Engine/Transmission (1994 - 1998) OK, somebody explain heater grids to me.

[Dennis Garrett]

Trying to run down a cold start problem, & replaced the original return hose after 6 yrs, & almost 180k. (It looked fine by the way). I took the intake manifold off to back my gov. springs off a click, and play with my #8 plate a little. I then decided it would be a good time to check the heater grids. The temp outside today was about 40 deg. I finally decided after starting the truck several times, and checking voltage that the top grid is not heating. It checks out good with a continuity tester, but only the bottom grid heats. I guess I don't know much about them, do they both come on at the same time, or do they come on at different temps? I'm thinking maybe only one is coming on at cold start. All the connections at the relays and the grids are clean & tight.

 

[JIM S.]

I am wanting to know about them too... seems like mine are not working fully eather, I have to cycle twice to start and its only mid to upper 20's and the grids used to have a high piched squeel when cycleing, now they dont.

Jim

 

[truckstom]

I THINK only one at a time comes on... one to start, then the other... they cycle back and forth... I THINK!!!!!

surely someone will verify or CORRECT me...

 

[JohnE]

Both elements should heat when the <strike>e</strike><b>P</b>CM calls for preheat.

If only one is cycling, you probably have a bad relay circuit.



<font size=1><em>edit;

busted by the 12 valve police.

Yes, properly valved have a <b>P</b>ower <b>C</b>ontrol <b>M</b>odule (PCM), which also happens to be an <b>E</b>lectronic <b>C</b>ontrol <b>M</b>odule (ECM).

24 valved have an <b>E</b>ngine <b>C</b>ontrol <b>M</b>odule (ECM) which also happens to be an <b>E</b>lectronic <b>C</b>ontrol <b>M</b>odule (ECM).

 

[JJW_ND]

One or both???

Based on how cold it is, I think either both come on (below32) or only one (between 40 - 32). Something like that. I also notice the difference in how much the Volt gauge drops depending on if both are engergized (pegs needle to the left of last white hash mark) or one one is "lit" (needle drops justbelow 14).



When I had a bad grid heater solinoid I ran on one grid heater for half a winter. My experience with my truck (it seems to be a good starter) is down to about zero, one grid heater starts it fine. I once tried it at about -5 and had to hook up both to get it to fire. Temps above 30 dergrees or so, I rarely wait... just hit the key like summer time. I rarely cycle mine, but them I keep my idle at or above 900 for very quick starts.



Dennis... . make sure you get power to the grids via the solinoids and relays. If one seems to heat, switch the heavy lead wires and see if it still heats the other (grids fine... . solinoids, relays, or PCM powering the grids are the problem. Could also be something simple like the IAT sensor (screws in the top of the intake. This tells the PCM that it is cold enough in the first place to turn them on!



jjw

ND

 

[shendren]

the pcm/ecm/computer on the 12v controls the grid heater...



did you tighten the nuts on the driver's side fender well? these come lose and can cause the heater to not heat well... .....

 

[JohnE]

one or both?

I wonder if different trucks tried different things?

No matter the temp, My volt meter appears to dip the same amount when the plenum heater(s) cycle. The only thing I noticed, the colder the air temperature, the longer it takes to cycle.



Of course, this is all depends if I haven't been running the Espar. Oh do I love that thing. If I can get in a good Espar cycle before running the Ram, it starts better than the poor gassers.

 

[T. Baker]

When I get around to it I'm going to put mine on high amp relay and use a push button switch. I'm just wondering if you keep them on too long with the egine stoped if they will melt and fall into the engine!!.

 

[BertM]

I had the same questions on how the heaters were acting. I installed two L. E. D. lights from radio shack in the plastic housing in front of the gear shifter. Wire the LEDs to ground and the engine side of the relay. My 94' has two relays, one per grid heater. The LEDs now become the wait to start light. You can tell if both are burning or if they even come on at all. When I start, both grids burn, then they cycle one at a time until 15 mph.

 

[Dennis Garrett]

Went out this morning at 18 deg & played with it a little. It started, but with the familiar cold weather difficulty, & a lot of white smoke. I did poke around with my tester, and found that the forward most relay on the fender is hot on the battery side, but does not cycle ,or send any current to the grid. The other one cycles on & off like it should, heating the lower grid. I'm off to work now, but when I get in, I need to decide if the air temp sensor is not working or if the relay is bad.

 

[QRTRHRS]

Check this link if you need to replace the selenoids.



http://home. adelphia.net/~npmrphy/relay.pdf



I just did this mod to mine but I made a "U" shaped plate out of stainless to hold the selenoids. The "U" is open towards the top. This way, the cables that lay against the selenoids are against the plate. If you peek down at your selenoids, this will make sense.



I ordered the selenoids online from Allied at 14. 24 each plus shipping.

 

[Dennis Garrett]

I've decided I've got one bad relay, I think they come as a pair crimped to the three hole mounting plate. I ordered a set for $65. 00, should be in in a day or two. Today I popped the hood, turned on the ignition, and let the bottom grid cycle while I hot- wired the top grid, (by-passed the relay, touching the cables together) and she cranked up just like old times.

 

[JohnE]

separate cycling

OK, the separate leads from the PCM now make sense.

The Banks Twin Ram intake manifold splits the grid heaters. I wonder how that affects cold weather operation.



Make sure to swap the coil leads first. By some strange quirk, it may be a PCM fault.



I've been watching the voltmeter closer the last couple days. It doesn't dip as much after the engine is running and I attributed that to the alternator helping.