89 first gen have no post-heat

[rollinblock55]

Does anyone no why i have a preheat but no post heat on my 1989 first gen dodge. the solenoids work on the preheat but will not cycle on and off for the post heat when running while the temp. is around 35 degrees outside

any help on this matter would be great thanks

 

[Missouri Mule]

Has it been running more than 3 1/2 minutes?

Post heat shuts down after 3 1/2 minutes.

Have you gone over 10 mph?

Post heat will shut down when truck goes over 10 mph.

This info was from 96 service manual 89's could be different.



PCM (computer) controls intake heater.

If you have pre-heat your intake manifold temp sensor is probably working.

 

[RMcGuffey]

The '89 & '90's don't have pcm. Mine has the same problem. There is a module that controls the heaters, but it really expensive, especially from dodge, but what isn't. I've been trying to find out what the problem is before I go that way. I think they require a certain voltage to run. My battery is about 7 years old, and it is due for replacement soon. If this fixes it I'll let you know.