I just bought a 2003 Dodge and the manifold heater was not working. Took in to the Dodge dealer and the mechanic changed out the EMC and the FMC boards. Said it worked. I live in Alaska and it is cold here. I let it sit outside at 0F temperature, plugged it in for 1.5 hrs. The heater relays did clunk when I turned it on so that was good, but it only stayed on for about 12 sec. I cranked on the engine for a about 15 sec and then stopped. I tried it again and the same thing and it did not start. I asked two friends that have trucks w/ the 5.9 and their heaters stay on for at least 25-30 sec.

I went in and talked w/ the mechanic and he told me I was incorrect and it was probably the injectors. I have found some info on how long the heater should stay on, but not for the '03 model. Does anyone know where I can find info on this so I can show him what I am talking about.

 

It should have still started. I think there is something else going on.

I don't have a grid heater at all and I am decompressed and I still started in below 0 weather without a plug in. Granted it was a tad slow and took a few seconds for the white smoke to clear... but it did start.

 

Bill, how long the grid heater stays on and cycles is a function of ambient air temps, engine temp rather than a set amount of time.
As a general rule, the colder the ambient air temps the longer they will cycle
How long is determined by how quickly the engine builds heat and the sensors shut them off
I think you have another issue, fuel gelling, bad lift pump, injector, that is causing your no-start
If it will start when it's not as cold,I'd look to your fuel or lift pump first
These trucks will usually start without the grid heater at all if all else is good