Magnum Salvage

Hi, I own a 92 3/4 ton 4x4 with getrag transmission. Recently I've been having a problem with the grid heater ( i believe that's what he called it) I'm fairly new to Dodges and diesels so bear with me here. I've had the truck for a little over a year and it has 143,000 on it. No adjustments ever to the motor as far as performance.

Anyway, I live in Wisconsin and its been about anywhere from 30 degrees to zero for the last two weeks. I noticed that recently when I turn the ignition to the "on" position the two indicator lights "Wait to start" and "Water in fuel" either dont come on or they flicker very fast. I also dont hear the grid heater kick out. Therefore, my truck has been hard to start. Before this problem, both lights would come on and stay on and I would here the grid heater cycle and no problem.

I took the truck to my mechanic, he also owns a first gen cummins truck. He replaced the solenoid for the grid heater but no change. He said he cant get any codes to come up on his computer tester either. I wasn't aware that my year of truck had a computer but he said it does. He called our local auto parts stores and they only sell computers for automatic trucks, about $325.00. Mine is a standard so apparently you have to go thru Chrysler to the tune of about $525.00. Still he isn't positive that the computer is the problem. I don't want to order it and then find out it isn't the problem and not be able to return it because it's electrical.
The other idea he had was to wire the solenoid direct to a push button in the cab and bypass the computer. I don't have a problem with that as the truck is not a showpiece but a work horse for my salvage business. Is this the only function the computer controls is the grid heater and water in the fuel indicator? I really don't want to fork over alot of money for parts if I don't have to of course. Please help with your ideas, knowledge and input. Thanks, Matt.

dpuckett

Matt,
An auto PCM will work in your manual truck.

The PCM controls the cruise, AC, voltage regulator, intake heaters, and a few other items. You will need to work around ALL of them to get it all working right.

I'd sugest plugging in the block heater when below 30deg. Then you wont need to worry about the grid heaters.

Do you hear a click when you first turn the key? If not, your relays could be bad, grounds, etc. Dont underestimate the ability of the little stuff to wreak havoc with everything. It could also be the PCM. Are you having problems with any other electrical stuff?

Daniel

Magnum Salvage

Thank you for the quick response. I did have a problem with my blower motor on the heater working. It was blowing so weak I couldn't defrost my windows and then at times it wasn't blowing at all but my mechanic looked at the connections and cleaned them up and apparently now it is blowing like it should be. The other problem I noticed also is that after having started the truck, the voltage meter needle jumps around until it the truck warms up. My mechanic said it is becuase the grid heater may be kicking in and out when the truck is cold, therefore drawing on the voltage. Once itwarms up it's fine. My cruise has never worked so I don't know if that's PCM related or not. Also my dash lights have never worked. Just the lights to illuminate your guages and speedo. All other guages work. So your saying that a PCM out of an auto is the exact same as a standard? What would you recommend doing? I'm just scared about the PCM not being the problem and then being stuck with alot of wasted money on a non-usable part (PCM).
I believe he would have checked the connections and the grounds but I hear what your saying about the "little things" we sometime overlook. I know it shouldn't but electrical problems scare me and I'm not that knowledgeable about them. Thanks for reading my ramblings.
Matt

Magnum Salvage

Also, I dont remember ever hearing a click when first turning the key but I do remember it clicking after cycling for 10 seconds or so based on the outside temp, that's when it was working properly before.

SkinnyBTN

I would replace all the fusible links with fuses. Just my oppinion, but when my truck started doing a bunch of crazy stuff I finally replaced them and no more probs. I too thought I had bad PCM, just a bad fusible link. Also, replaced everything in my charging system and spent $300 doing so. After all of it I feel I could have saved alot of $ and headache having replaced the links first. Again, just my opinion. Good luck, bud!

wannadiesel

That's possible. To check, pop the hood while it's doing it and put one hand on each of the heater relays. You will feel them clunk when they turn on and off, the PCM will turn them on and off for no more than 5 minutes after a cold start.

If the voltage is jumping around and the grid relays are NOT cycling - that's yet another sign of a bad PCM. The PCM runs the charging system, so if it is working intermittently, then the alternator will turn on and off.

Magnum Salvage

Thanks for all the replies. Is it true the computer from a auto 92 3/4 ton is the same as a standard tranny 92 ? Apparently, Dpuckett says there the same. Just curious on a second opinion, not that I dont trust Dpucketts response. Thanks, Matt

brainfade

There is a sensor in the head that tells the computer if the temp is low enough to turn on the grid heaters. Might take a pass at that before changing the PCM. I think it's on the intake side of the head, screwed in about 2/3rds of the way back. Should be closed below 90 degrees IIRC.

93beater

there is an ecm on ebay. just type is 1990 dodge cummins

93beater

1991 dodge cummins sry!!!

wannadiesel

That one won't work. He needs a '92 or '93 PCM.