Hi ya'all,

the tacho does not work now that I have replaced the engine (6G74 -> 6G72 MIVEC). The guys who did the wiring can't get the tacho in the TH to work with the MoTec.

So, a couple of questions for you knowledgeable folk to mull over, and provide answers pls. I know too little about this stuff!

a - where does the signal for the tacho come from ie where and what is the sensor?

b - what form does the signal take ie pulses or varying DC voltage?

c - depending on the answers to a & b, can I splice in (parallel wire in) a feed from sensor to the factory ECU (kept in to run all aspects of the TH apart from actual engine management), and have the factory ECU drive the tacho in the orginal TH dash?

The alternative being looked at is an aftermarket tacho, but I would prefer to use the existing TH one that is already integrated in the dash.

Looking forward to your (polite, of course) responses.

Cheers

i DO NOT KNOW THE ANSWER TO YOUR QUESTION, sorry.

However, how high does the mivec engine rev too? ie RPM Does it go beyond a standard magna tacho, if so i would be looking at something aftermarket and just throwing it into the tacho area on the dash cutting the plastic protector where needed.

MIVEC rev limiter set at 7,800 in the MoTec aftermarket ECU. I'll post the dyno tuning sheet soon, so you can see how the power drops off gradually after about 7,500 rpm. So yes, it does rev significantly higher than the standard magna. Having said that, the tacho in the dash goes up to 8,000 rpm or so anyway. Its the redline that's in the wrong place :bowrofl:

The signal is received from the coil i couldnt tell you wether its pulsing or difenrencial (cant spell)

Then i would consider keeping the factory one then... for the stelf look that way there are no hassles with the girls in blue.

Oh not you too!

Second person replacing their engine with a DOHC and not being able to get their tacho going.

You've got a MoTeC so I don't know how they output the tacho signal. Post the MoTeC wiring diagram and I may be able to help.

By the way, are you no longer using a distributor but using coil packs now?

The signal is received from the coil i couldnt tell you wether its pulsing or difenrencial (cant spell)


That is true for our SOHC engines. But I have a feeling that his DOHC, if it is similar to the 'other' DOHC person we know of, uses a totally different ignition system (Nothing to do with your 'key' by the way)

The majority of tachos take the signal from the negative side of the coil. This signal is a pulse.
If you have coil packs on each plug the signal from the coil packs would be NO good.

Reason: with a single coil ign (most common) the distributor would switch the coil 6 times for 2 revolutions. The tacho would receive 6 12V pulses from the neg side of the coil for 2 revolutions of the engine , the distributor spins at half the speed of the engine. The tacho converts these pulses into RPM. eg 1000 rpm = 500 distributor RPM x 3 pulses per Revolution = 1500 pulses/min

With coil packs on each plug you would only receive 1 pulse ?V per 2 revolutions, the tacho would read very low if wired like this. eg 1000rpm = 1500 pulses/min to achive this means the engine would be at 3000rpm for an indicated 1000rpm on the tacho :shock: .

You would need to get the signal from a dedicated o/p from whatever switches all 6 coils.

EDIT
I just had a look at the wiring diagrams for the DOHC with 3 coil packs and the tacho feed comes from the power transistor module which has 2 connectors, if this is what you have the white wire feeds the tacho. the blu/blk blu/red and blu/yell wires feed the coils which is the other connector to what you want.
I'm trying to copy the cct but Mitchell doesn't seem to let you. Done good old 'ctrl' * 'print screen'

Wow, thanks a lot for the responses! Excellent.

Will discuss this with the guy who did the wiring, and hopefully we will get the tacho working.

thanks again, team!

Hello all. I'm "the guy doing the wiring".

I'll explain the background information:

Old Engine:
A distributor based system for spark but still using an ignitor to fire the coils. The Tacho output from these is normally a pulsed ground signal. There is no internal pullup.
Pulse goes (Gnd, Float, Gnd, Float, Gnd, Float ...)

New Engine:
3 Separate Waste Spark systems. Each coil and ignitor is placed over the front 3 cylinders. There is no tacho output from these ignitors.

The MOTEC outputs 1 pulse per 1 spark, as per a normal distributor setup, however it has an internal voltage pullup to 12V (Well, it's battery voltage but you get the idea) Pulse goes (Gnd, 12V, Gnd, 12V, Gnd, 12V ...)

The particular issue we have is (well, we think it is), ironically enough, is the Air Conditioning controller. It shares the RPM input with the dash. Internally the Air Con box is exerting a 5V pullup which, is a little strange, but nothing suprises me now!

Anyway, the problem isn't unsolvable and we've got a plan at the moment. Going to examine the RPM signal from another Solara and go from there. I'm sure meansolara will keep you all updated.

Just confirming something philsTH, did the wiring diagram have three distinct ignitors/three coils or just one ignitor on three coils?

meansolara, All tacho feeds that I know of are pulse period based. You wouldn't be able to use a varying voltage due to the nosiy electrical environment. For your info, internally in the dash tacho unit there is a Frequency to Voltage converter which drives a simple coil based meter to display it to the driver. All this goes out the window if you have a digital dash of course :D . See you should've taken the one out the front cut after all :P

EDIT: I said pulse width based, I meant pulse period based

Use the attached pics for more of the engine cct.

The one igniter unit receives 3 seperate signals from the ECU to individually pulse each tranny in sequence with the firing order, the trannies generates larger pulses which switch the corrosponding coil pack.
The combination of the 3 trannies is fed to a *device* which then outputs the pulse feed to the 4th tranny, the output pulses of the 4th traanny is then used as the tacho drive.

*device* I am guessing that this device is a frequency counter/divider network to output the corrrect frequency, this would then pulse tranny 4 at the correct frequency for the tacho.
As nearly all tachos work on the same freq for no of cylinders I would imagine tranny 4 to pulse at the same rate as a standard coil ignition.

Hello all. I'm "the guy doing the wiring".

I'll explain the background information:

Old Engine:
A distributor based system for spark but still using an ignitor to fire the coils. The Tacho output from these is normally a pulsed ground signal. There is no internal pullup.
Pulse goes (Gnd, Float, Gnd, Float, Gnd, Float ...)

New Engine:
3 Separate Waste Spark systems. Each coil and ignitor is placed over the front 3 cylinders. There is no tacho output from these ignitors.

The MOTEC outputs 1 pulse per 1 spark, as per a normal distributor setup, however it has an internal voltage pullup to 12V (Well, it's battery voltage but you get the idea) Pulse goes (Gnd, 12V, Gnd, 12V, Gnd, 12V ...)

The particular issue we have is (well, we think it is), ironically enough, is the Air Conditioning controller. It shares the RPM input with the dash. Internally the Air Con box is exerting a 5V pullup which, is a little strange, but nothing suprises me now!

Anyway, the problem isn't unsolvable and we've got a plan at the moment. Going to examine the RPM signal from another Solara and go from there. I'm sure meansolara will keep you all updated.

Just confirming something philsTH, did the wiring diagram have three distinct ignitors/three coils or just one ignitor on three coils?

meansolara, All tacho feeds that I know of are pulse period based. You wouldn't be able to use a varying voltage due to the nosiy electrical environment. For your info, internally in the dash tacho unit there is a Frequency to Voltage converter which drives a simple coil based meter to display it to the driver. All this goes out the window if you have a digital dash of course :D . See you should've taken the one out the front cut after all :P

EDIT: I said pulse width based, I meant pulse period based

Hey Spektor, keep us updated on how you go with the wiring. Because I'm the other DOHC converted magna who's tacho doesnt work lol

philsTH,
Hrmmm I'd guess the *device* is a simple OR gate. The only way to tell would be to throw a CRO onto it and see what pulses are being generated.

Although, one other thing is that the RPM signal is going to the Automatic Transmission Controller. Something else to check out.

Killbilly,
Unfortunately, as you'd expect seem as though I'm a Lancer Boy, I don't visit AussieMagna very often. I'd image MeanSolara or Mitisiman will keep everyone in touch.

Oh Oh...me too...me too!

my tacho isnt working neither :(
frikkin DOHC conversion! hehehe

Chad

Hey i can't really help you with you question but i was interested in what Spektor said when he said that it all changes if you get the dash out of the import??? I am looking at replacing the dash and i was wondering if it is possible to change the Stock one for the Import one???

If anyone know could you please let me know :D

Hey i can't really help you with you question but i was interested in what Spektor said when he said that it all changes if you get the dash out of the import??? I am looking at replacing the dash and i was wondering if it is possible to change the Stock one for the Import one???

If anyone know could you please let me know :D

Can't help you with this one, sorry. The dash that came with my frontcut was setup for automatic eg had the gear selected lights down the centre. Also the speedo had 180 km/h upper limit :badgrin:

I think that I would still have some wiring to sort out if I had used that dash - but the electroluminiscent dials were very nice to look at!

Anyone figured the tacho problem out yet?

ahh nope, been too busy, I might have some time to look into it in about 2 weeks

What about the crank angle sensor?, how many wires are coming off it? if this motor runs one
Just a thought

What about the crank angle sensor?, how many wires are coming off it? if this motor runs one
Just a thought

Referred this question off to the guy who did most of the wiring. TH dash not yet sourced for comparison purposes.

Referred this question off to the guy who did most of the wiring. TH dash not yet sourced for comparison purposes.
The Cam and Crank sensors are the 3 wire optical/hall effect sensors. However the tacho input comes from the ignitor not the crank signals.

1. I would be very hesitant to use that as a tacho source given its critical nature.
2. Different cars use a different trigger style on the crank sensor e.g. 1,2 or 3 pulses per 720deg crank, falling or rising edge trigger.

The problem with Steve's car isn't so much getting the tacho to work, as that could solved relatively simply, it's how to get the tacho and air-con controller to work using the same signal. Being winter that's not too big an issue, but come summer :confused:


Hey i can't really help you with you question but i was interested in what Spektor said when he said that it all changes if you get the dash out of the import??? I am looking at replacing the dash and i was wondering if it is possible to change the Stock one for the Import one???What I meant was is the way the tacho works changes as it will display the RPM as a number instead of just an analogue dial. This means they don't use the normal simple setup I explained earlier. Even still, going from one instrument cluster to a very different one could be a very long and tedious process if mitsubishi is not consistent with it's plugs and wires across car models.

EDIT: Just a note for everyone, as I don't visit these forums at all really, you can send me a Private Message on the MOGWA Forums (http://www.mogwa.org/forum/phpBB2/) as I check that every day. I'm more than happy to answer questions.

The Cam and Crank sensors are the 3 wire optical/hall effect sensors. However the tacho input comes from the ignitor not the crank signals.

1. I would be very hesitant to use that as a tacho source given its critical nature.
2. Different cars use a different trigger style on the crank sensor e.g. 1,2 or 3 pulses per 720deg crank, falling or rising edge trigger.

The problem with Steve's car isn't so much getting the tacho to work, as that could solved relatively simply, it's how to get the tacho and air-con controller to work using the same signal. Being winter that's not too big an issue, but come summer :confused:

What I meant was is the way the tacho works changes as it will display the RPM as a number instead of just an analogue dial. This means they don't use the normal simple setup I explained earlier. Even still, going from one instrument cluster to a very different one could be a very long and tedious process if mitsubishi is not consistent with it's plugs and wires across car models.

EDIT: Just a note for everyone, as I don't visit these forums at all really, you can send me a Private Message on the MOGWA Forums (http://www.mogwa.org/forum/phpBB2/) as I check that every day. I'm more than happy to answer questions.

This ignitor, are you talking about an ignition module?

This ignitor, are you talking about an ignition module?Yup. In this particular case though, the "ignition module" I'm referring to (Steve's old engine) is integrated into the distributor assembly so you don't actually see it.