tallzag

Been reading on here for about two hours and could not find an answer to this question so here goes:

Just put in new Isspro gauges, the EGT and boost work great. The fuel pressure gauge did not work initially so I went through and bled all the lines again and it seemed to work find. Have a stock fuel and lift pump on the truck, it was about 11 pounds at idle, 9 pounds after giving it a little diesel pedal. I then really got on it and the pressure dropped to 4 pounds then 0-1 pounds at WOT. The truck ran fine, no stumbling, nothing. I got off the throttle and it would only go back to 4 pounds of pressure on the gauge. After I turned the truck off and back on again it goes right back to 11 pounds pressure.

So my question is, is my fuel pump going out or do you guys think it's the gauge? What is the proper method for bleeding the system? My procedure was to fill the mechanical line at the A-pillar and bleed it from the isolator. The isolator itself has a bleeder on it that I bled as well. Keep on getting air from that screw but not a lot. Any help is very much appreciated. Hoping I just didn't bleed the lines right and my fuel pump is OK. Going on a 5,000 mile trip towing heavy next week and don't want to get stranded somewhere in the middle of the country.

tspooner3

Assuming you have a mechnical guage, and there is an isolator somewhere in the line, the diaprham probably reversed. You'll need to push the diaphram towards the fuel pressure side using a blunt instruemnt. That swhould get your fuel pressure readings back to normal

samaf

My truck did the same so I ran the pressure line directly to the gauge to rule out the isolator and I found out my transfer pump was going bad. Replaced it with a DDRP from Genos and all is fine . Just finished a 7000 mile trip pulling the TT and never under 15 PSI. Yes I did go back and put the isolator in and had a heck of a time getting all the air out.

tallzag

I did take the isolator out and press it in and that made it work in the first place. Guess I'm going to have to try and bleed it again. The isolator should be in the correct way, has an arrow on it pointed towards the gauge and that is the way it is on. Just seems weird that it will be reading fine then go below 4 pounds and not go up again. Thanks for the help.

dkenny

bleeding should change the reading..its pressure..bleeding will make a difference in the rate of change..not the amount of change..

don't flame me..air compresses..fuel at these pressure doesn't..but what happens when the air is compressed!..yep same readings..
air doesn't change the readings only to rate of change in the readings. you loose the spikes that kill mechanical gauges.

have you tested the fuel pressure gauge with air? at 10PSI..does it work?
forget bleeding!
-dkenny