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Would anyone advise against buying a LML due to the CP4 problems? I'm looking for a truck and was just wondering what people think about this. I have read that 2017 and newer have Denso injection pumps so the CP4 problems must be real and not just a very small number of failures. I have also read that the CP4 pump was improved in 2014 but I haven't been able to find anything definite on it. Any comments would be appreciated. Thanks.
 

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Don’t run the fuel down past 1/4 tank and use a fuel addictive. I’ve heard of people going hundreds of thousands of miles on a stock cp4
 

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No doubt there are thousands of CP4s with a ton of miles on them with no problems. My personal experience, I have four friends with LMLs and two of them have experienced failures. A 2014 at 50k and a 2015 at 75k. I would only buy one with intentions of a full delete and CP3. Otherwise just save up for a L5P.
 

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Seems like these LML’s get the bad rap like the old 6.0 power strokes. I wouldn’t be afraid of buying one. Is it on the back of my mind that could have a catastrophic failure? Yes, but not going to trade my 50K 2015 off because of it. I just make sure I use an additive every tank and keep filter changed when computer gets to 50% life (which is usually well over 10K miles). I personally only know one guy that has ever had a HPFP failure with a LML and it was an hot-shotter. I know there are many that have had failures but it’s still a very low percentage, probably <5%. Keep in mind they made hundreds of thousands of LML’s between 2011-2016. Something to also consider is when the L5P came out they took quite a jump in price. I know a new 2020 spec’d out like my current 2015 is at least $6K higher in MSRP compared to the 2015 MSRP. Some of it is technology and annual price increases, but biggest part is the powertrain.
 

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treat your truck the way it should be treated and it will take care of you .. if you drive the shit out of it it will shorten it's service life. i love mine and it is at 115K with no issues. i tow a 42' 5th wheel 8 to 10 times a year the rest of the time it's my daily. used it this morning to kick a little hot rod Honda's ass at a red light but most of the time i just drive it normal
 

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Yes. I once said I’d never own a lb7 or an lly but here I am having had all but an lmm and l5p. They have all been pretty much trouble free.
 

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I had mine from 40,000 miles to 100,000 miles. Only issue I ever had was the TCM. It was 1,000 to fix. But I put the truck through it’s paces. I’m going to buy another one next year if I can find one with under 100,000 miles and under 25,000.
 

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I have never been happier with a truck purchase than I am with my LML ( 2013 bought at 80,000 miles; now approx. 93,000 mi.).

It does everything expected of it so well. ( primary use is towing my "toy" trailers - one is our three axle boat trailer, the other is my "box" / hobby car trailer - both "bumper pull" of about 1,300 lbs. load on the hitch - each weighs approx. 11,000 lb). Ocassional use as a "2nd car").

I am especially impressed with its ability to handle the meanest long up-hill grades on I-40 here in the high country of northern Arizona, combined with its ability to handle the extremes of temp. out on the Mojave Desert in the summer.

Yes, to get it the way I like it meant I treated it like a "do-it-yourself" kit...meaning did the CP-3 BEFORE a failure, air shocks with one spring leaf removed, to give a better more controllable ride.

To insure no problems with the DPF, plan on having it removed from the vehicle, cut apart, and PROPERLY cleaned, oh...say at 100,000 intervals ( at one of the facilities that does this for the DPF's on the big OTR trucks - I personally believe the "forced regen" that becomes necessary from time to time is hard on the truck).

If you live like I do in a "non-inspection" area, you might consider certain "parts relocations" that will result in your engine oil staying cleaner, and your fuel mileage improving by at least 3 - 5 mpg, and no more of those weird harmful "on road" DPF cleaning cycles.

Just remember that Greta Thornberg will hold you personally responsible for ending life here on Planet Earth in only the next 7 years, AND you will be held personally responsible for the deaths of all those cute little fuzzy chinned bunny wabbets.

Should you decide to "fix" your truck so as to become a murderer of the cute little fuzzy-chinned bunny wabbets, & want to deprive Greta Thurnberg of her childhood......bear this in mind - the "ecology freaks" are becoming more politically powerful every year.

So save every bolt, nut washer, gasket, etc. along with all of the hardware that came with your truck when new - it is possible in the future we MAY have to put all that stuff back in order to re-register our trucks.

There was a bill in Congress last year that would have turned our entire country into an "inspection" zone...it failed. This time.
 

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It would be interesting to see an actual failure rate on the CP4 pumps. I have heard in reality it is 10% or less but I have no factual data to prove it. When you consider the hundreds of thousands of these vehicles that run around the country every day, not only the Duramax's but the powerstrokes too what is an actual number of failures? Does it truly warrant the negative stigma? I would imagine if you look at the rate of failure of owners on forums, its possibly higher given people on forums are usually looking for advice on DIY repairs or modification. Hell hath no fury like a truck owner scorned.

I purchased my truck knowing full well what that little thing is capable of doing, but I'm taking care of it. Keeping water, air and contaminants out of the fuel, keeping the tank full, fueling up at popular stations that don't sell budget fuel, etc. Going to add a lift pump here before camping season just to make sure.

Another thing to keep in mind is the fact that there may always be a sentence missing when people talk about losing their CP4. Perhaps they have been fueling up at discount stations, maybe they let that fuel filter go 20K (hey, it ran great yesterday right?), maybe they start it up and hammer down cold, or constantly run around on half a tank or less, running the tank dry, or cranking it over too long. All of those things are factors to any diesel engine component failing. I know a guy who bought a brand new L5P and hates it. In less than three years, its been in the shop 6 times for emissions issues. Even left him stranded on the side of the road on a family vacation.

Just about every truck is going to give you some reason not to buy it.
 

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It would be interesting to see an actual failure rate on the CP4 pumps. I have heard in reality it is 10% or less but I have no factual data to prove it. When you consider the hundreds of thousands of these vehicles that run around the country every day, not only the Duramax's but the powerstrokes too what is an actual number of failures? Does it truly warrant the negative stigma? I would imagine if you look at the rate of failure of owners on forums, its possibly higher given people on forums are usually looking for advice on DIY repairs or modification. Hell hath no fury like a truck owner scorned.

I purchased my truck knowing full well what that little thing is capable of doing, but I'm taking care of it. Keeping water, air and contaminants out of the fuel, keeping the tank full, fueling up at popular stations that don't sell budget fuel, etc. Going to add a lift pump here before camping season just to make sure.

Another thing to keep in mind is the fact that there may always be a sentence missing when people talk about losing their CP4. Perhaps they have been fueling up at discount stations, maybe they let that fuel filter go 20K (hey, it ran great yesterday right?), maybe they start it up and hammer down cold, or constantly run around on half a tank or less, running the tank dry, or cranking it over too long. All of those things are factors to any diesel engine component failing. I know a guy who bought a brand new L5P and hates it. In less than three years, its been in the shop 6 times for emissions issues. Even left him stranded on the side of the road on a family vacation.

Just about every truck is going to give you some reason not to buy it.
Everyone speculates about the failure rate, but in my previous post I don't see how it can be more than 5%, probably more like 1-2%. If it was 10% then 1 out of every 10 LML's going down the road would have failed and there is no way that happens. The dealerships would literally be backed up with them with how many LML's were built and on the road. To me the bigger issue is the cost of repair. A couple thousand dollar pump can cost you 5 times that in repair which is absurd in my opinion. GM knows they have a problem. I think they should offer some assistance on this repair (maybe not the whole amount) for some extended time somewhat similar to what they did for the injector issues on the LB7. There aren't many of us that can afford a $10K+ repair and downtime especially if running a business. Or at the least offer some type of extended warranty or insurance coverage specifically for a pump failure.
 

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Everyone speculates about the failure rate, but in my previous post I don't see how it can be more than 5%, probably more like 1-2%. If it was 10% then 1 out of every 10 LML's going down the road would have failed and there is no way that happens. The dealerships would literally be backed up with them with how many LML's were built and on the road. To me the bigger issue is the cost of repair. A couple thousand dollar pump can cost you 5 times that in repair which is absurd in my opinion. GM knows they have a problem. I think they should offer some assistance on this repair (maybe not the whole amount) for some extended time somewhat similar to what they did for the injector issues on the LB7. There aren't many of us that can afford a $10K+ repair and downtime especially if running a business. Or at the least offer some type of extended warranty or insurance coverage specifically for a pump failure.
Your estimate is probably more correct than mine. And I agree, the average cost of the repair is scary and most people cant just shell out $12K like its nothing.

I think you have to take it like you take everything else. Weigh the options, look at the root causes of failure, the preventative measures, or even the minor adjustments (like the fuel system saver). I would definitely buy my truck again. Nothing has failed on me yet, and hopefully it wont, but the power is addicting, and I really didn't overpay for it either.
 

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2013 with 135,000 and no problems. Pretty much stock accept for dpf delete and egr block off. Primarily did those things just to avoid having to purchase a new dpf when that one plugged up for good. I've had the truck since new. Delete over 20,000 miles ago with no issues. I do run PS addative with every tank.
 

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One of my biggest regrets in vehicle buying and selling was getting rid of my 2015 GMC Sierra 2500 HD with LML. That was the most flawless vehicle I ever owned. I think it had 65K miles on it when I traded it because my accountant said it would be a good idea. Got a 2018 L5P that was nothing but trouble and finally convinced them to take it back. Got a 2019 and it hasn't been as bad but still bucks like a bronco at times with shifting being all hosed up. So needless to say I miss my LML.
 

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Would anyone advise against buying a LML due to the CP4 problems? I'm looking for a truck and was just wondering what people think about this. I have read that 2017 and newer have Denso injection pumps so the CP4 problems must be real and not just a very small number of failures. I have also read that the CP4 pump was improved in 2014 but I haven't been able to find anything definite on it. Any comments would be appreciated. Thanks.

i need to just make a macro to copy and paste this since it comes up so much.

forums consolidate like minded people, in this case, may of the people here came here seeking help for a problem. So forums are kind of like the spiraling drain of bad news since people are coming here to talk about this failure and see info on it, but people with perfectly working trucks are not posting "still running" posts. This skews peoples perception of the problem beyond what it is.

That said, even with this inflated value, this forum in a poll of 600-700 people if memory serves showed a failure rate of 8 -12% over 100K miles which while higher than i would like, is far from the eminent time bomb people make it out to be. This percentage is significantly higher than what would be sampled in real world data just due to the nature of the forum. I would guess the actual rate is under 1%.

The pumps are likely failing due to a few factors that have been discussed in great depth on this forum elsewhere. Basically it comes down to fuel quality over anything else. The CP4 was designed to run european grade diesel which has higher lubricity than US diesel. This is due to the sulfur removal process, but not the sulfur itself. so now you have a pump running fuel as lubricant, that does not meet the manufactures spec for lubrication. Already not off to a great start here. There is some evidence also to support that a lot of the fuel filters on the market are no where near as good as we expect them to be, so your choice of filter may be allowing water and other contaminants into the pump that you would assume are captured. This also adds to wear.

Basically, if you run quality diesel and dont shop for the cheapest pump in town, and you use an additive to increase lubricity (optilube is good by forum opinion) and change your fuel filter regularly with a good quality filter like the AC Delco, your odds of a failure are very low, and due to the fear people have of the pumps blowing up, the trucks probably a steal. I know mine was.


No doubt there are thousands of CP4s with a ton of miles on them with no problems. My personal experience, I have four friends with LMLs and two of them have experienced failures. A 2014 at 50k and a 2015 at 75k. I would only buy one with intentions of a full delete and CP3. Otherwise just save up for a L5P.
A first generation fuel system is not necessarily better. There has not been sufficient time on that system for any major issues to show up, so it might be better, it might be the same, or it may even be worse than an LML, we dont have enough data yet.
 

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Pretty sure with the number of CP4s out there the failure rate & issues are a very low percentile. Keep fuel lubed.
 

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I bought the first year 2011 new. During the first 5 years all 8 glow plugs were replaced, 1 at a time, 3 fuel injectors, fuel filter housing, TCM and parts of the DF system. And one of the wheel sensors for the brake system. I've got 70,000 miles on it now and I've only put 1 set of tires on it and still have the original brake pads. I replaced the driver seat cover with an oem replacement. My bony ass wore it out.I like the new ones but I can't justify spending 40-45,000 bucks for a new one when mine is doing great. I''ve got a long way to go before I will need a replacement.
 

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Mine is a 2014 3500HD Silverado with 121k miles on it. What has been done since new? Replaced NOx sensor, replaced DEF tank, and just had Radiator replaced (pinhole leak near bottom passenger side)

It will regen every 700 miles or so. When it gets 40grams of gunk in the DPF filter. Just get out on the interstate, put it on 70, and 30-40 min later it’s done.

GM mechanic said likely the only thing I’ll see before 200k miles is the water pump, but it’s fine right now and he didn’t see anything else to be concerned about.
Most irritating thing is the radio display gets flakey.

No fuel additives and no mods. I keep the tank full and refill when below half, and I’m mindful of where I fill up.

So if you’re used to a gas truck and zero service issues before 150k miles, then you might be bothered by the fact that diesels will have more issues. But all in all, just nitpick things gone wrong so far. $500 nox sensor, $1500 def tank, and $1500 radiator, all covered under warranty.

I would buy it again.
 

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I bought a New LML in 2011, drove it for 115K miles before trading for an '18 L5P in Jan of 2018.
Most of that mileage for towing 3 different Fifthwheels, 1st approx 14K, 2nd 17K, now 19.5K total mileage towing was approx 100K.
Had and EGR Cooler issue when still under warranty and had the bad Nox sensors replace, other than that never to a repair shop.
 
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