Engine/Transmission (1998.5 - 2002) Erratic Lift Pump Pressures!

[DKothe]

Hey y'all,

Just got back from a week long vacation trip to the Rocky Mountains of north central Colorado.

I have my fuel pressure gauge plumbed off of my filter housing outlet banjo fitting (Geno's), it is mechanical all the way into the cab gauge.



Friday the 30th of July I went to my local Cummins dealer for a fuel filter (spare) and noticed that my fuel pressure gauge was giving me some real freaky readings. It would run at 13-14 lbs for a while and then it would drop, hard, down to about 10-11lbs and sit there for a bit and got back up abruptly.

During our trip it continued to do this no matter what the load or speed I was going. Some times when it was at the lower pressure I'd "gas" (diesel?) it to pass a vehicle and the pressure would go back up to the higher level. Levels now continue to be about 14 on the high side but have dropped to about 6-7 on the low side when it drops.



I changed the fuel filter out while at the cabin but no change to pressures.

It has continued to fluctuate and it is bugging the heck out of me. I also noticed that as we went higher in altitude, the overall fuel pressures dropped little by little.



Is there a bypass valve somewhere after the lift pump that might be opening and sticking open?



I also have been using a different additive, could this be part of it? Although the last FULL tank did not have any additive in it.



Thanks in advance!

 

[jmtandem]

fuel press fluctuation

Dano,



I have had the same thing happen on my '01 taking the reading from the fuel inlet schrader port on the fuel filter. I have the Geno electric gauge and changed out the sending unit. It seems to have fixed the problem at least for now. While the gauge was flipping it's lid, I hooked up a mechanical handheld gauge at the fuel injection schrader port and it was steady and had good pressure (14 plus at idle) so I knew my problem was with the gauge somewhere. It is frustrating to watch a gauge and wonder if it is the gauge or the fuel pump. I don't know if the pressures drop slightly with altitude, but I kind of doubt it. There is a pressure relief valve that keeps the pressures from going over about 15-16 if I am correct. I suspect that the relief valve is not affected by altitude.

 

[azpete]

More than likely the LP. About once every week or two mine would drop to 7 at idle and back up to 14 on accelleration. Went like that for about 4 months. Then it finally stayed with those readings for three days so it was time to replace the LP. Readings back to normal. Oh, I did rule out the gauge first by hooking up a hand held gauge at the vp44.

 

[Sticks]

I went through the same thing a few weeks ago.



First, try cleaning the pigtail connections REALLY good.



Second, remove the pump, take the three studs out of the top plate, remove the plate, rubber gasket, and the metal disk about the size of a quarter. Pull the screen out, the impeller hub and vanes.



Using some brake cleaner or carb/choke cleaner, clean everything off and wipe them dry with a lint free cloth. Fit the vanes into the impeller hub and make sure they move freeley, and there are no burrs that would be hanging them up.



Inspect the pump housing innards for debri and rinse out (with some diesel if you have it, I would not use anything else in there since the pump holds alot of liquid). Reassemble and reinstall the pump and give it a try.



There is a thread called "Anatomy of a Lift Pump" with some good pictures of what you will be encountering. Doing the above steps cured my problems (at least for now).



Another thread called "Riddle me this, 3 lp's doing weird things" describes what you are going through and some other info.

 

[dezeldog]

DKothe I would buy a pump and then moniter that gauge that's why you put it on the truck. Next be sure to carry the pump and a10--12--18 mm wrenches with you you're pump is headed south :{

 

[Mad Bomber]

Lp

LP is going ,going and almost gone. Get it out of there before it totally goes

 

[Ajwalls]

Erratic lift pump pressures

Well you have lots of company with this problem. My lift pump went out at 47K, and was replaced by a dealership in New Mexico. Now at 54K my pressure guage is bouncing all over the place, from 15 psi to 9 back to 12, however when I go FT, goes back to 15 psi. Had the guage checked against another guage, guage checked out ok with the same readings from the lift pump. If this is the lift pump again, I will be a verry unhappy camper.



Going back to the dealership with a wonderful torque converter problem, and will attempt to replace the lift pump. I did have an Edge kit on during the period of 47K to 54K, maybe this lift pump can't take the extra fuel with the Edge. I have disconnected the Edge, however the guage is still going nuts. Back to the dealership, putting on my battle gear!





2001, 4X4, quad cab, blue, Leer Topper, Auto. Trans. , BD Ehaust brake, 3 Guage Piller ( TB, EGT, Trans. temp), steering column Fuel Pressure guage (All Autometer), 4" Ehaust, Afe air cone & lots of other deep pocket stuff!

 

[Mad Bomber]

Lp

Yep lots of company I lost 1st one at 36. 6 K

 

[DKothe]

Not what I wanted to hear!!

:{

Thanks guys, I pretty much figure the LP is going south but didn't want to listen to my gauge. Wife ain't very happy with buying another LP this soon. I only have approximately 4500 miles on this one in the 5 months it's been on the truck. GRRRRRRRRR

What about the Carter 4100 series I have seen postings about,,,,any comments on that?

 

[DKothe]

replaced LP

Called Cummins Southern Plains in Tulsa, who I bought my LP from, and they told me it was warrantied for 6 months... ... ... . Yahhhhhhhhhhhoooooooooo.

I bought it in late march.

So I drove it down, with pressures fluctuating between 14 and 4lbs and they replaced it with no questions asked. I just installed it and it fired up with 16lbs initially.

Towing my buddies 26' gooseneck back to his house a 100 miles away, will see how it works.



Cummins Southern Plains LTD, Tulsa OK

918-234-3240

Great service and friendly parts guys!

Oh ya... ... ... ... ... . LP price $155 on this one but for some reason I remember paying about 138 or so for the first one.

 

[RCone]

Cummins NW (Portland, OR) Just ordered one today (another spare as I always carry one). $155. The warranty is 6 months, unlimited mileage on the 3990105. Mine was on the frame rail pushing its whole life. Lasted 20K miles. Stanadyne Performance at every fillup. 1/2" line all the way forward. It may not have needed changing as soon as I did, but it would idle at 14 then in the last month on 3 occassions it would go to 5, and obviously lower when accelerating. Would shut engine off and it would come right back up to 14psi again. New pump now putting out 16 at idle.



Just goes to show, I've done everything right to preserve it. Am I gonna take it apart and look at it? Maybe but I ain't gonna put it back on. Not worth it to me.