Switched grid heater modules

[bgilbert]

Thanks to Alan- Paychk for all the technical info over the years. He's mentioned the grid heater module on the firewall driverside is what controls the grid heaters... at least on early non-intercooled trucks. Mine being an early 89, my grids don't preheat til 15*F as apposed to I believe 50*F for later grid heater modules/trucks. 15*F is fine if you don't have a bunch of fuel putting out your fire on startup early mornings and don't have a bunch of timing. Three previous winters I never had a problem with starting at temps just above 15*, which the grids would not preheat. Temps say between 18* to 30* the truck would fire instantly but not want to keep running. After a second try it may catch and hold on, but rump/romp romp, idle rough for a few seconds. If its cold enough to preheat, I'd get an instant start, sweet idle/ no white smoke almost like its 50* out.

So since I've had various parts from a 90 model Dodge Cummins laying around, I finally swapped out grid heat modules. Temp was 33*f out, normally I'd never see 'wait to start' - preheat at that temp, but after switching them out, I seen the WTS light come on as it should below 50*.

I'm not sure what the part number cut off is for early modules off hand, its in the search feature and in one of my Cummins manuals. The pn on the 89 module was something like 30,xxx. The 90 module was something like 110,xxx. The part number is found on the rear/firewall side of the module.