What Causes the RPM of a Single-Cylinder Diesel Engine to Fluctuate?
2 Answers
Air entering the fuel line, leading to poor fuel supply, prolonged use of the fuel injection system, and aging of the fuel injection system, among others. Common causes of unstable diesel idle speed are as follows: 1. Significant air leakage: During idle, excessive cylinder air leakage results in substantial energy loss within the cylinder, leading to lower compression temperatures and pressures, poor fuel atomization, and significant combustion fluctuations. 2. Insufficient fuel supply: At idle, the fuel supply is minimal, and slight variations in fuel supply to each cylinder can cause differences in their operating states. This uneven fuel distribution during idle leads to the diesel engine's idle hunting phenomenon. 3. Low nozzle precision: The direct injection in diesel engines has driven fuel injection pressures to higher levels, especially with the adoption of multi-hole injectors. This makes the nozzle less precise when delivering small fuel quantities, prone to fluctuations. Unstable fuel supply in diesel engines is a major cause of idle instability.
I just tinkered with the old tractor at home and also experienced erratic RPM fluctuations. Most of the time, it's fuel system trouble—either the filter is clogged and fuel can't keep up, or the plunger in the fuel pump is worn and leaking. Also, the governor's spring weakens over time, making it hard for the machine to control RPM. The most frustrating issue is air seepage at fuel line connections; the bubbles sucked in cause intermittent fuel supply. If you're using diesel mixed with water and there's black sludge buildup at the tank bottom, no wonder the RPM is unstable. If all else fails, disassemble the fuel pump—if the pushrod sleeve is too loose, replacing it with a new part will solve the problem immediately.
