I've got a 93 Cummins that surges when I start it. I know its supposed to do this when its cold out, but its 55 here. Anyways it goes like this: When I start the truck and turn the lights on the volts crank up and then there is an audible "click", at which point the lights dim and the voltmeter goes back down to say 8. It does this a few times and eventually stops surging but the voltmeter is pinned up at 14. Any suggestions? I have had a external voltage regulator put in a few years back because the truck was doing the same thing. Could it be a faulty voltage reg? Thanks fellas.

 

I think it's the grid heaters cycling.

 

how long will it cycle like that? I haven't driven longer than five minutes into work and back, so I don't know if it will stay up around 14, or should it cycle back down?

 

might want to check the temp sensor.. water temp i think triggers it? but a faulty temp sensor would let them cycle, and will keep cycling till that sensor reads a "warmed up" temp.

 

There is a separate temperature sensor for it in the intake manifold. Your grid heaters should not be coming on at 55° so the sensor is probably bad. The temperature threshold starts a timer in the PCM that cycles the grid heaters in decreasing intervals.

 

The grid heater will cycle if its below 60 degrees outside until the truck warms up.

 

Im having the same problem with my truck
volt meter goes to 18v and it pins and the lights in the truck get super bright, sometimes like that for 5 10 15 min. Measured the volts at the batt when it happen, 17.6 ish volts to the batt.
If the grid heaters are not hooked up will it still cycle or can i unplug this temp sensor and see if it stops?

 

It's the voltage Regulator is what I think but while your driving does it stay up high like 14, 16 or so? If you don't find the problem quit it might kill your battery.