It did this a couple times about 1000 miles ago but recently has been doing it more often.

Normally hands around 14psi at idle.. and now after i drive for a couple minutes idle will be 7psi.

If i cruise, it will be 5-6psi. Wheras before it hangs around 12psi.

But.. if i mash the pedal in gear and let it rev up a bit.. then the fuel pressure will shoot back up to normal.. Sometimes it will instantly drop right back down to the low 5-6, sometimes it will stay normal for 1 or 10 or 100 miles.


I have another gauge and isolator i will be testing soon.. thinking maybe air in the line or fuel leak?

Maybe early LP warning?

Will keep this updated if i try anything/find whats causing it in case anyone is wondering/for future reference.

Im quite lazy lately so I dont know when thatll be..

 

your Lp is going out. sorry.

dieselfan

 

My 2nd LP done the same thing. I only let it do it about a half-dozen times before I put my FASS system on it. Ever since the FASS, it idles at 19, and 17 at WOT.

Don't take a chance.......change that puppy.

 

And forget the Isolator! Run a needle valve in the gauge line... cranked almost completely shut down.

RJ

 

I agree.
I had one do the same thing. Loose pressure, mash the throttle and pressure would come back up. New lift pump with a big line kit and no problems so far.

 

My LP pressure drops then rises every time the grid heaters come on/off. Does this only in winter, I think just about everything electrical on the truck does this, as the grid heaters draws some amps.

 

I was having the exact same symptoms with my 02, a WOT run would run the pressure backup to ~15 psi. I ditched the isolator and after about a week (not instant for me) the fuel pressure is solid again, I guess getting the air out of the lines. I got the needle valve from Napa and a few -an fittings from a local parts store and I've never looked back.


Good luck.

 

This last week is was pretty constantly dropping to 6 psi..

Went and bought a new lift pump.. and new crush washers and filter and whatnot.

Decided to just replace the filter first and drive it a day then change the LP if needed..

And... turns out to look like it was the filter? Drove about 80 miles today after a new fuel filter for testing and sure enough full pressure the whole time.

Fuel filter only had about 10,000 miles on it. Needless to say im going to order bulk filters and do the fuel filter every other oil change. It was BLACK beyond belief.

Will post back if the fuel pressure drops again.. but seems to be normal now... for now..

 

I've had the same problem 3 times, it was the lift pump every time. Don't think a filter will change like that, it might have taken some back pressure off the pump. I could make the lift pump run with the engine off and could hear it change sounds when the pressure changed. Let us know what happens.

 

How often had you been changing it?

It's always been every other oil change for me, right around 10K.
Very cheap insurance (if you get the filters from Geno's or Cummins)


phox

 

Ive only had the truck for about 26,000 miles i think. I have changed it when i first got the truck, about 15,000 miles later, then this last time was about 10,000.

Had a new LP same time as filter last winter.. and a new VP a couple months later in february.

Definetly ordering more and doing every other oil change.. its so stupidly easy to do.

Oh dont worry Kennys, the lift pump isnt going back to the store its going in my toolbox. I know itll fail eventually, again. Gauge will have more eye-attention than normal for awihle.

 

Looks like youre proven correct quicker than expected Kennys, Got about 450 miles on it before it dropped again.

Went ahead and changed the LP again.. thankfully its only a 20 minute job. I can do that once a year.

Hoepfully this thread can die now.

 

This is why I didn't replace my failed LP with a replacement. Fix it right and be done.

 

i got a campagin pump and it started doin that after the first 3 days so i go out and buy 2 more and replae the stock on and put on back by the tank.....and it ran good for about a week and started doin it again so i unpluged the stock one and it didnt change.......so that was 2 out of 3 stock lp's in less than 2 weeks.....i'm done with carter pumps....i just ordered a holley blue and a draw straw, and am making a 1/2 big line kit. so hopfully this will fix my problems.




i checked it with 2 diff gagues and they all read the same, so dont waste your time just buy another lp and hope ya get lucky or get a aftermarket set up.

 

Mine does the same thing its also a 99 and A diesel mechanic told me that for a 99 due to emissions etc anything from 7-11 is good