Engine/Transmission (1998.5 - 2002) Erratic Lift Pump Pressures--What do you think??

[AHoltzclaw]

Erratic Lift Pump Pressures--What do you think??

Today, 02:22 AM #58

AHoltzclaw

Online

Join Date: Sep 2005

Location: Clayton, NC

Posts: 16



Erratic Lift Pump Pressures--What do you think??



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I relocated a new lift pump to frame rail (Vulcan kit) about 8 months ago and pressures were / are great 14. 5-15 psi at idle, about 13. 5 at 70 mph... never below 13 psi.

In the last 3 weeks or so I am seeing the pressure at 14-15 at start up and drops to 6-7 psi at idle. I punch the go pedal pretty good and get it back to 14-15, but at idle it wants to drop to 6-7 spi with a different pitched hum that I can hear below my seat (relocated lift pump).

Driving pressures are good... 13-14. 5 psi, it is just at idle that I see the fuel pressure drop and notice (listening closely) a different pitch of the Carter pump below my seat. I have a couple of spares below the seat so I guess I will swap it out and go from there.

I have checked to ensure good connections(both ends)with the provided electrical harness of the Vulcan relocation kit...



Any ideas... your thoughts / opinions would be much appreciated!

__________________

Alan



'02 QC SB 4x4 ETH/DEE/DiPricol FP/Boost/Pyro

 

[FourBarR]

I am on lp #5. never seen one that works like yours. pressures are 15-16 at idle and go down the more you press on the go pedal. mine runs 12-13 at 70mph.

 

[Joe Mc]

I like FourBarB replaced several LPs since I've had my truck. I'd notice fluctuation and soon after the LP would crap out. Is it cold in the morning and is the fluctuation grid heater related - after it's all warmed up does it still change? Since you have the Vulcan relocation kit you are not far off from an easy install on an other more reliable after market pump. - MHO

 

[Alphacowboy]

Im kinda having the same issue as you. Idle it drops to ~9psi, tap the go pedal and it jumps to 15+. Driving , its fine, only when its at idle it does this. I installed a clear tube in the fuel line(tank side), and have noticed, that when the pump changes pitches and the pressure drops, I get air in the line. but when I tap the go pedal, its full flow fuel again, and the pump sounds normal... I am confused as well.

 

[CMabrey]

I just went through this. Exact same concern to a T. If you spend enough time searching tdr you can find anything. I must have found 20 of these exact same posts. Long story short you need a new lift pump. Here's a little explaination. At idle your ip is not pulling very much fuel so your lp is hving to work pretty hard. That's why your only getting pressure drops at idle. When you get on it hard, your ip actually assists your lp. Your lp needs a little kick in the ***** to get it going. Eventually, it will quit working all together. Do some research on this site, you'll find a whole bunch of these posts.

 

[Alphacowboy]

I just went through this. Exact same concern to a T. If you spend enough time searching tdr you can find anything. I must have found 20 of these exact same posts. Long story short you need a new lift pump. Here's a little explaination. At idle your ip is not pulling very much fuel so your lp is hving to work pretty hard. That's why your only getting pressure drops at idle. When you get on it hard, your ip actually assists your lp. Your lp needs a little kick in the ***** to get it going. Eventually, it will quit working all together. Do some research on this site, you'll find a whole bunch of these posts.

my issue might be a completely different issue though, I took the bottom of the cansiter in the tank apart, but didnt put it back on when I put it back in the tank. by doing so, the canister doesnt stay full like it should, it says at the current level ov the tank. Mistake on my part, and its been pain in the *** to try and find a NON-liftpump sending unit to replace mine that I broke. :{

 

[CMabrey]

Well Alpha, I'm scratching my head on yours then. Good luck anyway.

 

[DFerverda]

Alpha , get a draw straw from vulcan(see post above) and put it back together with the straw, if you measure right you wil eliminate most of your problems, just keep the tank above 1/8, if lower then that when you stop and the fuel sloshes fwd, you will suck air.

Dirk

 

[Alphacowboy]

Alpha , get a draw straw from vulcan(see post above) and put it back together with the straw, if you measure right you wil eliminate most of your problems, just keep the tank above 1/8, if lower then that when you stop and the fuel sloshes fwd, you will suck air.

Dirk

I can just use that without the bottom of the canister? is that how it was designed to work?