25 replies to this topic

[toryman76]

Hi all,

 

I recently got my 5L LX Torana up and running for the first time. I spent a fair bit of time retro fitting a VDO tacho into the original dash cluster, and I have completely torn down the gauge to fit it and hence I could have damaged it but I would like to ask for some help in trying to diagnose whether or not I have damaged it. My setup is as follows:

- Tacho wired up as per the fitting instructions supplied. Sense wire to coil negative, 12V positive through ignition switch fused, ground to vehicle body

- Ignition system is a Bosch HEI electronic distributor out of an early Commodore with the large cap using a Bosch HEC716 coil

So when I first start the car, sitting at idle to tacho comes up, say 1000rpm. When I rev the engine in small increments, the tacho does not move. If I rev the engine in higher increments, the tacho begins to move. When I turn the ignition off, the tacho will stay at the last position it was in. I have read this is sort of normal and should reset to zero when the key is turned to ignition and back off again, so i did this and the tacho moves down to say 500rpm and thats it, it stays there. Now to make things even more complicated, when I disconnect the sense wire with ignition off, the tacho will come down to zero. My electrical knowledge is very limited but to be it seems that the tacho is not sensitive enough. Could this be the case or is there something else at play here?

 

Any thoughts or suggestions welcomed with open arms before I go off and buy a new gauge.

 

As a side note, I would also like to mention that I had an issue with the alternator regulator whereby I was seeing the dash light flash on and off so checked voltage across the battery whilst it was running and it read 15V using both digital and analogue multi-meter. So I believe the voltage regulator is stuffed (even though this was new!) and so the alternator is currently at the auto elec who rebuilt it for a full bench test. I don't think these two issues are related but just thought it was worthwhile noting.

 

Thanks!

[hanra]

Prob need a tach adaptor.

[toryman76]

I have been googling this issue non stop and so far I have not come up with any concrete solutions except for trying diodes or resistors. I also saw the tacho adapters for ignition systems such as MSD but I wouldn't of thought this would be applicable?

[VDO]

2 questions:

 

Which VDO tacho have you used..?

Did you paint the pointer..?

[toryman76]

Cockpit Vision 0-7000rpm 85mm part number 333015033. No I have not painted the needle. I wanted to but decided against as I didn't want to put it out of calibration.

[hanra]

Got access to a Signal Generator? Bang a 10v P-P square wave into it at 100hz and see if it reads 3000RPM.

[toryman76]

I am asking around see if someone I know has one but its not looking likely. Even my autoelec couldn't help me out. He went on to explain that 'those days are over mate' hahaha!

[hanra]

What days?

[toryman76]

He used to have a lot of this type of testing equipment but his business model has changed a lot over the years and he has moved away from that type of work. He told me to go to Howard's instruments to get it checked but I know it won't be cheap. Hence why I want to know if it's my setup or if it's the gauge before I proceed.

[hanra]

I just had a friends SLR tacho on the sig gen this arvy. I can spin it up if need be. But I live a long way away.

Edited by hanra, 09 August 2016 - 07:24 PM.

[toryman76]

Thanks for the offer mate. I will keep this in mind.

[toryman76]

Ok so today I got my old Subaru paddock basher running to check the tacho. Wired it up changed the coding switches to suit and it worked a treat. Needle moved smoothly and seemed to be reasonably accurate although I did not have another reference. So I thought maybe something is going on with my wiring so I dummied it up in the engine bay direct to coil battery and ground. Again it did not work correctly. So I now know it has something to do with the electronic ignition. Can anyone who has thus setup of ignition system shed any light on this issue?

[rodomo]

"Back in the day" a lot of cars used this module (falcon, telstar, corolla, sigma) and I seem to remember people telling me their tachos had played up in days prior to module failure. First thing I would do would be loosen then retighten the two screws that hold the module cover down. I think one of these screws supplies an earth? If that fails, try another module.

[toryman76]

Interesting. I have had the distributor regraphed when my engine got built but the engine has done zero work since. When regraphing would they pick up if the module is suspect?

[Sven]

I have an LX with a v6 fitted. I retro fitted a vdo tacho into the instrument cluster. When the car was started and running, the tacho needle did not move. After some web searches, I found instructions to connect a 12v supply with a resister into the signal input. I made up a quick dummy wiring harness to test and it worked. I think that because the commy v6 tacho signal is a square wave, the vdo tacho needs some voltage all the time. IE. Not ever 0v. The resister is 680 Ohms 1/4 watts sourced from Jaycar.

[toryman76]

I let this issue sit for a few months whilst I fitted out the rest of the cars wiring system just to make sure there wasn't something else giving me a false result. I tested it again today, and still the same issue. I had an old Sigma tacho here which is for a 4cyl. and so I tried that on the car and it worked fine besides the needle being wrong to the numbers on the dial.

 

I am at a complete loss now... I am starting to think I need a different tacho, or a different coil? Any more suggestions?

[toryman76]

Or plan B maybe try wiring it into the alternator and tuning it to suit? I have heard this can be quite challenging though...

[fuzzypumper]

If you use an original torana tacho on a HEI ignition (blue Motor dizzy) it will never ever show correct.

The torana dizzy circuit is too simple and only ever designed to trigger off an exact signal a points ignition system makes.

 

Having said that, you could replace the internal circuit with a proper Frequency to voltage converter to drive the torana

meter element, assuming your meter element is in good condition and still calibrated correctly.

But in reality the meter element was probably calibrated to suit the old circuit anyway and you'll be wasting your time,

unless your and instrument technician.

 

Your best bet is to graft the guts of a more modern cars tacho into the cluster.

[fuzzypumper]

Heres a circuit of a 1980s model aftermarket VDO tacho which used the same style meter element as the Torana VDO tacho. 

I made a pcb using this circuit and ran it for many years, while it worked far better than the original torana circuit on my HEI ignition, it was only ever as old worn meter element allowed it to be.

Attached Files

•  P1060660 VDO Tacho Circuit Vintage 1980 (Custom).JPG   84.34K   8 downloads

Edited by fuzzypumper, 07 January 2017 - 11:59 PM.

[toryman76]

If you use an original torana tacho on a HEI ignition (blue Motor dizzy) it will never ever show correct.

The torana dizzy circuit is too simple and only ever designed to trigger off an exact signal a points ignition system makes.

 

Having said that, you could replace the internal circuit with a proper Frequency to voltage converter to drive the torana

meter element, assuming your meter element is in good condition and still calibrated correctly.

But in reality the meter element was probably calibrated to suit the old circuit anyway and you'll be wasting your time,

unless your and instrument technician.

 

Your best bet is to graft the guts of a more modern cars tacho into the cluster.

 

Hi Archie,

 

Thanks heaps for the info. I don't have an original Torana tacho. What I have done is use a brand new VDO tacho, part number 333015033, and grafted it into the Torana cluster. I would of thought this being a brand new tacho would be much more modern than the original Torana one?

[fuzzypumper]

Hi,

.

Reading back in the begging of this post, its funny you mention this behavior because i had the same thing happen when I building the the initial replacement circuit to use with my old torana meter. The problem was I had blown up the LM2917 freq to voltage chip that drives the meter.

It behaved exactly like that.

 

I think a faulty coil or Module may have killed your Tacho.  

 

 

So when I first start the car, sitting at idle to tacho comes up, say 1000rpm. When I rev the engine in small increments, the tacho does not move. If I rev the engine in higher increments, the tacho begins to move. When I turn the ignition off, the tacho will stay at the last position it was in. I have read this is sort of normal and should reset to zero when the key is turned to ignition and back off again, so i did this and the tacho moves down to say 500rpm and thats it, it stays there. Now to make things even more complicated, when I disconnect the sense wire with ignition off, the tacho will come down to zero. My electrical knowledge is very limited but to be it seems that the tacho is not sensitive enough. Could this be the case or is there something else at play here?

Edited by fuzzypumper, 08 January 2017 - 04:49 PM.

[toryman76]

Ok I am starting to think now maybe this is related to an issue I had early on when I first started the car. I was experiencing 14.8-15V across the battery terminals since day one from firing up the engine. After I ran the engine in I started fault finding and I've established that the charge light is causing this issue because when it's removed I see 13V across the battery. Initially I thought it was the alternator but that was bench tested and was found to be fine. I thought these two issues were unrelated but could it be that during the period I had high voltage something was damaged? If so would it more likely be the coil or ingnotion module?

[bags]

Hey mate did you end up getting it sorted? I'm wanting to fit a Vdo tacho into my dash too. Any chance of a couple of pics of it all mounted up?


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[VDO]

I believe your problem is that the HEI puts out a low voltage pulse, where as your VDO tacho requires a full 12 volt square wave to function correctly.

 

You should install a "pull up resistor" to the pulse wire.

 

Connect a 1K ohm resistor from the 12 volt+ ignition switch wire to the tacho pulse wire.

 

This should fix your problem.

[toryman76]

Hey mate did you end up getting it sorted? I'm wanting to fit a Vdo tacho into my dash too. Any chance of a couple of pics of it all mounted up?
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Hey mate. No I never ended up resolving the issue. I stumbled across a decent slr cluster which the tacho works perfect.

I have a feeling it was something more to do with the way in which I mounted the tacho. If you do have a go at this yourself just be real mindful of this.