speedometer problem

if I'm not wrong, the KW Trans harnesses still have the provision for the transducer module for the early electronic engines. It may be as simple as its unplugged. Look for a two pin Deutch style plug on top of the Trans. The speedo sensor should be female....look for another male plug and try that. Otherwise is the yoke loose on the Trans? That will let the speedo rotor ring spin, although it will read erratically other than not at all.

 

Reading your post again, I'd bet the speedo sensor is simply unplugged or in the wrong plug.

 

I would start by following the harness from the sensor to the frame rail. Somewhere it's unplugged. I bet it's like the old PEEC KWs....the speedo signal went through the Autoshift, and has to be plugged back in to the factory harness.

 

I am having the same problem with a 2001 Western Star except that my speedometer worked for a year after changing to a manual shift transmission. Then the speedometer started to work erratically, then quit completely. Four shops and still no dice. One thought it must be ECM because signal was coming in from sending unit, but not out to interface. Sent ecm for repair. Supposedly had a couple of bad circuits, but nothing to affect speedometer. I am beginning to suspect the ecm-firewall wiring harness because one of the four shops repaired some bare wires that had been rubbed by a broken clamp. I am currently using a Tom-Tom gps unit for a speedometer and a hubometer for mileage. I hope you find your problem. Please let everyone know. I could use some help myself.

 

My '89 pete didn't have a working tach or speedo when I got it. The sensors just needed to be pushed in further to get a signal (they had slid out of the outer brass sleeves that screw in). Then the tach was hit or miss. The solder joints on the connecter had come loose. It's a ##### to get it open but I did and resoldered the connector. Cracked the glass in the process but a quick trip to the glass shop fixed that.

 

I replaced the speed sensor first. Then, two out of four shops replaced it again. Blamed a bad battery, so replaced all three batteries. Spliced some worn wires in harness from the ecm to the firewall. Ran new wires from speed sensor to the ecm. I borrowed a speedometer head and interface from another truck. Sent ecm for repair. Think now I need a new wiring harness.

 

Has anyone hooked it up to DDEC and see if the engine ECM is getting a VSS signal? I know nothing about auto's, but if the auto's ECU drove the speedo, there's your problem, it's not there any more.

You can rewire it to use the engine ECU to drive the speedo, which will also require the proper dip swtich settings for an ECM driven speedo. Or you can use a 4 pin sensor and use the extra plug to drive the speedo (you'll need to find the speedo wires to hook it up. The 1st step is verifying that the engine is getting a signal though.

 

It worked for a little over a year after the swap. Regardless, there is signal coming from the sensor to the ECM , but apparently not from there to the interface.