Throttle Body Cable Adjustment = Original Power Restored ?
#261
01-02-2013, 04:11 PM
I just adjusted my cable yesterday and had an 
experience.
Thanks to SeismicGuy for explaining that there was no need to use the special tool.
I just removed the clip, took out the slack (about four or five notches) put the clip back in and then pressed the accelerator straight to the floor and held it for 5 seconds to make the final adjustment.
Wow, what a difference!!!
I never did work out what "Make sure 14 teeth are visible on the outer cable" ment but I don't seem to have broken anything so all is well.
Thanks to everyone who contributed to this thread. It really is a simple and most rewarding thing to do!
experience.Thanks to SeismicGuy for explaining that there was no need to use the special tool.
I just removed the clip, took out the slack (about four or five notches) put the clip back in and then pressed the accelerator straight to the floor and held it for 5 seconds to make the final adjustment.
Wow, what a difference!!!
I never did work out what "Make sure 14 teeth are visible on the outer cable" ment but I don't seem to have broken anything so all is well.
Thanks to everyone who contributed to this thread. It really is a simple and most rewarding thing to do!
#262
04-10-2013, 02:06 PM
Probably because (as I posted numerous times before) the basic mechanism resets the cable to a "correct" position. In the JTIS, the step that does the actual adjustment is the final step where you floor the pedal (with the engine NOT running, of course) and that sets the final position. With my previous car, there was a similar adjusting mechanism and you could initially position the cable anywhere you like (even tension it too much so that the throttle blades were open when the pedal was being pressed) but the final step of pressing the pedal re-adjusts the cable to the right position. The perceived "performance gains" with this adjustment are only due to the fact that you are opening the throttle body quicker (assuming the original adjustment was way too slack) but once you floor the pedal, the mechanism resets to a "correct" position.
once again.
Doug
once again.Doug
#263
04-10-2013, 03:14 PM
Veteran Member
My 4.0L is manual for the cable adjustment. I did the "press to floor and release" cycle JIC, but not sure it was needed. These are not 100% drive by wire, hence the cable.
You will need to give it some miles to relearn your driving style given the better throttle response. You'll like it to. It "feels" much better depending on how bad it was out of adjustment.
You will need to give it some miles to relearn your driving style given the better throttle response. You'll like it to. It "feels" much better depending on how bad it was out of adjustment.
#264
04-11-2013, 12:43 AM
Veteran Member
I believe the procedure is quite different for the 4.0 vehicles and more like a traditional linkage than the drive-by-wire. As I mentioned my 95 Corvette had a similar throttle cable adjustment to my XKR (i.e., take out the tautness in the cable and then push the pedal to the floor to reset the proper position).
But, just like with the Jaguars, the adjustment mechanism in a slightly older Corvette (maybe 93 or 92) was totally different. So there were always guys on the Corvette forum who were screwing up their throttle adjustment by following instructions for a different year.
I still cannot quite figure out what is going on with the adjustment in the 4.2 Jaguar models. The JTIS explains the procedure but not the physics of what is going on. If someone had one of the mechanisms to dissect it would be interesting seeing what is happening inside that gizmo with the notches.
Doug
#265
04-11-2013, 10:19 AM
Veteran Member
On the side of the TB is the throttle position sensor (TPS). The TPS output is in voltage, usually 0.5 to 5.0 volts. The computer reads change in voltage, not absolute values. Therefore, whenever the TB, the cable, or the TPS is worked on, it is advisable to effect a reset. This reset helps the computer by reading the top and bottom of the voltage range (throttle plates shut at idle, or open as in WOT)..
In reality, if someone doesn't reset, the computer eventually compensates for the new changes. On our cars the TB also has a pedal position sensor which functions the same as a TPS.
For the record, I also am a little skeptical of the miraculous improvement in performance associated with a simple cable adjustment. A better driving car, yes; but everything done to keep a car tuned also provides for a better driving car.
In reality, if someone doesn't reset, the computer eventually compensates for the new changes. On our cars the TB also has a pedal position sensor which functions the same as a TPS.
For the record, I also am a little skeptical of the miraculous improvement in performance associated with a simple cable adjustment. A better driving car, yes; but everything done to keep a car tuned also provides for a better driving car.
#266
04-11-2013, 11:21 AM
Veteran Member
You should be skeptical, there is no change in HP gained. However, the throttle response improves, and in my case, the butterfly was only opening about 80%. I was never getting a true WOT condition. The difference in how it drove and felt was instantly noticeable.
#267
04-11-2013, 11:26 AM
Veteran Member
Absolutely--not at all a performance improvement but just an adjustment. I recall some guys on the Corvette forum who would go through the adjustment but forget to do the last step which is pushing the pedal to the floor. In the best case they would end up with a very responsive throttle since there was now no slack at all so they thought they gained some performance (I guess you can argue that they did compared to a throttle that was not opening all the way). In the worst case they would end up with a car idling at 2000+ rpm if they over-tightened the cable. In any event once they floored the pedal once it reset the cable to the correct position.
With the Jaguar I think the reset mechanism is going on inside that tubular gizmo with the notches.
Doug
#268
04-11-2013, 08:40 PM
Senior Member
On an older xk8
On the 97 Xk8, this adjustment is a little different and more like traditional cars. The circle is the area where you adjust 2 bolts. Mine was just off by just one full turn of the bolt. I idle just under 1000 rpms. The arrow is pointing to a vacuum that broke while I was cleaning the throttle. Had to go to auto part store to buy a new vacuum hose. They get brittle with the engine heat. Anyway, not much of a difference for me.
The following 3 users liked this post by lunaticpro:
#269
05-01-2014, 03:05 PM
I wasn't sure in my own mind about the actual differences between the early and late model setup for pedal and throttle plate position sensing and have turned to JTIS and Jaguar product training documents to try and make sense of it.
The conclusion has to be that the pedal position learning procedure is only applicable to the later models fitted with an Accelerator Pedal Position (APP) Sensor. Throttle Cable adjustment is applicable to the early models.
LATER MODELS
The ECM monitors the angle of the accelerator pedal through the accelerator pedal position (APP) sensor (circled in red):
Attachment 25928
This is my RHD vehicle. It's under the opposite side cover on LHD vehicles.
The APP sensor sends a signal to the ECM which is proportional to the angle of the accelerator. The APP sensor is connected to the accelerator pedal via an accelerator cable. The APP reverts to default settings after a battery disconnect and this is why resetting the pedal travel limits is required.
The ECM also monitors the angle of the throttle plate within the Throttle Body Housing through the throttle position (TP) sensor (circled in blue):
Attachment 25929
The TP sensor sends a voltage to the ECM which is proportional to the angle of the throttle plate. The voltage from the TP sensor increases with the angle of the throttle plate. There are two sensor tracks within the TP sensor.
The later vehicles therefore have two separately located sensors inputting pedal position and throttle plate to the ECU.
EARLY MODELS
The Throttle Body also has an accelerator pedal position (APP) sensor consisting of twin potentiometers which provide separate analogue input signals, proportional to driver demand to the ECM. As a further safety feature the two potentiometers have different input/output characteristics for unique signal identifications and any corrupt signal between the expected outputs will cause the ECM to switch the throttle to limp home mode.
The early models combine sensing of pedal position and throttle plate within the Throttle Body. This is why correct adjustment of the throttle cable is important on these models.
Graham
The conclusion has to be that the pedal position learning procedure is only applicable to the later models fitted with an Accelerator Pedal Position (APP) Sensor. Throttle Cable adjustment is applicable to the early models.
LATER MODELS
The ECM monitors the angle of the accelerator pedal through the accelerator pedal position (APP) sensor (circled in red):
Attachment 25928
This is my RHD vehicle. It's under the opposite side cover on LHD vehicles.
The APP sensor sends a signal to the ECM which is proportional to the angle of the accelerator. The APP sensor is connected to the accelerator pedal via an accelerator cable. The APP reverts to default settings after a battery disconnect and this is why resetting the pedal travel limits is required.
The ECM also monitors the angle of the throttle plate within the Throttle Body Housing through the throttle position (TP) sensor (circled in blue):
Attachment 25929
The TP sensor sends a voltage to the ECM which is proportional to the angle of the throttle plate. The voltage from the TP sensor increases with the angle of the throttle plate. There are two sensor tracks within the TP sensor.
The later vehicles therefore have two separately located sensors inputting pedal position and throttle plate to the ECU.
EARLY MODELS
The Throttle Body also has an accelerator pedal position (APP) sensor consisting of twin potentiometers which provide separate analogue input signals, proportional to driver demand to the ECM. As a further safety feature the two potentiometers have different input/output characteristics for unique signal identifications and any corrupt signal between the expected outputs will cause the ECM to switch the throttle to limp home mode.
The early models combine sensing of pedal position and throttle plate within the Throttle Body. This is why correct adjustment of the throttle cable is important on these models.
Graham
Is it possible that TPS should be recalibrated like this guy has made?
She's Fixed! TPS Problem Resolved! | Jeeves and the Jaguar
" The next part of this challenge was making sure the TPS was calibrated properly - start by disconnecting the battery. Because this part isn't meant to come off there isn't an exact science to this, but essentially you want to get it as close to how the other one was sitting as possible. You can rotate the TPS slightly (before you've screwed it down) to calibrate how the TPS will respond to the throttle. The TPS is essentially just a spring with a sealed sensor, and the part it hooks to on the throttle body is a just a pin that will push that spring. Rotate it too much one way and the car will floor it on start up and too much the other way and your throttle will feel completely limp. "
I appreciate if anybody has exact tips...
Last edited by XJR-99; 05-01-2014 at 03:07 PM.
#270
09-13-2014, 11:58 PM
Veteran Member
#271
09-14-2014, 08:49 PM
Veteran Member
#273
09-15-2014, 04:50 PM
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#275
09-16-2014, 06:25 PM
#276
09-17-2014, 11:19 AM
#277
09-17-2014, 11:24 AM
Veteran Member
I went to adjust mine but it appears it was already done. By the look of the threads.... but to be sure I had my neighbor press the accelerator as I manage to pull it a "lil" further (one thread).
How would I know for sure if it was done? I didn't improve any throttle improvements
How would I know for sure if it was done? I didn't improve any throttle improvements
As previously stated, it would be misleading to consider this to be a "performance improvement mod" but rather a routine adjustment to make sure that the throttle is opening correctly. Kind of like making sure all the spark plug wires are properly seated (probably a bad analogy). Once set you should theoretically not need to adjust again but it could be that things just slacken up over time. Consequently a routine look every so often couldn't hurt.
Doug
#278
09-24-2014, 08:25 PM
98% without adjustment
I guess I'm good to go. 98% on the first read with no adjustment. I'll verify by checking the cable position at wot when my copilot is around. Don't know why I'm not getting readings on the other position indicators.
Regards, Fred
Regards, Fred
Last edited by newXKRguy; 09-24-2014 at 09:29 PM.
#279
09-25-2014, 10:02 PM
Veteran Member
