yep 15.9 is a bit high
max should be 14.8 :o)

glad it straightened it out
good deal

Thanks guys. Rechecked charging system. This time it was doing 15.96vdc. R&R the alternator has been good now for a couple days. Once again thanks for the input.

The charging system should be putting out 13.8-14.0. Tighten your drive belt and recheck. If not then for grins and giggles, replace battery temporarily and recheck output. A dead or shorted cell can cause this issue.

Thanks Swoop. I cleaned the throttle body & fuel controls. I then test drove it for about 30 mins with no more failure. I didnt get a call from the customer today. But i did test the charging system it was @ 13.26 vdc.

the cat trucks had this same problem and it had to do with the alternator overcharging, they released a service bulletin explaining on how to check the system for this condition and repair it.

The over voltage condition was causing the ecm to over compensate the over voltage condition causing it to fluctuate the fuel controls which made the engine surge.

They said it was either caused by bad grounds on the system (engine) to chassis frame or a bad alternator regulator which ultimately led to replacing the alternator.

You may want to consider this truck might be suffering from the same problem being it is basically the same nissan system in it most likely.