Throttle travel - seeking 100% !!!

Topics relating to the Lotus Exige S1 (series 1)
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Evoman
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I've been tinkering with the Lotus over the last few days and with the kind assistance of Klaus now have nicely balanced throttle bodies having replaced the adjustable balance screw for a longer one and tensioned with a spring. Disconnected the IACV, adjusted the idle then the new balancing screw and now way closer to where it should be. This took some work to see how the adjusting screw brings the two throttle bodies into balance but now very happy with the result.

However with engine diagnostics plugged into the OBD I tried a throttle reset and noticed the throttle pedal at full travel is only measuring 92.94% not 100%.

So simple question and I'm hoping there is a simple answer though being a Lotus perhaps that is being ambitious! How does one adjust the throttle cable and / mechanism to realise 100% travel ? I assume this is a mechanical adjustment required as the TPS is not 'seeing' full travel, i.e. 100%.

A quick look on the Search function hasn't found what I was looking for as yet.

Cheers

Rich
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trackrod
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As no one else is answering I give it a try:
If I remember right you can turn the TPS a little within its fixing screws. You may drill slightly bigger holes into the plactic housing of the TPS if there is not enough movement available.

On the other hand the most important thing is that the butterflies are fully open on full throttle and not that the TPS reads 100%. The EFI ECU calculates the engine load from the MAP readings. The throttle position sensor is mainly used to detect sudden changes when accelerating. So I'm not sure if the full throttle reading of 93% at full throttle is really a problem.
I'm not 100% sure about all that and someone with better knowledge may correct me.

Klaus
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Sounds good, what was the reason for changing the bolt and didt it make any difference? Never used a synchrometer but I love an excuse to but a tool...

I can check the throttle pot on mine and compare if you like?
Evoman
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Thanks for that guys. I will look into it a little further. That said I do wonder if it is a limitation of the OBD reader that I have which isn't detecting a small throttle movement from idle. I say this as I pressed the accelerator really gently to pick up the the revs by 300/400rpm (which is recognised on the OBD reader) but still showed 0% throttle...

Craig - the balance adjustment screw replacement was as described by Klaus in his thread "improving VHPD driveability". Reason being the original may not provide enough range of adjustment (it is a very short allen headed bolt). Cylinders 1&2 were distinctly quieter that 3 &4, now they are very close the car feels like it has bigger lungs, low and mid range pull is notable.
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trackrod
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Evoman wrote:
Sun Jun 21, 2020 3:25 pm
That said I do wonder if it is a limitation of the OBD reader that I have which isn't detecting a small throttle movement from idle. I say this as I pressed the accelerator really gently to pick up the the revs by 300/400rpm (which is recognised on the OBD reader) but still showed 0% throttle...
I don't think that this is an OBD reader limitation but that the travel of your TPS is not in sync witht the throlle shaft movement. Unscrew the TPS fixing bolts and then turn the TPS against the throttle opening sense while the OBD reader is connected showing the throttle position read out. When the throttle read out just starts to rise you found the position where the TPS should be fixed.

In our private message exchange about the balancing topic I wrote you about turning the idle adjustment screw in as much as possible. Yours was nearly closed and that may be the cause for the non existing TPS readout on the first bit of throttle shaft movement. So best would be to first adjust the idle screw by turning it in as much as possible before the idle rpm inceases (the IACV needs to be connected). If that is done you set the position of the TPS as described above.

The VHPD drivability is very sensible to all sort of faults. To eliminate sensor failure I would suggest to just buy a new TPS before setting all the things up. They do wear out as there are electro-mechanical items. There are cheap ones on Ebay UK, have a look here: https://www.ebay.co.uk/itm/162364189261

Klaus
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Thanks Rich - just had a re-read of that thread so that's a job to add to the list. Is that all you did or did you use a synchrometer as well?
Evoman
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Klaus - excellent advice as always. That does make sense that the TPS is not in sync with the throttle shaft movement.

My TPS was replaced last year but no harm ordering another to be sure. I hadn't appreciated the reset process and of course doing this with OBD reader connected will help ensure the correct position for reset,

Craig - I followed the advice from DVA of listening to the volume from each cylinder. Once you 'tune in' your ear it is very clear where there is a variation from one trumpet to another. So it won't be exact but the set up is now way more in balance than previously. I don't have numbers for each cylinder without a synchrometer but I am confident they are really quite close. I have also marked up the balance screw head and spring to act as a reference point for that 'balance point'. I plan to pull the plugs after engine is up to temperature and see how they look.

The throttle bodies had been balanced by a garage not long ago using a synchrometer so one can only guess how well they did that job.

Looking forward to the next test drive once this rain passes!
Evoman
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By way of update for any interested party (may be of use for future reference).

New TPS installed. TPS reset procedure followed to calibrate to ECU (seems the ECU is a little slow to respond to new sensor installed and resetting throttle range). A couple of attempts and values appeared normal.

Plugs pulled following throttle body rebalancing procedure. All a nice carrot colour, no blackening or soot and all consistent colouring.

Compression test on warm engine followed.

Cylinder 1 - 240psi
Cylinder 2 - 240psi
Cylinder 3 - 235psi
Cylinder 4 - 245psi

Process was carried out with fuel relay disabled, all plugs removed and full throttle. Numbers certainly appear consistent, no idea where they should be or what is a typical range?

Idle inlet manifold pressure readings around 62-64kPa.

Short term fuel trim around -7 to -14% so still rich on idle.

I feel the car is really getting there now (test drive proved very positive pull throughout rev range) though so still something to chase with slight rich running at idle though maybe this is somewhat attributable to the 190bhp ECU and no CAT?
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