Drive By Wire Throttle Wiring Question
 

looking at the service manual, it apears that there are 6 wires connecting the PCM to the Throttle Body Control. From the wiring diagram and the service manual, it appears that there are 2 wires that send the signals to the TB to control the throttle plate. the other four are grounds, power and a return signal?

When you view the info on the throttle position sensor, which ties to the TB, one of these two wires have as voltage range 0.4 to 4.095 (wire 1J) and the other has a votage range of 1.18 to 4.303 (wire 1M). Obviously there is some over lap there.

can someone help me understand why there are two wires? why the overlap?

i dont have the book in front of me. ill give you a call when i find it:)

There are two throttle position sensors that act independently of each other, acting as a sort of parity check. The throttle actuator is actually a servo and runs on a PWM signal.


https://www.rx8club.com/attachment.p...id=88510&stc=1

https://www.rx8club.com/attachment.p...id=88511&stc=1

never mind:)

It ia a feedback potentiometer system. As the volts go up on no.1,volts go down on no.2 and vice/versa. Really not a hard system to understand if you have worked on Const. equipment, pretty much all machines use this system now.

Interesting. my reason for asking is I'm trying to better understand your typical DBW system as thats the last engine related subsystem I don't know how to manipulate.

If you wanted to alter the throttle plate outside of the pcm, would you just tap the throttle actuator wires? Jeff, could label the six wires in that diagram so I know which ones are power, ground etc....?

Here:

https://www.rx8club.com/attachment.p...id=88518&stc=1

ah, redundancy, makes me feel much safer about the DBW system on my 8 lol

So from the pics I assume that the PCM reads the various TPS signals and then sends the voltage to the throttle body motor?

so the flow of info would look like

TPS -> PCM -> Throttle Motor / PCM reads the new TPS info -> Thottle motor etc....

The PCM is going to see that the TPS shows some minimum value at startup, and then just constantly plays a back and fourth game with motor adjustments?

My canscan always shows a min load of 17%, is that its way of showing how the throttle is always slightly open?

It is a pulse, not a voltage. Duty cycle determines throttle opening.

Yes. That is the idle %.

Duty cycle? thats interesting. Not how I figured it would work. Is that more for most DBW vehicles? Any idea why they did that? I guess its similar to how the PCM treats the fuel injectors then?

Exactly. Wider pulse equals more throttle opening. That is why the thing makes that "buzzing" sound.
Try putting the key in the run position without starting the motor in a quiet place and listen how the sound changes as you step on the gas. The pitch stays the same, but the timber changes from a tiny, "buzzy" sound to a rounder, more "flute" like sound as the throttle opens.
This is the pulse width going from a short duty cycle (5% or so) to a longer duration (50% or even more) while the period remains the same.

For a little lite reading this will give you a better idea of FBW.


http://www.picotech.com/auto/applica...e_control.html

it seems wierd to me that they would use a duty cycle approach to the throttle motor, i understand why it makes sense for fuel injectors or ignition, but seems wierd to me to use the same methodolgy for throttle control. Maybe they do it because the stock PCM sends out so many pulse signals already, its a more cost effective setup?

back to manipulating the DBW for a minute, I know the stock pcm has some wiggle room as far as what it deems ok for idle before it throughs a CEL, what if you were able to tap the TPS wires and send the PCM a signal back that has a voltage lower that "reality"? would the PCM then try to adjust the throttle by opening the plate more thereby raising the rpm?

could you build a device that basically allows the TPS voltage to be adjusted up or down for the PCM? Hopefully my concept makes some sense.

Cajun - excellent article which I didn't see before my post, thanks.

^^ You would have some "interesting" issues when driving.

PWM is just a more accurate way to control a positional motor. This is the way it is done in robotics and aeronautical endeavors. If you just feed a motor DC until it is in position, it will drift. By having a stepper motor referenced to a pulse, it will always be in an exact position each time it is commanded by that pulse.

Are there relatively simple was to adjust PWM? my limit EE knowledge doesn't stretch that far.

Well the pulse signal will index the motor 1 degree per pulse, as duty cycle is increased, the pulse is longer and the motor travels more degree's per pulse.

This is a stepper motor, the output shaft moves in steps as a driver signal is sent to the motor, is also reversable by flipping the A-B motor wire polarity.

Yes you can/could tap the signal and change the readings, however if you get above below the preset values in the ECM it will spit a code and the second TPS will have to be manipulated also otherwise the 2 values won't match

Why do you want to attempt this?? The system is redundant to prevent throttle motor from going full open or closed due to a short or broken wire. Tapping into the harnesses is not really good to do in this system. Any resistance introduced in the system can cause it to go into limp home mode if the feedback signals are out of range.

Hope this helps, Steve

I'm curious about all this as I've got a good idea how to manipulate nearly all the engine functions with a standalone except throttle control. Its a subject that I'm trying to learn more about as obviously DBW is hear to stay.

in addition, I would like to be able to make some small idle adjustments for smoothness. I believe the changes I would need to make are small enough not to be noticed by the pcm as they fit in their margin for error.

dont mess around and get a run a way--its not purty.
OD

hence my questioning before I even really consider anything :D:

several japanese tuners offer an electronic throttle control modifier, as I understand it you can change the rate at which the throttle body responds relative to gas pedal position change, not sure if it works on US models, don't know that anyone has ever tried it or not

I looked at Greddy, HKS and RE Amemiya didn't see anything, you don't recall who made one do you?

BTW, you get full throttle well before the pedal hits the floor.

Actually, you get all you're gonna get around 80% of pedal travel, which is about 90% of WOT.
The PCM doesn't do WOT for some reason.

100% of 90% at 80%.....that's pretty good.

Gotta be happy with that!!

I suppose. I imagine Mazda found max power at something less than WOT.

A-RF sells one, good luck, classic f'd up japanese site:

http://www.a-rf.com/PC/PartsList/Car...rts/index.html

brillo if you want to change your idle why not just drill a small hole in the throttle plate:)

I could do that (not sure if it would work) but I really want to understand how to manipulate the DBW system. I've learned how to basically through a standalone ECU on virtually any car now thanks to my experiments with the megasquirt and Interceptor, but neither of those can control DBW.

I'd like to be able to know if necessary how to defeat DBW should I find myself looking at another car wanting to modify/tweak it.

Why aren't you trying to mess with the throttle pedal instead of the throttle plate?

I don't think the car will be happy if you open up the throttle plate without the ECU asking for it. It's really easy to just mess with the resistance at the throttle pedal and let the ECU do whatever it wants based on that.

I would be willing to bet you that the fault tolerance in this system is less than 1/2 a percent. Therefore any changes you make will be seen by the PCM, if they are not seen it will not effect any noticeable change.
As for idle adjustments, what are you looking to really do? Is it an issue with smoothness at a perticular idle speed or more with loading at certain speeds.
These issues might be better addressed with fuel mapping.
My 0.02

Also, it sounds like Cobb and others are about to let us change a whole bunch of stuff in our ECU's very soon. Waiting to do that and tweaking the code is probably going to be the best option out there.

Hopefully Cobb will be able to alter and flash all parts of the PCM. Racing Beat, the only company to have sucess with flashing to date, was not able to alter the DBW settings as they were stored in a seperate part of the PCM they could not access. That doesn't mean Cobb won't have better luck, but its obivously not a easy process.

sorry to resurrect an old topic. But couldn't find the information I require

I'm looking for the 0-5 volt input to ECU wire on the Throttle body connector or on the ECU.

I'm performing an engine swap and am reusing the drive by wire system and the new engines ecu requires this input. I'm pretty sure it should exist but could not find it with a multimeter....



Thanks,

P0222 can cause stalling 3 sec after start?
 

Hate to resurrect, but I have a very odd situation. 2006 GT, 6spd. Car dies 3 seconds after starting, and throws a P0222 code. Doesn't flood, and will restart eagerly multiple times in a row. Tried 4 different TBs (2 used, 2 remans) and the remans won't respond at all, while the used ones will open after start, if I go WOT, but wont hold RPM and die, if I let go. I tested every single wire on the TB and the PCM for continuity and shorts, and they all check out. The top-of-the-engine harness, in fact, is new, I got it from Mazda a year ago. Car ran fine, until one day it just wouldn't start (dies right after starting). My understanding is that even with a broken TB or pedal (also swapped that back and forth with another used one) the car will idle, just poorly and respond to throttle inputs, also poorly. It's not throwing any other codes, so I have no reason to believe it's another component. Right now, I am thinking it could the be PCM itself. Using torque, I can see the requested pedal position change as I depress the throttle pedal. but no change in the TB, even after it starts (again, unless I use the older TBs which will react to WOT only).
Any ideas?