Duramax low on power, then fixed after refueling?

So I made a lightning trip to from the bay area down to San Diego to buy a trailer yesterday. Drove my truck down, bought the trailer, towed it halfway back, stopped for the night, then did the rest of the return journey this morning. Total came to just over a thousand miles.

For most of the trip, the truck was quite happy. It's a 2002 Chevy 2500HD with the LB7 Duramax, and had the fuel injectors, FICM, and filter replaced about 1500 miles ago. It pulled the 3900 pound (empty) trailer over the Grapevine (4100 foot pass) with no problems at all, happily going up the hill at 65+. OTOH, later on in the trip, it started struggling up the other mountain pass along the way (Pacheco Pass, only about 2000 feet), and didn't seem to want to go over 55. After getting out of that pass and back to level ground I filled it back up, and it seemed to be much happier after that. It's hard to say for sure because there weren't any other major hills along the way, but just comparing the level-ground performance it seemed to be better.

Does that make any sense? I know the LB7 lacks a lift pump, meaning that the high pressure pump has to suck fuel all the way from the tank up to the motor. Is there any way that having low-but-non-zero fuel in the tank would impact power that way? It's nominally a 26 gallon tank, and I put 21 gallons into it after that pass.

ObPhoto. It's not quite as huge as it looks in the photo, the perspective is a bit odd.

And yes, I need to peel the previous owner's business graphics off the side and find a GRM sticker or two to put on instead. :)

Dad ended up putting a fuel pump in his 04 duramax after letting the filter change go overdue and hurting it and the injectors.

Sounds like a similar problem I saw on an Isuzu box truck. The short version is, someone had the fuel tank out, and when they put it back in they pinched the fuel tank vent hose in one of the straps. The more you drove it, the more vacuum would build in the tank, until the non-lift-pump style injection pump couldn't pull enough on the fuel line to get fuel out of the tank.

The clue was the giant sucking sound when opening the fuel cap.

Huh. I know the CP4 pump in the 2010-ish Duramaxes has a reputation for self destructing and taking out lots of other expensive stuff at the same time, but the CP3 in mine (and in that 2004 of your dad's) isn't supposed to have that problem.

The vacuum thing makes sense, although I don't recall a huge sucking sound when opening it. Googling, I'm finding people reporting failed vents in the fuel filler cap so maybe it's that simple.

When you did the injectors and FICM, was it all stock parts or did you upgrade? Tuner?

Some Dmax folks have trouble with a stock fuel system keeping up with the extra fueling needs and the ECM does something to limit power.

Another question. Have you ever had the "range limited" warning come up on the dash and it stays in 3rd? The MLP is a common failure, and if the ECM is getting a spotty signal from it, it limits fueling assuming something is wrong with the Allison.

curtis73 wrote: When you did the injectors and FICM, was it all stock parts or did you upgrade? Tuner? Some Dmax folks have trouble with a stock fuel system keeping up with the extra fueling needs and the ECM does something to limit power. Another question. Have you ever had the "range limited" warning come up on the dash and it stays in 3rd? The MLP is a common failure, and if the ECM is getting a spotty signal from it, it limits fueling assuming something is wrong with the Allison.

The motor is completely stock, injectors and FICM were installed at the Chevy dealer (needed it fixed on short notice -- that wasn't cheap).

I've never seen a "range limited" light, the only glitch with the transmission that I've seen is the standard problem where the anti-drainback valve on the torque converter leaks. 155K miles on it.

Ok dumb question, because I have a LMM and I'm not sure if the LB7 is a different configuration, but is the fuel filter housing next to the motor on the passenger side?

I just replaced the hose that goes from the filter to the high pressure pump because they are known to suck themselves shut and mine was dry rotted and no longer round. My truck could barely manage 45 mph up a 6% grade. The fuel filter was a bad and I didn't realize it until I replaced it, so it was also part of the issue. Both would cause the truck to go into limp mode.

SyntheticBlinkerFluid wrote: Ok dumb question, because I have a LMM and I'm not sure if the LB7 is a different configuration, but is the fuel filter housing next to the motor on the passenger side? I just replaced the hose that goes from the filter to the high pressure pump because they are known to suck themselves shut and mine was dry rotted and no longer round. My truck could barely manage 45 mph up a 6% grade. The fuel filter was a bad and I didn't realize it until I replaced it, so it was also part of the issue. Both would cause the truck to go into limp mode.

Yes, the fuel filter is in the same location. The dealer replaced the filter when they replaced the injectors (and scolded me for using non-GM fuel filters, supposedly the wix I had in there doesn't have the same filtration level as the AC delco one). I'll take a look at that hose.

It's been chucking down rain all day so I haven't had a chance to look at the motor yet. The truck doesn't fit in the garage at the moment. :)

In reply to codrus:

Just take the entire air cleaner set up out including the flex pipe to the intake, it makes it easier to see the whole hose.

As for filters, I've been running O'Reillys house brand and it's been fine. Don't understand paying $60 for a fuel filter you have to replace every 3000 miles.

3000 miles? The spec in the manual is 15, the dealer suggested 10, but you're suggesting 3?

Sorry I was over-exaggerating

My filters last about 10k before the meter says to replace it.

SyntheticBlinkerFluid wrote: Sorry I was over-exaggerating My filters last about 10k before the meter says to replace it.

Oh, air filters? I've owned my truck 30K miles and replaced it once, but even then the meter has never said it needed it.

I was talking about fuel filters earlier. :)

[edit] or is there a meter to check on the fuel filter status that I don't know about?

I'm talking fuel filters. I only get about 10k out of them (two oil changes) before the fuel filter life meter flashes on the screen telling me to change it. They are still somewhere around $45-$60 dollars. I get them for $30 at O'Reillys. $15 is the cheapest I can find on Rock Auto.

As for air filters, my truck has that giant cylindrical one and the cheapest I can find it is for $32 on Rock Auto, otherwise they are $60-$80 at the box stores.

The OReilly filters are built by Wix, not as nice as a Wix branded filter, but good enough/OE grade. IIRC they're the same as the napa silver/pro select line.

SyntheticBlinkerFluid wrote: I'm talking fuel filters. I only get about 10k out of them (two oil changes) before the fuel filter life meter flashes on the screen telling me to change it. They are still somewhere around $45-$60 dollars. I get them for $30 at O'Reillys. $15 is the cheapest I can find on Rock Auto.

Huh, I wonder if that's something they added on the LMM? I've never seen a message on the dash saying to change the fuel filter.

codrus wrote:

SyntheticBlinkerFluid wrote: I'm talking fuel filters. I only get about 10k out of them (two oil changes) before the fuel filter life meter flashes on the screen telling me to change it. They are still somewhere around $45-$60 dollars. I get them for $30 at O'Reillys. $15 is the cheapest I can find on Rock Auto.

Huh, I wonder if that's something they added on the LMM? I've never seen a message on the dash saying to change the fuel filter.

Possibly, plus I have GMT900, you have a GMT800, so it was probably added for my generation of truck. I also have a little percentage countdown in the DIC options so I can watch it count down.