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wheel speed sensor & gear calibration issues


James Wingfield
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I’ve just added a wheel speed input to my LEM G3 and it seems to be working in as far as the speed display shows something when the car is moving. I’ve got a couple of issues with it though: 1) The display seems to be in kph (and the pulses per 100m value is worked out in metres) yet the actual speed appears to correlate with my speedo – in mph. That’s not really a problem but does seem to be confusing. Is this a known bug? 2) I’ve tried to perform a calibration for each gear and this has worked for gears 2-5 but gear 1 fails to calculate and I don’t know why. What could cause this to fail in one gear only? 3) I’m using the gear identification to provide a boost map for each gear. My concern is what happens when the ECU identifies the car as being in neutral? I haven’t yet checked which wheel the speed sensor comes from but if it’s a front wheel then I don’t want to end up in the situation of wheel-spin causing the ECU to switch to an unsuitable boost map. In the short term, I’m also relying on this “neutral†map when I’m in first gear so would like to know what it does. Thanks, James

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Have never seen it not calibrate unless there is no signal or it is erratic  have you scoped it to see the pattern... maybe there is an issue with how the speedo has been converted to read mph

 

The ecu will never see neutral it either has a speed input which means its in gear and driving  if you are costing down the road in neutral it will assume a gear position based  of the wheel speed and engine revs  whichever cal mathches it equates to a gear position  

if the whhel speed is done from an undriven wheel then there can be issues with gear detect in extreme wheel spin cases    but if the speed is derived from a driven wheel as long as it is a lsd diff or from the speedo drive from the gearbox then you should never see an incorrect gear position unless the cluch slips

Regards

Dave

info@dtechmotorsport.com

 

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so what happens if i am in neutral and coasting along at 50mph? none of the gear calibrations will match. I'm sure i recall seeing somethng in the help files about the ecu assuming it is in neutral if none of the gear cals match but i dont know what boost map etc it will use. I understand that this isnt normally an issue as the engine wont be doing anything sigificant when in this state but it does become relevant for me as i cant calibrate first gear. I'll try switching from rising edge to falling (or visa versa) but i cant think of anything else to try. I dont have access to a scope but the signal works for my car speedo and for the ecu calibration in all other gears so i'd be suprised if that is causing the failure. James

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I've done a bit more experimenting and answered some of my own questions. It seems that the ecu currently doesn't recognise being in any gear even though 4 of them are calibrated. I guess this is because first gear isn't calibrated? The result is that the ECU assumes it is in neutral and then defaults to the first gear map. This answers one of my questions but it's still not working properly. I also tried typing in the first gear ratio manually but then it came up with the error: "Input must be between 0 and 100" I think that's why it can't calibrate gear 1. The pulse frequency is 251 and the ratios are: 280, 169, 111, 79, 64 two of which are well outside the ECU's allowable range. (Oddly gear 2 still calibrated though?) Is there anything I can do about that? The only thing I can think of for now is to scale the ratios by a factor of 5 (or so) to get them all under 100 and then accept that the ECU speed will always read 1/5 of the real value. Obviously that's not ideal though. I'm also wondering if I can do something along the lines of scaling the ratios but then modifying the DI Speed calibration to compensate. This might work but I'll end up with an extreme value in the calibration box that may cause it's own problems/errors. Unfortunately there doesn't appear to be any help pages on this subject. I'll keep trying a few different ideas but just wanted to update this post to see if anyone has any pointers... Do any firmware updates exist that remove the 0-100 limitation for gear ratio? James

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have you set it up with          gear detection = ecu calculated

  have you selected a  gear that is closest to 1:1 to normalise the table

Have you selected the correct DI channel that the speed sensor is conected to    

                                              

Regards

Dave

info@dtechmotorsport.com

 

 

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I tried ECU calculated which is how it found gears 2-5 but it failed to calibrate gear 1 like that. Then I tried adding the calibration number in manually by selecting User defined instead. This then gave me the error that the number was too large (more than 100). I haven’t yet been able to try again but normalising the ratios is next on the list. I’ve not done that at all so far so maybe it will help? The speed signal is set up on the digital input and selected in the software. As it work on most gears I doubt this will be causing any issues. James

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