Wait to start. Where does the signal come from?

[RSchwarzli]

Where does the signal come from for the grid heater and wait to start light?



I gather it must come from the coolant temp sensor or the air intake temp sensor.



I ask as I am replacing both of those with aftermarket gauges and want to make sure I am not shooting myself in the foot by doing this..... :-laf



Thanks!



Robert

 

[Greenleaf]

OK. You did not specify what truck. I see you have two of them. It is different between the early and late FIRST gen trucks.



Another thing; you are going to replace the intake manifold temp senor with a gauge????



I'm sure if you PM Joe Donnelly, the TDR writer, he would know.

 

[RSchwarzli]

OK. Now you sparked my curiosity.



How does it work on the early trucks, the IC trucks, (and for the hell of it) the 2nd gen 12V's?



Robert

 

[PToombs]

I know on my 92 there is a sensor on the intake plate behind the air horn. 2 of them actually. 1 is the KSB, the other is the grids control. The sensor feeds the PCM the signal, which controls the grids.

I didn't realize the early ones are different, must be because of no PCM?

 

[Greenleaf]

No pcm, though some refer to the controller of the grid heater(s) as the PCM which it is, but isn't.



These trucks to have a sensor. It has been so long since I have removed all this useless stuff from both my trucks, I simply cannot recall where the sensor(s) were located. I believe Pete be correct. They both were there in the intake cover (near the rear of the head). They also have a KSB sensor and and between the two trucks (early/late 1st Gen) this can become complicated. You removing the KSB also?



It would be really cool to have an intake temp sensor. Not to mention an exhaust pressure gauge. Seldom done, but that would be useful information even if you are not developing a custom intake system or compound turbos.

 

[RSchwarzli]

What is KSB?



As for intake, yes I will have an Autometer intake temp and a backpressure guage.



As for the sensor, I have one on the top of my intake as well. That was replaced with the autometer probe already, but then I realized while attempting to re-wire the 1st gen harness to the 97 motor that something was feeding the grid heater. That is where all of this started.



If I can, I would eliminate the factory probe as it is useless other than the grid heater. Simplification is good! The truck will not ever see snow again, so I am not that worried from that end. As it is the pre heater on the lift pump (97 Motor) will not be wired in, but as for the grid may want to have that for colder fall mornings.



Wonder if the Autometer probe will work with the 93 Grid Heater Controller (PCM)? My guess is not but... ...



Robert

 

[Ncostello]

Would you just wire the heater grid to a solonoid for power and use a momentary normally off switch to control when temps are below ideal?

 

[JLEONARD]

use a momentary normally off switch to control when temps are below ideal?

That's actually the best way to go... then you don't have to deal with the grids cycling and dimming the lights, stalling the wipers, etc. once you get running.

 

[Greenleaf]

I like that idea, if you are going to install the heaters, but not use them much. You *could* look up the specs of the mopar sensor and compare to the autometer sensor in terms of operation, but then I would simplify and use a switch.



You won't have to worry about the rotory injection pump advance (KSB function) if you have the 97 model year engine. That harness and sensor wouln't even be there.

 

[RSchwarzli]

I like this switch idea. Might just make it the easiest all around.



In thinking about that, is the air really needing heating if it is lets say, 40 deg outside? Does it even need to cycle at that temp? I can see when it is below freezing but at 32 or above?

 

[Greenleaf]

They normally do come on at 40°F but you got to remember. The heaters are also an emisions device. They heat the air to prevent/lower white smoke (incomplete combustion) so you really don't HAVE to have this. I have a fleet of buses with the 12 valve engine and some white smoke at start-up isn't going to spoil my day. They start-up pretty durn well at freezing with out any aids. The engines that do have 'em operate long after the engine is running.



You could always plug in the block warmer and you wouldn't need any grid heater, ever.

 

[JLEONARD]

You could always plug in the block warmer and you wouldn't need any grid heater, ever

yes but everyone can't always plug in. I used to at night but coudn't plug in at work so grids are still necessary to have working.

I once experimented by trying to start with them disconnected when the temp was below zero. Yes it finally started but I wouldn't want to do it again.

No problem until below about 15 F from my experience... below that the grids are neded.

I would never wait if the temps were above 20 F or so. Mine would energize above 56 F by the temp switch in the intake.

 

[RSchwarzli]

Well, that pretty much sums up what I have been thinking all afternoon.



Might try the switch, then no juice is used unless I feel the need.



Thanks guys! This site would not be the same without y'all.



Robert

 

[sdstriper]

The technical name for the sensor is the Thermistor IIRC.



FWIW, here's some more info on the grid heater controller from a previous post of mine...



Grid Heater Control Modules preheat cycle, ignition key on, before cranking the engine. Grid Heater Control Modules with a serial number below 0080000A do not preheat cycle unless it is 15*F or below. That serial number and/or higher has a preheat cycle from 15* to 59*. They all post heat cycle according to the manual, no other info on post heat.



Serial numbers below 0080000A



15* to 59* No preheat

0* to 15* fifteen seconds preheat

-15* to 0* seventeen and half seconds preheat

below -15* twenty seconds preheat

 

[RSchwarzli]

SD - Man you have some good knowledge floating around your head!



Thanks!



Robert

 

[sdstriper]

Thats just good FSM and/or Cummins manual stuff! And I'm in hibernation this time of year

 

[Greenleaf]

yea. I have all that stuff memorized, but at the moment, I didn't want to take the time to type it all out... ... ... ... ... I figured somebody else would.



LOL

 

[JLEONARD]

sdstriper = mister thermister??

:-laf:-laf

 

[sdstriper]

yea. I have all that stuff memorized, but at the moment, I didn't want to take the time to type it all out... ... ... ... ... I figured somebody else would.



LOL

Well I wish I would have had half the interest I have in these old trucks when I was in High School ! Boy oh boy, I could have been a C student then