Cruise control issue - intermittently stops and starts

(tylerwerrin) #1

Hi guys,

My cruise control has developed an odd situation; I’ll be cruising along at 60-65 and suddenly the cruise control will drop out, then turn back on, drop out and eventually cut out completely.

The issue seems to happen when the car has to go uphill (or is going downhill), thereby modifying how the module is adjusting the throttle… but it may just be a coincidence.

I’m using a GM cruise control module; the system has been bulletproof for several years. I don’t know why this would happen. Does anyone out there have any thoughts on this?

(Carl Hutchins, Jr. ) #2


Don’t stay away so long. Kinda getting lonely around here. Good in way, the lumps are OK!!!

I suspect a loss of vacuum in some way. No vacuum, no pull on the throttle cable by the bellows.

Or a stray ground wire, Simulates brake application and opens the power circuit to the CC.

Decades ago, the after market CC I installed on my IHC Scout II “kicked out” on climbing a rather steep hill. I thought a bout it and realized, lots of throttle and slowing speed depleted vacuum. Should have dropped down a gear.


(tylerwerrin) #3

Ha, yeah! I’ll try not to - been focused on my TR lately and the Jaguar is stored out in the country so I don’t get to drive it as much as I’d like… so less problems to report!

The GM unit isn’t vacuum operated, instead it’s operated with a stepper motor. It was working fine and then suddenly… started giving me problems. I suspect it has something to do with the readings it’s getting for speed - perhaps a faulty reading from the VSS - so the cruise control doesn’t know what to do and then just cuts out. But I have no idea…

(Paul Wigton) #4

@Ray_Livingston… any hints?

(Carl Hutchins, Jr. ) #5

Another idea away from the complexities of
pulse matching. although so long as the pulses are steady, the CC should react. A clue might be in the speedo. Steady needle or erratic. Each relies on VSS.

But, I sense an issue at the brake light. errant closing of the circuit, kicks out CC!!