What are the symptoms and causes of diesel engine misfiring?
3 Answers
The symptoms and causes of diesel engine misfiring are as follows: 1. Symptoms: Engine misfiring mainly refers to one or more cylinders of the engine not working properly. It is usually manifested as: abnormal engine operation or insufficient power, uneven engine operation at high, medium, and low speeds with rhythmic shaking, black smoke from the muffler, and backfiring. 2. Causes: (1) The cylinder pressure of individual cylinders is lower than that of other cylinders. (2) Large clearance between the cylinder liner and piston rings, leaking valve seals, and improper closing of intake and exhaust valves. (3) Insufficient fuel injection in individual cylinders, caused by issues such as clogged fuel injectors. (4) High-pressure fuel consumption, low-pressure fuel circuit, water separator failure, or rail pressure sensor failure. (5) ECU malfunction or issues with checking the fuel injector and injection timing.
I've been driving trucks for over a decade, and the most obvious symptom of a misfire is the engine shaking like a sieve, with black smoke puffing from the exhaust pipe and a complete lack of power when climbing hills. Once on the highway, I experienced a sudden misfire—the entire cab was vibrating, and I had to pull over immediately. Common causes of misfires include clogged fuel injectors, unstable fuel supply from the high-pressure fuel pump, burnt valves, or insufficient cylinder pressure. Last time it happened to my truck, it was due to severe carbon buildup on the injector, which ruined fuel atomization and caused one cylinder to stop working. Nowadays, with electronically controlled diesel engines, you also need to watch out for loose sensor wiring harnesses, as that can cause the same issue. Prolonged misfiring damages the engine, so immediate repair is a must.
In auto repair shops, cases of diesel engine misfiring are frequently encountered. The symptoms are quite typical: rhythmic knocking sounds can be heard when the engine is running, intermittent white smoke is emitted from the exhaust pipe, and the tachometer needle fluctuates up and down. The main root causes are concentrated in three areas: abnormalities in the fuel injection system are the most common, especially injector sticking or poor atomization; followed by cylinder sealing failure, such as piston ring wear or valve not closing properly; and issues with the fuel supply circuit, like high-pressure fuel pump plunger wear leading to insufficient fuel supply to a single cylinder. In such situations, we first retrieve the ECU fault codes, then perform a cylinder compression test to pinpoint the problematic cylinder.
