Wednesday, October 20, 2010

The Downside of Electronic Engine Controls

Failed Main Engine wiring harness SIM module connector

Last week we decided to go to Victoria, BC for a few days since the Fall weather has been so nice. Joe and Sarah Dreussi were going to go with us and had placed Gracie, their black lab, into doggie playschool for a few days. We had most of the lines off, the shore power disconnected and went to start the engine.


No lights, no displays on the Smartcraft gauges – NOTHING.

Patrick checked all the fuses and breakers, everything looked normal, so we called Cummins Northwest and they suggested we contact North Harbor Diesel who sent down a technician the next morning. In the process of checking connectors he detected an electrical burning smell and pulled a connector off the SIM module, which promptly burst into open flame when the watertight seal was broken and oxygen reached the overheated and shorted connector.

At that point Patrick rapidly pulled the fuses rather than have the technician cut the wire and the flame could be put out. In the process of removing the main harness, a leaking coolant level sensor was discovered. Apparently the slow leak, under pressure when the engine was operating, forced conductive coolant up the inside of the wiring harness, through watertight connectors and eventually reached a connector which shorted, overheated and failed. Many of the connectors on this harness were wet with coolant. There were no indications of leaks on the outside of the harness!

A new harness was ordered, as well as a new coolant sensor, new SIM module and the ECM, which showed corrosion on some of the connector pins was sent to Cummins Northwest for checkout.

In the process of reinstalling the new harness we also discovered that 24VDC power may be present at the engine even with the engine battery switches off, if the Blue Seas ACR's (automatic charging relays) are in the "AUTO" position and the battery chargers are on, or in the "ON" position at any time. Apparently the battery safety switch (to remove power from the engine room in the event of fire) is only between the batteries in the engine room, so the ACR's provide an alternate path between the house and thruster battery banks and the engine starter, which actually makes sense from an ability to cross connect the battery banks to start the engine in the event of an engine starting battery problem. This fact also implies that the "echo charge" connection from the chargers to the engine starting batteries is redundant when the ACR's are in the "Auto" position. Just another addition to the manuals!

The ECM uninterruptible power from the engine battery has a similar issue. The only way to remove power is to go into the engine room and open the battery box and pull a fuse. We have asked Cummins for permission to install an emergency shutdown switch outside the engine room for use in the event of a fire.

Today, Wednesday, October 20 we hope to have a test run and then take Spirit to Seattle in the morning. We expect Spirit to be in the yard for approximately one month.