Cruise control question
Thread Starter
Racer
Joined: Oct 2008
Posts: 298
Likes: 0
From: Durty Dena Maryland
Cruise control question
Wife has a 79 automatic........When she tries to use her cruise control the car surges approx 8-10 mph.......It will be set at 55 and car surges from about 50 up to about 60........Other than that car runs fine....Suggestions on where to start looking?????
Racer
Joined: Mar 2002
Posts: 406
Likes: 1
From: Maroochydore QLD
Yep, this one's easy to diagnose, not so easy to fix.
You have vacuum leak(s) in your vacuum system somewhere, the vacuum that drives the C Control is tapped from the same source as your headlights and heater controls, if a leak is present then you get unstable vacuum at all points, including the C Control diaphragm, in fact, as a simple test try this, get on to a freeway or open road, get car to 35 MPh and engage CC, put up with surging and I bet that over time the surging will reduce, maybe even eventually stopping. This is because the vacuum will eventually settle down to a constant state.
how do your headlight operate? Are they Ok too, what about your air vents? Do they operate perfectly? I am guessing they dont operate perfectly, they may still operate but irratically or slowly.
good luck finding your leak but be aware that the vacuum system isnt as scary as some on this forum will have you believe, you just need to learn and understand it, it all makes sense eventually. I may be a sick puppy but I actually like the vacuum system on later C3's, its challenging but fun.
Cheers, Dennis.
You have vacuum leak(s) in your vacuum system somewhere, the vacuum that drives the C Control is tapped from the same source as your headlights and heater controls, if a leak is present then you get unstable vacuum at all points, including the C Control diaphragm, in fact, as a simple test try this, get on to a freeway or open road, get car to 35 MPh and engage CC, put up with surging and I bet that over time the surging will reduce, maybe even eventually stopping. This is because the vacuum will eventually settle down to a constant state.
how do your headlight operate? Are they Ok too, what about your air vents? Do they operate perfectly? I am guessing they dont operate perfectly, they may still operate but irratically or slowly.
good luck finding your leak but be aware that the vacuum system isnt as scary as some on this forum will have you believe, you just need to learn and understand it, it all makes sense eventually. I may be a sick puppy but I actually like the vacuum system on later C3's, its challenging but fun.
Cheers, Dennis.
Racer
Joined: Feb 2007
Posts: 271
Likes: 25
From: Buena Vista Colorado
......When she tries to use her cruise control the car surges approx 8-10 mph.......It will be set at 55 and car surges from about 50 up to about 60........Other than that car runs fine....
Good luck!
Jerry
Advanced
Joined: Dec 2008
Posts: 52
Likes: 0
From: Medina Ohio
There is a good discussion on how to fix this issue on this forum. Here is the link.
http://forums.corvetteforum.com/c3-t...ain-speed.html
http://forums.corvetteforum.com/c3-t...ain-speed.html
