Diff Swap but speedo not working

[SAE30]

Had the internals of the e36 m3 diff swapped into my e30 casing, only problem is the speedo does not work, keeping in mind that the fins that spin in the diff that pass through the sppedo sensor were also changed to the e36 ones, should i change the sensor to the e36 one as well or would the e30 one work, my speedo was working fine before the diff swap

[DHFiS]

Vibration makes the wiring to the diff very brittle over time. Maybe it has cracked during the change over.

[Brianmoooore]

IIRC, the sensor from an E36 is longer than an E30 one, so possibly the vanes are shorter.
If so, the E30 sensor probably doesn't reach the vanes. A lot of 'ifs' and 'possibles', but it would explain your symptoms.

[SAE30]

Problem sorted.... the e36 sensor is actually shorter than the e30 one, it also has 2 of the same size pins where as the e30 one has one long and one short.
I fitted the shorter e36 sensor and the speedo works.

btw. with my s50 swap, when the speedo is not working the consumption metre also does not work, it just moves from side to side continuously


Thanks

[Brianmoooore]

Problem sorted.... the e36 sensor is actually shorter than the e30 one,

Well, I was right that they're different lengths, even if I got it the wrong way around!
Eco meter problem is caused by injector pulse width info not reaching it (or not being recognised.)

[SAE30]

Problem sorted.... the e36 sensor is actually shorter than the e30 one,

Well, I was right that they're different lengths, even if I got it the wrong way around!
Eco meter problem is caused by injector pulse width info not reaching it (or not being recognised.)

any way of sorting the eco metre out?

[Boyraceruk]

with my s50 swap, when the speedo is not working the consumption metre also does not work, it just moves from side to side continuously

This happens on my E30 too since the speedo is used to work out fuel consumption. That fact it's moving from side to side probably means you're lifting off too much, keep your foot planted and it should stay on 0. Also your mapping requires a working speedo, although I can't work out if it makes the engine run lean or rich at speed if the speedo doesn't work.

Still, glad to hear you have it all sorted now.

[SAE30]

with my s50 swap, when the speedo is not working the consumption metre also does not work, it just moves from side to side continuously

This happens on my E30 too since the speedo is used to work out fuel consumption. That fact it's moving from side to side probably means you're lifting off too much, keep your foot planted and it should stay on 0. Also your mapping requires a working speedo, although I can't work out if it makes the engine run lean or rich at speed if the speedo doesn't work.

Still, glad to hear you have it all sorted now.

thanks

[Brianmoooore]

with my s50 swap, when the speedo is not working the consumption metre also does not work, it just moves from side to side continuously

This happens on my E30 too since the speedo is used to work out fuel consumption. That fact it's moving from side to side probably means you're lifting off too much, keep your foot planted and it should stay on 0. Also your mapping requires a working speedo, although I can't work out if it makes the engine run lean or rich at speed if the speedo doesn't work.

Not sure I understand what logic may be in the above, but I can assure you it's all drivel!
The eco gauge works by measuring the amount of fuel used, which it does by counting the number and width of the injector pulses, and dividing this by the cleaned up speed signal, which it obtains from the speedo.
I said the fuel signal was missing in my last post, but since I don't know exactly what the gauge is doing, I suppose it could be the speed signal missing instead.
Fuel signal comes on a white/black wire from the ECU, and the speed signal path is from the speedo PCB to the SI board in the cluster.
There is an uncommon, but known fault, with the speed signal path, where a fault on the SI board destroys a small resistor on the speedo PCB