G1625S

ok, I've read about all the ksb threads I can find, but I'm still not sure how it should be wired on my 89. Right now, it's getting voltage all the time, yet it doesn't look like the factory harness has been touched...I understand the older trucks had a different setup that didn't use an intake temp sensor--is this correct? What shuts the voltage off when warm? Does it even shut off at all? I'm concerned because in one thread I was reading, someone said that hot wiring the ksb could eventually damage the pump, but that was with the temp sensor in the circuit...anyway, I'm confused---btw, pulling the wire from the ksb didn't change the sound of the engine this morning...

greg

wannadiesel

Power comes to the thermal switch on the manifold from the ignition switch. The thermal switch should open at 90 degrees and break the circuit. If it doesn't, the switch is bad. On most trucks there's a resistor in the circuit between the switch and the solenoid that drops the voltage to about 10 v.

If the solenoid has power and unplugging it makes no difference in how the truck sounds, follow the directions in this thread.

G1625S

I've read there are two switches in the intake--should this be true for my truck as well? I unplugged the only one I saw while the truck was running and the 'wait to start' light began to flash. Does that switch also control the ksb or is there another switch I should look for? I will check the solenoid itself tomorrow. thanks.
greg

wannadiesel

My bad, I was going off the '93 FSM and your truck is different. I did some more poking around in my Cummins book, the '89 and '90 trucks are supposed to have a wax motor KSB solenoid (like a thermostat). Temp switch for that is in the water jacket of the head. The switch sticks out of the side of the head, just to the rear of the fuel filter. It opens at 160 degrees. There is a 3 ohm resistor in line on some applications, on others the wiring harness is made of resistance wire. There should be less than 10 ohms of resistance in the harness. The wax motor reacts much slower than the electromagnetic solenoid used on the '91 and up. If you pull the wax motor out to test it, Cummins says it must move within one minute. So wait for a minute or two before and after unplugging the solenoid when trying to diagnose the old trucks.

G1625S

Thanks! That's some very useful information! I wonder if that's why my egt's are high when cold---the pump has been advanced plus the pokey ksb=lots of timing untill 160*...sound right? Seemed to run much better today with temps in the 30's. Thanks again for the info. Methinks it's time for that Cummins manual

greg

wannadiesel

Advanced timing should lower your EGT.

I can hear the difference at idle when the KSB is on (the truck sounds like a 2nd gen). Monday it was 15 degrees here and the KSB stayed on the whole way home from work (40 minutes in traffic). I popped the hood and felt the intake tube, it was cold to the touch. The old style system would have shut down the KSB before I got halfway home.

Let me know if you need more info when you get deeper into the diagnosis, the Cummins book has detailed procedures for testing all the parts of the system..

G1625S

huh, interesting. I try to be real easy on the go pedal when it's warming up, but my egt will hover around 300-350 when cold at cruise, but once it's warmed up, the egt will not even register at cruise. I just thought it was weird. Maybe it has something to do with the probe being post turbo, or the probe being toast? otherwise, it runs great! prolly just shouldn't worry....even at -10 on monday, plugged in for 2 hours, fired on less than half a crank and ran smooth instantly. Just a nervous new parent

greg

wannadiesel

I wouldn't trust that pyro probe.

G1625S

Yeah, new probe (pre-turbo) next week, I think.

Den

Anybody have a part number either factory or Sorensen for the 91 KSB sensor?
Mines dead it seems. Have 14 volts on one side and 0 on the ksb side.


Den

torquefan

Is yours the old or new style? 91 I believe could be either. I know the Dodge P/N for the temp switch on the later style is a 4713521.

wannadiesel

If the temp switch is in the side of the head (coolant temp - wax motor KSB) the switch is Cummins p/n 3915945. Electric solenoid KSB switch is in the top of the head (intake air temp) and is Cummins p/n 3921642. Coolant switch opens at 160, air temp switch opens at 90.

Den

Thank you both.
It's a 91.5 and it's located on the top of the head.

torquefan, "later style is a 4713521" do you mean the one located on the top of the head?




Den

torquefan

Yes, on top and measuring air temp. I've replaced lots of those. They seem to fail a lot more often than the earlier style.

vavtx

Anybody have a number and supplier for the KSB solenoid for the later style using switch 4713521(3921642)?