Tuesday, July 9, 2013

Cummins Crank Speed Sensor

I’ve been spending far too much time debugging. I was hoping to have the truck on the road by this point but there were a few things I didn’t quite get right. One that took a surprising amount of time to correct was that I wired the KSB (Cold Start Advance Solenoid) to the same switch as the intake heater relays. I figured that I would only need the KSB when it was cold and therefore I would be using the intake air heaters too. Well the engine doesn’t like to start even in my 95 degree shop without the KSB so I had to rewire it to another switch. The other mistake I made with the same feature was that I wired the supply voltage to the switch off the 12v supply to the dash panel. When you turn the ignition key to crank it, cuts the power to the dash panel, so having features needed for starting wired to a power supply that cuts out during starting is one of my lesser achievements. Got that sorted and now she starts easily. Even on B100. The other bug I spent the last 6 hours chasing was that the new electronic tach read 0 when the engine was running. I found a number of problems, but cut to the chase, I think the crank sensor is bad. I had miss wired it and didn’t include the current limiting resister that it needs and running it at 12v instead of the 8v used by the factory dodge ECU may have well damaged it. Two oscilloscopes and a multi meter later I can get no signal from it. Instead of buying a new OEM replacement I happen to have a Cherry 3 wire Hall Effect toothed gear speed sensor (GS100502)that should work fine. With a 2.2K pickup resistor soldered between Vcc (+12v) and the black signal lead I get signal on the scope right in the voltage range the tach should trigger on. I bracket made from some precision 1-1/2” angle iron and I should be at least back where I started. That, I leave for next time.

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