ULLLOSE

iTrader: (1)

OK so on the way back from the UT prosolo I had an interesting thing happen with the Cruise control. Had it set at 75mph, was in 6th gear towing my small tire trailer. Started up a hill and the car slowed to 71 mph then as it crested the hill it got up to 81mph. Then it stayed there and started surging bad. It felt like if I was stepping on and off the gas, to the floor then lift, it did this until I turned off the cruise. After turning the cruise back on all was ok until the next big hill.... Works fine the rest of the time. Anyone else seen Cruise issues?

Labop

I've seen the variance in speed due to changing pitch (due to going up/down hills), but I've never experienced the surging.

TRZ750

You didn't mention if this was on the down hill part. If you waited until the road flattened out the surge would probably stop. The cruise probably closed the throttle completly and when the speed droped it tried opening the throttle a little, but with the weight of the trailer it was too much and the speed increased too much - repeat. Mazda has a delay in the cruise to prevent too harsh operation. Probably using 5th gear would increase the engine breaking and stop the surge. Since you said it slowed from 75 to 71 it sounds like you were in 6th (off the sweet power band) or the trialer was heavier than you thought.

ULLLOSE

iTrader: (1)

Well I said I crested the hill, did not say I went down hill.... I went up the hill then at the top it was flat.

I said I was in 6th if you read it.

Trailer is not heavier than I thought, I have had it on the scales.

The surge is not engine breaking... The surge happens on throttle not off.

Rasputin

Same surge behaviour happened to me once, and to two of my fellow RX8FRance forum members.
The system frequently overshoots.

I posted something on that topic on the UK owner's club forum (Warning : may contain Metric units! ) :
http://rx8ownersclub.co.uk/forum/vie...654&highlight=

Fabrice

TeamRX8

iTrader: (25)

I had the same issue when I was driving there, no trailer for me but fully loaded

I crested several hill tops at high altitude and the cruise control just started accelerating the car quite aggressively, I was having runaway Audi visions

Rasputin

I did some testing yesterday at 160 kph (100 mph) to induce surge. I was connected with my Hymee sCANalyser to check what was going on.

First, as mentionned before, if you go over 10 kph above the requested speed, it actually shuts the throttle aggressively and maybe (need to see the logged data) the fuelling, as a safety feature, and causing the surge. This time I did not disable the cruise and the vehicle speed came back again under 170 kph and towards my requested 160 kph.

Also, the overshoot is probably due to a voluntary limitation in the authorised rate of throttle angle change, possibly in order to avoid surging.

These tests were all made in Germany, officer...

Fabrice

Anze

Did you know, that Mazda disabled the capability of the Cruise Control in European cars? With the latest verion of calibration data the complete CC function is disabled. Mazda Motors Germany is not willing to explain the reason why or how to bring the CC to work again.

We have about 100 RX-8 here in Europe, self equipped with the original CC parts as you have it installed in yours. Some of them are already disabled.

This ist only to inform you about the fact, maybe yours will be disabled too!?

best regards

Anze

p.s.: sorry about my English!

Rasputin

Hi Anze,

By now, most European owners fitted with cruise are aware of the potential threat of a PCM re-calibration. Personally, I've instructed my dealer to put an hold on all future PCM reflashes on my car until this problem is sorted out.

Thanks,

Fabrice