I'm not getting much help on this so I guess I will post here. Two newish gensets, each with a Lombardini (Kohler) 3.4 engine. Both have intermittent failure to start, always after sitting one day or more. I have never witnessed it, they always work when I am on site. I did see a bad video of it once, it appears to start and then stumble low RPM for a while before the controller is not happy and shuts down. They use a 2 cylinder Denso HPCR pump connected direct to the tank with no lift pump. Through official channels it was suggested to check dip tubes, hose connections, etc. I did all this and installed a clear hose from tank to filter. Also resealed all pipe fittings with utmost care. After I did this I noted that with a completely empty dip tube and clear hose section about 2 feet long it will start and run and suck down all that air and keep running and never stumble, there must be a good reservoir of fuel inside the pump and a good return to tank. Last thing I did at their request was install a 1 psi check valve at tank return fitting to be absolutely sure fuel system remains full but the return was also through a dip tube well sealed so I doubt any air was getting in that way either. I am starting to lean toward a flaky HPCR pump but that is an expensive fix for an unknown problem. No codes logged in the engine ECM either. I watched it with a laptop for things like rail pressure and nothing out of ordinary. Will start cold and accept a full load with no problems.
How about a clear line on the return side? I don't know Lombardini/Kohler too well, but on the Deere engines I have experienced air ingestion through the injectors themselves as well as through the injector sealing washers leading to either power issues or hard start issues. The clear line on the pickup you mentioned will not show engine sourced air ingestion. Also, is there a fuel filter with a clear fuel bowl that could have a missing seal?
Good suggestion. But how would air/compression in the return tubing lead to any kind of effect on the high pressure side? How would the air get to someplace where it could cause problems?
I have seen air ingestion via compression/combustion through a nozzle tip several times. Then that air works its way to the return circuit.
Maybe a clicky clack lift pump? Force feed that sucker.
I did read in a service manual that was sometimes an option, this is the first HPCR I saw that had no lift pump of any kind. Still since I pulled the pickup tube and installed the clear hose and started the engine it started right up and devoured all the air in over 3 feet of line without missing a beat, so I am starting to suspect "losing prime" may not be the right way to describe what is going on here.
Maybe you have a shutoff solenoid that's possessed by satan? Or Will Farrell maybe?
HPCR do not have shutoff solenoids, they have suction control valves that are open by default and closed by the computer to limit rail pressure, if they fail the pump goes full stroke and can damage all kinds of stuff. Another great feature of this modern technology.