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97 Ram 3500 with Cummins 5.9L diesel. Voltmeter jumping around, seems like intake air heater is cycling even when the truck is warmed up. Anyone else have this problem? Is there a relay that controls it? Thanks for any help you can provide.
J.D.
 

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I think on a `97 the PCM should be getting an air temp. signal and controling the grid heat cycle. How cold has the weather been? Do they ever go off and stay off?
 

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Flake said:
I think on a `97 the PCM should be getting an air temp. signal and controling the grid heat cycle. How cold has the weather been? Do they ever go off and stay off?
The weather here has been cold, but basically normal for this time of year. The voltmeter charges and then discharges almost constantly while traveling down the road.
 

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Try blocking off most of the air going thru the rad. The truck might not be getting warm enough to cycle off the grid heaters. Be careful not to block off all the air to the tranny cooler if it's an auto though, you might have to get a winter front for the truck to get the engine to warm up in the winter. P.S. please fill out the location and signature so we can tell where you are and what you drive. Thanks Dave.
 

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I'm no diesel spert and I don't have a 97 manual but here is some theory from a 93 manual...maybe it will help?

Description and Operation
These relays are controlled by the PCM. Their purpose is to ENERGIZE the air intake heaters so that they can warm the incoming air as it enters the intake manifold. The air intake heaters can be ENERGIZED before and/or after engine cranking, depending upon the intake manifold air temperature. The PCM receives a signal from the charge air temperature sensor that indicates the air intake temperature. If the air intake temperature is at or below 59°F (15°C) the PCM will start the air intake preheat or post-heat cycle.

PREHEAT CYCLE

The air intake preheat cycle will start if the following conditions exist:
The ignition switch in in the ON position.
The PCM has not received a crank signal.
The air intake temperature is at or below 59°F (15°C).
If the preheat cycle is started, the PCM will illuminate the Wait-To-Start lamp. Once the preheat cycle has finished, the Wait-To-Start lamp will go out, and the engine can be started.

If the PCM receives an engine crank signal while the preheat cycle is running, the air intake relays will be DE-ENERGIZED causing the preheat cycle to be aborted.

POST-HEAT CYCLE

The air intake post-heat cycle will begin if the following conditions exist:
The engine has been started and is running.
The air intake temperature is at or below 59°F (15°C) when the ignition switch was turned ON.
The intake air heaters have two different modes of operation depending upon the intake manifold air temperature, either both heaters are ENERGIZED or they are cycled ON and OFF individually (while one is ENERGIZED the other is not and vice versa). The amount of time that the air intake heaters remain ENERGIZED depends upon the intake manifold air temperature.

Testing and Inspection
Discussion
The PCM provides a ground path for the air intake heater relays. When the intake manifold temperature is below 16°C (60 °F), the ignition is in the ON position, the controller grounds the relays, allowing the intake heaters to engage and start the preheat cycle. If the temperature is above 16°(60°F), the wait to start lamp will not come on and the heaters will not be energized.

Caution: Do not energize the air intake heater relays more than once per 15 minutes. If the relays are cycled, the key turned OFF and then turned back ON, the engine could be damaged. Wait 15 minutes before turning the key back to the ON position.

With the engine off, and ambient air temperature below 16°C (60 °F), turn the ignition key to the ON position.
The Wait-To-Start Lamp will come on and the air intake heater relays should click on signaling the start of the preheat cycle.
Check for battery voltage at both air intake heater terminals. Note: The heaters will only be energized for 10 to 20 seconds, and must not be recycled for at least 15 minutes, so the voltage check must be done quickly.
 
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