Engine/Transmission (1998.5 - 2002) Gauges are in... LP Failure?

[Billy Diesel]

You mean you paid them to drive your truck around? Can I work on your truck too?!?



I had the dealer check mine about 1000 miles ago. It came back with an idle pressure of 12psi, and an "under load" pressure of 8psi. I don't know what the conditions of the test were (what does "under load" mean?), but at least they had a pressure gauge! I guess they had a diesel shop in there!



--

-Will

 

[Jim Ross]

Hi Troy,

I have a 2001 4x4 and I had DriPicol gages put in a couple of weeks ago and I have almost the exact same readings you are reporting and my fuel pressure gage is hooked into the banjo bolt just the same as yours--right at the inlet side of the injector pump. I am lucky to get 11. 5 psi at idle and at WOT it drops to 5psi. I am not worried, the truck run great. Like you, I recently changed the fuel filter, too.

I'm still learning about these Cummins, so I am no expert, but I am not worried about my fuel pressure readings. You and I are both plumbed into the fuel system "after filter" so we should expect the preesure to be a little less than a gage that is plumbed in "pre-filter". I have considered changing out my banjo bolts to the ones with larger orifices (and I might yet do that), but when or if I do it, I will expect the fuel pressure readings to drop even lower due to the larger orifices. Basic physics/fluid dynamics. What we really and truly should be installing in our trucks is a GPM (gallons per minute) gage instead of a PSI gage... . fuel FLOW is the important part of the whole picture.

Hope this helps... I think your truck is OK.

Jim

 

[Troy S]

Originally posted by wrhuston

You mean you paid them to drive your truck around? Can I work on your truck too?!?



I had the dealer check mine about 1000 miles ago. It came back with an idle pressure of 12psi, and an "under load" pressure of 8psi. I don't know what the conditions of the test were (what does "under load" mean?), but at least they had a pressure gauge! I guess they had a diesel shop in there!



--

-Will

I'm not that gullible! That was a FREE test provided courtesy of the dealership! (wonderful work huh?)



At least I had them "test" it for documentation purposes. I have a friend of mine checking with a cummins diesel mechanic about the numbers I'm getting. I've definitely got my gauge hooked up post-filter so that should mean my pre-filter numbers are a little higher than what I'm seeing. I'm hooked into the fuel pressure test port that is just prior to the injection pump.

 

[jmtandem]

Jim,



If you are taking the readings from the test port on the injection pump there is about 1-1. 5 psi difference through the fuel filter. That means you are getting about 12. 5 or 13 psi at idle and about 7 WOT measured pre filter. A new lift pump is about 14. 5 -15 psi at idle pre filter.

 

[Troy S]

While reading through the fuel delivery section of the FSM I thought of this. I wonder if my overflow valve could be slightly stuck open. The overflow valve is not supposed to open until 14 PSI. If I'm never seeing 14 PSI, that means either the pump is never reaching 14 PSI worth of pressure,the overflow valve is releasing prior to 14 PSI, or the overflow valve is slightly stuck open (buy perhaps a manufacturing defect).



I may try and test the overflow valve to see if that could be the problem.



Does anyone know if the overflow valve is a common failing part?

 

[jmtandem]

overflow value or gauge

Troy,



My opinion only, but look at the lift pump first, let somebody with test equipment check it. I have not read any posts that the overflow valve is defective.

 

[Elite1]

Originally posted by Troy S

The gauges are in. Pics can be seen here: http://smallnet.webhop.net/truck/index.htm



I need antoher opinion on my fuel pressure readings. I bumped the starter and I get 9 PSI. When starting it the FP drops below 5-7 PSI (the FSM guide), although I didn't pull the fuel system relay to the PDC to really check the cranking PSI. The truck starts very easily so it's a little hard to tell cracking PSI for sure. Fired up the engine and I only get 7 PSI at idle.



Last night while driving it I remember seeing 7-8 PSI under normal driving conditions (70 MPH with 3. 55's). Under WOT I saw VERY low FP readings, like 0-2 PSI. Under idle at times I would see 11 PSI.



At this point I'm thinking that my LP is bad? Does everyone agree?



Also, under WOT I was seeing my boost hit 22-23. I thought the max for stock is 20 or 21?

Please excuse my ignorance, but what is WOT??? (I assume it has something to do with flooring it)

 

[Troy S]

Re: Re: Gauges are in... LP Failure?

Originally posted by Elite1

Please excuse my ignorance, but what is WOT??? (I assume it has something to do with flooring it)

WOT = Wide Open Throttle

 

[Troy S]

Re: overflow value or gauge

Originally posted by jmtandem

Troy,



My opinion only, but look at the lift pump first, let somebody with test equipment check it. I have not read any posts that the overflow valve is defective.

Cool. I'm sure I'm making this a lot bigger deal than it is right now. I just like to cover all possibilities.

 

[BillGotthelf]

I have a fuel pressure gauge located before the filter and one after. After I got a new lift pump installed by Dodge my readings (with a clean filter) are within 1/2 lb. of pressure. I get 14. 5 at idle, 12. 5 cruisin at 65 and see 5-6 at wot drag racing. I am running the banjo bolts and I changed the supply line from filter to injector pump to a #6 line with a 90 degree fitting.