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LMM GOING INTO REDUCED POWER UNDER LOAD

6K views 45 replies 15 participants last post by  Angus Mike 
#1 ·
Hey Fellas, Well, the rabbit's out of the hat. Picked up a 08 dually with 180K last fall for a great price.

I have learned whenever you haul under medium to heavy load (Round Baler on Deckover, maybe 8k) or 14 haylage bales (4.5 by 4, maybe 16k) the engine goes into a reduced power mode. The dash will show "check/change fuel filter" or "low fuel rail pressure" or "DPF soot build up". The FF was changed just prior to getting truck.

I stopped at a local diesel shop. They said change the Fuel and air filters with genuine GM parts. Then the kid said "how do you drive it?" I said, "I have gray hair." He said, "there's your problem". I said "I know, haven't been laid in 6 months".

Point being is he said I need to drive it like I stole it.

Anyone care to weigh in? I love the truck and it's power, when it's there.

Had another mechanic tell me 08 to 15 were really sucky years for the Duramax. You guys agree?

I have to replace it one point and would consider a new Duramax but not if I have to drive it like a maniac all the time. Some maniac time is good for the soul and I ain't no saint, but....

Comments fellas'. Thanks, Mike
 
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#2 ·
First, the mechanic who said 08 to 15 were "sucky years" probably doesn't work on them as much as he claims. Every year of Duramax has that one thing that makes it "the worst Duramax ever made". It just depends on who you're talking to when they tell you which one is the worst.

The DPF soot build up is definitely a sign that you're probably not driving the truck hard enough. The truck is smart enough that it won't let you over work it, so when you're pulling that 16k lbs, let it rip. It will do its job.

As for the low fuel pressure, you likely have collapsing fuel lines, and that's why it is only showing up when you're working the truck. The fuel system on the 08 is under vacuum from the tank to the high pressure pump, so when those rubber lines coming from the tank get old they tend to collapse under high fuel demand situations.

Your homework assignments:

1) Buy a monitor of some kind for the truck. Edge CTS3, Banks iDash, or one of the bluetooth readers (I can suggest one if you want to go this route). The most popular monitor right now still seems to be the Edge CTS monitors due to the larger screen. The Banks iDash does all the same things, just in a smaller package. Both are great. The monitor will let you read and clear trouble codes and on the 08 you'll be able to see a lot more information about the runtime environment of your truck.

2) Replace rubber fuel lines between the tank and the filter head. NAPA fuel lines work fine.

3) Replace fuel filter again. I know it hasn't been many miles, but I've personally had 2 filters become clogged in less than 2000 miles. It's a cheap part and it helps rule out potential issues.

4) Get the truck hot. Don't baby it, especially when it's doing a regeneration cycle. If you aren't able to tell yet when it's regenerating, you'll notice the truck idling closer to 1000 rpms at stop lights/signs, and a charcoal like smell from the exhaust. When this happens, if you're able, get the truck on the highway and run it like a rented mule for 20 miles or so. The DPF needs to get nice and hot to burn off that soot it has accumulated over the last 200 to 400 miles. The monitors I suggested all have the ability to tell you when you're in regeneration mode, so you'll know you need to drive it a little harder or longer to get it through the cycle.

If after doing all this you're still getting the change fuel filter message, you may have a leaky filter head. It's also a cheap and fairly easy install.

If you're still consistently getting DPF clogged messages, that Edge or Banks monitor will let you do a manual/stationary regeneration. This is going to run your truck REALLY hard in park for 15 to 20 minutes and burn off the junk in the exhaust. You'll need to do it outside, hood open, and make sure that nothing combustible, including dry grass is within like 8 feet of the exhaust pipe. You will start a brush fire if you're not careful.

Good luck, and welcome to the family.
 
#5 ·
Thanks for the reply and welcome Melon.

I will start down the road to figuring this out by replacing the FF and the Air filter for good measure. Replacing the fuel lines sounds good too.

Edge CTS3 monitor sounds like a good idea if it'll let you do your on regen.

I will keep you guys posted on this as it evolves.
 
#3 ·
Ok, fuel filter was replaced last fall just before you got it- how many miles has it been? How is the quality of fuel that you run?- hard to know for sure. Start by changing the fuel filter.
Only happens when you are demanding higher pressure and higher flow/volume while you are hauling.... a couple of us were just having this discussion on another thread a couple days ago. I say you need to get someone to run a return rate test on the fuel injectors. It needs to be done at the same conditions when this happens- engine warmed fully and under high demand- I would almost bet your injectors are returning too much fuel and when you have high pressure/high demand they are returning too much fuel and creating the low power under load. I've seen it several times, had two trucks of my own do it.
 
#4 ·
Ok, fuel filter was replaced last fall just before you got it- how many miles has it been? How is the quality of fuel that you run?- hard to know for sure. Start by changing the fuel filter.
Only happens when you are demanding higher pressure and higher flow/volume while you are hauling.... a couple of us were just having this discussion on another thread a couple days ago. I say you need to get someone to run a return rate test on the fuel injectors. It needs to be done at the same conditions when this happens- engine warmed fully and under high demand- I would almost bet your injectors are returning too much fuel and when you have high pressure/high demand they are returning too much fuel and creating the low power under load. I've seen it several times, had two trucks of my own do it.
I thought maybe injectors too, but I haven't heard of it giving the fuel filter message with injectors, though. And the injectors on the 08's are a lot better than previous generations, so I wouldn't think that at 180k they would be my first stop on the troubleshooting train.
 
#11 ·
CTS will not be able to do the return rate test- can show balance rates, but not run a physical return rate test where it actually measures the fuel coming out of the return side of the injectors.
 
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#14 ·
Every filter including DPF's have a lifespan- what is it though is kinda hard to say. For the most part in what we are seeing in my dealership group on our large ag products is averaging say 6000hrs or so. Lots make it farther, some don't make it there. What is it on an LMM or LML truck? I varies vastly in how the truck is used, maintained, how much it idles, how hard it is worked, how many sensor issues it has, def quality on the newer stuff.... SO many things can make a difference
 
#15 ·
Shoot cant hurt to try that spray in DPF cleaner to help aid with the DPF. Sounds like it gets it back to fresh again (or close to fresh as can). Any idea of your regen mileage? I used get about 300/regen pretty consistently if i recall. About a tank of gas...this was daily driving no load.

Pretty much as stated:
-Fuel Filter
-Filter head? (common as well)
-Collapsing supply line? (seems be more common as of recent as trucks our vintage age..these are up in the engine bay)
-FPRV (prematurely relieving making it unable to build desired pressure)
-CP3 (weak not making the pressure if below checks out)
-Injectors (returning too much fuel yielding low rail pressure)

I drove my truck 1 year with a dpf at 190k with zero issues daily driving it stock as stock can be. No idea its background but from Texas so likely a 5th wheel hauler of some kind.

I know i've been a dmax fanatic about 5 years now but once you know these engines, they are fairly easy to diagnose say, 80% of the time. Those other 20% boy they really make you work for answers ha.
 
#17 ·
Shoot cant hurt to try that spray in DPF cleaner to help aid with the DPF. Sounds like it gets it back to fresh again (or close to fresh as can). Any idea of your regen mileage? I used get about 300/regen pretty consistently if i recall. About a tank of gas...this was daily driving no load.

Pretty much as stated:
-Fuel Filter
-Filter head? (common as well)
-Collapsing supply line? (seems be more common as of recent as trucks our vintage age..these are up in the engine bay)
-FPRV (prematurely relieving making it unable to build desired pressure)
-CP3 (weak not making the pressure if below checks out)
-Injectors (returning too much fuel yielding low rail pressure)

I drove my truck 1 year with a dpf at 190k with zero issues daily driving it stock as stock can be. No idea its background but from Texas so likely a 5th wheel hauler of some kind.

I know i've been a dmax fanatic about 5 years now but once you know these engines, they are fairly easy to diagnose say, 80% of the time. Those other 20% boy they really make you work for answers ha.
Thanks Goat.

The only thing that makes this tricky is in order for it to F up, it needs a fairly decent load hooked up. Last time it did it was Saturday, 16K in haylage bales on a hay wagon (i.e. no electric brakes) 2 miles almost all up hill. On a 15% grade. And, just discovered the e brake cable was broke. Hmmmm. Coulda been interesting if the engine died.... Replacing the e brake cable tonight...
 
#20 ·
Engine RPM vs speed vs engine load can play a large part in keeping P0087 away. I usually end up in 4th gear, sometimes 3rd if I think it is beneficial, pulling a hill of size, rpm's 2400-3000, and keeping the speed down, tow-haul engaged, gears manually shifted. Lots of people say just to let the Allison decide on when and how to shift - I DON'T, not when pulling hills.
 
#22 ·
Adding a lift pump on a truck with a low rail pressure problem is 100% a bandaid, IF it even fixes it.

Sent from my SM-G960U1 using Tapatalk
 
#28 ·
Hey Dawg, No problem. Glad I could help out. Did you ever figure yours out? Full disclosure: When I changed the fuel and air filters, I also added a fuel additive, (Schaeffer's Carbon Treat). I got it from a guy I get bulls from. Turns out he is an oil man in real life. IDK if iot made a difference but...
 
#24 ·
The problem with P0087 is determining what the actual problem/cause is. When you don't have the knowledge, test tools, procedures, information, etc, you just don't know where the problem is and/or isn't. The bandaids are just that, a way to get by for a while, MAYBE. A fuel filter head is about $150 with a filter and installation is fairly easy. Lift pumps go from $200 - $800. If you guess injectors, you have to have a wad of cash. If you guess correctly, you call it money well spent, but if the problem still exists, well, it's a lot of money for many people and then you still have the problem.

It would be nice to collect the possible causes of this P0087 code, the likelihood of a given thing being the correct fix by itself, the cost, the difficulty, pertinent tests, and the order of the tests, and maybe some other things. Maybe a decision tree. Or a spreadsheet. Or ??

Usually fixing the problem is not that difficult, though it can be expensive. But determining what the cause of the problem is, that's key.
 
#26 ·
The problem with P0087 is determining what the actual problem/cause is. When you don't have the knowledge, test tools, procedures, information, etc, you just don't know where the problem is and/or isn't. The bandaids are just that, a way to get by for a while, MAYBE. A fuel filter head is about $150 with a filter and installation is fairly easy. Lift pumps go from $200 - $800. If you guess injectors, you have to have a wad of cash. If you guess correctly, you call it money well spent, but if the problem still exists, well, it's a lot of money for many people and then you still have the problem.

It would be nice to collect the possible causes of this P0087 code, the likelihood of a given thing being the correct fix by itself, the cost, the difficulty, pertinent tests, and the order of the tests, and maybe some other things. Maybe a decision tree. Or a spreadsheet. Or ??

Usually fixing the problem is not that difficult, though it can be expensive. But determining what the cause of the problem is, that's key.
Ron you are correct, these parts are not cheap and the time involved to go through the list is expensive in its own right. I have been acquiring parts along the way to go through my truck to hopefully bring longer term reliability into the truck. I know that she is a 2008 and I have no clue how she was handled (Maintenance wise) before I bought her in 2019. I know that she was a 5th wheel hauler based on the brackets that I removed from the bed when I installed the cap and Bed Rug. I am starting with the cheapest items first and working my way up the expense list, the parts that I have can sit on the shelf if I don't need them immediately. I will report back my results later.
 
#34 · (Edited)
@Angus Mike have you checked the supply line on the drivers side to see if its kinking?

I've seen so many people on here with the 87 code and its like ground hog day "I've gotta diesel buddy and he thinks its the injectors". "My cousin's uncle's dead brother knows a guy who says its the CP3" :unsure:

Check the daggum supply line. If its kinked, fix it and see if that addresses the issue.
Start simple. If that doesnt address it then we can perform rocket surgery.

This guy... look for this
Wood Auto part Office supplies millipedes Terrestrial animal
 
#35 ·
So I took a few minutes today to do some exploratory inspection and found exactly what is pictured above. My LMM has a kink in the hose outboard of the transmission on the drivers side as well as a kink under the hood on the drivers side. The larger diameter hose is kinked twice, once before the plastic chafe wrap under the truck and and 3 inches below the metal connection point under the hood. So in my case its time to address this issue before all others.
 
#37 ·
You can do a temp fix (mine lasted for 10 years) by just putting a wide hose clamp around the kink just enough to keep it from kinking. Very easy, very cheap, very quick And you'll see if that is really your problem.
 
#38 ·
It's a quick and cheap fix to check for 2 fuel hose collapse on driver side near trans bell housing- there was TSB from GM for this problem by cutting the factory crimp and replace with hydraulic hose (reinforce inside and thicker) then retighten with 2 worm clamp each end for total of 8 clamp on 2 hoses.

When engine under load and hot, fuel hose get soft and the high suction suck the hose closed- I got stranded 20 miles from nearest town and cost $600 tow with trailer on Sun. Bought parts for $40 from O'Reilly and did field repair in 2 hrs to get back on the road.
 
#39 ·
Wow you guys are amazing.

I posted, tiredly, last night about my own 2007.5 having similar issues. My main concern was could I just get it another 225 miles down the road. This makes it seem like despite the intermittent low power issue I might get it 1300 miles before addressing it.
 
#41 ·
Hey Fellas, Well, the rabbit's out of the hat. Picked up a 08 dually with 180K last fall for a great price.

I have learned whenever you haul under medium to heavy load (Round Baler on Deckover, maybe 8k) or 14 haylage bales (4.5 by 4, maybe 16k) the engine goes into a reduced power mode. The dash will show "check/change fuel filter" or "low fuel rail pressure" or "DPF soot build up". The FF was changed just prior to getting truck.

I stopped at a local diesel shop. They said change the Fuel and air filters with genuine GM parts. Then the kid said "how do you drive it?" I said, "I have gray hair." He said, "there's your problem". I said "I know, haven't been laid in 6 months".

Point being is he said I need to drive it like I stole it.

Anyone care to weigh in? I love the truck and it's power, when it's there.

Had another mechanic tell me 08 to 15 were really sucky years for the Duramax. You guys agree?

I have to replace it one point and would consider a new Duramax but not if I have to drive it like a maniac all the time. Some maniac time is good for the soul and I ain't no saint, but....

Comments fellas'. Thanks, Mike
i wouldnt say they are sucky years. they just have weak points that need attention. on a lmm im sure its the fuel lines. take somewhere and get the fuel lines changed and a FASS lift pump installed and youll be good to go! a delete would help the soot lol
 
#44 ·
Pushes the fuel to the CP3, rather than it siphon/suction from the tank. Helps out the CP3 than from having to draw it all the way from the tank. Its a popular upgrade. There is no fuel pump in our tanks like a fuel injected car. The pump is on the motor, and suction gets it lifted.
 
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