Weird Cruise control problems

[Chief915]

So, back before my head gasket blew a couple months ago, my cruise worked just fine. Then the head gasket blew and I replaced the engine. After the engine swap, the cruise didn't work at all. It stayed that way, not working at all, for about 45 days or so of everyday driving until yesterday. Beginning yesterday, the cruise comes and goes all by itself.

The cruise switch can be off and I don't try to set the cruise or even touch the turn signal lever. When I am cruising along and let off the throttle, the engine stays steady like the cruise is on. It doesn't maintain speed, it slowly drops 1 or 2 mph every few seconds and touching the brake pedal will kick it down to idle just like the normal cruise control was working. The cruise will not come back on again until I acclerate again. After accelerating, again without ever touching the cruise switches, I can take my foot off the pedal and it will do the same thing again.

It doesn't rev up or act like it's going to run away or anything, just acts as if the cruise is set. I flicked the cruise switch on and off, wiggled the turn signal around, etc and it still does the same wheter the cruise switch is in the on or off position.

My grounds are good and clean, double checked that. I have 2/0 ground cables, one to the engine and the other to the frame. The grounds on the back of the intake are clean and tight and has a ground wire going from that stud down to the frame by the down pipe. Other than the cruise thing, everything seems normal. No check engine lights, stalling, hard starts, fish biting, etc.

Any ideas?

 

[Woody35]

http://www.thetruckstop.us/forum/showthread.php?34249-Cruise-Control-Kicking-On-By-Itself

I would like to know too. I have a similar problem and in my thread there was some very good suggestions.

 

[WarWagon]

I can't say for later years. I know on 1993 there is a single thin wire that goes to the multifunction switch cruise switches. There is a connector by the column for this thin wire.
Perhaps you can unplug this connector and eliminate switches and the wire shorting to the switches.
The next step would be checking pins at the ECM to the connector.

All that is left is the ECM and PMD after that. And of course related wiring to the PMD...

Used to bump the R/A switch on the 1988 while using the turn signal. GM put a plastic guard by the switch to help prevent this accidental R/A activation.

Remote, but, possible that noise from a failing alternator could be mucking things up as well as low voltage from dirty fuse contacts or ignition switches. Ask the scanner or check ECM voltage with a voltmeter.

 

[Chief915]

Well, it must have known that I was on here telling on it.

Got up this morning and headed to work. I turned the cruise switch on and set the cruise.... it worked perfectly all day, just like new.

No rhyme or reason...