I believe only the 4.2 models throttle is totally 'Drive By Wire'.

I also seem to remember reading a setup procedure, for the 4.2, were you taught the ecm your throttle pedal positions. So it knows were 0 and 100% are, without any cable adjustment.

I think it involved pushing the throttle pedal slowly between 0% and 100% 5 times, after a battery reset.

Obviously if you take the slack out you will end up with finer control. (bigger range)

Does anybody recall this procedure and know if it does apply to this model?

 

You are correct, same procedure on my SRT8. The drive by wire system is totally reliant on the training.

 

4.0 (AJ26) = only idle and torque reductions (closing the butterfly) are controlled by the ECU, sortoff semi drive by wire.
4.0 (AJ27) = full drive by wire, but added mechanical limp home function (iirc for only 30% max open at 100% pedal down).
4.2 2003-2006 = full drive by wire, no mechanical link anymore, limp home is also electronically controlled.

All 3 have a cable attached from the gas pedal to a Pedal positioning sensor, but on the 4.2 it is not attached anymore to the TB so also no mechanical link anymore.

 

I think the sensation that is most often felt after tightening the throttle cable isn't actually more power but rather more response, or to put it more succinctly - more immediate response when pressing the accelerator from a dead stop. On the other end of the scale (WOT), the result is actually being able to achieve WOT! An intermediate result is that a 1/2 or 3/4 press on the gas pedal will allow the vehicle to downshift rather than a full "cram down to the floor." At least those are my experiences. If any of it is in my mind - oh well! LOL

 

Does anybody have the JTIS direction on throttle setting and or repair for those systems with true drive by wire?


As for some of you guys grouping everybody here with vivid imaginations as to increased HP after resetting throttle for true WOT.....you should define your broad and antagonistic statements.
Stolen from my friends at DSL

How Does a Drive by Wire Throttle Work?

This is going to be a quick and dirty explanation of how a drive by wire throttle works.

It is not centered on any one manufacturer's design. The basic concepts are universal and brand agnostic.

Questions and comments are welcome, however a minimum level of knowledge is assumed.

This thread is about tech only.

First, a circuit diagram:

By scotiapilot at 2012-05-24


Basic operation:
1. The accel pedal is the input
2. The engine computer receives this signal and drives the throttle motor (output)
3. The engine computer uses the throttle position sensor as feedback to confirm the throttle position achieved.

Note:
In the following, "a failsafe" refers to action (such as shutting off power to the throttle motor or performing fuel cut) taken to ensure safety.

Redundancies on the hardware side:
-Two separate sensor circuits in the accel pedal.
-Two separate circuits to and from the engine computer.
-Separate +5V power supplies and grounds are used for these circuits.
-Two separate sensor circuits in the throttle position sensor.
-Two separate sensor signal circuits to and from the engine computer.
-A pair of springs that close the throttle immediately if power is lost (The throttle closer spring is the stronger of the two. The throttle opener spring opens the throttle a few degrees to prevent it from freezing closed.)
-Redundant power supplies to the engine computer.
-Multiple CPUs in the engine computer that are making the same calculations, and a watchdog function. (This ensures that the computer doesn't start making 'bad decisions'.
-Multiple transistors that must operate in cooperation to power the throttle motor (no single 'stuck' transistor can cause the throttle motor to open).

Redundancies/falisafes on the control side:
-The input section compares the two signals received from the accelerator pedal sensor. There must always be a fixed voltage relationship between the two signal wires. If there is an out of spec difference, the MIL illuminates and a failsafe mode begins. (See the following diagram)
-With the separate CPUs/RAM, the watchdog monitors for calculation differences and if there is a difference, the MIL illuminates and a failsafe mode begins.
-The engine computer controls a set of transistors to operate the throttle motor. The engine computer monitors voltage and current flow. If either voltage or current is out of spec, or occurs at an improper time, then the MIL illuminates and a failsafe mode begins.
-The engine computer monitors the throttle position sensor to confirm the position of the throttle. If it is not responding correctly, then the MIL illuminates and a failsafe mode begins.
-In addition to the types of monitoring mentioned above, the engine computer also monitors each of the input and output lines for logical inconsistencies, and open and short circuits.

Next, a representation of the voltage outputs of either the Accel Pedal sensor or Throttle Position sensor.

By scotiapilot at 2012-05-24

 

The Throttle By-Wire (TBW) aka Drive-By-Wire (DBW) systems appears to be more complex than they actually are due the the redundancy which is built into the systems for safety reasons. Most TBW systems contain four major components; (1) the Throttle Actuator Control Relay, (2) the Drive Circuit for the throttle actuator which is located inside the ECU, (3) the Accelerator Pedal Position (APP) assembly, and (4) the Electric Throttle Body Assembly. With the implementation of the TBW system, manufacturers were able to eliminate the Idle Air Control (IAC) system because they are able to use the electronic throttle body to control the engine's deceleration and idle. The below diagram will demonstrate the basic TBW system operation, please notice that each sensory component of the TBW system has 6 wires connected to it; we will later explain what each of these wires are for.

The first part of this system is the Throttle Actuator Control Relay which powers and protects the TBW circuity. The second part of this system is the Accelerator Pedal Position (APP) assembly which transmits two pedal position inputs to the ECU. The gas pedal (APP assembly) is effectively two independent pedal position sensors which each contain a +5V reference, a ground reference, and a signal which is sent to the TBW circuitry located inside the ECU. One signal is considered the “Main” APP signal and the secondary signal is considered the “Sub" APP signal, both of which tell the ECU what the driver's foot is doing as far as requesting torque from the motor (how much the driver is pushing down on the gas pedal).

The next part of this system is the Electric Throttle Body Assembly which consists of the throttle actuator motor, throttle valve, and 2 throttle position sensors. Like the APP assembly this part contains 6 wires; two of which are the shared +5V reference and shared ground reference wires which power the two TPS sensors, The next two wires are the redundant TPS sensor signals (Main and Sub) which transmit the position of the throttle blade to the ECU. The last two wires are for the throttle actuator control signal, these lines control the opening and closing of the throttle blade.

The last part of this system is the TBW Circuitry located inside the ECU. This circuitry receives the Main and Sub APP signals so it knows what the driver's foot is doing (as far as requesting torque) then it sends a square wave, 12 volt signal across the two throttle actuator control signal lines to step the throttle actuator motor with a duty cycle; 100% duty cycle would open the throttle blade to WOT & 0% duty cycle would keep the throttle blade at the fully closed position. Based on the feedback received from the two TPS sensor signals located in the Electric Throttle Body Assembly, the TBW system is constantly receiving inputs (APP & TPS) and controlling outputs (throttle actuator motor) in order to control the throttle blade movement on the vehicle.
What this means to you:
...most modern engines will never show a 0% TPS since the throttle blade is always kept open (by 2-7%) to start the engine and to maintain idle.
...some modern engines will never report a 100% TPS while at WOT since their TBW system may have been programmed to only open up to a predetermined point.
...you can be able to change the Rev Limits on an engine by tricking the ECU about the reported RPM but you may not be able to get the motor to accelerate past a certain RPM since the throttle body has been programmed to close by a predetermined RPM.
...porting of most modern throttle bodies is not a good idea unless you have the ability to fully re-calibrate that system.
...most modern engines will not allow the motor to start immediately after the battery has been disconnected then re-connected or if the ECU has been re-set because the systems needs approximately 5 seconds to fully calibrate the TBW system. If the battery has been disconnected then re-connected or if the ECU has been re-set, please allow the key to stay in the ON position for a minimum of 10 seconds to allow the TBW system to calibrate before you try to start the engine.
...providing a constant +12V to the throttle actuator motor will fully open the throttle blade, providing a constant -12V (reversing the polarity) to the throttle actuator motor will fully close the throttle blade.
...most modern EMS logic has been calibrated to control the throttle blade opening and closing speed. We have seen where the throttle blade actually opens slower if you slap down the gas pedal versus gradually depressing the gas pedal.
...most modern EMS programming was established to lessen the emissions output of the motors, so throttle opening and closing delays have been implemented to lessen the emission output of the motors...not to **** you off.
...most modern vehicles have some sort of Traction Control System which use the Electric Throttle Bodies to control engine torque output.
...most modern vehicles have some artificial throttle response programmed into their control. For instance, if the driver is pushing down on the APP 20% the TPS sensor may report a 50% reading. The ECU is creating artificial throttle response by opening the throttle valve much more that the driver is requesting.

 

AVOS help me out here.

My 2000 XKR according to your notes is a AJ27S? or AJ26?

My throttle body butterfly valve is directly connected to my throttle pedal. Can you show me through the JTIS the drive by wire components?

 

You have indeed AJ27 engine, so the throttle is operated by the ECU, ie drive by wire.

 

I am searching and find no such animal on the JTIS,

 

Sorry if I have missed it, but what are you looking for?

 

I believe this is the throttle body used on the XKR, on a drive by wire system the throttle plate is opened by an electric motor. That means that the throttle cable on the 2000 XKR is not directly attached to the butterfly valve.


By Scotiapilot at 2012-05-24

By scotiapilot at 2012-05-24

By scotiapilot at 2012-05-24

By scotiapilot at 2012-05-24

By scotiapilot at 2012-05-24

 

The pictures above are from an AJ26 throttle body.

As said, on the AJ27 engines, you have fail safe mode, so the axle is connected to the butterfly so you can operate it but only for 30% max opening or so (which is pedal to the floor).

You don’t have to take my word for it, so just try it yourself. Have a look at the butterfly and move the cable to 100% pedal to the floor.

 

Well if that is the case, that a 2001 XK8 is a Drive-by-Wire and the Accelerator Pedal/Throttle Cable does not actually control the Butterfly Valve, then I do not understand:

a) My Jag after purchase would not kick into passing gear.
b) Made a Post on this Forum and the 'Rev' answered (along with his video) as far as adjusting the Throttle Cable at the TB.
c) Adjusted the Cable and 'lo and behold', now it kicks into passing gear with some authority.
d) Is this because at first, the accelerator pedal couldn't be depressed enough to actuate the switch below the pedal or what?

Just a little confused about the Drive-by-Wire in a 2001...

 

You still have a mechanical cable to the Pedal Positioning sensor that gives input to the ECU. So cable to loose, PPS does not go 100% and thus the ECU will also not further open the butterfly.

 

I believe you.

Thus more power and/or restored power by resetting or setting the cable to function as intended.

 

I've searched for a reference to the training technique with no result.
Does anyone have any documentation?

 

For the 4.2 throttle arrangement, JTIS requires the adjusting collar to be set such that 14 teeth are visible externally and then, with the 'special tool' in place, the pedal to be slowly pressed, through kickdown, to the floor and held there for 5 seconds. To train it? Why else? Ignition On/Off is not mentioned!

 

My goodness,

The fact is quite simple....Adjusting the throttle cable, cleaning the air intake, cleaning the oxygen sensor --- results in optimal performance....Period!

Eaglei.

 

The Accelerator Cable is connected to a Dual Potentiometer Assembly AND a Fail Safe Linkage.

Normally the Potentiometer Signals are used to tell the ECM to open or close the Throttle Plate. The Fail Safe Linkage does NOT contact the Throttle Plate directly.

If the Throttle Motor Fails, the Fail Safe Linkage comes into play and DOES Connect to the Throttle Plate Mechanically.

There is a Rotational Lag (in Degrees of Rotation) between the Fail Safe Linkage and the Throttle Plate Shaft Assembly.

This Lag is maintained during normal operation.

In Fail Safe Mode, this Rotational Lag must be taken up before the Fail Safe Linkage contacts the Throttle Plate.

This Lag is subtracted from the Maximum Possible Rotation of the Throttle Plate, Limiting Throttle opening in Fail Safe Mode.

 

After resetting Throttle Body Cable I would think one then would need to reset the following:

Resetting kickdown travel limits
After battery reconnection, the engine management
system must ‘re-learn’ the limits of throttle pedal travel.
This is to ensure correct adaptive settings are stored for
kickdown operation. Re-programming is done with the
ignition switch in position II a follows:
• Slowly press the accelerator pedal fully through the
kickdown detent to the floor. Release the pedal and
repeat the action.