High fuel differential pressure Cat 3512b 1

[axmans]

I am an engineer on a private motoryacht with 3512b's. Yesterday while underway, the ecu alarmed because of High differential fuel pressure. Alarm is set at 15psi, and the value went as high as 30psi, but was oscillating. when the captain increased rpm's to 1200, the pressure returned to normal values. I changed the primary filters upon arrival in Port, and the pressure starts out at 10psi(should be 3psi) and starts gradually climbing. I have checked that the return lines are clear, so I am guessing it must be the sensor. Does anyone know how to test the fuel differential sensors? any input would be appreciated.

 

[MikeHalloran]

To my untrained ear, it sounds like you got a load of water and dirt with a little fuel in it.

What did you find in the filters you removed?
Even if you never had to before, you need to start cutting open old filters and keeping records of what you find, including photographs.

Got a pair of Racors and a pump so you can polish what's in the tank?
Run 'em or get 'em.

As for checking the DP gage, temporarily plumb in a couple of ordinary pressure gages, one upstream, one downstream, and just subtract the readings. My bet is they'll verify the DP gage is ok.


Mike Halloran
Pembroke Pines, FL, USA

 

[axmans]

Thanks Mike,
All the fuel goes through an Alfa Laval system before it then travels through 4 Racor 20micron's, after that it goes through 5 Primary Cat filters....nothing of note in the filters that i removed, that's why I think it is the sensor...

 

[catserveng]

When you said you changed the "primary" filters did you really mean the CAT engine mounted filters? These are normally referred to as the secondary filters and your Racors would be considered the primary filters.

The only real way to service the engine mounted fuel pressure sensors is with the CAT computer based service tool, called CAT ET. Frankly if you're on a yacht that travels around quite a bit having a customer version of ET would be in your best interest.

With ET connected you would go to the status menu and with the engine stopped first observe the inlet and outlet fuel pressures, since these are absolute pressure sensors with the engine stopped they should both read about 14.6 PSI. If not, there is a calibration procedure that can be accomplished by using the service menu in ET, requires the engine not running and the atmospheric sensor to be working correctly.

Your other option is to remove both sensors, and connect up a known pressure source, like a calibration hand pump, and observe the readings on the electronic gauge panel (if installed).

There was a known issue with fuel pressure sensors and ECM flash files a few years ago, you may want to check with your CAT dealer to see if your engines fall into the serial number ranges affected.

Something else you may need to know, depending on the age of your engines, they have been originally fitted with 10 micron secondary fuel filters. The old part number now changes to to 2 micron filter that has become the currect CAT standard for electronic unit injected engines. I've had quite a few customers over the past two years complaining of poor secondary fuel filter life, not realizing the filter element has changed. Recently ran into this on a research vessel that had a large stock of older filters they finally got thru, and started seeing shortened life after changing to the new part number.

Personally I think a motor yacht that can afford an engineer ought to have the primary service tool for the main engines on board. Your local CAT dealer can set you up with a customer version of ET, does everything the dealer version does except functions that require a factory password, like a power rerate.

Hope that helps,

Mike L.

 

[axmans]

Hey Mike,
Thanks for your great input....and yes, I am calling the Cat filters the primary filters because that is what most manufacturers call the Filters when looking up the parts in the manuals....but the first filters are the Racors. Not sure what the microns are of the Cat filters, but they are 1R-0765 stock Cat filter. They didn't seem to have been obstructed, and my return line were good, so that is why I was suspicious of the sensors. I will check into tool you mentioned, i think it would be helpful for times like these.
After another 4 hours cruising, i didn't have any alarm condition, but the baseline diff pressure was high for new filters(10 psi). It has since gone back to normal operating perameters of 2-3 psi. I will call Cat tomorrow about the ECM...the engines were fitted in 2010, and are still under warranty.
Thanks for your time and valuable input.
Axel