Engine/Transmission (1998.5 - 2002) fuel pressure question

[CEpp]

my fuel pressure guage has started acting up, it drops when i slow down or at idle, jumps to 10 when i start then falls to 8, stays at 10-12 when im above idle or cruising, and every now and then it falls to about 7psi and cant get it to climb back. just replaced l/p 3 months ago and my isolator is mounted higher than the lift pump and filter, wondering if the air is going into the line and being trapped, i have also switched from after filter to before and really havent seen any change. what about the overflow valve? one other thing, if it idles for extended periods and warm out side i see about 15-18 psi on guage. and daig pointers will help. thanks.

 

[John - K5AWO]

You probably need to install a pusher pump at the tank with a prefilter there to keep trash out of the pump.

 

[cumminspwr01]

I wonder why it is showing 15-18psi on the gauge. Have you tried it without the isolator on it. I've heard people have had the diaphram inside some of the isolators tear and sends the wrong readings. Just a thought

 

[Slightly Modified]

Mine is also acting up. It reads about 14 at idle, which is what its been doing since I put it on in January with the new lp, then it drops to 8 psi. When I hammer on it the pressure climbs to about 11 and sits there for about 30 seconds and then drops back down to 7 or 8 psi. I have double checked all my connections and cleaned the plug on the lp and put dielectric grease on it. Can the lp be going out again after only 3 months?

 

[andrewkoperdak]

I have been plagued by air in my lines and I get similar readings. What I do to temparily fix it is. . I hang my pressure sensor as low as possible in my engine compartment for about 5 minutes. This get the air out of my line and then my sensor works fine for about 3 months. Then I repeat. I have never found the source of the air entrapment.

 

[CEpp]

i did some pressure checks last night and hooked up another guage, the flux is seen in the other guage as well, must be the lift pump, kinda weird, but when the pressure drops i can feel the lift pump and feels like it works twice as hard, and it starts airating the line to the other guage i installed, l/p is only 90 days old. calling cummins to find out what warranty is on it. in the book it says i may have a leak in the tank because of no noticable leaks anywhere else, is this possible or has anyone had this prob as well?

 

[CEpp]

good news, l/p , well i guess its good news, its fixed, and cummins warranted it. they come with a 1 yr warranty over the parts counter. . 12-13 at idle after filter and 9-10 at wot with box on 3-5. when the guage wanders its time for another. told the guy at cummins see you in 90 days, and he just laughed. . well im on my 3rd in 90 days. well see if this one lasts.

 

[cumminspwr01]

Just a suggestion if your having this many problems maybe you should try looking into an alternative fueling system like the fass, the preporator, a pusher pump and some bigger fuel lines. I seen in your sig you where gonna get some injectors and other stuff so the new lift pump will probably be living on borrowed time when you put it in. The injectors are going to void your warranty as it is so youll have to pay for the next lift pump(s) anyhow Just a suggestion

 

[Gary - K7GLD]

Sounds to me as tho' you are experiencing cavitation inside the pump...

 

[RobbyRam]

I logged on tonight to post a new topic and found found this one. It's exactly what I started experiencing today for the first time.

Tomorrow, I'm going to hook up my mechanical fuel pressure gauge and tape it to my window to determine if it's my gauge or my lift pump.

 

[John - K5AWO]

Holly has the neatest little 1" fuel pressure guage with 1/8" pipe threads. I just screwed the thing directly into the top of the filter on the input side.



Fantastic quick check on the cab guage. I will install my pod guage at the VP44 port, the difference will indicate any fuel filter problems.

 

[PKleine]

I was looking for this post last week



I was driving home from Southern Oregon and several times the fuel pressure would drop to 2 or 3 psi when I would take my foot off the go pedal. Normally I see 13 - 14 psi at idle, 10+ going down the road and around 9 wot. It bothers me that it did that, and it bothers me even more that it hasn't done it since. Kinda hard to fix it when it acts that way.



PK

 

[Slightly Modified]

Mine cured itself all of yesterday and today until I was on my way home tonight and the needle started dancing again. I bought the pump in January so I will take it back to Cummins and get a new one if they warranty it for one year.

 

[CEpp]

slightly mod, contact or find a cummins service center and explain to them thats happening and what uve done to determine its bad and they should replace.

cumminspwr01, first, truck is out on warranty, im eventually going to install the fass system and as long as that pump is under the 1 yr warranty, there going to replace it, they may want to see your truck and do tests to check, i didnt have to do that, due to company acct that fathers dealership has with cummins, awesome benefit.