Chevy and GMC Duramax Diesel Forum banner
  • Hey Everyone! Enter your ride HERE to be a part of this months Ride of the Month Challenge!
1 - 7 of 7 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter · #1 ·
So I decided to swap from a Ford to a GMC this week. I bought a 2015 Denalli HD with 86k on the LML and Allison transmission. My question is, what do I need to be concerned with on this truck? Every vehicle make has its issues. What kind of overall miles can I expect to get out of this truck? So far I love it and having no regrets. I’ll be pulling a 15k pound bbq trailer with it and only putting probably 3-4K miles on it a year. It’s never been tuned and is 100% bone stock and that’s how I intend to leave it. I’m not into making it fast, I’m into it lasting me a loooooong time
 

·
Registered
Joined
·
64 Posts
Welcome, with only 4K miles a year it will last you forever.
 

·
Registered
Joined
·
44 Posts
Your biggest concern is going to be the possibility of a fuel pump failure down the road. If you do some research there is a lot of information on it. This CP4 fuel pump is especially sensitive to fuel related issues like debris or bad fuel. Apparently fuel in the US is low on lubricants compared to the Europe diesel the Bosch CP4 was designed for. It’s basically the the potential Achilles heal of the LML. From what I can gather it’s something like 5% of the LML duramax engines have this failed. The biggest issue is the cost of the repair when it fails. It’s somewhere around the $10,000 range or more when it fails since it takes out the entire fuel system when it fails.

There are many things you can do to increase your odds of avoiding it. Making sure the fuel you use is good quality. Making sure the station is well used so fuel gets moved fast and doesn’t sit. I have decided to use my local Costco as it has Top Tier certified Diesel plus 5% bio diesel. The top tier cert at least makes sure it’s decent stuff and the bio diesel is supposed to have better lubricating properties. This is supposed to be a good thing. Yet I still run a fuel additive that helps with this as well.

Another thing you should consider is swapping your fuel pump out for the CP3 design used on the older generations that are more reliable. Other options are adding a lift pump. This increases the fuel pressure and ensures that there’s never a lack of fuel under heavy load. This lack of fuel can starve the system of fuel and cause issues that take out the fuel pump. Or at least increase odds. Most lift pumps also have extra filters that filter the fuel more then the factory system and that alone helps lower odds of a issue. Also it seems to be popular advice to replace the fuel filter every 10k and not wait till the trucks system tells you to. The trucks system only tells you the max you should wait. It seems most don’t chance it tho and replace more often.

Other issues you may run into with low miles being out on your truck is the DEF fluid getting old and having issues with clogging up that system. I know the truck I just bought recently (2016) only had around 8500 miles and had not had any trips longer then a mile or two in over 18months. So I was told to get a pump and suck the old fluid out to make sure I didn’t run into issues. The fluid was already cloudy which I was told was a indication that is was getting too old and could become a problem. Starting out with DEF fluid that was made very recently is the goal to make sure you avoid issues with old fluid.

I have only had this truck for a 3 weeks or so and this is what I have been able to come up with so far. It took a while to come up with this info so I thought I would save you some trouble. I’m no expert and may be leaving stuff out or maybe have some details wrong. I hope the more experienced members swoop in to correct anything I may have got wrong or left out. In fact I would appreciate being corrected if I got something wrong.

Besides the fuel and DEF/other emissions stuff I love this truck! I got a Denali as well and still am still in awe of how awesome it really is. I will in future be adding the lift pump and preemptively swapping fuel pump when warranty runs out. Hope you enjoy your truck.
 

·
Registered
Joined
·
3 Posts
Discussion Starter · #4 ·
Thanks for that info! What is everyone using for a fuel additive that seems to be working the best?
 

·
Registered
Joined
·
694 Posts
Your Ford had the exact same pump, a CP4. As far as leaving it stock & thinking that's gonna make it last forever couldn't be further from the truth, The EGR system is filling your intake system with crap.
I am in the middle of deleting all the emissions junk off my truck now that warranty is done. I also only put about 5K miles a year on & have all ready had 2 P21DD issues & assuming there will be other emission, "Reduced Power" issues.
You don't have to put a big power tune in, only enough of a tune to allow emissions to be disabled. Just my $.02
 

·
Registered
Joined
·
694 Posts
Your biggest concern is going to be the possibility of a fuel pump failure down the road. If you do some research there is a lot of information on it. This CP4 fuel pump is especially sensitive to fuel related issues like debris or bad fuel. Apparently fuel in the US is low on lubricants compared to the Europe diesel the Bosch CP4 was designed for. It’s basically the the potential Achilles heal of the LML. From what I can gather it’s something like 5% of the LML duramax engines have this failed. The biggest issue is the cost of the repair when it fails. It’s somewhere around the $10,000 range or more when it fails since it takes out the entire fuel system when it fails.

There are many things you can do to increase your odds of avoiding it. Making sure the fuel you use is good quality. Making sure the station is well used so fuel gets moved fast and doesn’t sit. I have decided to use my local Costco as it has Top Tier certified Diesel plus 5% bio diesel. The top tier cert at least makes sure it’s decent stuff and the bio diesel is supposed to have better lubricating properties. This is supposed to be a good thing. Yet I still run a fuel additive that helps with this as well.

Another thing you should consider is swapping your fuel pump out for the CP3 design used on the older generations that are more reliable. Other options are adding a lift pump. This increases the fuel pressure and ensures that there’s never a lack of fuel under heavy load. This lack of fuel can starve the system of fuel and cause issues that take out the fuel pump. Or at least increase odds. Most lift pumps also have extra filters that filter the fuel more then the factory system and that alone helps lower odds of a issue. Also it seems to be popular advice to replace the fuel filter every 10k and not wait till the trucks system tells you to. The trucks system only tells you the max you should wait. It seems most don’t chance it tho and replace more often.

Other issues you may run into with low miles being out on your truck is the DEF fluid getting old and having issues with clogging up that system. I know the truck I just bought recently (2016) only had around 8500 miles and had not had any trips longer then a mile or two in over 18months. So I was told to get a pump and suck the old fluid out to make sure I didn’t run into issues. The fluid was already cloudy which I was told was a indication that is was getting too old and could become a problem. Starting out with DEF fluid that was made very recently is the goal to make sure you avoid issues with old fluid.

I have only had this truck for a 3 weeks or so and this is what I have been able to come up with so far. It took a while to come up with this info so I thought I would save you some trouble. I’m no expert and may be leaving stuff out or maybe have some details wrong. I hope the more experienced members swoop in to correct anything I may have got wrong or left out. In fact I would appreciate being corrected if I got something wrong.

Besides the fuel and DEF/other emissions stuff I love this truck! I got a Denali as well and still am still in awe of how awesome it really is. I will in future be adding the lift pump and preemptively swapping fuel pump when warranty runs out. Hope you enjoy your truck.
Can't comment on sitting for 18 months but, my truck sits from Oct - Apr for the last 4 years & have never had a " bad DEF" message pop up.
 

·
Registered
Joined
·
239 Posts
Don't have to be fast after deleting. If you want it to be reliable and last............. you need to delete it. This is 90% of issues these trucks have.
 
  • Like
Reactions: Jbeck1986
1 - 7 of 7 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top