If you compare the CP3 in the Duramax to the CP3 in the Cummins, the one on the Duramax has to do a lot more work. But just because it can doesn’t mean it should. If you have a stock truck with no desire to add horsepower, then sure, the engine can run fine without a lift pump for a long time. You might be thinking to yourself, “wait a minute, LT… there are plenty of Duramax’s on the road with well over 200,000 miles and no lift pump, and they don’t seem to have any problems” and you would be partially right. Yet the mystery remains, why didn’t GM put one there in the first place. Interestingly enough, the 5.9 and 6.7 Cummins trucks which were equipped with an almost identical CP3 were equipped with a lift pump, and the newest L5P Duramax has one, all of which suggests a lift pump is an important part of a diesel fuel system. This is true on every Duramax from the LB7 in 2001 to the LML in 2016. The fuel takes the same path from the tank, through a filter, and into the injection pump, except now the CP3 is responsible for sucking fuel from the tank. But for some strange reason, the 6.6 Duramax came from the factory sans lift pump. Finally, once the pressurized fuel enters the injector, it either gets sprayed directly into the cylinder to make a big boom, or if there is extra, it flows back to the tank through the injector return to start its journey all over again.Įvery one of those components can be found on just about every diesel pickup made in the US for at least the last 20 years, whether it’s an HEUI Powerstroke, a 12-valve Cummins, or even the old 6.5 GM Diesels. Most of the high pressure fuel inside the rail gets sent straight into the injectors, but there are some conditions like sudden deceleration or a drop in fuel demand which will cause a pressure relief valve to open up and send excess fuel from the rail back to the tank. Next, the fuel enters the injection pump, where it can go one of two places: it either gets pressurized and sent to the rail or goes back to the tank in a return line. Since diesel by nature is a dirty product, there is always at least one filter between the low-pressure pump and the engine to remove any dirt and contaminants, and likely there will be a water separator to remove any H2O which condenses in the tank. Depending on the model, you might have between 25 and 40 gallons of capacity, and on most trucks there is a low-pressure fuel pump which sits inside the tank and pushes the fuel toward the engine at a relatively low pressure. It all starts in the tank, which is where the fuel is stored whenever you fill up. There are many parts which make up the fuel system on a common rail diesel truck, and the path the fuel takes is like a choose your own adventure book there are many different options. It was a great powerplant and was the first of the big 3 to come equipped with common rail fuel injection, but there was one item missing which every other diesel pickup had before and since: a lift pump. One such automotive mystery was started in 2001, when GM introduced the Silverado HD’s powered by the 6.6-liter Duramax diesel V8. While there have been several theories, to this day nobody knows the answer to either. There are many great mysteries which have remained unsolved over the years, ranging from what’s at the bottom of the Bermuda Triangle to what happened to D.B.
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