V6 rev counter wiring

[kes205 0]

Hi,

 

Just purchased 205 CTI with a 3L v6 installed and trying to get all the gauges working on instrument cluster. Currently only speedo and fuel level works. Just trying to work out how the rev counter should be wired from the V6 into the cluster, where is the signal taken?.  Not sure if the rev counter ever worked i.e. whether the wiring has been installed and there is just a issue with it. Just wondered if anyone knows how this should be wired or has ever done it before.

 

Thanks

 

Kerry

 

[welshpug 1,662]

you need a motronic tacho from a bx or a coil pickup, you can make this with a small handful of diodes and resistors, covered a few times on here for gti6 conversions etc.

[kes205 0]

Well after taking the cluster apart I found a broken wire to the tacho which I thought brilliant that's the issue and soldered it.  Then noticed the rev counter already had a wire mod. However even after wire repair tacho didnt work. I then tried doing the resistor wiring mod and the tacho still didnt work.

 

Then bought another rev counter in case original was broken and performed the resistor mod and still no go on the new tacho.  I checked the earth to tacho and that's fine.  What else can I do check?  Is there anyway to check tacho off the car. 

[kes205 0]

Well next update. I managed to get wire 426 which is the ecu rev counter signal wire (pin43) and connector it to wire 112 in the pug. So the tacho kinda works and kind of doesn't. The tacho seems to take 10 seconds before it starts working. Then it jumps around a lot and is really delayed in response. You rev and it kinda of increases 10 seconds later. Anyone know why the tacho would behave like this. Is the signal from the ecu too small for the 205 rev counter. I have also used thicker wire than original signal wire would this cause an issue 

Edited July 2, 2020 by kes205

[welshpug 1,662]

they never work with a signal from an ecu, you need a diode mod, aka tacho converter, or mod the tacho itself.

 

it'll take about a pound or so of zenner diodes and a resistor or two to make a pickup that works off the ignition coil triggers.

[kes205 0]

I thought doing the tacho resistor mod enables the tacho to read a low voltage ecu signal. Will have to resolder the resistors back on and try the diode technique or signal amplifier. 

[welshpug 1,662]

I don't ever touch the tacho/rev counter itself unless I fit one from a motronic car (bx!)   I tried and failed so just made the pickup thing with the diodes, much cheaper than frying an instrument cluster and risking damage to the dashboard plastics.

Edited July 3, 2020 by welshpug

[jackherer 543]

Presumably if you use diodes connected to the coils on a V6 you need to connect to only four out of the six coils to make it read correctly on a 4 cylinder tacho?

[welshpug 1,662]

there's only 3 outputs, its a wasted spark setup on the D8 V6.

 

why would you use less than the full number?   it'll bounce if you do that

[jackherer 543]

Because 1000RPM on a 4 cylinder engine and 1000RPM on a 6 cylinder engine is obviously a different number of ignition pulses!

 

Aftermarket tachos usually have a 4-6-8 cylinder switch but 205 tachos only expect a 4 cylinder signal.

 

Unless I'm missing something if you connect it to all the coils (3 or 6 depending on type of coils...) your tacho will over read surely?