Troubleshooting my Tacho Woes

[Scott]

Between stripping my car down and putting it all together I've managed to mess something up with the tacho. Unfortunately this isn't going to be a straight forward troubleshoot as there are a couple of variables to consider.

 

To mitigate one of those variables I'm trying to get a hold of a set of facelift clocks, just so that I can see if the tacho is working (Out of curiosity, would a set of pre-facelifts work on the facelift loom?).

 

Variable 1 - It's a Syvecs ECU rather than a stock ECU

Variable 2 - The tacho has the heckler redline module in place.

 

Here is what the back of my tacho looks like:

 

 

 

I have tried absolutely nothing yet. I've simply removed the unit to take the picture. I would rather have a collection of things to try at once, rather than a whole load of in and out.... although if that what it comes to then fair enough.

 

My first plan is to remove the tacho module and see if it works. After that, I'm out of ideas. I've been advised that I can check if the tacho is getting a signal from the ECU but I'm unsure of how to check this. I believe that it's the tacho signal is the screwed on eyelet right where the tacho is (orange cable attached, + just below it). If that is indeed the case then following that trace takes me to the 4th connection from the right (from the left on the plug) that connects in the back of the unit. Again, if that is correct then I tried checking the voltage between pin 4 from the left and ground (door shut) and got zero. Whether that means anything I have no idea.

 

The syvecs angle could be down to me breaking the resistor that's in place (pull up with 12v attached). If I can't get anywhere with the tacho this will be my next port of call.

 

Thanks for any help

[heckler]

The tachograph signal is the top orange wire. Facelift dials will not work with post facelift dails as the plugs are different

[heckler]

Like I said, you need to disconnect the PCB completely and see if the tachograph works, then you know where the problem is.

[Scott]

Yup, I'm gonna do that first. While I've got it off, what sort of signal should I get from the orange tacho wire? Do I just check for DC voltage to ground(black wire)? I'm guessing it'll start where it starts and should then increase with the revs?

[Scott]

Went out and tried it anyway, just to knock it on the head. No luck with the module removed.

 

I checked across the tacho signal and the black ground wire with the ignition off - 0V

With the ignition at position 1 - 0V

With the ignition at position 2 - 0V (with the alarm still enabled)

With the ignition at position 2 and the alarm disabled (Syvecs enabled) - 2.9V

With the engine running - 2.9v constant, no variance regardless of RPM

[heckler]

Went out and tried it anyway, just to knock it on the head. No luck with the module removed.

 

I checked across the tacho signal and the black ground wire with the ignition off - 0V

With the ignition at position 1 - 0V

With the ignition at position 2 - 0V (with the alarm still enabled)

With the ignition at position 2 and the alarm disabled (Syvecs enabled) - 2.9V

With the engine running - 2.9v constant, no variance regardless of RPM

 

the tacho outoput is a squarewave signal - can't remember the voltage off the top of my head, but a multi-meter would pick it up. you would see a value, its the frequency that changes. Its quite possible the tacho it self had died.