Though I've searched pretty thoroughly on the boards, I've yet to find a definitive answer. Do I need the ECM to run the cruise control in my 85 IROC (recently I've swapped in a 350 HO Deluxe) or not? Cruise worked in advance of the swap. I ditched the computer but still have it and all the wiring. Any advice would be great.

JamesC

 

As far as I can determine, the '85 ECM doesn't need to be present to operate the cruise servo. As long as the servo is geting vehicle speed reference, and the brake switch is wired correctly, it should work. Of course, the cruise servo also needs power.

 

Yes the computer is required because of the Vehicle Speed Sensor. However some members have been using the Digital Dakota system with their carburated engines for this function. If you will do a search you will find this info. There is also one model of the Dakota system that has been known to cause problems. I am not sure which one it was but have heard that a newer model came out to fix the problem.

 

It seems that the problem lies in the infamous brown wire that not only routes to the cruise module but also routes to the ECM from the VSS. Could I simply reinstall the computer, eliminating all wiring but the brown wire to ECM along with power, ground, etc.? That said, there's appears to be nothing in the shop manuel that refers to the ECM and cruise control problems.

First plug is numbered 1-22:

1. Barometric Sensor Input
2. Throttle Pos Sen Input
3. Coolant Temp Sen Input
4. Air Control Sol Output
5. Diagnostic Enable Input
6. EFE
7. Analog Lo Input
8. Throttle Control SW Input
9. 02 Sensor Hi Input
10. Distgrib Ref Pulse Hi Input
11. IGN Module Bypass Output
12. Spark Timing Output
13. Distrib Ref Pulse Lo Input
14. O2 Sensor Lo Input
15. Cold Start Program Mod Input
****************16. Vehicle Speed Input
17. High Gear Input
18. Carb Fuel Sol Output
19. +8V Supply Output
20. Map or Vac Sensor Input
21. +5V Ref Voltage Output
22. Analog Lo Input

Second plug is lettered A-U:

A. ECM Pwr Grd to Eng Grd
B. Air SW Sol Output
C. IGN 1 Pwr Input
D. Not Used
E. Throttle Kicker Relay
F. Idle Speed Motor Hi Ext Output
G. Check Eng Lamp Output
H. Park/Neu Sw Input
J. A/C on Sw Input
K. Not used
L. ESC Retard
M. Idle Speed MTR Lo Output
N. 4th Gear Discrete
P. Torque Convtr Clutch Output
R. Continuous Battery
S. Not used
T. EGR
U. ECM Pwr Grd to Eng Grd.

JamesC