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Gary, ASE Certified Technician
Category: Chevy
Satisfied Customers: 298
Experience:  ASE Master Truck Technician,24 Years GM Shop Foreman,Fully Trained GM Trucks Light and Heavy.
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Chev. 3500 my duramax is losing fuel pressure, dealer told

Customer Question

my duramax is losing fuel pressure, dealer told me pump was cracked and losing a small amount of vacuum. They replaced it but continue to lose a small amount of pressure. Explanation given was now it losing pressure at the injector and recommend replacing them all for a huge cost. Can each injector be individually tested to determine which is bad or requires replacing? I have owned 6 diesel trucks and never had an injector problem, now I am told all eight on this engine need replacing, I am very skeptical. Can you help.

Submitted: 5 years ago.
Category: Chevy
Expert:  Gary replied 5 years ago.

Hi, the 2004 Duramax has the first generation duramax, the"1" engine, or LB7. This engine utilizes internal injectors, (under the valve cover), as compared to the newer engines that have external injectors. The newer engines are easier to diagnose , as the injectors can be tested individually. Your engine can only be tested in groups of 4 injectors, (one bank at a time), when the engine is together.With a lot of teardown, and some internal injector testing,there is a small chance you can pinpoint individuals, but usually results in replacing all.With a high side pressure volume return test, the return fuel volume can pinpoint what side of the engine has a fault, narrowing it to 4 injectors. If there is excessive fuel return volume on both sides, then we are back to 8 possible injectors. If you have smoke at an idle when it is warmed up, you may be able to pinpoint an injector, by cancelling the cylinders, with a scanner, one at a time. If the smoke clears, then that injector is at fault.I would not assume it needs all 8, untill testing is properly performed. If your dealer does not agree with this, I would consider finding another facility that is more familiar with the diagnosis of this engine. If I can be of any other help, please ask. Good luck...Coop

Customer: replied 5 years ago.
My engine is 2004.5 LLY not the LB7 you referred to previously, my research notes that this engine/injection package was specifically designed to make injector access without removing the valve covers. With this additional info what do you suggest. You have a paying customer here, you are making me feel better already.

Expert:  Gary replied 5 years ago.
Hi, the LLY is in fact the first generation external injector engine. You can feel better, as this engine is easier to diagnose.There are fuel return lines that attach at each injector to group unused fuel , and send it back to the fuel tank. These lines can be removed from each injector, and a graduated cylinder is used in conjunction with a special tool that snaps into the injector, then runs to the measuring cylinder. After 15 seconds of cranking, the fuel volume in the cylinder is measured, and the ones that put out too much return, are the faulty injectors. Even though you have an LLY, this is still a hard procedure, as you need to gain access, and have the special tools , and procedures. Paying a dealer to perform this service will cost less than the price of one injector, and will tell you exactly which injectors are at fault. If you have smoke at a hot idle, I would still do a cylinder balance / cut out test with a scanner, as this cold show the issue quickly. Unless you have been using dirty farm fuel, or have had multiple trouble codes, with a check engine light on for a long time, I surely cannot see all 8 injectors going bad at once. Once the injectors are replaced, each injector has a "flow rate". This is a series if numbers that must be programmed into the engines control module, to calibrate the fuel flow rate to the engine.With this information, I am sure you can make the best decision on which direction you want to go.If I can give any other advise, plase ask, good luck...Coop

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