LMV Pressure Low on Cummins QSC

[jff]

I changed the Racor fuel filters this morning on both engines and did my usual 'priming' by turning on and off the ignitions a few times (waiting for the noise to stop). Then I started up the boat and took the boat out. I started to go on plane, I noticed a lack of power and seconds later got a System Alarm on my SmartCraft. The alarm said "LMV Pressure Low" on Port engine. I throttled back to idle and went through each of the displays on the Smart Craft, both engines looked about the same except on "Gear Pressure", the Starboard was 60 psi and the Port was like 350 psi. So I anchored the boat nearby and went through the priming process again, hitting the port ignition half way and waiting for the buzzing to stop. Did that about 5-10 times. When I restarted I *think* the problem has been corrected but I'm not sure, will know for sure in the morning when we try and run home. Curious if anyone knows exactly what "LMV Pressure Low" means exactly and can confirm it was most likely from air in the system post racor fuel filter change (and not some other problem entirely)?

Thanks,
Jason

 

[fwebster]

I think your problem may be in how you primed the Racors.

The Racor canister has to be primed by manually re-filling the filter body from a container of fuel. THe inlet and outlet are at the same elevation on the filter body, so unless you re-fill the filter by hand, the top half of the Racor is full of air. It cannot refill itself with the Cummins prime method. Once you add power to the engines, the demand for fuel uses all the fuel above the outlet in the Racor and you ingest some air. Slow down and it runs ok. To test this, open the racor and try to refill it.......it it takes more than a tablespoon or 2 to make it over flow, then it was not primed.

 

[jff]

Thank you for the information Frank. I had thought that priming would remove the air (sounds like that's not the case). I did add some fuel but nowhere near all the way back up to the top (once you put the new filter in it's tough to get fuel in there, I'll try pushing down on the filter and adding). In the morning I'll go open up the port engine racors and add some diesel although I'm afraid I don't have near enough diesel to do the job - maybe I'll just try and get one full and run back to the dock on that one instead of both. Anyway, thanks for the insight/info.

Regards,
Jason

 

[jff]

Update- so I opened the Racors backed up, filled them alllll the way to the top with diesel, re-primed via the ignition switches 3-4 times, started up the engines .... same problem. Port engine showing Gear Pressure of 350 psi (STBD showin 60 psi) at idle. If I throttle up at all the PSI goes up. I know it is not just a bad reading because yesterday when I went up on plane I had about 60% of the expected/normal power and second later the System Alarm went off. 350 psi is still within the guage without alarming so I am thinking (hoping) it is fine to idle around but unless anyone has any ideas (I'm out) I guess it is time to have Cummins come out and see if they can figure it out. In summary, what exactly does it mean if 'Gear Pressure' is way too high? And what exactly can be done to fix it? Any ideas?

Thanks,
Jason

 

[fwebster]

I don't have Cummins engines, but the QSC has a limp home mode that is triggered when you get an out of tolerance indication on one of the engine sensors. All I can think of at this point is that you have one of those sensors telling the ECM to put the engine in limp mode.

Unfortunately, this is most likely going to require a Cummins guy and a laptop to diagnose.