Early '89 Thermistor replacement

[cmann250]

(PREVIOUSLY TITLED "AIR TEMP SENSOR MIA")
At SOP, I noticed one of many things my truck is lacking. Air temp sensor. I could swear that i saw the WTS light when i first got the truck (march), but it hasn't been cold since. This would explain why it rattles so bad on cold-ish mornings, right?
I assume it's a Cummins-dealer-only part.

What puzzles me is the PO said it started so well that he never bothered to plug the truck in

[PToombs]

There are 2 of those, 1 for the grids and 1 for the KSB. You need to figure out which one. If ypou open the loom and trace the wires it should be obvious though.

[cmann250]

I'll see if i can get a pic up. There's two threaded plugs in the "intake log" on the side. I have nothing electrical coming out of that side of the head Do the intake heater and KSB get their readings from those ports side by side?

If i understand correctly, the truck decides to run the intake heater or not before it's started, and it decides to run the KSB or not after it's running. So like you said Mr. Toombs, there is 2 sensors, right? I don't have whichever one that is about 5/8" threaded and there's a hole in the throttle bracket to make for easy access

[PToombs]

The sensors are in the intake plate, on the top of the head, just behind where the air horn is, on an IC truck. I didn't realize you have a non-IC truck, that may be a little different for the KSB sensor, I'm not sure. I know on the IC trucks there are only plugs in the side of the intake where you are looking. It's where we tap in for the boost gauge. And those ports are pipe thread, NPT.

[cmann250]

I pulled up a pic of the IC'd intake plate and i have no sensors on it what so ever.

It's where we tap in for the boost gauge. And those ports are pipe thread, NPT.

Yes, the smaller one is often used for the boost pressure, but i think the bigger port is used for the air temp sensor (2 wire sensor) on the non-IC engines. I'll figure it out. I'll have the truck down for the 47RH swap this weekend anyway. Thanks for accompanying me on my wild goose chase Pete

Derek, who came to SOP, has a '90 and is helping me with the swap. Non-IC'd to non-IC'd comparison will be easier

[PToombs]

Let us know what you find, and good luck on the swap.

[cmann250]

I arrived at a resolution for this, a month later I got an intake temp sensor ordered. It has gotten cold, so the grid heaters and KSB have a reason to cycle. I had no "Wait to Start Light" this morning and it was below freezing. The truck fired and ran rough until it got warm, so i don't think the KSB engaged.

Sounding right?

[PToombs]

I'd try to help ya, but that non-IC stuff is before my time.
On the later trucks the grids and KSB were powered from different sources. On yours the KSB is advanced with no power, then when power is applied it retards.

[cmann250]

Should i be cautious accepting help from you in the electrical section of the forum considering your sig? Just kidding Pete.

I remember Douglas saying something something about wax and the KSB on a non-IC'd engine at SOP. I can't remember exactly what though

[PToombs]

non-IC KSB is a wax pellet. Power is applied, wax gets hot and expands and retards timing. Now you know as much as me, FIX IT!

[cmann250]

My $60-some dollar part comes in tomorrow. And we got 2" of snow/slush today. Oh joy!!!!!! 5300lb. 2wd pick-up

[cmann250]

Strange things happen when you carefully read the FSM. There are 2 types of sensors that tell the grid heaters/KSB to turn on. One measures air temp and the other measures coolant temp. I have the one that measures coolant temp and it's hidden under the intake log. I traced wires (light blue and black) to find it. I don't think this is a IC'd/nonIC'd thing because I have seen several '90s and they have had a sensor in the intake log. I should have been suspitious when the replacement sensor that I got was brass.

Just one more thing that makes my truck a horse of a different color For the record, it started when it was 12* this morning

[cmann250]

I put the sensor in today. A deep 7/8" socket, 1 wobble, and a 12" extension easily reached it. I didn't drain the coolant as the FSM suggested, I just worked fast and lost only a quart. Starts niiiicely now I'll be able to say for sure if I did it right tomorrow morning

[jesehowells]

where did you get the senors you have a part # or pics of where its at i have a 89 that the grid heater wont come on

[cmann250]

I lost the receipt, so I don't have a P/N from Cummins. I'd call up Schied (or your favorite Cummins shop) with your ESN handy and they'll find what you need.

OR

You could test some stuff and hopefully save money. The coolant-triggered sensor is under the intake log straight up from the lift pump. I think it's impossible to see it when it's installed. Follow the blue and black wires disappearing under the intake log. Do you hear a click/whine when turning on the key? WTS light flashing?