Cruise Control Experts Please Read

[Brat4by4]

That means if you are not cruise control knowledgeable, do not comment

Anyways, for arguments sake I propose this scenario to get the idea across: Let's say you have an ECU that has lost its ability to run the cruise control. To get CC back, you install another ECU and run only the wires necessary to control CC to the extra ECU.

What would these wires be? I am assuming something to do with the Vehicle Speed Sensor, Tach output, and ???

I have a limited understanding of how the cruise works in this car, so filling me in would be great. Isn't there a CC computer of sorts in the car, does it need the main ECU to function correctly? Any help is greatly appreciated.

William

[BAC5.2]

Vehicle Speed Sensor, Tach output, Neutral Switch (because cruise control won't work if in neutral), and I'd imagine the starter switch (as depressing the clutch turns off CC in neutral).

If I were you, I'd program a STAMP chip or something to control the cruise control. That way you won't have to deal with having a second ECU (which will be FREAKING out with no other sensor input).

When does the Legacy go under the knife? Or is it already?

[vrg3]

By ECU do you mean the engine control unit? Cuz the ECU's not involved in cruise control except for its output signals.

The cruise control system has its own computer mounted behind the dash kind of to the right of the glove box.

[Legacy777]

What vrg3 said.

cc has its own computer......

[Brat4by4]

so I just need to feed it the signals it desires? Do these have to be interpreted by the ECU somehow so it can digest the numbers? I need the cruise to be able to work on its own without any help in this theoretical situation. Any FSM cover this?

Legacy hits the operation table around Sep. 6th or so. First is exploratory surgery on the interior, nothing exciting... running wires, re-running wires that were done half-aped before. Cleaning up previous installs that all got to 85% finished and never completely done.

[Legacy777]

ecu is completely out of the loop as far as the cc is concerned. The ECU and CC computer however may share the same input sensors, i.e. neutral safety switch, etc.

[vrg3]

What Josh said. The cruise computer doesn't need any help aside from getting the signals it needs. Aside from the signals from the cruise main switch on the dash and the set/resume switch on the steering wheel, it also taps into the signal from the vehicle speed sensor, the ECU's tachometer output signal, and the clutch switch or inhibitor relay. It also has its own switch for the brake pedal.

The factory service manual does cover cruise control in the electrical section.