I had a nice little "Eureka!" moment this evening and thought I'd share my findings.
First though, a quick history lesson.
My wife owned (briefly) one of the new MX5 PRHTs. Fun little car, but not our cup of tea. One of the first irks we discovered with it was that there was a rather peculiar amount of throttle lag post shift. This was very noticeable on brisk shifts from first into second under WOT. It felt like the car was holding back a bit for say a 2 count, then giving you what your right foot had originally requested. When really stomping the loud pedal from a dead stop, you felt it on the fist 3 shifts and it drove you MAD!
It felt this way, as it turns out, because it WAS this way. In an effort to extend the life of the clutch (and by association the entire drivetrain in general), Mazda engineered a software version of BMW's infamous CDV - clutch delay valve. The clutch in the MX5 triggered two switches. One switch, at the bottom of full travel, to indicate that the clutch was fully depressed to allow the car to start. A normal feature on all manual cars. But the second switch was the culprit - it resided at the top of the clutch arm and was always "IN" when the clutch wasn't depressed. So, when you pushed the clutch in, this switch would release "OUT" and the ECU would slightly retard timing for just under 2 seconds. This made for smoother (though laggy) throttle response from a dead stop in 1st gear, smoothed out the throttle uptake post shift for most drivers, and in, theory added life/miles to the clutch.
So WTF does this have to do with our 987?? I'm getting there...let me put this whiteboard away...
Our 987 has exactly the same arrangement as the MX5. I searched here and abroad (googleahem) and found nothing relating to this topic, so I'm bringing it up here in as much detail as I can muster at 4am.
It took me 30 seconds to verify that this is what I was hearing (as described in my first post) once I had the switch removed. Press the switch pin in while holding RPMs at 1,000 and the engine sounds (and is) normal. This is the state that the clutch is normally in (foot off the clutch, pushing this second switch pin IN) If you release the pin however while holding 1,000rpm and "Braaaaaappppp" - note change. Timing change. It lasts just at or under 2 seconds.
In the MX5, disconnecting this switch (or taping it shut to be always IN) resulted in a CEL after 50~80 miles. Nothing major, just the modern cars way of telling you that something was amiss. My scan tool resulted in, yup, "CLUTCH SWITCH ERROR" on the MX5 which was easily erased and reset. In that car, where HP and response was much more dear, it made a world of difference and was worth the slight inconvenience of having to hook up the scan tool every so often. In fact, I'd say that the acceleration times that magazines posted for that car were nigh impossible without having defeated the clutch delay switch. It was THAT intrusive in those first 3 upshifts under full giddy up.
In the 987, I'm guessing it will do the same (throw a CEL over time) but if we're lucky it will throw a soft code, store it, realize that it's not the end of the world and not trigger a CEL.
I drove 25 miles tonight with the switch taped IN (to replicate what position it is in during normal driving). As expected, the difference is dramatic. The flat engine note "Braaapp" when leaving a light in 1st gear with the top down (obviously a Boxster here but windows down in a Cayman would be very similar) is gone. Throttle response is very quick from a dead stop, which takes all of 4 stoplights to readjust to (to compare, think of non-sport to sport mode throttle response and it's similar).
Before the switch defeat, I had subtle but noticeable delays on moderate (low speed) low RPM shifts that are now gone. In my case, this always happened right around 3,000rpm under normal driving conditions (not too slow, and not having fun either) and because it was rather consistent in this regard, it felt like a brief surge or hiccup when it happened. What I was feeling was the clutch delay (just under 2 seconds).
So, to illustrate, you'd pull away from a stop in 1st gear, accelerate up through say 3,500rpm, shift into second, revs falling to 2,300 or so, and as you accelerated through 3,000, right at that point you would get what felt like a slight hiccup or surge. This didn't happen all the time, but was quite noticeable when it did happen.
As with the MX5, that brief hiccup or delay is gone making for very linear, smooth throttle take-up and response, post shift. I have a rather sensitive backside and if you're like me, you'll appreciate this change. Anyone who owns (or has owned) modern BMWs and has performed the CDV-ectomy will know what this feels like, pre and post.
The advantages for me are simple - the embarrassing and annoying "braaaaap" is gone, making for much more enjoyable 1st gear starts (as well as driving up any inclines, parking the car, backing up, and so on). And, of course, linear and smoother shifts.
The disadvantages for someone doing this are perhaps a slightly lower life expectancy of the clutch, the possibility of a CEL (check engine light) and/or stored "CLUTCH SWITCH" error and, quite probably, the lose of clutch triggered cruise control deactivation. If these things bother you, this probably isn't something you want to try.
But if you want to try a 30 second experiment to see how your car feels with this "feature" disabled, it's a piece of cake, and just as easy to restore if you don't like it.
To have your own little Eureka! moment, poke your head down in the footwell and peer up at your clutch pedal. Operate the pedal and observe the two switches - one beneath the clutch arm, and one at the top of the clutch arm. The one beneath the clutch arm will be pushed down (IN) as you push the clutch in. This switch is the "Have you pushed the clutch in yet, you sod?" switch before the ECU will allow you to start the engine. Ignore this switch.
The reddish switch at the top of the clutch pedal is the one you want. By pushing the clutch in, you will observe the pin releasing OUT as the clutch pushes in. When the clutch is up, the pin is pushed IN. The switch module is a sort of terracotta/red color. If you grasp it and turn it gently anticlockwise, you can remove it from the bracket holding it in place. You will see the pin is now out. All you have to do is tape that pin in (I wrapped mine end over end several times with black electrical tape) - you can use a zip tie or rubber band as well. Once you've taped it down, you can simply snug the whole bit behind the carpeted fuse panel surround trim (if you've done the
Mods4Cars module, you know which panel I'm referring to). You can also probably push it back into the bracket, but this will weaken the tape in the fashion it was wrapped around end to end. Alternatively you could probably just disconnect the harness wired to this switch, but in the hopes that the switch being plugged in, just simply not used any longer, will not result in a CEL. Unplugging it may result in a CEL straight away.
Anyhow, if you're bored or curious to see how your car drives with this "feature" switched off, have a go and report back on what you find. I quite like it and intend to keep it this way, CEL or no. I'll simply keep my pocket scan tool in the door cubby and clear the code as needed.
But here's to hoping that it simply stores a soft code and won't light up the dash after 100 miles (25 miles so far and no CEL).
What would be grand, if I may dream for a moment, is for someone like Scott at
Softronic to see if it's perhaps possible to // this particular switch activity altogether, or perhaps ignore the error message (if generated) by having it disabled.
Keep in mind that this will make the throttle snappier off the line, so if you're clutch uptake challenged, this may frustrate you more than tickle you. On the other hand, if you enjoy full control over the tactile and feedback heavy controls of your car, you will quite enjoy this tweak. For me, it's a 50/50 affair...50% of my joy comes from no longer having the flatulent flat "braaaap" when parking/backing up or leaving a stoplight. It's not the most pleasing tone in the world and now I'm left with that glorious flat six arrangement, sans drunk trombone player. The other 50% of course comes from having linear throttle response post shift(s).
Apologies for the lengthy post here, but I figured I'd better explain myself if I was going to offer up a solution to my own question and go over the "why".
Cheers!
'07 CS, Meteor Grey, stone grey, 19" Carrera Sport with meteor grey spokes/polished rim, headrest crests, bi-xenons, Bose, power seats, rain sensor, fire extinguisher, heated seats, dimming mirrors, FabSpeed Maxflo II catback
