What is acceptable lift pump pressure?

[Sean Flanagan]

Hey all you turbo heads,

I have been pulling my hair out trying to diagnose some rough idle & stumbling problems. I recently cobbled up a fuel pressure tester and connected it to the water drain on the fuel filter housing. Anyway here is what I got:

Key On: 10psi then quickly drops to zero after lift pump quits running

Idle: 9psi

Normal Driving: 7psi

Wide Open with all the goodies turned on: 4psi

Is this pressure out of spec? I changed my fuel filter (15k miles since last change) and had no significant effect.

------------------
98. 5 2500 QC LB 4x4 5spd, white. BFG 285x75x16
Cummins 24v w/ TST PowerMAX w/EGT and Boost gauges on A-Pillar. VanAaken CPC. K&N In the factory air box. Stock Injectors, Stock Exhaust (Geno's Muffler Eliminator). Re-routed breather stink tube, 2WD-low kit, SnugTop, JJ Stainless Running boards, Tow Hooks, Bushwacker Street Flares, and a Cup Smoothie.
78,000 miles (11/17/00)

 

[JB @ C and L Machine]

If you update your fuel lines with the -06 aeroquip. . you should see a 2 psi increase AWOT... JB

 

[Fuzz]

Sean,
That's pretty much what mine reads,maybe a lb. or two more. I tapped in off of test ports.
I mean mine reads a couple higher than what you have.
y2k 3500.

[This message has been edited by Fuzz (edited 01-03-2001). ]

 

[sport bike]

4psi is about where you will start to notice a stumble at higher rpm.

 

[icarus33]

Sean,

Those numbers are inline with the readings of my truck, also a 98. 5 but measured on top of the fuel filter housing.

Darryl

 

[MikeR]

Well,your pressures aren't terribly bad and the pump isn't dead,but with my setup,I wouldn't keep that lift pump. It just seems on the low side to me.
If you're not interested in uprgrading your fuel lines,at least drill out the holes in the banjo bolts.

-Mike

 

[Steve Campbell]

Sean, after changing to 4601 hp lift pump from summit, my lift pressure post filter does not drop below 12 (@ WOT) unless the filter is dirty.

 

[DavidTD]

Sean,

I too am having a rough idle problem. As the truck warms it develops a solid miss. Dead cold it is smooth. As it warms it gets worse. Dealer has replaced VP44 and transfer pump with the "c" version.

No matter how bad the miss, just off idle it appears to go completely away. Dealer is stumped. I am seeing no decrease in mileage or power. Cummins Powermaster seems to think the truck is sucking air somewhere.

Keep me posted and I will do the same for you. Really weird!!

------------------
David
1998 3500 QC 4x4 5 speed 4:10, 235-85-16, VA CPC via JRE, PS Boost Module, K&N air filter. Emerald Green w/tan leather. B&W turnover ball.
1/4 mile 18. 2 @ 74. 75mph
1999 Exiss 3 horse slant, 4ft midtack, 6ft shortwall dressing.
70k miles as of 6/21/00

 

[jkern]

ok guys, i have done the required research, and need a conformation opinion. i have 22k miles on my '99 (built 1/99). i just put a JVD box in it 10 days ago. i also have just noticed in this time that with the JVD on or off that my truck seems very "flat" from 2500 rpm to the redline. could this be a lift pump failure in progress?? also what is everybody using to replace the stock pumps with? haven't checked my serial # yet, but i am still reluctant to have it replaced by DC or Cummins. i think a higher volume/pressure aftermarket pump may be better, any thoughts?



------------------
Jeremy Kern
1999 2500HD 4x4 QC,SB, ISB, 5spd, 3. 54LSD, 33x12. 50 cooper STT's Denver off-road bumper with Ramsey RE12000, PIAA series 520, Rancho RS9000's, heavy ft. springs, JVD Torque Enhancer, DiPricol boost and pryo gauges, and a bunch of other little things! www.geocities.com/phrn30 for pics!

 

[Sean Flanagan]

I doubt my miss & stumble is a result of low fuel flow because it runs fine at full throttle. If I wade through, It sounds like my readings are within the norm of what everybody else is getting.

DavidTD,

It sounds like we have the same problem... almost. I have the miss at idle, only when warm, just like you, but, does yours also have an intermittent stumble just at light throttle position. It runs fine when you are on it.

I am glad to hear that the dealer replaced your injector pump and it didn't help. I was beginning to suspect it might be on its way out.

I am beginning to think the miss might be an injector problem. Here is one thing I tried... With the engine running I carefully loosened the injector lines one at a time and noted the severity of the miss that would create. Don't worry, I used all the safety precautions... Well anyway, all off them had about the same miss except for the #1 cylinder whose miss was about half of the others. Anybody have a good set of standard injectors they want to loan for diagnostic purposes?

As for the low throttle stumble... Could it be the same thing or the TPS. My truck is a 98. 5 so there is no TSB for a stumble. Besides, it has run great for 80k miles.

Occasionally, the Check Engine Idiot light comes on so hopefully, I can connect it to a scanner and find out what the computer thinks is wrong with it. If it's the TPS, the scanner should say so.



------------------
98. 5 2500 QC LB 4x4 5spd, white. BFG 285x75x16
Cummins 24v w/ TST PowerMAX w/EGT and Boost gauges on A-Pillar. VanAaken CPC. K&N In the factory air box. Stock Injectors, Stock Exhaust (Geno's Muffler Eliminator). Re-routed breather stink tube, 2WD-low kit, SnugTop, JJ Stainless Running boards, Tow Hooks, Bushwacker Street Flares, and a Cup Smoothie.
78,000 miles (11/17/00)

 

[GTX]

I have a stumble under a load, going uphill running on the interstate. My ECM has been reflashed 2 times and the injection pump has been replaced. I am waiting for a new ECM now. There has been 2 codes, P0216+P1693. The check engine light has never came on. The dealer has cleared the codes and they are back the next time I have them check. Since the same codes reappear and the ECM is unresponsive to some commands is why they want to change the ECM.

Even tho the check engine light does not come on there still maybe a problem with the ECM.

------------------
99 2500 QC Auto 4X4
Amsoil Dealer

[This message has been edited by GTX (edited 01-04-2001). ]

 

[Vaughn MacKenzie]

OK, time for me to chime in with my idle annoyances #ad


My 2001 ETH has never had a nice smooth idle since new, but I never brought it to the attention of the dealer for fear they'd dismiss it as being too petty to deal with. It is caused by one cylinder firing weaker or stronger than the rest, the gearshift shakes back and forth slightly and the exhaust has a throb/pulse to it.

It improved considerably with mileage but never went away. Trading out to RV injectors made it a little worse, so I think it's ECM control related (irregularity was probably amplified by higher-flow injectors). Like Sean and DavidTD, it is rock smooth when cold and roughens up as it warms up. It is smooth with any load or slightly increased RPM.

I have installed Aeroquip fuel lines, relocated lift pump to the tank, etc. and have good fuel pressure, so fuel supply is not a problem. Fuel pressure is 10psi cruising and doesn't fall below 7. 5-8psi WOT.

To complicate things my boost module has given me trouble. Not long after installing it I noticed surging power and a little more engine noise. I fiddled around with it thinking there was a connection problem causing the ECM to see erratic MAP sensor voltages. I also thought I might have gotten bad fuel because the problem started all of a sudden soon after a fillup. I tried removing the boost module a couple of times and the engine seemed happier without it (idled and ran smoother) and sometimes not. When you cannot make concrete conclusions from your "testing" it drives you nuts. I have been running without the boost module for a few days and I still have slightly surging power (and constantly changing engine pitch/sound even holding throttle dead even) so I am wondering if a flaky MAP sensor or some other sensor that is causing the problem.

In line with that thinking, the idle problems could be caused by the ECM receiving or ouputting flaky or noisy signals. Maybe there is some sort of spike in time with engine firing that causes one cylinder to get more fuel than the others each time its turn is to fire? The electronic controls of our engines seem to react within milliseconds to stimuli and then adjusts each engine firing event on a case-by-case basis. That's a good thing if you want lightning throttle response, but a bad thing if you want a smooth idle. A good ECM should be able to make very fine firing adjustments in response to changing sensor iputs and spread them out over a couple dozen firing events, and yet react quickly to throttle changes. That would result in a nice, smooth idle so long as the injectors are equally matched.

Vaughn
- - - - - - - - -
'01 2500, QC SB 2wd, HO 6-speed, 3. 54lsd
RV inj, SS fuel lines, Amsoil filter, straightpiped, living with 20psi max boost #ad

 

[DavidTD]

Sean,

I have never felt or heard a stumble under load with mine. I did check fuel pressure and mine was what others report. Again dealer repalced it anyway and it was not under warranty due to me being at 80k also.

One diesel guru I spoke to said if it was an injector it would react the same off idle. I don't know. I figured maybe it has something to do with pop off pressure at idle. ??

I'm at a total loss here. Don't know where to turn next other than Cummins.

I also have never had a check engine light.

Keep me posted

------------------
David
1998 3500 QC 4x4 5 speed 4:10, 235-85-16, VA CPC via JRE, PS Boost Module, K&N air filter. Emerald Green w/tan leather. B&W turnover ball.
1/4 mile 18. 2 @ 74. 75mph
1999 Exiss 3 horse slant, 4ft midtack, 6ft shortwall dressing.
70k miles as of 6/21/00

 

[MikeR]

I think it is an ECM and not an injector problem. My truck used to idle bad when it was hot,but when it was stone cold,it purred like a kitten. The NW Bombers could tell you,when my engine was hot it idled like a big-block chevy with a lumpy cam... really,it was that bad when hot. It did it with the original injectors,and the DD stage II injectors. It also did with the original lift pump as well as the replacement pump.

Since it was new it always did it,and for the first 15k miles,I kept taking it back to the dealer telling him it was an ECM problem,but they couldn't find any codes and wouln't persue a fix or simple reflash.
I was on vacation in Utah (when truck has 15k mi)and my truck was idling real badly one day,so I took it to the Dodge dealer next to where I was staying and told the tech about the problem. The tech said the first thing he would do is to reflash the ECM. All he did was reflash the ECM,and my truck has never been better... it purrs like a kitten (with 30k mi now).

-Mike