04-12-2012 03:03 PM
I have a 3126B in a truck that starts fine in the morning. You crank it a few moments and it fires right up. If you try and start the vehicle again the vehicle cranks but the starter cuts out. The starter is fine. When you jump it cranks. The auxiliary start solenoid is fine. The start button is fine.
I dont know about other CAT 3126B applications but this one uses oil pressure to provide a ground for the start switch. Once the oil pressure switch is actuated the start button will not work and the alternator is excited. A ground is broken when the oil pressure switch activiates. It is normally closed.
When we unplug the oil pressure switch and jump the harness (providing ground) the truck will crank and start all day long.
We suspect that oil pressure has something to do with it but at this point we dont know what to look for. We have 55 PSI at Idle. We have tried a new 6PSI switch which is what is called for. We have 3116s in our fleet that call for a 12PSI switch which we tried but we still get the same result.
Any advice would be appreciated.