more 91 ecm questions, speedo/cruise?

[mpascino]

Is there any way to run an electric speedo without the ecm? I really really really want to clean up the wiring associated with the ecm. Im sure I could get the cruise functional on it's own. Any ideas? thanks,
Mike

[Bobbie Martin]

All you need is a VSS and the proper signal. Your transmission/transfer case may have a reluctor ring and/or sensor installed. If not, you would have to install one. Then, most any GM VSS could be wired in and it will provide the signal for the speedo. There is some excellent info on sensors & VSS HERE. (http://www.jagsthatrun.com/)

[garysleeman]

I am converting a 90 gasser to 6.2J and have been working with an electrical manual and service manual both GM books, I also have an 89 donor truck. The speedometer for both those years is not connected or wired to the EMC. The two wires on the speed sensor go through the engine harness to the instrument cluster plug. The service manual says if the speedo isn't working replace the speed sensor. The sensor should have between 900-2000 ohms resistance.

The cruise control circuitry is tied to the EMC but it doesn't appear to run it, could be tied in to the ALDL. From the Electrical Diagnosis And Wiring Diagram Book
"The Cruise Control requlates the speed of the vehicle in response to driver commands.
The Cruise Control Module contains electronic circuitry and a stepper motor. The other systems components are:
Cruise Switch
Set Switch
Brake Switch
Clutch Switch
Vehicle Speed Sensor
The Cruise Control Module receives voltage from the GAGES Fuse in RUN, BULB TEST or START. A speed signal is received from the Instrument Cluster Speed Sensor Buffer. The driver gives his imput to the Cruise Control Module through the components listed above. The Cruise Control Module circuitry receives the driver's imput and generates electrical pulses. These pulses cause the stepper motor and its' output reel to rotate. The throttle is controlled by
a cable wound on the output reel. The Cruise Control Module also contains a clutch which release the cable when the Cruise Control System must be shut off. This clutch will operate when the Brake Pedal is depressed, the Clutch Pedal is depressed, the Cruise Control System is turned off, or the Cruise Control System detects a failure."
The last sentence may tell you what the EMC does but that's only my guess.
The trouble shooting charts do not specify checking the wire that goes to the ECM.
If your speed sensor is bad it would be the cause of both the speedo and cruise not working.
As for what works on my truck I'm still a week away from a road test!

[mpascino]

making a little head way now, thanks for the input. I think I have everything figured out except for the coolant temp sensor. Originally it ran into the ecm and disappeared from there. I assume there had to be a lead from the computer to the cluster. Anyone have any ideas?
Thanks again,
Mike

[gmctd]

One Engine Coolant Sensor for the ECM - use this for glow controller, if needed.

Separate coolant sensor for the gage, driver-side head, front.

[garysleeman]

As GMCTD said the sensor by the number one cylinder is for the temp. gage (this has a green wire). The sensor by the number 8 cyliner is used with the cold advance and glow plugs. The sensor in the crossover-outlet pipe with a yellow and a black wire is the one that goes to the ECM that would be left unconnected.

[mpascino]

AWESOME guys! Thanks, that takes care of everything. I knew it was a coolant sensor, but I had assumed it was for an idiot light that I either didn't notice or didn't have anymore. Removing the ecm was a lot more straight forward than I thought it would be.....Now all I need to do it put everything back together and make it work.... Minor details.. Thanks again.
Mike