st205 with cop conversion rev counter?

[Adzn3k]

hi guys,

since converting to coil on plug and deleting the igniter the rev counter now has no signal. whats my best option to get the rev counter back?

Adrian.

[Brad Burnett]

Msd tach adaptor pn 8920

[Simon]

Another 2 options are to use a gutted relay coil that the ECU switches to provide a coil negative signal. Or get the rev counter converted to accept a low level signal direct from the ECU.

 

[cj]

Theres a realatively well known tacho mod you can do to 90's toyota tach's to change them from needing a coil level signal to just needing a "normal" signal from any aftermarket ECU. 

http://www.6gc.net/forums/index.php?showtopic=89365

Read down the page about halfway. I've done it myself on an MR2 and it works perfectly. Basically these toyota tach's are internally capable of accepting a normal 12v or ground pulse that every aftermarket ecu sends out, but they put a couple massive resistors in there to dampen the signal that comes off the ignnitor down to the right level. Obviously if you feed it lower level signals it dampens them to bascially nothing.

 

You desolder a resistor, solder in a much smaller one, and then it works perfectly.

Heres another version of the same thing

http://club4ag.com/forums/viewtopic.php?t=20847

 

 

 

[Brad Burnett]

Theres a realatively well known tacho mod you can do to 90's toyota tach's to change them from needing a coil level signal to just needing a "normal" signal from any aftermarket ECU. 

http://www.6gc.net/forums/index.php?showtopic=89365

Read down the page about halfway. I've done it myself on an MR2 and it works perfectly. Basically these toyota tach's are internally capable of accepting a normal 12v or ground pulse that every aftermarket ecu sends out, but they put a couple massive resistors in there to dampen the signal that comes off the ignnitor down to the right level. Obviously if you feed it lower level signals it dampens them to bascially nothing.

 

You desolder a resistor, solder in a much smaller one, and then it works perfectly.

Heres another version of the same thing

http://club4ag.com/forums/viewtopic.php?t=20847

 

 

 

I have also done this on my ae86 Toyota corolla.   It does work.

[Adzn3k]

cheers for the replies, so looking at that thread on 6gc.net I need to get a 1kohm resistor for the signal wire, will I have to put a pull up resistor or does the link output a positive signal for revs?

also will any type of 1kohm resistor work any links to the type I need?

[cj]

No pullups or new resistors needed. You just replace a couple that are already on there with smaller ones. 

From memory I used a 5k ohm in place of the 43kohm one you take out. A couple of those internet threads talk about repalcing the resistor with just a wire but that feels like a bad idea. I used either a 1/4 or 1/2 watt resistor from jayar. About $2 for a pack of 5 or something. 

[edit] Just to be clear, you need to remove a resistor from the back of the tacho and replace it with a smaller one. Comments about "a resistor on the signal wire" actually refer to the traces on the back of the tacho between where the signal wire connects, and where it enters the processing chips of the tacho. You do no add resistors to the wire between the ecu and the dash.

Edited September 5, 2017 by cj

[mikegt4dude]

I have the same car and conversion and have already wired up an Aux Output Tacho Out to the interior connector that previously took an IG- splice, it's working flawlessly without ever touching a resistor. What is the purpose of touching resistors? Is something going to burn up? Or did I just luck out by having a facelift cluster from a Beams version that already has coilpacks?

[cj]

Yep I think you got lucky. Coil packs means the ECU was already driving the tacho directly, just like a link or other aftermarkert ecu will do. The older Toyotas that had distributors had the tacho driven from the ignitor, and while I seem to recall its still from the IG- pin on the ignitor, its pushes way more voltage than an ECU would (either 40 or 80v from memory), so the tacho is set up to drop that voltage to something safe for its internal circuitry.

We are talking about replacing the resistors that perform that voltage drop with something that drops it a whole lot less because now our source voltage is 12v instead of 80v.

[Adzn3k]

I've Diss assembled my tach ready for the resistor to turn up is it the ig- wire I need to splice the signal from the link to

Do I need to add the 0.56k pull up one in this picture? 

[MGV101]

Hi, I just got converted by MR2 which shares the same Gen 3 3SGTE engine with your ST205 to COP too. I knew about the tacho problem in advance and gutted my own relay to provide the coil signal but have misplaced it after getting the COP setup so I also don't have a tacho for the time being.

Other than the tacho my AC also refuses to function. Looking at the wiring diagrams, I noted there was a tacho input for the AC amplifier and assumed it isn't working due to not receiving a tacho signal. However, I don't see you mentioning any problems with the AC unit and just wanted to confirm whether your AC works. If it does worth without the tach signal this would mean I have another problem to sort out.

Thank you!

Edited September 7, 2017 by MGV101

[Adzn3k]

My ac is long deleted 

[MGV101]

Oh, alright. Thank you for the quick reply!

[cj]

You dont need to add any pullups or any other new resistors.

 

Just take out this one and replace it with a smaller one (around 1k-5k). Note that your tacho layout may be slightly different, follow the traces from the IG- input pin, its pretty obviously the first big resistor the trace hits.

[mikegt4dude]

Interesting. After a bit of private discussion, I pulled apart the Gen3 and Beams tachos, Here is the resistance I measured
(White is Beams)

Edited September 7, 2017 by mikegt4dude

[Adzn3k]

Sorted thanks for the help, soldered a 1k resistor and now I have a rev counter  

[cj]

Interesting. After a bit of private discussion, I pulled apart the Gen3 and Beams tachos, Here is the resistance I measured
(White is Beams)

Thats really interesting that the factory beams tacho's are that high a resistance. The 43K on the ignitor driven tacho sounds like the same number I found, but the guys providing the details of this mod long before I did mine all talk about <10K resistors being put in place on the 43k one. I cant remember exactly what resistance I used but it was less than 20, and anecdotally quite a few other people have had it work with smaller numbers too. I'd guess we should have all used 23k resistors to match toyota spec, but its a lot of effort to swap it when its already working.

Hopefully the next person who tries to do this finds your info above and tries a 23k resistor so we can be certain that there's not some other change in the beams cluster to go with this.

[Toliski]

Hello guys i just make the COP and every think works fine except the tacho.

i have 3s but on mr2 spyder.

I don't find any resistors like mentioned above at my tacho.

I just make the mod with the relay like that picture and works fine but i have the annoying relay clicking with every engine rev, if i rev to 7000 rpm i feeling that the relay might blow up!!! is there any other type relay or other mod to do?

 

This is my tacho ( Microsoft drive link)  https://1drv.ms/f/s!AmIEUc98EM73hokm5iFJV-DY5ZFTxA

[MGV101]

Yes, open up the relay and take out the switch. You don't need that part, just the coil. 

I used a relay on mine too (although a little different and involved the use and a transistor) and have removed the switch. 

[Toliski]

3 hours ago, MGV101 said:

Yes, open up the relay and take out the switch. You don't need that part, just the coil. 

I used a relay on mine too (although a little different and involved the use and a transistor) and have removed the switch. 

I try it!

i have never opened a relay 

[Thierry]

Does the msd tach adaptor work with the factory rev once install??

[Island_Racer]

I soldered in the new 1K ohm resistor in place. Do I now simply run the wire from the igniter connector to my link g4x in an auxilary pin and assign it to tacho?

Or is there more to set up to get this to work?

[Adamw]

That would be all that is needed.  Connect Tacho signal wire to an aux output and assign that output to the tacho function.

[Island_Racer]

Adam,

 did that and the counter doesnt go past 2000 rpm when driving. I did the tacho wire to pin 12 and reassigned it as tacho…what could be missing? 

[Adamw]

The ECU is outputting a 0-12V squarewave, the tacho originally worked off the high voltage coil primary (~100V), the tacho needs to be modified to work with the lower voltage signal,  or you can use a tacho booster with an unmodified tacho.  

I have never studied the MR2 tacho or modified one so I cant offer any advice on what it needs.