C4 Cruise Control vacuum lines
My '86 Coupe began "surging" when in cruise control. The shop manual described an adjustment for taking the slack out of the cable that goes to the throttle from the cruise servo. I did that and the surging is less noticable. I still suspect a vacuum leak somewhere as I still notice the problem mainly at the 40 to 50 mph range. Has anyone else had this problem? Where is the most likely place to have a vacuum leak?
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Re: C4 Cruise Control vacuum lines
Art, check the vacuum module under the hood for a pin hole in the diaphragm, if not the system works with a vacuum reserve canister that that helps operate all the accessories make sure that the hoses are attached and none of the vacuum hoses on the engine have no leaks.New England chapter member, 63 Convert. 327/340- Chapter/Regional/national Top Flight, 72 coupe- chapter and regional Top Flight. -
Re: C4 Cruise Control vacuum lines
Don't forget to check for cracks in the plastic vacuum lines.Bill Clupper #618Comment
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Re: C4 Cruise Control vacuum lines
Art you are correct, servo is next to battery.vacuum canister is drivers front cubby holeNew England chapter member, 63 Convert. 327/340- Chapter/Regional/national Top Flight, 72 coupe- chapter and regional Top Flight.Comment
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Re: C4 Cruise Control vacuum lines
I've observed the same cruise surge issue on my '85. Will try to adjust cable and track any vacuum leaks with my vacuum bleeder and advise results.Comment
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Re: C4 Cruise Control vacuum lines
Well, after vacuum testing both lines running to the cruise unit (clamped off tubing run going to manifold), the lines checked fine.
Did not spot any obvious holes or tears in the diaphragm either.
Took the whole thing off and removed the cover exposing the electrical components. 2 solenoids and some sort of rudimentary rehostat (position of cable?).
At any rate, be careful with the loose solenoid plunger...it will come out with the black plastic cover removed.
Cleaned up the electrical terminals with contact cleaner and re-installed.
Road tested and problem still exists. I suspect either a short in one of the 3 coils or something in the dash (I can hear what sounds to be a relay clicking on and off there) with the cruise still surging +/- 2 mph around the set point .
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Re: C4 Cruise Control vacuum lines
Art & Chris, make a few checks like the correct engine vacuum most small block are about 18+ in. at idle,(you'll need a vacuum gage) if not around this spec. check the engine timing, set to spec.s. and the other thing that happens with these car is at cruise speed the EGR valve will be working causing the engine vacuum to fluctuate, hence the vacuum will be doing the same thing. check this by unhooking the EGR valve vacuum hose and road test.
New England chapter member, 63 Convert. 327/340- Chapter/Regional/national Top Flight, 72 coupe- chapter and regional Top Flight.Comment
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Re: C4 Cruise Control vacuum lines
Ed,
Good point on the EGR. I will try that after vac check @ idle with my bleeder pump gage.
-CKBComment
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