Engine/Transmission (1998.5 - 2002) Lift pump goes to 2psi and back to 15?

[jmos4]

Hi,



Ok I have a 99 with the factory lift pump relocated to the frame and also another lift pump in the tank (Chrysler Retrofit) both got to shut off valves and into a tee before heading to the fuel filter



I was having a issue with 5-7psi from the one in the tank and with both on only about 11psi so after reading alot here and from another post I tried to shut off the tank and just run on the external and wow 18psi



yet on my first trip and hard brake the pump goes to ZERO-2psi for about 30 seconds and back to 14-16 psi and about 11psi at WOT, on my second trip from sitting for a while making a rolling left turn the same thing occurred



is this a sign of the external going bad or electrical issue?



I have about 1/4 tank, but afraid to fill it up as I fear I may need to pull the tank



anyone come across this before or am I just watching my gage too closely?



Thanks,

 

[BigPapa]

What gauge are you running? Does it have an isolator?

 

[JLandry]

Hi Jim,



I suspect your fuel level reading is inaccurate and you actually have much less fuel than you think you do in the tank. What you could be seeing is the fuel pickup at the bottom of the tank being momentatrily uncovered due to the fuel sloshing and it's sucking air.



Add another 5 gallons of fuel and check it again to see if there's a substantial change. If so, you'll need to install a new fuel level sending unit.



I had this same thing happen to my truck a couple of years ago.



Best regards,



John L.

 

[jmos4]

John,



Yeah you may be right, as I added some fuel and now it hasn't happened again but only been on a few short trips



though funny thing is that it only occurred on the first stop and no matter how hard I nose dived it afterwards I could not get the PSI to drop, even down hill, could this be a sign of something else messing up?



Thanks for the input,

 

[JLandry]

... though funny thing is that it only occurred on the first stop and no matter how hard I nose dived it afterwards I could not get the PSI to drop, even down hill, could this be a sign of something else messing up?

Boy Jim,



You've got me stumped on that one!



If not a fuel starvation problem, I suppose it could be a loose electrical connection to the lift pump. After activating the lift pump by bumping the starter, you could crawl under the truck and wiggle the lift pump wiring and connectors to see if anything turns up.



If you do decide to swap out the fuel level sender, dropping the tank isn't particularly difficult. This would also give you the opportunity to carefully examine the fuel pickup for any obvious problems. I dropped the tank on my truck by myself out in my driveway using only a couple of ratchet straps and a smallish floor jack. It was a piece of cake with only about 5 gallons of fuel left in it.



John L.

 

[stebbyron]

I have a FASS pump on my truck (01) and when I put the pump in I also installed a pressure gage. After a year the pressure started to drop gradually to near 0 and sometimes suddenly while driving. I had an in line pressure gage in my toolbox so I put a tee between the sending unit and the port and placed the sending unit on the tee as well. Next time the pressure dropped to 0 I looked and the pressure was at 14 on the gage which relieved a lot of stress. The problem was the sending unit.

 

[jmos4]

Hi all,





Well been driving it for a few days now and not another hick-up, the only thing I can guess is it must be cold enough not to let the fuel flow in the tank real well, until the heater gets it up to temp as I checked all the connections and even swapped the connections from the infuel pump and relocated pump.



I am almost getting back to the same 1/4 tank level so will see if it repeats itself of not



good thing is I am now at 18psi to 10 at WOT



Regards,