Problem still exists; Engine Fuel Rate ... is this extreme?

[truckmen]

Can anyone tell me what they think may be the problem as I think I am into new territory here.

I am losing power on a regular basis as I hold the fuel pedal to the floor. Let me explain (again)

I am grossing 34,000 lbs pulling a slight grade into a headwind at 65 - 75 MPH when my engine power will just drop as if my fuel consumption exceeds the fuel pump's ability to keep up.

Below are a few screen captures of my OBD-II reader watching the fuel rate while under a load. What it shows is my fuel rate dropping after my CEL throws a "low fuel rail pressure". The CEL only shows the symptom or result. During this time, my turbo boost also drops from a maximum under load of 25 PSI down to 10 PSI or less. I already know I've lost fuel rail pressure because the 6.7 is starved for fuel. Early on, I'd already gone through the day-long job of removing the fuel tank twice, inspecting the fuel pump and actually replacing it completely one of those times to no avail. By the way, I've had numerous opportunities to pull over right as this happens and discover my fuel water/separator to be almost completely empty.

This has been an ongoing problem that I'd spoken of several times over the past 12 months and still have not found a solution. Everyone here has been telling me to change the fuel filter. I have both with MoPar filters at $100+ for a sea as well as aftermarket for far less expensive. It makes no difference so, now I know it has nothing to do with the filter.

Also, I have seen as high as 15.5 GPH fuel rate telling me that at that moment, I am consuming more than a quart of fuel each minute. Could it be that I just need to go with some sort of after-market fuel delivery system that can keep up with this consumption?

This is was taken on July 18 in Death Valley.

 

[DonFitzwater]

Tank venting properly?

 

[jhenderson]

What mods to the truck?

 

[DonR]

Does this only happen when the fuel level is low? I noticed in one pic that the fuel is showing almost empty. Could it be that maybe the gauge is maybe a little out of calibration so that when hauling a load the remaining fuel is more toward the back on the tank and the pump is maybe siphoning some air along with the fuel? Just a thought.


Don

 

[Dan_69GTX]

Have you checked the volume and pressure of the fuel pump, when the truck is sitting at the angle when the problem occurs.
As mentioned in the previous post, duplicate as much as you can: fuel level, angle of truck, temperature (Do this right after you ran the truck), etc. Make sure you have a container large enough to let that pump run for several minutes, such as how long does it take from when you apply that much Fuel to to when the issue occurs.

Another thing you could do, what about checking voltage/amperage at the fuel pump when the issue occurs. Obviously will have to set up test wires to do that. Could there be a relay that is overheating when the pump is requiring more amperage?

Another thing would be to use a scope and look at the waveform of the pump when the issue occurs. You have navigate down a lot since you proved that the separator was low on fuel.

 

[Cummins12V98]

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[SnoKing]

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Looking at other posts it is a DEF truck with G56 manual transmission.

So in 2015 with 3.42's truck was rated at 24,300 combined and with 3.73s it is rated at 26,000 combined.

So he is way over what RAM says the truck can do. Most likely just running out of steam for what he is trying to do with it.

 

[truckmen]

Tank venting properly?

Yes, I am quite sure that there is no problem with venting. Actually, I was fueling up from my 102-gal auxiliary tank to my stock fuel tank along the side of I-80 in Wyoming a few weeks back and the wind blew my flimsy stock fuel cap away. I've ordered a new one. So I know it's venting. :-/

 

[truckmen]

What mods to the truck?

No real mods yet actually.

 

[truckmen]

Does this only happen when the fuel level is low? I noticed in one pic that the fuel is showing almost empty. Could it be that maybe the gauge is maybe a little out of calibration so that when hauling a load the remaining fuel is more toward the back on the tank and the pump is maybe siphoning some air along with the fuel? Just a thought.


Don

Hi Don,
It seems to begin happening when I get down to ~ 1/3 tank but not all the time. There are a few days when I am running the tank right down to almost empty as depicted in the picture. But that now has become rare forcing me to stop and top up my tank from my 103-gal auxiliary at ~120 miles.

You mentioned that last line has made me pause. If I am down at the rear due to the weight and, I am climbing a grade, could the combination of the 2 actually be enough to have as much as 1/3 tank find its way to the rear of the tank and away from the pick-up tube?

 

[truckmen]

Have you checked the volume and pressure of the fuel pump, when the truck is sitting at the angle when the problem occurs.
As mentioned in the previous post, duplicate as much as you can: fuel level, angle of truck, temperature (Do this right after you ran the truck), etc. Make sure you have a container large enough to let that pump run for several minutes, such as how long does it take from when you apply that much Fuel to to when the issue occurs.

Another thing you could do, what about checking voltage/amperage at the fuel pump when the issue occurs. Obviously will have to set up test wires to do that. Could there be a relay that is overheating when the pump is requiring more amperage?

Another thing would be to use a scope and look at the waveform of the pump when the issue occurs. You have navigate down a lot since you proved that the separator was low on fuel.

Hmmm, okay, I see what you are asking.
So, this may be what I need to do regarding the pump. I can read up on the wiring diagrams too, to locate the relay. I wonder if that relay could be giving me trouble.
For the scope I will need to locate one that I could run. I have a generator on the trailer and could power it from there to the test. I am also sure I could run some wires from the pump to the interior and somehow monitor that as well. I suppose I could take from just abov the tank where the wires go in to the pump there.

 

[Dan_69GTX]

For hooking up the scope and seeing what the waveform should look like, there's a bunch of stuff on the Internet. Also, if you have any mechanic friends, they should be able to help you. If you know someone with an automotive scope, that operates off 12 V so you don't need the generator. Something like a Snapon vantage pro, would be great, should also give you specs on how to connect it.