Engine/Transmission (1994 - 1998) Excessive grid heater cycling?

[JGheen]

Last night while in the drive through I was getting a quick bite to eat and I usually shut the engine down so the drive thru person can hear me correctly. Well, it was somewhat cold, probably in the high 50s or so and when I turned the truck back on waiting for my food at the window, I noticed that my grid heater seemed to be cycling quite a bit more than normal. Usually when the engine is warmed up and been running it never really does that, but could I be looking at ny potential problems with this? I am very sure it was the grid heaters cuz I was not running any air or heat in the truck(had a pretty heavy jacket on) and the volt meter would drop below 14 volts when it happened and the head lights would dim out some. The alternator is acutally pretty new as my stock one went out at about 150,000 miles and I got a remaned Denso from Napa in there right now.

Please, let me know if this is normal or if I should look into it before my Xmas vacation trip tomorrow, TIA.



Joe

 

[biggy238]

Since you have a manual transmission I don't forsee any major problems. I do think it's strange for it to be cycling though if you had driven the truck a while.



Mine has only been cycling below 40* here lately, and about every 15-20 seconds until it heats appropriately.



Last year It would suck just enough juice for ther heater to kill the solenoids in my transmission. I'd be running 55-60mph and the truck would hit hydrualic 2nd gear. I thought the truck was gonna blow from overtaching when it did that.



Oh yeah, my new Napa-Denso keeps the truck at about 13 volts with the heaters on and everything else running. The solenoids need 12-13volts to hold a gear if they are old. (If anyone with an auto reads this thread)

 

[CNichols]

Last year It would suck just enough juice for ther heater to kill the solenoids in my transmission. I'd be running 55-60mph and the truck would hit hydrualic 2nd gear. I thought the truck was gonna blow from overtaching when it did that.

Thats odd... your grid heaters should stop cycling once you hit 20mph... you might have another problem. In my truck you can watch the volt meter go up as soon as the truck sees 20mph. And never come on again after that speed... then they will come back on once i slow to under 20 if the truck is still not to a decent temp.

 

[JGheen]

Man, everyday I feel better and better that I chose the manual transmission over the auto for things like this.

But as for the cycling, it's like the intercooler is really cooling the heck out of the intake air or the manifold temp sensor is bad and not reading right and causing the cycling. Isn't the heater supposed to stop cycling once the intake temp reaches 90*F or something like that?

I did notice once I got driving again the cycling seemed to stop, but it's just weird that it would go through the motions when the engine is nice and hot. Even after a quick shut down the thing should heat soak and when I start it back up the heaters cycled intially but when idling last night they just seemed to keep coming on.

 

[Cooker]

Even if the engine it warm my heaters have always cycled after a start in the cold winter months. I thought at shutdown the turbo moves some cold air in the charge air system and if the air is cold enough that it will fire the heaters again up on startup. I am always assumed this to be normal. The heaters will stop when the truck reaches something like 18MPH or the air intake temp exceeds 59 degrees.

 

[biggy238]

I had a battery cable and some solenoids doing their own thing to cause the problems I was having. If the power system isn't up to par though, the grid heaters won't run correctly. They'll run for prolonged periods of time.

 

[MontyDyer]

A bad intake temp sensor will also cause the grid heater to stay on when it shouldnt. The sensor is what sends the signal out to the relays to fire the grid heater. If you have a failing sensor, it can actually burn up your grid heaters.



I had a faulty intake sensor and the grid heaters would stay in post cycle running down the road in hot weather.

 

[Tomahawk]

My heaters have been cycling even when the air temp is 50 to 60 degrees. I'v been trying to come up with a way to put a manual switch in to turn them off if I feel it is warm enough. Any suggestions?

 

[dodge cummins]

i noticed my voltmeter after it cycles it stays kinda high about a quarter above the middle line. its still in the white though

 

[CarlJensen]

Grid heaters come on when manifold temp is 59 or lower. Should stop cycling at 10-12 mph. Put a switch in the trigger lines to heater relays to lock them out. Relays look like old Ford starter solenoids on drivers side fender well below battery.

 

[Kirwin]

Truck changes over the years

Not all PCMs use the same speed setpoint to turn off the grid heaters. There have been several revisions to the software program that is used to control grid heater system. I think that 97 and later second generation trucks had the 20 MPH limit to grid heater operation. The temperature set point also changed from first to second generation trucks. As long as the truck is running the grid heaters can cycle for up to 3 minutes after start up based on the sensed intake manifold temperature. Ken Irwin

 

[GAmes]

My heaters have been cycling even when the air temp is 50 to 60 degrees. I'v been trying to come up with a way to put a manual switch in to turn them off if I feel it is warm enough. Any suggestions?

To keep the heaters from cycling when the engine is running I installed an oil pressure switch in the unused hole on top of the oil filter. I disconnected the ground leads from the heater relays and ran a new ground wire to the switch. Now the grid heaters cycle when I first turn on the ignition switch, because with no oil pressure the ground is complete thru the pressure switch. Once the engine has started and there is oil pressure the switch opens and the heater grids won't activate.

 

[Cooker]

I like that idea. Man, I really don't need any other projects

 

[GAmes]

I wish I could take credit for it, but I can't. Got it from the TDR last year.

 

[Tomahawk]

Thanks GAmes, I'll have to give this a try. Sounds like a easy fix.

 

[JGheen]

I guess I'll check the intake temp sensor and see how it looks and functions. I bet they are a pretty penny from the stealership!

 

[Jim Fulmer]

I might have a little clarification here. The grid heaters will do there cycle till it warms up a bit or you drive off and get to the right speed(whatever that is) then the PCM will turn them off, if you stop and/or shut it off you reset the PCM's brain and all it knows it the temp it's getting, if the temp is below 59F then the grid heaters will go through a cycle again. On the IAT sensor issue I had a bad one that was making the grids turn on for just a sec then off, I would see a blink of the lights even at highway speed, not a cycle but a blink, cleaned the sensor off and it fixed it.



Jim

 

[BPonci]

You can wire them to a toggle in the cab. There hard on batteries if your not driving far.