I literally did my throttle cable today. It was slack. I reckon about 4mm of adjustment. Tightened it up and honest, the car picks up much better. I was only saying before how I thought my other p38 felt faster/sportier or whatever. Can't believe the difference a couple of mm has made. (said no woman ever!) lol
The Classic (14CUX) had a (hidden) idle adjustment screw in the throttlebody, preset by factory. Don't know if the P38 Gems/Thor has something similar and if it has anything to do with the adjustment related to TPS discussed here, because idle is monitored by the ECM
blueplasticsoulman wrote:
I literally did my throttle cable today. It was slack. I reckon about 4mm of adjustment. Tightened it up and honest, the car picks up much better. I was only saying before how I thought my other p38 felt faster/sportier or whatever. Can't believe the difference a couple of mm has made. (said no woman ever!) lol
With slack cable you'd have to press the accelerator further to open the throttle the same amount, might not even be able to get to WOT, and with these models having long throttle pedal travel a bit of slack might make for a fair bit of difference to how far you have to press the accelerator to open the throttle valve the same extent. Can't affect TPS though because that sits on the same shaft as the actual throttle flap.
Simon
It's all in the mind. The car picks up quicker because you are giving it more throttle for the same amount of foot movement. It doesn't affect the TPS or throttle at all.
it's gotta affect something or Rave would be specific in saying it has to be adjusted up properly for the auto box to work right. However, i have no idea and i only ask the questions to learn. :-)
If the gearbox is taking a signal from the TPS and believing that signal to be true to what the engine is doing and using this information to control the behaviour the gear box, then the cable adjustment would be critical.
If the cable is too slack or too tight then the engine would doing something different to what the TPS is telling the gearbox it should be. You could then end up with mismatched gearbox and engine behaviour and poor gear changes etc.
RutlandRover wrote:
If the gearbox is taking a signal from the TPS and believing that signal to be true to what the engine is doing and using this information to control the behaviour the gear box, then the cable adjustment would be critical.
If the cable is too slack or too tight then the engine would doing something different to what the TPS is telling the gearbox it should be. You could then end up with mismatched gearbox and engine behaviour and poor gear changes etc.
so in a nutshell, i might be right in thinking my car is better now then?
The cable drives the throttle butterfly shaft. This shaft drives the TPS sensor. Adjusting the cable, either making it slacker or tighter, is not going to have any influence on the TPS's relation to the position of the butterfly. Just because its in RAVE doesn't necessarily make it correct - I'd be inclined to believe its a copy and paste from previous designs that wasn't noticed on review.
Hell, you could remove the cable entirely and sit on top of the engine, and control the throttle by hand - the engine and gearbox would be none the wiser.
Steering might be an issue, but that's another problem.
With mine, the box would "hang" if you like. It's like it wanted to change up but couldn't, and I'd have to lift off the throttle slightly to get it to do so. Cold or hot, traffic or no, although it was obviously more noticeable in Manila's notorious queues.
Having adjusted the cable as per RAVE, the changes were where and when they should be and no pedal lift-off was required.
Don't ask me what the deal is, I don't know, but the results were startling.
Watching this thread with interest. I've always had both my cables set with no slack, I've never had any problems with gear change or kick down , as mentioned you could work it by hand and I don't think it would make the slightest difference. Is it possible that maybe there's some pattern sensors on some cars,, I used one once, lasted a few months before I had problems, readings were all over the place, which would of course cause problems.
We've all bought our cars second hand and don't know the full history,,
Our cars rely on running 100% as so many sensors are linked to something else, will carry on following the thread with interest..
blueplasticsoulman wrote:
RutlandRover wrote:
If the gearbox is taking a signal from the TPS and believing that signal to be true to what the engine is doing and using this information to control the behaviour the gear box, then the cable adjustment would be critical.
If the cable is too slack or too tight then the engine would doing something different to what the TPS is telling the gearbox it should be. You could then end up with mismatched gearbox and engine behaviour and poor gear changes etc.
so in a nutshell, i might be right in thinking my car is better now then?
I think I might need to alter/clarify my statement. Initially, I assumed that the Throttle Position Sensor was reporting the position of the accelerator pedal. Given Sloth's statement about the TPS being on the butterfly shaft, the TPS signal doesn't care where the pedal is. If the cable is adjusted correctly then the pedal should correctly correlate with the TPS signal.
As the TPS sensor is separate from the pedal then a poorly adjusted accelerator pedal cable shouldn't result in mis-matched engine and gearbox data - as the TPS is actually reporting how far open the butterfly valve on the engine is.
I guess an argument could be made for improving throttle response as a poorly adjusted cable would allow the pedal to move for a distance without actuating the butterfly valve. This inactive movement would vary depending on how slack the cable is. It would also mean you could never reach "full throttle". However, it wouldn't result in mis-matched engine and gearbox as the butterfly valve is still working exactly as it should be.
As the TPS is attached to the shaft of the butterfly valve I can't see that it's possible to report an inaccurate reading unless the sensor is missing, faulty, loose or something is snapped inside the sensor or butterfly valve.
I think that if the TPS is in good condition and fitted properly without any damage to the sensor or valve then the gearbox is receiving a correct TPS reading regardless of pedal position. If the gear change is poor then I think there must have been another cause.
I'm by no means an expert about this though, these are just my thoughts trying to figure it out from what's been said here. I didn't even know where the TPS sensor was!
Reading through the Disco 2 manual, which covers the HP24 extensively, made clear to me that the way the box behaves itself is 100% electronics and can vary from box to box.
The details are beyond my capabilities, I just copy one sentence from the manual regarding wear:
Quote:
Shift control
To provide the different driving characteristics for each mode of operation, the EAT ECU incorporates different shift
maps of throttle position/engine speed. Base shift points are derived from the appropriate shift map. When a shift is
required, the EAT ECU sends a request to the ECM for a reduction in engine torque, in order to produce a smoother
shift. The percentage of torque reduction requested varies according to the operating conditions at the time of the
request. When the EAT ECU receives confirmation of the torque reduction from the ECM, it then signals the shift
solenoid valves in the gearbox to produce the shift. To further improve shift quality, the EAT ECU also signals the
pressure regulating solenoid valve to modulate the hydraulic pressure and so control the rate of engagement and
disengagement of the brake clutches.
With time, the components in a gearbox wear and the duration of the gear shifts tends to increase, which has an
adverse effect on the brake clutches. To counteract this, the EAT ECU applies a pressure adaptation to each shift.
To calculate the adaptations, the EAT ECU monitors the pressure modulation used, and time taken, for each shift. If
a subsequent shift of the same type, in terms of throttle position and engine speed, has a longer duration, the EAT
ECU stores an adaptation for that type of shift in a volatile memory. The adaptation is then included in future pressure
calculations for that type of shift, to restore shift duration to the nominal.
Kickdown
The EAT ECU monitors the input of the throttle position sensor to determine when kickdown is required. When it
detects a kickdown situation, the EAT ECU immediately initiates a down shift provided the target gear will not cause
the engine speed limit to be exceeded.
Torque converter lock-up
The EAT ECU energises the lock-up solenoid valve to engage the lock-up clutch. Lock-up clutch operation is
dependent on throttle position, engine speed, operating mode and the range selected on the transfer box.
High range
Unique lock-up maps, similar to the shift maps, are incorporated in the economy and sport modes for all forward gears.
Engagement and disengagement of the lock-up clutch is dependent on throttle position and engine speed.
Low range
To enhance off road control, particularly when manoeuvring at low speeds, torque converter lock-up does not occur
when there is any degree of throttle opening. When the throttle is closed above a preset engine speed, the lock-up
clutch engages to provide maximum engine braking.
Increased load/reduced torque compensation
To aid performance and driveability in the high range economy mode, the EAT ECU has three adaptive shift and lockup
maps. These maps delay upshifts and torque converter lock-up similar to the sport mode if the inputs from the
engine indicate:
- A sustained high load on the engine, such as occurs when the vehicle is ascending a steep gradient or towing a
trailer. - A lower than normal engine torque, such as occurs at altitude or high ambient temperatures.
The EAT ECU monitors the engine inputs and selects the most appropriate adaptive map for the prevailing conditions.
End quote.
There is more to it than just the cable-adjustment.
BTW even not inclined to it, the whole section is an interesting read!