I just got my fuel pressure guage hooked up and i apparently have a problem..it reads about 7 ideling, and drops to 3-4 at WOT. i know this reading is incorrect cause the truck runs so well, and puffs out some black smoke from time to time, so that doesnt seem like i could have that low of fuel pressure...i went to a very well respected diesel shop in springfield and got some fittings and stuff and did it like they told me. i went with just some fuel hose from o'reillys and tapped into the test port, went to a fuel guage isolator, then from that to the guage with the 1/8 line that came from the kit...so is my problem with the isolator? i know all you guys said not to use it, and i had decided not to untill when i went to the shop to get sum parts and they were HIGHLY against not using one, they said they always use them, and that they are accurate.and wouldnt want fuel goin into the cab..however in my case its apparently not true...so what should i do????

 

I do not see a performance fuel mod listed in your sig, therefore I don't understand why you don't want to believe the pressure gauge. A stock LP can develop pressures that you are seeing.
To check, get another, mechanical gauge and hook it up to your schrader valve. This will leave no room for doubts. But I would bet your LP is doing all it can at 7 psi.
-P

 

i thought i had read sumwhere that it should be like 13-17 while ideling??????

 

fuel filter replaced recently?

 

Have never hade good luck with a isolator. But with your stock LP I could see 7psi and 3-4 at WOT. Check it without the isolator. If it is still the same upgrade the pump.

 

I recently installed my fuel pressure gauge as well. I did NOT use an isolator, but did use a ball valve in case of failure. Also if you crack the valve open, it could act as a snubber to stop fluctuation at the gauge. That said, I replaced my stock LP at 88K with another stock pump and I get 13 psi at idle and between 8 and 9 WOT. Since I don't beat on my rig too often, I feel comfortable with these numbers. Is your pump in tank or external? In tank would sound about right with those numbers. hope this was of some help.

 

If you are very lucky, and if your stock LP is new. Otherwise, it can be anywhere from 0 to 15.
Just test with a mech gauge - remove all doubts.
-P

 

alright, thanks guys, ill do some checking..the fuel filter is about 3 weeks old..

 

My guage reads ~7 1/2 @ idle and ~4 WOT, but it has only been doing that for two years and 50k miles. Original external lp.

 

mine is 17 @ idle, maybe 13 @ WOT... of course i just replaced/relocated the LP 3 weeks ago... filter is ~2 mos old