Slayer Posted October 17, 2020 Share Posted October 17, 2020 Hi guys, I have a stock 1995 UK spec Supra Auto. Is it normal to be sitting at 80 MPH, with RPM around 3500? Seem high to me, is it normal, because of the 4 Speed Auto box? Apart from that, car feels perfectly fine... Quote Link to comment Share on other sites More sharing options...
Dnk Posted October 18, 2020 Share Posted October 18, 2020 http://www.mkivsupraownersclub.com/forums/showthread.php?t=5584 Quote Link to comment Share on other sites More sharing options...
Slayer Posted October 18, 2020 Author Share Posted October 18, 2020 http://www.mkivsupraownersclub.com/forums/showthread.php?t=5584 Thanks for the link. This means the rpm of 3500 is way to high sitting at 80, anyone got any suggestion on what could be wrong? Thanks. Quote Link to comment Share on other sites More sharing options...
Mike2JZ Posted October 18, 2020 Share Posted October 18, 2020 Either you aren't in 4th gear, or you have the wrong differential in the car. Quote Link to comment Share on other sites More sharing options...
rider Posted October 18, 2020 Share Posted October 18, 2020 It'd be hard to figure out what is different with your car without counting teeth on the gears to check the ratios are correct but a different diff casing/oil cooling would be an easy spot on a UK car. Its actually quite common practice on particularly US muscle cars to proactively raise the gear ratio to give a car a much faster take off and 60 times so a previous owner could have set it up as a street racer if the casings are all factory correct. Another factor to calculate any contribution to the discrepancy will be any difference to the OE wheel size and tyre profile. If these haven't been matched optimally its very easy to get yourself a fair few % out on the circumference of the tyre, though not as far as 15%. Quote Link to comment Share on other sites More sharing options...
rider Posted October 18, 2020 Share Posted October 18, 2020 This might help you work things out. So long as you are OK at working things out.Supra-Gear-wheel-size-Calculations.xls Quote Link to comment Share on other sites More sharing options...
Dnk Posted October 18, 2020 Share Posted October 18, 2020 (edited) Tyre/wheel diameter would be a mile out if it was that Has it recently started doing this ? Edited October 26, 2020 by Dnk (see edit history) Quote Link to comment Share on other sites More sharing options...
rider Posted October 18, 2020 Share Posted October 18, 2020 The tyre and gears calculator which someone must have spent a bit of time generating does point to the gearbox potentially being stuck in 3rd gear. Which could be the dreaded ECU or something like an oil change needed. Quote Link to comment Share on other sites More sharing options...
Scooter Posted October 18, 2020 Share Posted October 18, 2020 Are you in 'manual mode' or is overdrive on/off (never remember which). Both of these would have you stuck in 3rd. Perhaps your dash lights are faulty and you don't realise? Quote Link to comment Share on other sites More sharing options...
Slayer Posted October 19, 2020 Author Share Posted October 19, 2020 This might help you work things out. So long as you are OK at working things out. Thanks for the advice and information, I will definitely follow this and try it out. Much appreciated. Quote Link to comment Share on other sites More sharing options...
Slayer Posted October 19, 2020 Author Share Posted October 19, 2020 I see, would this be a problem if I changed from the stock to 19inch wheels ? I would have thought odometer reading may be off slightly but did. It realise that it would impact the RPM? Quote Link to comment Share on other sites More sharing options...
Dnk Posted October 19, 2020 Share Posted October 19, 2020 Try using the od button and see what happens Quote Link to comment Share on other sites More sharing options...
Dnk Posted October 19, 2020 Share Posted October 19, 2020 (edited) I see, would this be a problem if I changed from the stock to 19inch wheels ? I would have thought odometer reading may be off slightly but did. It realise that it would impact the RPM? It would be the other way round, overall smaller diameter = higher rpm at same speed So if you had say a diff ratio of 3.45 with 20" diameter tyre at 80 mph = 4637 rpm And if you had a diff ration of 3.45 with 26" diameter tyre at 80 mph = 3567 rpm Edited October 19, 2020 by Dnk (see edit history) Quote Link to comment Share on other sites More sharing options...
Dave Posted October 19, 2020 Share Posted October 19, 2020 Ive got the same problem AGAIN a cap had blown in the ecu had it replaced and now it’s faulty again so back to have a new cap in tomorrow . Problem : OD will not engage it only goes into 4th when I brake then lift off the brake back into 3rd. - - - Updated - - - Hi guys, I have a stock 1995 UK spec Supra Auto. Is it normal to be sitting at 80 MPH, with RPM around 3500? Seem high to me, is it normal, because of the 4 Speed Auto box? Apart from that, car feels perfectly fine... It’s your ECU mate same has happened to me Quote Link to comment Share on other sites More sharing options...
Scooter Posted October 19, 2020 Share Posted October 19, 2020 Dave can you ID the specific cap if poss as I have an ECU that won't allow a shift to 4th at all but is otherwise perfect, ta Quote Link to comment Share on other sites More sharing options...
Slayer Posted October 20, 2020 Author Share Posted October 20, 2020 Hi Dave, thanks for the info, hopefully an easy enough fix. Could you help identifying which cap that needs to.be replaced? Quote Link to comment Share on other sites More sharing options...
Iky Posted October 20, 2020 Share Posted October 20, 2020 Hi Dave, thanks for the info, hopefully an easy enough fix. Could you help identifying which cap that needs to.be replaced? For the amount they cost, I think best to replace all of them on both the engine and throttle control ECU's. The only issue you may come across is finding a competent electrical repair guy than can actually solder properley. The boards are double sided so the solder has to flow through the hole to the other side without screwing up the track/traces and pads. Nichicon, Rubycon and Panasonic capacitors are usually the better options that will actually last and need to be of the correct values. You can have higher voltage ratings but the capacitance has to be the same. Quote Link to comment Share on other sites More sharing options...
Slayer Posted October 20, 2020 Author Share Posted October 20, 2020 For the amount they cost, I think best to replace all of them on both the engine and throttle control ECU's. The only issue you may come across is finding a competent electrical repair guy than can actually solder properley. The boards are double sided so the solder has to flow through the hole to the other side without screwing up the track/traces and pads. Nichicon, Rubycon and Panasonic capacitors are usually the better options that will actually last and need to be of the correct values. You can have higher voltage ratings but the capacitance has to be the same. Yeah I definitely wouldn't mind replacing all the caps, but not sure where to take it to. Also, my O/D Off light only flashes when I put the car in diagnostic mode, error code 27 - something about oxygen sensor, so not sure if related. Anyone know what it means when O/D off flashing only in diagnostic mode and not during normal driving condition? Also, when I was driving at 80 MPH and turned O/D off - rpm went from under 3500 to around 4500... Does it mean that it went from 3rd to 2nd? I thought the O/D Off button only disengage the 4th gear. Quote Link to comment Share on other sites More sharing options...
Slayer Posted October 25, 2020 Author Share Posted October 25, 2020 I took the car to a garage, the mechanic told me that there was nothing wrong... or he was not aware of the capacitor issues in the ECU. Would changing the stock wheels and tyres to 19 inch wheels cause any issue ? I am only asking because I noticed that my speedo is now way off - google maps showing I am doing 70mph when Speedo is just over 60mph. The overdrive button also appears to be working - when turning off the overdrive at 70 or 80 mph, the car would shift down a gear. Although I had no idea if I was actually on 3rd shiftiness down to 2nd or 4th shifting down to 3rd when cursing at 80, but the overdrive off only disengage 4th gear right - it would not have disengaged 3rd? Not sure if my thinking is correct, but it appears as if the big wheels are causing some issues, at least making the odometer reading incorrect. How do I recalibrate the odometer for bigger 19” wheels? Thoughts ? Quote Link to comment Share on other sites More sharing options...
Dnk Posted October 26, 2020 Share Posted October 26, 2020 What size tyres are fitted to your 19" wheels ? Quote Link to comment Share on other sites More sharing options...
Slayer Posted October 27, 2020 Author Share Posted October 27, 2020 30" and 35" I think (car in storage now). Quote Link to comment Share on other sites More sharing options...
Dnk Posted October 28, 2020 Share Posted October 28, 2020 [quote name='Slayer']30" and 35" I think (car in storage now).[/QUOTE] Need to know the width and profile of the tyre to work out the percentage difference to stock Quote Link to comment Share on other sites More sharing options...
Slayer Posted October 28, 2020 Author Share Posted October 28, 2020 [quote name='Dnk']Need to know the width and profile of the tyre to work out the percentage difference to stock[/QUOTE] 285 rear and 245 front. thanks. Quote Link to comment Share on other sites More sharing options...
Dnk Posted October 28, 2020 Share Posted October 28, 2020 [quote name='Slayer']285 rear and 245 front. thanks.[/QUOTE] Its not your new wheel/tyre combo then Quote Link to comment Share on other sites More sharing options...
Dnk Posted October 28, 2020 Share Posted October 28, 2020 Less than 3% difference on both front and rear compared to OE Quote Link to comment Share on other sites More sharing options...
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