Engine/Transmission (1998.5 - 2002) lift pump pressure drop?

[vette75406]

The lift pump pressure on my truck is falling off to about 4psi and on down to 0 under acceleration. What is strange is i can stop the truck with engine running at idle I can unplug the pump and plug it back in, the pressure will return to normal 14psi it may stay for a several miles as normal but more often than not by the time I put my step back in the truck, close the hood and buckle my belt it falls off to around 4-5 psi at idle and will not return until I unplug it and plug it back in. This pump only has about 6k miles on it . I thought it may be the connector as mentioned in other posts , so I wired in a new connector that I still had which came with new pump . I did not get to road test after the repair until the next morning , after about one mile it fell to 4psi , I did tried to check voltage at the connector but of course my voltmeter was dead . Does this sound like a internal pump problem, maybe check valve or circuit board, or does it sound like a voltage drop from what ever sends the signal to the pump ? Thanks , vette75406







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2000 QC LWB 4X4 3. 54 MAGNAFLOW FROM RIP LIGHTFORCE 140'S HUSKY RHINO

 

[R-N-R]

Replaced my LP yesterday, a word of caution to the "schedule" pressure checkers...

Changing the pump was easy enough, call your local TDR friend for advise, it should not be too difficult to find someone that has already changed at least one, and watch him change yours when they stop over to help Many thanks to FMcClaren!



My LP died a very slow death! I've monitored my gauges since installation, idle and cruise were fine, WOT has been a problem since bombing but that is a different issue. A few PMs with Digger taught me to keep a closer eye on the gauges while driving. I quickly learned that the FP pressure would decrease very easily while driving, hence the beginning of the LP's slow death. The pressure drops increased to the point where I would swear the gauge needles were directly attached to the fuel pedal. Naturally I began driving with a feather foot and leaving the comp box off as soon as I noticed the rapid psi decrease while driving easy.



This is the note to those without gauges installed: idle and cruise pressures were fine for a long time while I could have been starving the injector pump ($$$) when driving easy on surface streets.



I received three warnings over several months, the first when I noticed the gauge needles bouncing from 0 to 12psi while driving on the highway, the second when the needles dropped to 0 while cruising, this happened twice. Each of these were a least a month apart. Aside from the rapid decrease when accelerating (note: not launching, just easy driving), the pump continued to operate for several months. I certainly adjusted the driving to maintain a minimum of 5psi and normally was able to keep it above 8psi during this period. The idle pressure eventually dropped to 9-10psi, from there the pump died within a couple of weeks.



The presure dropped to 0 while driving last Sun. I could shut the engine off and restart which would enable the pump to run for a few more miles however after a few restarts the pump only lasted a few minutes before losing pressure. This seems similar to what you are seeing Vette75406. I parked the truck and picked up a replacement pump. Just for kicks, I checked it right before replacing the pump and sure enough it had pressure with key-on.



After several years of reading here on the TDR, my impression is that these pumps are purely luck of the draw. It seems that the stock pumps have a longevity of anywhere from 2k to whenever. My old pump, even right before replacement, would provide 7-8psi on key-on, the replacement pump barely makes the gauge needles flicker. Fortunately the new pump seems to have cured the crisis, but it does not seem to be as strong as the original pump, meaning that I seem to be able to pull the pressure down faster than when the original pump was in good working condition. Yep, the comp and the right foot stay off until I fix the system correctly.



Vette, my story does not directly coincide with your post and I realize that you monitor FP realtime, but your current condition seems to be very much like what I experienced at the end of my LP's life so I thought that I would share the whole story here for TDR readers as opposed to starting yet anothe LP thread. Hopefully you are cool with this.



So after 2 LPs, are you replacing with stock again, Carter/Holly, etc. . , FASS/AirDog, or RASP???

 

[vette75406]

Thankfully I work for a Chrysler dealer and my warranty ended on the 15th , which was monday and we wrote the truck up on the very last day of its warranty life , I'm Just under milage and have now run out on time , after the shop finally gets a chance to work on my truck , I hope its just a bad pump and not other problems , To answer your question , once the repair is on my dime I plan to repair it with a Carter/Holley or maybe a mallory 140 since I already have one laying around from another project.

 

[R-N-R]

Good deal on the warrenty timing! Unfortunately I expect the average dealer would hurt themselves laughing if I brought mine in for warrently repair. I am still on the fence as to mount a second "booster" pump on the frame or spend the big $$ on a high ticket unit (hate the thought of this!), larger lines and fittings are a given but the pumping is still a question. My truck is also a daily driver and being down is a royal inconvenience so finding a solid solution while getting the most bang for the buck is my quest. Warrenty issues aside, the problem I have with adding power is after a while you get used to it and "need" more... .