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Old 06-10-2006, 04:55 PM   #1
stanleyr
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1992 SL2
2003 ION-3 Sedan
Dazed Cruise Control Hunts - Always Has. Gain Adjustment?

When I bought my '92 SL2 new, I noticed that the cruise control hunts +/- 1 to 2 MPH (63 to 65) on straight and level roads every minute or so. I could literally rest my foot gently upon the accelerator pedal and feel it move back and forth. Only on one occasion, with an extreme load while towing a light trailer, the cruise control stopped hunting. Since my previous vehicle had vacuum operated cruise control, I was accustomed to rock steady speeds. Anyway, even today the hunting continues, but has never worsened.

I was able to prove that this oscillation over time will take away from fuel economy when compared to using a steady foot instead - which becomes tiresome of course.

I quizzed the Saturn dealership about this and they said it was the nature of the cruise system to do this and that it was not like the vacuum operated type of yesteryear's.

My co-worker who owned a 92 and 93 S-series confirmed the same thing with his too. I have also queried the S-series forum and found a few other members that have mentioned this, but had no responses. I've also driven my mother's 93 Honda wagon and its cruise control system hunts +/- 2 to 3 mph.

So I am bringing up the following:
  • Since the CC module is a slave to the PCM, and I am assuming the module contains a servo motor in it, what causes the module to hunt minutely, the PCM or the CC module?
  • Can this be cured by simply opening up the module and adjusting a "gain" potentiometer or something like that?
  • Or if the problem comes from the PCM, can it be reflashed to desensitize the output signal for lighter loads?
I realize that the factory specs are all the system needs to adhere to, and if a +/- 1 to 2 mph hunt is acceptable, then so be it.

Your thoughts?

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Old 06-10-2006, 08:08 PM   #2
fdryer
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2003 L-Series 3.0L Sedan
Default Re: Cruise Control Hunts - Always Has. Gain Adjustment?

A +/-2 mph difference at 65mph equates to just a 3 percent change in speed. I think (as Saturn stated to you) that is within factory parameters. The comparisons with other makes and models seem to bear this out to suggest that the car makers have arbitrarily set this as a standard.

Here's one for you to ponder. I added cruise control to my '77 Datsun 280Z 5-speed that used a vacuum servo to work the throttle. It had two adjustment pots; one for calibrating the 'set' parameter and the other for 'sensitivity'. The sensitivity adjustment allowed for fine tuning how fast the +/- drift would be detected and corrected to maintain speed. When I set it low the cc would leisurely take its time to adjust speed corrections. Set high and the cc would correct too fast as evidenced by the gas pedal quickly moving forward and back creating the sensation of not knowing whether to go too fast or slow down. This was designed to accomodate vehicles with low to high torque engines. Since mine was a high torque engine (in a light chassis) I elected to set the sensitivity on the low side and never had a problem after installation. The other setup made the car too twitchy and couldn't make up its mind in effect saying to me its too slow so I'm going to speed up and now its too fast and I'm going to slow down and now I'm going too slow so I'm going to speed up and on and on.

It would be interesting if the module you're pointing to has an adjustment for this sensitivity, gain or undershoot/overshoot. My cc in my L300 works fine for those long drives on the NJ Turnpike.

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