I wonder if my pump is on the weak side as I seem to need a filter change every 8k to 10k miles. Anyone with a failed pump been running some sort of fuel additive ? Canada seems to have a problem with diesel fuel as there is a rash of failures.

 

I recommend a large dose of lubricity. Take your pick.

 

Scotty,

Why can't you run a CP3 without the lift pump? The Duramax uses the same pump and does not have a lift pump. I am not trying to be critical, I just want to be informed.

I currently am one of those that doesn't correlate a failed lift pump directly to a failed CP3.

I definitely think if you starve your VP44 from a failed lift pump, you will be replacing the VP44. I just think people are trying to make the same correlation to the common rail engines and it is just not the case. The common rail fuel system is an entirely different design compared to the injection pump system.

 

I think I'll have mine checked, and will probably get a gauge.

http://www.schoolbusfleet.com/forum/...?TOPIC_ID=9909

This is my first post. Please excuse my poor penmanship. I have been reading all your comments with great interest, especially the 5.9 Cummins. We have a couple of Freightliners (2002's) that I checked fuel pressure on. Both units had less than 10 psi at idle and less than 3 psi at wide open throttle. I took the first bus to Cummins and they said they would not worry about fuel pressure unless they got a code 368 on the insite tool. Imagine that! We are now running both buses at these pressures (and I'm keeping my fingers crossed we don't have a failure on a trip). Our supervision will not buck Cummins because we want to keep a good rapport with them. What do you all think about this charade? Thanks for any comments I get.

....Yes. I used a low pressure gage from an air conditioning set of gages. I purchased the fitting that comes out of the fuel filter (from Cummins). I drilled a hole in the fittind and tapped the hole to accept a union. I installed a flex hose from the fitting to my gage. All you do is remove the banjo fitting on the fuel filter and install your fitting (I use the washers from the fuel line). I then crank up the bus and check idle pressure. Run the engine at WOT and check again. Our good buses are running 15 psi at idle and 10 psi at WOT. It takes about 10 minutes total. A technician at Cummins Tulsa uses the same setup. I think it works great.

 

Installed my gauges today.

Lost a lift pump at 10K miles, as well as three injectors.

Well on the gauge readings, 5psi at idle.....1-2psi at WOT.

Not sure if this is normal??? Bad??? Indifferent??

I am just used to seeing 50-60psi on a PSD.

 

No new CP3 with your new lift pump, hmmm?

Your PSD uses whats called HEUI (hydraulic electronic unit injection), which is not a common rail system. Totally different pressures.

I would say that your lift pump readings are normal for having the Banks setup. If you do anymore mods, you may want to upgrade the lift pump.

 

Will you get P0629 Fuel Pump Relay Circuit High, or Fuel Lift Pump Control Circuit High without also seeing a check engine light?

Other than "loss of power" which is pretty subjective unless it gets to the point of hesitation or sputter on accleration.... any other early warning symptoms?

Not for nothing, but I don't want to join this club - especially 500 miles from home with a trailer in tow and my vacation days burning.

Any idea what tapping it is doing to help? What is the failure mode?

 

Those sound like electrical problems (circuit high means short to ground, circuit low means open circuit).

No early warning that is reliable. I keep one in the truck, but I get a good deal on them.

Not sure what you mean by tapping? What is the failure mode? Do you mean what happens when the lift pump fails? The motor stalls.

 

Are others of you seeing ZERO psi of pressure at WOT, or do I have something to worry about??

Truck seems to run great, but that pesky ZERO reading has me worried a bit

 

Mine was getting weak and went with the RASP. The RASP uses a Hobbs switch to kill the factory LP after prime. I was worried about setting codes and the CEL when the Hobbs cut the power to the LP. Guess what? No codes and no CEL. I even tried unplugging the LP's power feed while the truck was running and still got no codes. Just an FYI. The last three that I know of set no code and gave no warning when they went. The trucks just stopped.

On another note, the CP-3 can't pull fuel thru the stock LP. It's a zero leak design. If it wasn't there the CP-3 might be able to pull fuel from the tank like the Duramax but as it sits it can't. Before anyone tells me I'm crazy hear me out. The RASP is putting 17-1/2 psi AHEAD of the LP and if I pull the feed line to the LP off I get just a single drop of fuel at a time. This tells me that the stock LP makes a pretty good seal when it's not running.

Just my observations,

Richard

 

My dealer has no problem with me installing an aftermarket lift pump, however they said if I ever had to take my truck into another dealership for warranty work, there may be problems. My dealer recommended installing a gauge and monitoring the fuel pressure. If the pressure starts to drop off, they would not hesitate to change the pump.

I have decided to install and Air Dog unit and a guage. The cost of the Air Dog is insignificant compared the money I would loose if I my truck quit before a job.

As a matter of fact I have started to use my old 1987 6.2L for work again sometimes. It is a very dependable truck and it has a Mechanical Fuel Pump

Carl

 

What I meant by "tapping"?

Up in the thread someone said a mechanic limped them to the shop by tapping the pump with a hammer. If I get stuck and suspect the lift pump I would sure try this... just wondering if anyone understands what tapping may possibly do.

What I meant by "failure mode"?
Not the symptom of the truck... yep it should act like it ran out of fuel I'd guess.
I wondered how the pump fails. A lot of pumps leak a bit first then lose pressure or can't prime themselves. I'm guessing the LP doesn't do that. I was just curious why it's croaking, if anyone knows.

btw - assuming I've got this on my 04. It's under the hood? in front of the firewall? before the filter? How big is it? I didn't see anything large there on a quick peek....

 

Looking in there today I could not find it either, but from what I read here it’s the little black pump bolted right on the filter. If it is I can see why they are gong bad it’s not very big and does lots of work.

I am getting an FASS right away; I want to make the truck as reliable as possible before I start upping the power.

 

I saw a little black box on the back of the filter. Plastic... maybe 2" deep and 3"x3" square?
I was guessing it didn't need to be too big, it's not pumping in gpm... then again if that's it, it's smaller than I was expecting.

 

The manual states that the minimum pressure for the lift pump should be 11.5 psi, which is pretty much what the school bus mechanics were accepting.