I am in the process of replacing my brake vacumn booster and I am waiting for the part. While everything is apart I thought I would repair my cruise control. I will replace all the hoses. Based on other's experience what is the most likely part to fail???? (eg. pedal switch, the vacumn control, etc.) Thanks.

 

On the right side of the intake manifold under the fuel rail cover you will find a vacuum check valve with 3 ports, (the white & black plastic piece) seen below just under the fuel pressure test port.



It is a one way check valve that prevents loss of vacuum to the A/C controls and cruise under acceleration when manifold vacuum drops. The valve is known to fail, usually the ports just break off as it becomes brittle with age but the valve can also fail to function as designed.
To test it remove the valve from the hose connections, if you apply vacuum on the manifold side (black port) it should not hold, next apply vacuum to one of the white ports and cover the other white port with your finger and again apply vacuum, it should hold.

 

You will need a multi meter to check the electrical.

Remove the plug from the servo & test the servo ohms following the procedure in the shop manual. If the servo fails the ohm test replace the servo.

Switch the multi meter to dc voltage, key on, cruise switch on electrical connector disconnected from the servo. Test the voltage between terminal B & D on the servo electrical connector. It should be 8 volts.

If you have 8 volts to the servo plug your good to go. If the cruise fails to operate go to the check out procedure for the switch(s) on the clutch & brake pedals.

If you do not have 8 volts to terminals B & D at the servo plug do not follow the manual for the cruise module check at this time.

Go the the switch check out procedure. Check the fuse & voltage to & from the switch on the turn signal lever. If no voltage locate & repair the open circuit from the ignition switch to the cruise switch. Or replace the multi function lever (turn signal lever) if you have power in & no power out.

Check voltage again at terminal B & D at the servo plug.
8 volts = control system ok.
No voltage = go to the the check out procedure for the cruise control module.

If the above tests check ok & the cruise fails to operate test the switches on the brake & clutch pedal(s)

 

My cruise was not working correctly and I replaced the check valve Toptech pointed out and now it's like new again. Autozone had it in stock.

 

Thanks all, very helpful !!!!!!!

 

The lines of vacuum hose can become brittle with age and leak. That'll make the cruise not work.

 

 

Don't mean to hijack this thread, but can you tell me which one of those vacuum lines goes to the heater/AC feed from the firewall?

I'm having a heck of time locating mine, think it may be broken off and that info (plus your pic) would be a big help...thanks!

 

I'm going to try the valve on mine first to see if it fixes the problem

 

The vacuum line coming from the servo goes to the fuel vapor canister on mine.

 

my cruise control/cc doesn't work, I'm reading your alls steps, but I have a question. If the cc isn't actually working, do you still see anything on the dash? like should it flicker cc on or set or something like that? or is it going to show no sign of cc until its repaired? or does the dash ever even show cc is active? I bough the vet used and it didn't work when I bought it so I don't know if it is even supposed to indicate it is active on the dash. thanks all.

 

on the 85 no dash lights at all for cruise but mine works and is hooked up this way.

 

See your new (Iceweasel) to the Forum so welcome.

There's nothing in your profile about you or the car. The year of the car is not in your post. The C4 spans 84-96 and all the cars are different in their configuration and construction.

You need to state the year of car and if the cruise stopped working or never worked. Any and all additional details are a plus so a picture can be formed of what your working on. Without this information you are not going to get answers that are accurate or sometimes no answer at all cause people don’t know where to start.

You also hooked on to a thread that is 8 years old. You can use it for reference but should start your own new thread with as much info as possible for new future problems.

 

Ok thank you for the tip! I thought I was in C4 tech area, but maybe the C4s CCmodules differ from early to late models. Ill try a new thread

 

This was my only issue in both my C4's The 92 and the 94 had no cruise control when I bought them. Changed the vacuum hose and all was good.

 

There is no Cruise light or any indication on the IP on any year C4 that cruise is set.

 

I changed the brake booster. Had to remove CC and support brackets. Reinstalled everything, but CC doesn't work. This is for a 1988 C4

 

Can you hear the relay click when you switch the system on at the lever with hood open and IGN to on?

 

What relay, and where is it located?

 

Sorry, meant to say servo. This may help you: https://www.corvetteforum.com/forums...-t-work-2.html. There are other threads on the forum if you do a search. YT has one or two good vids also.