Engine/Transmission (1994 - 1998) Grid heaters cycling?

[WMonroe]

Last night when I went to start my truck I waited for the wait to start light to go out (in the low 40's outside) but it didn't appear the the heaters were cycling ( I was watching the amp meter). The truck started fine but while I was giving it a moment to warm up I saw the headlights dim slightly and the amp meter was dropping and the going back to normal. It did this several times and didn't stop till I drove away. Was this the heaters cycling on and off or do I have a problem with my alternator?

Will

 

[Cooker]

When the air intake temp sensor reads below 59 degrees, the gride heaters will cycle unitl the intake air is over 59 degrees or you start driving and reach a speed over 18 MPH.



The fact that the heaters didn't stay on during the pre-start was probably due the the retained heat left within the engine compartment if the truck had not been sitting a very long time.

 

[y-knot]

The last poster was correct about the grid heaters cycling at less then 59 degrees. Above that there is no cycling, or heating. What the pcm (power control module) does thou is look and ask what is my temp reading. If less then 59, it gives you the wait to start lite, and at the same to signals the grid heaters to start. If the temp is above 15 degrees, it will cycle for 10 sec, 0-15 degrees 15 sec, below 0 30 sec. Then the wait to start lite goes out, and you start the truck, the grid heaters should not be on. They will be turned off by the pcm, to allow full battery charge to start engine. After the start, the pcm goes into post heat cycle, two conditions have to be meet here. One,the intake air temp has to be 59 degrees or lower, and the engine rpm has to be 475 or higher. the pcm will continue to cycle the heaters till the intake temp is more then 59 degrees, till the truck exceeds 10 mph, or till the engine is turned off. There is also a fuel heater that comes on when the fuel is below40 degrees. All of these will show-up on the volt Gage, when on they have quiet a large amp draw.

 

[WMonroe]

Thanks for the replies everyone. That answers my question.

Will

 

[illflem]

If what you mean by cycling is the grids turning off and on your truck is normal.

They come on and stay on till you start the truck then only cycle off and on after it's running. The temp inside the intake manifold determines how long they will be on before starting. The same temp after starting determines the length of each cycle and how long it will continue cycling.

The fuel heater doesn't draw enough to show much on the gauge and doesn't turn off till the fuel is 80°, it might be aways down the road till you see any movement.

 

[Cooker]

illflem,

That is a new one for me on the fuel heater. I always assumed it cycled like the grids, but then that would not do any good would it

 

[SEmerson]

What temp does the fuel heater come on?

 

[illflem]

The fuel heater has an internal thermostat that turns on at 40°, off at 80°.

Even at 32° very small wax particles are starting to form in #2 diesel, the beginning of phase of gelling. Without the heater your filter can plug rapidly.

 

[JJW_ND]

Regarding fuel temps....

I can not speak for the 24V but our 12V return alot of fuel. Very warm fuel. Such that once under what and driving the change of gelling will most likely not occur (in the lower 48). I have driven many 1000s of miles starting out in single digit temps, fill up with straight #2 (do not add any additive) and drive 500+ miles through temps down to or below -30 with no drivability problems. Park your truck in these cold temps for a day or more and you will have problems. But once running the combination of the fuel heater and the maintaining the fuel temps really helps.



Also, if you have a choice, underground fuel tanks (truck stops) will have somewhat "warmer" fuel at the time of fueling that will be fine to continue driving with.



jjw

ND

 

[Cooker]

Here is a little bit of info I thought was interesting. The fuel heater draws 300 watts. No wonder they are notorious for melting the plastic plugs on them.

 

[R.ebel]

Fuel Heater

The fuel heater on my truck burnt up the connection at the wire loom and then started to leak fuel where the wires exit the heater According to my OHM meter, the heater element had shorted to the housing probably causing the excessive current draw that melted the connector. I replaced the heater to stop the fuel/air leak but elected to not reconnect it to the wire loom. I'd rather just run an additive during the cold weather than worry about a possible electrical fire.