Engine speed sensor functions?

[Archive]

Other than the tach, what function does the engine speed sensor perform in a 5 speed truck? Today I talked to a guy at Cummins Rocky Mountain who thinks this is the culprit that's causing my performance problem. (see: "signs of pump failure" thread)

Wouldn't my tach not work if this sensor had failed? Does the engine speed sensor have anything to do with pump timing advance under acceleration or is it purely mechanical?

I'm beginning to think it might be the KSB solenoid that is to blame. Maybe its not closing and allowing the pump pressure to rise? What do you all think?

Please help! I need to exorcise these demons from my truck! #ad
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Rob

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93 W250 LE, CC, 4x4, 5spd, 4. 10's, exhaust brake(tailgaters nightmare), turned up pump, boost/pyro guages, lund moon visor, weatherguard tool box.

 

[Archive]

The sensor only operates the tach, as far as your performance questions go.

The KSB raises the pump's pressures above normal, while it's in the cold start mode. If it doesn't work on your truck, the only thing it does is fail to cut the blue smoke during warmup.

 

[Archive]

One other thing the speed sensor indirectly does by its speed signal to the PCM is to enable the generator field circuit to be energized. When engine RPM is 384 or higher the PCM closes the Auto Shut Down relay. This electrically connects the generator field to the (+) side of the battery, then regulation of generator field current is acoomplished by the PCM intermittently grounding the other side of the field circuit. The generator output regulator (voltage regulator) is threfore in the PCM on '92 and '93 trucks. So if the sensor fails your battery will eventually go dead. A low voltage reading would be present with a failed speed sensor. A bad speed sensor should set off the check engine light.