案例分享：FO index calibration in limit & M/E misfire.

2023年11月30日，某轮正常航行时，主机突然出现FO index calibration in limit警报，随后出现No.6缸Pmax和排温偏差警报。按照FO index calibration in limit警报的Info提示，更换了燃油泵的反馈传感器，并进行了Function Test，且测试结果正常。启动主机后，随机出现1~3个缸不发火（主要集中在Cyl.1\2\4\5\6缸）。维持主机低速运转一段时间后，各缸陆续恢复供油。

On November 30, 2023, when a ship was sailing normally, the main engine suddenly appeared FO index calibration in limit alarm, followed by No.6 cylinder Pmax and exhaust temperature deviation alarm released. According to the Info of FO index calibration in limit alarm, the feedback sensor of the fuel pump was replaced, and the Function Test was carried out, and the test result was normal. After starting the M/E, 1~3 cylinders do not fire randomly (mainly concentrated in Cyl.1\2\4\5\6 cylinders). After maintaining the low speed operation of the main engine for a period of time, the F.O supply of each cylinder is gradually restored.

加速后正常运行14小时后，Cyl.5再次出现Pmax,Pcomp,Pi及排温低的情况。停车后，再次启动主机，依旧出现随机3个缸不发火，同样的低速运转一段时间后恢复正常供油。2小时后，Cyl.5和Cyl.6再次先后出现不发火情况。

After 14 hours of normal operation after acceleration, the Cyl.5 again showed low Pmax, Pcomp, Pi and exhaust temperature. After stopping and then start the main engine again, there are still three random cylinders misfire, and the same low speed operation for a period of time to restore normal oil supply. Two hours later, Cyl.5 and Cyl.6 failed to fire again.

前期针对船上反馈的FO index calibration in limit警报及主机低负荷随机不发火情况，常规性的建议船上检查：吸油阀、喷油器开启压力、燃油泵和燃油高压油管泄漏及燃油系统除气等。经排查，燃油系统不存在泄漏、集油井也未放出空气及燃油压力也正常。由于船舶处于海况较差区域，暂时未能进行喷油器及吸油阀排查工作。

In the early stage, according to the FO index calibration in limit alarm reported on board and the random misfire situation of the main engine under low load, it is recommended to regularly check on board: oil suction valve, FIV open pressure, fuel pump and fuel high pressure pipe leakage and air in fuel system. After investigation, there was no leakage in the fuel system, no air was released from the collecting well and the fuel pressure was normal. Due to the poor sea condition of the ship, the fuel injector and oil suction valve can not be checked for the time being.

随着主机持续低速运行，虽然各缸恢复正常喷油，但恢复喷油缸的PMI性能参数依然偏低.就算负荷提升，依然会随机出现不发火或者单缸性能差及排温低情况。

With the continuous low-speed operation of the main engine, although the cylinders return to normal fuel injection, but the performance parameters of the recovery cylinder in PMI computer are still low. Even if the load is increased, there will still be random misfire or poor performance of single cylinder and low exhaust temperature occurred.

针对这种特殊情况，觉得事情并非这么简单，期间船上老轨提出检查各缸蓄压器氮气压力，确实是解决问题的一个方向。为进一步定位故障点，指导船上进行手动截取故障时的HCU event曲线进行分析。最终发现各故障缸都存在ELFI主阀芯运动信号弱的情况，于是故障点锁定在ELFI阀上。如下图所示：除Cyl.2/3正常外，其它缸都存在异常。

In view of this special situation, I feel that things are not so simple, during the Chief engineer proposed to check the nitrogen pressure of each cylinder accumulator, which is indeed a direction to solve the problem. In order to further locate the fault point, guide the ship to Log manually the fault HCU event curve for analyzing. Finally, it is found that the movement signal of the ELFI main spool is weak in each faulty cylinder, so the fault point is locked on the ELFI valve. As shown in the figure below: Except Cyl.2/3 is normal, other cylinders are abnormal.

什么原因导致ELFI主阀芯运行不到位？反馈探头故障？先导阀控制信号故障？但这么多缸同时故障也不可能，加上ELFI比例阀的控制信号及反馈信号都未发现类似电噪音的情况。因此，排除了ELFI比例阀本身故障及MPC故障的可能。

What causes the ELFI main spool to run improperly? Feedback probe failure? Pilot valve control signal failure? However, it is impossible for so many cylinders to fail at the same time, and the control signal and feedback signal of the ELFI proportional valve have not been found like the electrical noise condition. Therefore, the possibility of ELFI proportional valve failure and MPC failure is excluded.

为保护先导阀，从2021年开始ELFI/FIVA升级加装了内置滤器。因此，ELFI滤器被最终定位，并逐一拆洗。ELFI滤器清洗后，PMI性能及HCU Event曲线也都恢复正常。如下图所示：

To protect the pilot valve, ELFI/FIVA has been upgraded with a built-in filter from 2021. Therefore, the ELFI filter is finally positioned and removed for cleaning one by one. After ELFI filter cleaning, PMI performance and HCU Event curve also returned to normal. As shown in the picture below: