Engine/Transmission (1998.5 - 2002) Fuel Pressure gage Wacko

[MHughes]

I installed a new fuel filter. Now all of a sudden my fuel pressure reads 15-16 at idle and 12-13 down the road and all of a sudden it drops to 3 and then it goes back up, drops down and will stay there for awhile then might go back and also bounces. If I accelerate real hard while it reads low, it will go back to normal and sometimes stay there for awhile or drop immediately back to 3. Is it the Isolator. I have a 0-30 Deprico gage.

 

[dnesbitt3]

my experiences tell me that your lift pump is getting ready to take a puke. The first 2 times that it happened to me I was sure that the guage was wrong or malfunctioning (i can be an idiot). Now I have access to a mechanical guage and can verfiy in cab guage. Last lift pump lasted a whopping 13K, luckily my Cummins store warrantied it... .

 

[Texas Diesel]

I had that problem once and the overflow valve was sticking. After replacing it that stopped.



Definately check the LP first. I went through 3 LP's before I realized it was the overflow valve. Never did get steady pressure, had to add a snubber to the FP gauge.

 

[NoSeeUm]

The change out of the filter is just a co-incidence if I were to make a guess. Possibly the old one was of a different type or was becoming clogged.



But your other symtoms, as you describe them, are very close to my symtoms when my first LP went south. I found this out after installing the FP gauge. I also have an isolator installed on the FP gauge. It took me all afternoon of fooling with the gauge and isolator to realize that is was the LP and not some problem with the gauge installation.

 

[tareynolds]

this is most likely the lift pump, check to make sure that it is running, this is easy, just bump the starter over and go listen and see if it is running. if it is, the the volume should be checked. IF the volume is good, then you can look at the flow valve, this does not have to be replaced, this can be fixed in the driveway in a few seconds.

 

[DLausche]

I agree it is best to rule out any issues with your lift pump first as it is the most likely candidate for giving troubles.

I installed a new fuel filter. Now all of a sudden my fuel pressure reads 15-16 at idle and 12-13 down the road and all of a sudden it drops to 3 and then it goes back up, drops down and will stay there for awhile then might go back and also bounces. If I accelerate real hard while it reads low, it will go back to normal and sometimes stay there for awhile or drop immediately back to 3. Is it the Isolator. I have a 0-30 Deprico gage.

This is exactly what mine is doing. I've had 4 different lift pumps in recently so I think I can rule that out. The one thing that in my mind is telling me it is not the LP is how the pressure pops up when I tromp on the pedal. Normally one would expect the pressure to go down instead of dramatically up when under heavy load.

I had that problem once and the overflow valve was sticking. After replacing it that stopped.

How difficult is this overflow valve to replace? Expensive or cheap part?





-Deon

 

[duaneparks]

Just a quick thought. Mine did this too after a filter change, and I was just sure my lift pump was headed south. Then, one day the gauge showed steady pressure and has ever since. I attribute mine to having air in the line going to the gauge.



Same symptoms:



Starts high, drops to 3-5 psi, romp it and the pressure goes back to 15psi then later falls back down to 3-5psi.



HTH.



Duane

 

[JCyrbok]

I would have the same thing as Duane, would usually clear up with in about a day. If you can get the filter canister to fill with the starter bump technique, the LP is working.



J-

 

[MHughes]

Where is the overflow valve located? The first filter I put in, I found that the O ring was cut, so I installed another filter. I'll check the overflow valve and make sure the air is out of the line. I drove it to Ill. and back, then to Atlanta and back and it acted up the whole trip.