5 Things I Hate About the 6.6 L5P Duramax Diesel Engine
Welcome to Mark Martin Motors, your trusted local truck dealership right here at 4126 Oregon Pike in Ephrata, PA 17522. If you are within a 4-hour drive of our lot, you probably know how important a reliable heavy-duty truck is for work and play in our region. Today we are talking about the 6.6 L5P Duramax diesel, which is easily one of the most trusted engines on the market. But contrary to popular belief, I want to share five things I actually hate about this engine. Stick around though, because a lot of these complaints are the exact reasons why I would still highly recommend buying one.
The Reality of the Modern Duramax
Introduced in 2017, the L5P puts out a solid 475 horsepower and 975 pound-feet of torque. It is an absolute powerhouse, but there are a few quirks that drive truck enthusiasts crazy. Let us dive into the details.
Performance and Customization Roadblocks
If you are a diesel head who loves to tinker, these first two points might hit close to home.
1. It is Strangled From the Factory
This engine is massively overbuilt for the horsepower and torque it produces. GM essentially detuned this motor right from the factory for the sake of emissions and warranty durability. It is frustrating because they leave so much power and efficiency on the table. However, the trade-off is why I would still buy it. GM sacrificed that extra 40 horsepower to give you an engine that can easily run to 350,000 miles. The longevity you get in return is incredible.
2. The Hardest Computer to Crack
For years after it came out, you could not tune or delete the L5P because GM made the computer system the hardest one to crack. If you want a project truck to maximize fuel economy and completely alter the emissions systems, this engine fights you every step of the way. But here is the silver lining for used truck buyers. When you are looking for a pre-owned truck, the L5P is the least likely to have been tuned, deleted, and abused by previous owners doing burnouts. You are much more likely to find a truck that was treated right.
Emissions and Maintenance Quirks
Modern diesel engines are highly regulated, and the systems that manage them can be a headache.
3. It Punishes You For Short Trips
If you are not towing regularly and only use your truck for 5 or 10-minute trips to the grocery store, this engine will punish you. The truck needs a solid 20 to 30 minutes of driving to complete an emissions regen cycle. If it cannot finish, extra diesel fuel washes past the rings and dilutes your engine oil, making it thin and dirty. The good news is this tells you exactly what to look for when shopping for a used Duramax. You actually want to avoid the super low-mileage garage queens and look for trucks with average miles that were properly driven and used for towing.
4. The CP4 Fuel Pump Fear Factor
If you search the internet, you will see endless horror stories about the CP4 fuel pump grenading, sending metal shards through the engine, and causing a massive repair bill. I hate that this misconception gets tied to the L5P. The truth is, the 2017 and newer L5P engines do not even use the CP4 fuel pump. GM switched over to a reliable Denso HP4 pump and added a factory lift pump to feed it. So you get all the peace of mind without the fuel pump anxiety.
5. Cheap Sensors Can Cause Limp Mode
The L5P engine itself is basically bulletproof, but the emissions system that babysits it is not. A cheap part, like a $40 to $200 DEF quality or knock sensor, can fail and throw your entire truck into a speed-limited limp mode. It is incredibly annoying to be on a 10-hour towing trip and have your truck shut down over a cheap sensor. But ultimately, that annoying emissions system is doing exactly what it is supposed to do, which is protecting your expensive L5P engine from real damage. I would much rather replace a small sensor than pay to replace a whole diesel engine.
If you are looking for an honest deal on a long-lasting truck, come visit us at Mark Martin Motors in Ephrata, PA. We are proud to serve our local community and anyone making the drive from the surrounding 4-hour radius.
Check out the full video breakdown here: https://www.youtube.com/watch?v=GlnVM97TRPY