vs series 3 5l manual ute. change ppk for diff gear swap

[ben044]

What needs to changed in the ecu if i swap my diff gears from 3.08 to 3.45 ratio. I know how to change the dash just want ecu to work correctly after the swap.

[Jayme]

nothing specifically. the speed sensor reads tailshaft speed and the auto gearbox shifts accordingly. changing the ratio after the tailshaft, like the diff, will not change what engine RPM the shifts actually happen at. you m ay encounter small differences in the actual shift time, due to the engine revving our quicker, so shift points *may* need to be tweaked to anticipate the shift a little earlier. my advice, is to try it and more than likely, it will be fine without touching the ecu.

[ben044]

Thanks jayme.
But its a series 3 v8 manual. All speed outputs are done through the ecu so i would think that changing my diff gears it will change the way the ecu behaves and the speedo reading aswell.

[Jayme]

oops didnt read that hahaha. I Assumed it was auto and didnt read the title.... in that case, there is absolutely nothing that needs changing, apart form fixing the dash, which you know how to do. the manual ecu only cares whether a car is moving or not. it doesnt matter specifically how fast it is going. the only thing that will change if you fix the ecu speed is the aldl data will have the correct speed reading. it will not affect the behaviour of the engine.

[ben044]

So not altering the ppk or the diff ratio in the ecu it won't alter or effect the readings to the the dash for speed and fuel usage info

[Jayme]

ppk will not alter the output. the speed out of the computer into the dash is fixed regardless of what you set in the tune. the only way to alter it is to alter the dash, or intercept the signal with a speedo corrector. the fuel usage to the dash is fuel info only. the dash uses the speedo reading to do its /100km calculations.

if you were planning on using a corrector, there is no reason you cant intercept the signal between the gearbox and the ecu, then you fix the aldl speed, and speedo all in one hit without ever touching the memcal.

[ben044]

But wont putting the right ppk or diff ratio in the ecu automatically correct this and thus meaning i wont need the speed corrector

[Holden202T]

like jayme said, you can change the PPK value which will offset the speed that the ecm sees from the gearbox sender, but it wont change the output to the dash, which means your dash reading will still be wrong and the fuel economy readings may be effected by it also, so either way you need to get a speedo corrector, so you may as well just do that and not need to mod the ecm at all.

[ben044]

I might be wrong here but this ecu puts out the signal to the dash for speed so I would have assumed it would also change the output pulses, this is not setup where the dash and ecu get signal from the same signal wire as the two wires go from speed sensor to the ecu and the speed output is from a different pin on the ecu

[Jayme]

yep, we realise that, and have had experience with this exact situation before. all the ecu does is converts it from a sine wave signal to a square wave signal, and reduces the signal speed by a fixed %. it is not influenced by the ppk at all.

you may be thinking of the ls1. on the ls1 computer, the settings in the calibration DO affect the output pulses...... it is not true of the VS series 3 computer though.