Cruise control problem

[jcc3inc]

Good morning,

My '91 has a cruise control problem. It will Set all right but after a short time will disengage. The speed regulation is poor, with several MPH change when going down a grade. On Resume, it goes past the set speed.

I went over the vacuum motor and valve setup and I believe it is all OK. Also checked the switches on the stalk and the brake pedal switches, both OK. Also there is a diagnostic check of the switch functioning; it showed to be OK.

A year ago I had problems in getting into the diagnostic mode; it seemed to exit diagnostics all by itself. But now all the diag. works OK.

Has anyone had problems with the PCM where the cruise control is governed?
Could the computer be the problem? Would the computer froom a '91 Riv be a replacement?

Thanks in advance,
Jack C.

[ekvh]

The manual describes a procedure to test the cruise module under the hood. Most here seem to think the problems are usually related to the issues you have checked. I have done the same and the procedure in the book says I need a new BCM, if it isn't one of the other issues: vacuum leaks, switch problems on the brake. There are a few who have had the BCM switched and it worked. I have been over a year now without cruise. The first symptoms were like yours. I haven't mustered the money up for a new one yet, I keep thinking it will be one of the other issues. I have had one speeding ticket which would have more than paid for the new BCM. If you do an advanced search you will find a way to block a port ( I think in the vacuum line to the brake pedal.) If you do this and the cruise engages and holds the speed, it is not a problem with the module but with the switch or the vacuum switch dump mechanism. Mine does not work when I block the port. Understand that to disengage the cruise if you try this, you must shut the cruise off by turning the system off via the button on the dash. Since it was slowly losing speed at first, it makes me think it is vacuum related, but I haven't been able to find anything yet. Apparently, ignoring the problem hasn't helped me.

[padgett]

Sounds like sticky ports in the cruise module, same thing that causes a surging idle with a dirty IAC.

I just have collected a few spares when the UPullIt has a 2 for 1 sale. Same unit was in millions of GM cars & is an easy swap.

[wally888]

You can somewhat disassemble and peek into the CC Switch.
I had 2 switches w/ corroded and broken wires. The wires are tiny and bend each time the switch is used, break.