Went to pickup my wife's truck today. Mechanic had told me that he checked the lp to confirm it's demise. He said he seen 10 psi @ 2000 rpm but the volume was too low. Now, to me, for the volume to change, in a given pipe, then the pressure would also have to change. Am I right on this line of thinking or not? I am discounting a bend or kink in a line, nothing out of the ordinary. I mentioned I was thinking of installing a pressure ga. and he said in this case it wouldnt have helped at all. Is this guy for real? He also said that 24v's were easier to work on? How much easier can a manual engine be? I'm assuming he meant to troubleshoot. What's your take on this?

 

I think he is trying to sell something. I don't know about the 96 lift pump but the 24Vs go like this.
Idle-----15 to 16 psi
Cruse –10 to 12 psi (for me that is about 1800 to2000 RPM)
WOT—no less than 8 psi
The WOT is the one to be most concerned about. That is when the pump is working the hardest.
If there is pressure at the injector pump then there is more fuel then the pump is using.
Hope this helps

 

I wasn't paying enough attention to the signature (Hers: 01, 5spd, qc dually)
If you are out of warranty he is just trying to sell something. I would check the pressure at WOT.

 

That is the way dodge is testing them these days, flow test. And about the only thing that could happen is got some bad fuel or some sort of gunk in your lines ( if you replaced your fuel filter) and its restricting the flow. 10 psi is 10 psi. weither its a 1in diamiter hose or a 2ft hose. Flow is what keeps the pump alive.

Ive never tried this so not sure if it would work. but crank the key of ( if that will start the lift pump im assuming that the lift pump just works at one speed) and pull the hose off of the pump. Since you have good presure you should get a healthy amount of fuel that comes out of the pump. Then throw the hose back on and take it off the end of the filter. If its good there. then so far so good. Then jump up to the injector pump and see how its flowing. Like i said im not sure

I also think that the lift pump is osmething like 60 or so GPH(gallons per hour) once agian im not sure. but if you can find that info you could flow a gallon of fuel and see how long it would take. Then take that and figure it into a hour. So say you get a gallon a minute its 60 gallons a hour. gallon every 2 then its 30 gallons a hour. 3 minutes then 20 gallons a hour..... so on.

Im sure someone whos had these problems pry has the tech info on it. But currently my 99 is running 9psi WOT on the origional pump and vp

 

Have a look at this TSB:

http://dodgeram.info/tsb/2003/14-002-03.htm

Should answer a few of your questions....

FYI, I just had the LP replaced on my 2001 H.O. @ 47k.....my dealer did not do the volume test and check pressure with the old FP guage method....funny that they didnt know it needs to be checked at WOT.....at least it was replaced under warranty.....charged me $45 to replace the fuel filter though....

Good Luck

 

dr. evil,

do you have any fuel system mods on your truck?

 

Not yet....bone stock at the moment, as Im still under warranty..

 

Yes 10 pounds is 10 pounds. However, 10 pounds of PSI in a 1/4 tube will not give you the GPM as 10 pounds in a 1/2" tube.

I currently have a fuel pressure gauge in my truck, monitering post-filter. I am getting ready to purchase another sending unit, to moniter pre-filter pressures. I have a toggle switch that is ON-ON, to use the same gauge to moniter both. This way I can rule out the filter. I was also told, by the mechanic at Dodge, anything below 10, at any time, is bad.

 

Exactly. wonder if theres a guage out their that monitors flow/volume. Are you using an electronic FP guage then? Or runnin a valve?

 

I could be wrong but I think the stock lift pump flows 100-120 GPH.

 

Here's a little more information, that I forgot to include. This mechanic's been doing this for fifteen yrs., fifteen yrs., fifteen yrs.-he told me three times too Anyhow, according to him, as mentioned before, Dodge has him testing the flow, not necessarily pressure(maybe he did that for his own satisfaction?) He told me that I should get 45oz. in X amount of seconds(he said between 30 and 45 seconds) What I was getting at, about the no kinks in line, was that that's the only way I can see that the pressure would not change, while the volume dropped

 

not sure what ur getting at or what his experience has to do with anything but even though u have 10psi you could still need a LP. do want to get into the physics debate but. her is a quick senario. if u have a pump that pumps 10psi through a 2inch hose and will pump 1 gallon of fluid in 10 seconds and now you change the diameter of the hose to 1 inch you will now need a pump that will pump 20psi to get the same 1 gallon in the same 10 seconds. the relation ship between the pressure and hose may not be exactly the way i explained but i hope u get the idea.

 

I have not seen one small enough for that purpose. I have a set-up for hydraulics, but it is rather large. Electronic, Westech Gauges.

 

DF, now I'm not sure what you're getting at. Do you not think a mechanics experience has anything to do with what or how much he knows? When someone gets to braggin about what all they've done or how much they know, do you never wonder if they are trying to convince you or themselves? Now, I dont know what your little seenareeoo is supposed to mean. I didnt change the size of the fuel line, so my 10 psi should be delivering the same volume as when it was put on at the factree

 

getting a bit personal...lets leave that out of this...

I think you mechanic is missing something....while its true that DC NOW uses the volume test to test lift pumps (not always the case as I just had mine replaced under warranty and I seen the pressure readings)....anyway.....the best scenario is to have a FP guage post filter and check the pressure at WOT....a FP guage tells you nothing when the truck is ideling in the shop....the reading at WOT is probably the best indicator of LP health....u should be showing 7-8 psi at WOT, anything less and the LP is likely shot....