Engine/Transmission (1998.5 - 2002) Fuel psi gauge or lift pump??

[sljohn]

Gauge is an Isspro 30 psi mechanical, hooked up post filter and ran straight into the cab. The lift pump from Hoesli diesel is 4 months old with ~10K miles on it. I just noticed 2 weeks ago that the pressure would drop every now and then down to 5 psi while cruising, then go back to 13-14 psi. I've really been watching it the last few days, and this morning it stayed a little below 5 psi my entire 50 mile commute. When I pulled into the parking lot, sure enough I notice that it was reading back normal again. I shut the truck off, then turned it on and bumped the starter... the gauge bounced a couple of times before climbing to 15 psi. Started the truck, and it's reading 14-15 psi at idle, but it's climbing and falling 1-2 psi. It's always been pretty steady in the past. I've changed the fuel filter. Do these mechanical gauges have problems like this? I haven't experienced watching a lift pump going out... when I installed the gauges mine was reading a solid 8 psi at idle and would drop to 1 psi @ WOT, so I replaced the lift pump. Do the pumps act intermittent like this? I don't suspect air in the gauge line since it's always read rock solid since the install. Experiences??

 

[SHobbs]

Same prob here. Changed the fuel filter and at idle the guage reads 11lbs steady used to be 13lbs. Had no problems priming and starting the engine after the change. Been having isolator trouble for a while as well. Usually my readings return to normal after a couple of starts but not this time. Seems the guage is about 2-3 lbs off, or the L. P is slowly dying not sure which. With the guage reading the way it is I can drop it below 5lbs which I could'nt do before. Checked all the lines for air leaks and such and found nothing. I wonder that since the isolator has gone south and I have fuel to the guage if the B100 didn't fry the gauge.

 

[sljohn]

Hey, where are you getting the B100?

 

[SHobbs]

sljohn

I am getting it in Ft. Worth at a place called DFWbiodiesel. It's off of I35 and Long Ave. The guy that owns the place is having a heck of time keeping up with the demand. He runs the same stuff through his truck and understands what it means to have a good quality fuel. No operating trouble at all just had to change the fuel filter a few times to get the crud out, dang bio did a number cleaning out the system.

 

[amnewsom]

I was seeing the seem numbers on mine, LP changed out, numbers up then lots of dead pedel a few weeks later. I would get a on top of it in a hurry.

 

[SSabick]

I had same problem in mine, and I had the flow checked, and found out that my isolator needs replaced. Could be worse though, could have been the LP.

 

[gitchesum]

Mine did that.



Replaced and relocate the lift pump to the frame rail, and replaced the banjo fitting with a high flow kit. Idle psi is 16, never gets below 11 at WOT with the TST PM3 Comp on level 9.

 

[JKinney]

I had a pump from hoelsi do the same thing, I called them and they shipped me a new pump I trouble shot the whole system prior to putting on the new pump. It was the old pump.



But now pressure is already falling of on the new pump. I got it back with a new filter but with a thousand miles on the new filter pressure is falling off again, makes me believe I got some bad fuel, Ill be changing the filter again this week.

 

[HeberRam]

my guess is it is the lift pump. . Change it out and it should be fine. I would also recommend installing a carter pusher pump in line and you should not have anymore lift pump issues for a long time.

 

[sljohn]

I just called Hoesli and they're sending me a new pump under warranty. I think I'm convinced it's the pump.

 

[sljohn]

Yep, definately the pump. Yesterday on my drive home from work it dropped to a consistent 3 psi @ cruise . I made it home and replaced it with my old pump that I switched back in June. This one at least holds a steady 7 psi @ cruise and will work until I receive the new one. Getting pretty good at swapping... 45 minutes from hood open to hood close.