Kas

Please read! dont skip bits.

Driving to work this morning trying to crack the mystyrious case of the dyno problem and wondering what feature of the car is stopping us apart from the wheel speeds. It occured to me that the front xenon lights actually change angles if you are driving up a hill or down a slope to stay focused on the road.

This brings me to know that the car has a tilt sensor OR gravitational leveling system!!! whoopie doo, however this may also be telling the ECU that there is x amount of gravity either +/- on the car, hence driving forward, under brakes or in the dyno's case, still.

I think i'm onto something here. I believe that the speed of the wheels has no effect whatsoever provided the DSC is turned off. 5kmh difference in wheel speed from the front to back would indicate traction loss, not to mention the back wheels doing 180kmh, it'd shut the throttle and remove all power to the wheels as we've all seen when you throw it round a corner.

Can anyone else offer ideas based on this. Once we have the idea, the solution will appear.

Doctorr

Kas, I definately think you are on the right track...

The levelling system is a set of sensors on each wheel, if you get under, you can see each one is a little arm from the suspension to the body, that sends a signal as to how loaded the suspension is.

There IS however, a 'YAW SENSOR' in the wiring diagram, at the exact centre point of the wheelbase, by the mid 12 volt outlet in the console.

I suggested some time ago that it would probably have a 'fit' if the speedo said 100mph, yet it was saying the car was standing still.......
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doc

Kas

thanks doc.

Looking at the way g-tech's and alike work, from g-force only they can measure so many things including speed and HP. The g-tech concept has proven to work extremely well as far as acuracy goes.

A signal to the suspension would indicate load/mass/weight that can be used to measure output/hp etc..

Its been said before that the 8 is a driving super computer!

MazdaManiac

iTrader: (3)

Interesting theory, but no. Sorry.

The combined sensor (the accelerometer located in the center console) is only setup for lateral g's and yaw. It won't notice longitudinal movement.

The self-leveling headlight system is not attached to the PCM or TCS/ABS/DSC system except for power (it shares the green/red power buss with the stereo and a bunch of other unrelated systems). It has its own control module.
Plus, this would mean that cars not equipped with HIDs (base model and sport package) would work on the dyno.
They don't.

Furthermore, if the vehicle could measure acceleration, it would see none if the vehicle were moving along at a steady speed - a condition that will still trip the ABS system if a differential exists across the ABS sensors.

Kas

whoa, shutdown.

I'm not saying it uses the gravity for all features of the car, but then again, the sensor for the lights etc is not connected to anything else.

hmm, i'll still ponder this for a while

MazdaManiac

iTrader: (3)

Yes, absolutely. Please continue to ponder.
I consider this forum to be a kind of distributed computer network, working on breaking the encryption code that is the RX-8.
If we all keep taking educated guesses at it, we will figure it all out.

Kas

yeap. WE as a team are nearly there. few things still dont add up. We'll make the bridge somehow

Kev

A sort of Alan Turing network heh?

Hymee

iTrader: (1)

Kas,

The sensor that tilts the xenons up and down is a physical device near the rear axle. It measures the amount of suspension squat, and adjusts the lights accordingly. I'm not sure if there is one on the front as well. I have not looked for it, nor studied a wiring diagram, but it would make sense.

Nice lateral thinking though (pun intended )

Cheers,
Hymee.

Wildcard

Hymee - maybe the fact that you don't have the headlight leveling sensors explains why your car dynos higher and goes faster than any one elses!

Hymee

iTrader: (1)

Yeah - it did dyno a little bit higher than yours that morning didn't it?

Remember you said you did not have the good juice in it though...

Cheers,
Hymee.

canzoomer

Some facts, derived from the wiring manual and testing and observations:

1) The pitch sensors for the headlights are only connected to the headlight leveling circuit, NOT the ECU.

2) There are two sensors for this, one at the front suspension, left wheel, one at the rear left wheel.

3) If you want to disable the DSC and ABS control in the Bosch DSC computer from preventing a successful dyno run take the rear wheel speed sensors, unbolt them from where they attach by the wheels, and tie them back out of the way.
LEAVE THEM CONNECTED.

They will then measure no wheel speed, just like the front ones.
The ABS/DCS unit ( the Bosch unit at the drivers side under the hood with the brake lines going to it) then thinks the car is motionless.


I have on a couple of ocasions still seen a check engine light after about 20-30 seconds on a dyno with these set up this way, so it is a possibility that the ECU eventually got speed sensing from somewhere else. We were doing sustained speed drag measurements on the dyno to determine torwue, not horsepower. This involved setting the dyno to a fixed resistance figure, and using the throttle to keep the speed approximately constant. LESS than full throttle. During these runs the duration is quite long, up to 60 seconds.

I suspect that there is a tranny speed sensor used to manage the variable assist on the electric power steering.

I am not *certain* how it would do this.
The Bosch unit does not send wheel speed to the ECU, only a fault condition if it detects it.

In any case, the resulting "limp mode" from an ABS/DSC event is clearly noticeable. Lights go on the dash, power clearly drops, just as if you had spun the rear wheels and the DSC corrected.

Press the little button on the dash all you want. If the DSC control in the Bosch notices the rear and front wheels are travelling at different speeds for more than 3 or 4 seconds it WILL cut power, regardless of what you did with that button.

Pressing the button only turns it off for short "events", not ones over 3 second in duration.

This issue is solved by moving the sensors as described above.

I hope this makes it all clear to everyone?

MazdaManiac

iTrader: (3)

I noted this earlier in the thread.

VSS - Vehicle Speed Sensor.
Mounted on top of the tranny, this is the sender for the speedo.

canzoomer

Yes, you did. This is an encapsulation of things posted across this thread and othes earlier, by you, me, and a few others.
A lot of these topics have a habit of recycling.
I was hoping to help people avoid the pitfalls of a long thread to eventually get to the same points we already have determined.
Thanks!
Yes, it is there, but I have not been able to determine if the ECU actually uses it for anything else BUT steering and speedo.

With the Bosch traction control unit being used this type of functionality makes a redundancy in the system if it works this way. As redundancy costs money, and as there is no apparent safety or performance reason for them to do this, I wonder if it is the cause of these long duration caused error faults,or if something else is triggering these.
It also does not cut power nearly as noticeably when this fault type occurs. It is a solid light rather than the dreaded blinking check engine.

One does not need to do a battery disconnect to clear. Simple shutoff and restart clears it.

Anyway, this about covers the sum of the issues surrounding dyno testing.