I did then was; first made sure the isolator was full of 50-50 antifreeze. Then I took the line off the back if the gauge and loosely tightened the fitting on top of the isolator, then with a small squeeze bottle filled the line with antifreeze. I forced it into the tube, from the gauge end; until it ran with no bubbles then I tightened the fitting on top of the isolator and reconnected the line to the gauge. Next I loosened the bleed fitting on the isolator with the engine running and let fuel drip into a cup for a minute or so and tightened the fitting while the engine was still running. I thought I did everything right the first time but obviously I had air in the lines somewhere. FP runs 8-10 psi depending on temperature. Everything is working great now.