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| NLGHIA5.0 |
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{USERNAME} wrote: As long as you have not changed the speedo cog, tyre size has nothing to do with shift points. the shift points are a function of tailshaft speed vs throttle position. even if you took the wheels off, it will still shift at the same speed on the speedo thats programmed into the TCM. As pete suggested, the shift points can be scaled with a speedo corrector if required. Have you tried resetting the TCM and performed a throttle calibration? But wouldnt smaller tyres rotate faster, and increase the tailshaft speed? |
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| 66 coupe |
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the 'car' does not care what size wheels are on it, if any at all.
The TCM is preprogrammed with a map which is VSS vs TPS vs gear. The only reason for the TCM to shift early in the RPM is if the TPS signal is reading low, or you have changed the speedo cog indicating a higher VSS to the TCM. (or other factors such as incorrect TCM for the vehicle in question) It has nothing to do with physical road speed, wheel size or diff ratios providing you have not changed the TCM or the speedo pickup cog. Test your trans TPS with a multimeter and see what the open and closed throttle reading is, or even swap the TPS's around at the plugs and see if that makes any difference. Or it could be that your tacho is out |
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| v8cortina |
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Posts: 39 Joined: 10th Jun 2011 |
so changing the speedo pick up cog to a different ratio should set the shift point higher? so to set the speedo 7k back what size would i need?
im usles when it comes this stuff 
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| 66 coupe |
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if you use an XR6/XR8 speedo cog, it will probably get you close to the 7k difference, otherwise a digital speedo corrector will be required
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| NLGHIA5.0 |
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I went out today and did 3 0-100 runs, and every time it shifted at a different point. First time was 5200 rpm, 2nd time was 4400 rpm and the 3rd time was 4700 rpm, all in D with 100% throttle.
Previous 5 litres i've owned have all upshifted at full throttle bang on redline every single time, got me stumped why this car shifts at different revs every time. Can't figure it out. |
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| XR9UTE |
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Have you checked your trans TPS yet? Be a good idea to do a self test too.
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| NLGHIA5.0 |
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Tested the TPS with this, but not the auto TPS, didn't think to do it, might have to try it. Are they exactly the same as each other, and require the same voltages ie. 0.98 v at idle up to around 4.5-5v at full throttle, and smoothly up and down as the throttle is opened?
Engine TPS worked just fine. http://www.cjponyparts.com/digital-tps- ... 95/p/TPS1/ |
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| XR9UTE |
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You have auto trans shift problems so you need to check the auto trans TPS.
Read the TCU codes because you may have throttle learn problems as Jamie was referring to. Trans TPS needs to be lower than engine TPS as a general rule around .75v but check with the workskop manual. |
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| NLGHIA5.0 |
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Auto TPS checked out around the same as the engine TPS, 0.98 or so at idle, went up and down smoothly as throttle was applied. Basically mirrored what the engine TPS did.
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| NLGHIA5.0 |
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Changed throttle position sensors and problem is now gone. 5000 rpm upshifts everytime.
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| v8cortina |
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Posts: 39 Joined: 10th Jun 2011 |
i have a cable drive speedo, (cortina) im not sure of the gear colour, but changing it, how much will that slow the speedo down? or does it vary?
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