GENSET ONAN CUMMINS cannot restart after fuel filter and oil change

Songhui Ma


I have tried the following to no avail: 

- prime up to 5 min

- unmount the new filter - no air;  full of diesel fuel

- open the pipes going to the injectors, then crank; no fuel appears [?!] but the injectors seem full of fuel

Oil and coolant are at appropriate level. 

Fuel Pump. I checked and the pump is receiving 12V during priming. 

However I am not hearing it but the fuel filter was fuller than when we mounted it, so I infer it is working.

The fuel tank level is above 250 liters, So it should not be the security that disconnect the genset and give priority to the main engine. 


This genset is from 2012, has 720 hours and has been maintained. 

The reference is 7MDKBL-5871F 

Any idea or suggestion will be greatly appreciated. 

Many thanks in advance 

Dominique Guenot 

+1 917 826 0945 

S/V Viva Currently in Hiva Oa, Marquesas, French Polynesia

amelliahona <no_reply@...>


I just replaced my electric priming pump on my SM #335 Onan Genset.  I did not have access at the time to a proper FLARE NUT WRENCH when I did this.  I ended up distorting the "B-nut" on the small copper fuel line that goes from the fuel pump to the fuel filter adapter and could NOT get a proper seal upon replacing this line (a continuous small seep of fuel that was really annoying and messy).   I had to order a replacement line (not that expensive) and buy a proper set of flare nut wrenches to adequately get a seal.   I wish I could remember the size of the flare nut but it was SAE (not metric) sized.    Make sure the fuel tank is low on fuel (think 250 liter will work) otherwise a continuous stream of fuel will flow by syphon from the fuel tank fuel return line while you make this plumbing change.  I managed to turn this otherwise simple replacement into a major project based on A) not using the proper tools to loosen and re-install the B-nut of the fuel line, B) not have lowered the fuel in the tank (mine was full at the time of my work).  

Good luck.  The pump was about $65 as I recall (not that expensive in the scheme of things) and the fuel line was about $8


Gary S. Silver
s/v Liahona
Amel SM #335    Puerto Rico