I called Cummins and asked about diagnosing a LP problem. They replied the spec does not give a pressure requirement, but a volume one (something like 38 gallons/hr which is about 0.63 gallons/min). It seems to me this could be checked by opening the filter drain plug and measuring the volume of fuel transfered into your container in a minute (or some other unit of time). If you turned the key on for 15 seconds and let the lift pump run you should collect at least .158 gallons, or 1.27 pints.

Has anyone done this to check their LP?

 

I have checked and I don't think this works with the drain valve, but I'm not 100% either. You could do both methods and compare results. If you do, let us know.

The process is as you described as far as letting it flow for 1 minute and measuring how much is in the cup. The spec is flowrate based, not pressure based.

 

Thanks for the reply.

How did you check your LP's volume? What's the second method you suggest (you said I could check it both ways and compare-- but I don't know what the other method you are suggesting is).

I took my truck to the dealer yesterday for a low pressure/weak lift pump. They tell me they checked it and it met spec. I kinda doubt this as I can still get the engine to stumble/hesitate at WOT in the 2300-2600 rpm range when stock. Before I removed the TST box (process of elimination) I could get it to stumble on everything, setting 1 included (which should only be timing/no extra fuel). After the removal I could still get it to stumble in the above mentioned circumstances, if the weather is cold and the fuel in the tank has cold soaked. It's interesting because when I pull out of my garage in the morning (it stays in the 40's in the garage) the idle fuel pressure is ~8-9 psi, but by the time I get to work it's usually 7-8 psi, and if it's really cold it's 6 psi.

 

My CD manual for the 2003 states that minimum fuel pressure is 11.5 psi. Maybe if you take a page of the manual to the dealer they'll fix it.

 

I suspect that you could take the line off that goes from the bottom of the filter housing to the main pump (take it off at the main pump) and bump the starter to engage the liftpump. It will not pump for 1 minute, but should pump for 30 seconds. measure the amount you get and do the same test by opening the drain valve. Do you get the same amounts?

I believe the spec was changed with the intro to the 325 engine, so your 203 manual has the old "pressure" spec, whereas the new manuals should have the "flowrate" spec.

Again, I am very skeptical that the lift pump is causing your misfire. I don't see how that could be possible.

 

Yesterday afternoon I was barely able to limp my truck home. Engine was sputtering and unable to maintain 45 mph up some hills. I think I've diagnosed what' s going on, and it isn't the lift pump . . .

Issue #1.) I've been filling up a truck stop and at the diesel island each fill up spot has two pumps labeled #2 and #1. I assumed the #2 was blended, but turns out it's straight #2 according to the station. This way the semi drivers can blend whatever % they want. So my last several tanks have been pretty much straight #2.

Issue #2.) We've had a cold snap recently as well. Yesterday morning was in the low teens and stayed cold until later in the day when it got up to ~32. I'm pretty certain my fuel was starting to gel (the morning drive was fine as my garage stays >45).

Issue #3.) The thermostate which controls the fuel heater doesn't work. When I got home I drained my fuel filter and examined the fuel. It was thick, cloudy and cold. I thought this was odd since my fuel heater should be warming the fuel. Put a thermometer in the diesel and it registered ~35 degrees. Got out the shop manual and on page 14-63 under "Diagnosis and Testing - Fuel Heater" it says that "A malfunctioning fuel heater can cause a wax build-up in the fuel filter/water separator ... this build up can cause engine starting problems and prevent the engine from reving up. It can also cause blue or white fog-like exhaust. If the heater is not operating in cold temperatures, the engine may not operate due to fuel waxing." This is exactly what my truck symptoms were.

I followed the diagnostic procedure (which involves using an ice pack to force the thermostate below 45 degrees) and determined the heating element was OK, but the thermostate which allows current to flow to the heating element was not turning on. The thermostate is not connected to the ECM or PCM so if it goes bad the computer does not know. So I hard-wired around the thermostat until I can get a new one.

As a side note: The pre-filter pressure gauge does let you know when the filter is plugging. The pressure will not pull down at WOT when it's plugged. At least that's what it did on my truck when the filter waxed up.

 

Thats some good work there

 

The engine doesn't care what the flow rate is, it only responds to fuel pressure; when it drops too low it doesn't run. A flow rate seems like a spec designed for the pump manufacturer.

Another item that I noticed after glancing at the manual is that we have a 'dumb pump', in that it just pumps at whatever rate it's capable of, regardless of what the fuel pressure is, and some overflow gets routed back to the fuel tank. Has anyone looked at diddling with the overflow system in an attempt to adjust the fuel pressure ?

 

As far as lift pumps go, the engine doesnt care what pressure its at. The ECM is only looking to see if the driver feedback is saying that the pump is on.

Pump manufacturer creates the spec to diagnose a bad pump, so you are right about the flowrate.

I don't think messing with the fuel return system will help.

 

The pumps used in the 03 and 04's run full pressure with the engine running. The injectors need about 5000 psi to fire the engine. if you start getting a long crankl time, you probably have an injector starting to stick open. The pump builds pressure as its turning over and starts at the 5000 psi , thats why it doesnt take off as quickly as the 02 and earlier ones. If you are noticing low power , it could be the pressure relief valve opening at a lower pressure than it should (seen 4 of those fail in the last 4 months). The lift pump seeems to fail quickly with liitle warning , usually some stalling at first then no start. Tapping on the pump while cranking will get them going again for a short time..............another stupid design....they got it right for the o5's at least.

 

"The pumps used in the 03 and 04's run full pressure with the engine running"

I disagree, but which pump are you talking about. The lift pump provides as much as it can all the time, but as lots of people here have stated that can be 0 at WOT.

The main pump is nowhere near full pressure when the engine is at idle. Its around 35MPa. Peak system pressure is over 100MPa.

 

I installed a Holley Blue back by the tank, along the frame last night.

Pressure was at 13-14. I broght it up to about 15-16 at idle.

At cruise, it doesn't move.

At WOT, pressure drops to 10psi.

Before, it was 5-6 at idle, and would drop to zero in a heartbeat with the six-gun on 6. Even stock, I could suck it to zero.

Start-up is quicker, idle smoothness is the same. WOT runs are much stronger.

But one question, why are some you guys running the pressures up at 20psi or more??? Is there an advantage?

 

We have put plenty of mechanical fuel gauges on the 03 and newer and ive never seen them drop that low in pressure unless there was something wrong with the lift pump which runs at 100% duty cycle between 9 -11.5 psi at 3.5 amps.More lift pump pressure is not needed unless there is major power mods. The injection pump supplies pressure from 4300 - 23000 psi.

 

What about a Stanadyne lift pump/filter unit with a 2 micron filter on it? Here's a link to the brocure:

http://www.stanadyne.com/new/ppt/showfile.asp?id=1434

it has a regulator set at 10 psi. I thought the Holley Blue pump was a 14 psi unit. Any thoughts:

 

The Holley is 14psi. But you have to add the lift-pump pressure which is about 6-8, giving you a max psi of 20-22psi. Because the Holley is pre-pressurizing the fuel, then the LP pressurizes it some more.