Resolved Tach help needed 1990 gsx

[Chris2388]

Hello all.

I have had no luck getting my tach to work on my 1990 gsx 5 speed.
I have read countless threads trying to find the solution.
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I am still running a 90 coil.
I have a 91+ ecu. I swapped pin 6 and 14 on the ecu. I also replaced my my 90 PTU with a 91+ PTU along with wiring in the correct pigtail, spliced the thick Black/white wire to the coil plug Black/white wire, also ran the white wire from the PTU harness to pin 109 on the ecu, I followed the instructions from this thread (1991-1994 ecu swap into a 1990 DSM ignition wiring) Thank you SPOONMAN.
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After doing the above mentioned my stock 1990 tach still does not work at all. So I kept reading and found info on the noise filter. I found mine

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I then unplugged it and jumped the connector just in case my filter is dead.

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This still made no difference the factory 1990 tach is still not working at all..
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This is where i am stuck at so far. I would really like some help here.

Is it possible for me to tap into pin 21 (Crank angle sensor) and run a wire to my tach maybe to get it up and running?

 

[19Eclipse90]

Did you read this one: 90 Dead Tach with 91+ ECU?

BTW, do not touch the CAS wiring. It is not utilized for the tach signal.

 

[Chris2388]

Did you read this one: 90 Dead Tach with 91+ ECU?

BTW, do not touch the CAS wiring. It is not utilized for the tach signal.

I have NOT touched the CAS wiring. I was only asking.

Im reading thru that threads now. But i am still running a 1990 coil and 1990 cluster, with a 91+ PTU and a 91+ ECU.

Im currently going to fallow this unless instructed not to.

Here's what I would do. Put the original white wire back to pin 109. This means that from the ECU and gauge cluster up to the noise filter plug, the wiring is all original so you should have continuity up to that point.

Now, trace the wire running from the noise filter connector to the '90 coil pack. Take it from the coil pack and run it to pin 4 of the PTU. That will get the tach signal from the PTU to the noise filter and, consequently, to pin 109 of the ECU. Then, using osbidian'strick, you'll loop a signal to the gauge cluster as well. It still won't be the right signal for the '90 tach but it ought to be the right signal for a '91+ tach. Swap one in and go.

To continue using the '90 tach, you need a '90 coil pack as it uses the tachometer interface on that coil pack for the right signal. Stock tach doesnt work, but tach works on SAFC.

 

[19Eclipse90]

I have NOT touched the CAS wiring. I was only asking.

And I was only informing you. Carry on.

Im currently going to fallow this unless instructed not to.

Not a bad way to go. It is a very fool-proof way of doing it.

However, because of this:

But i am still running a 1990 coil and 1990 cluster, with a 91+ PTU and a 91+ ECU.

You might skip down to the last post and check what it suggests. If the original white wire is still intact at the coil pack and you still have a black w/ white going to the coil pack pin 4 (you should in order to power the coil), I don't see why the tach wouldn't work, even while running the new white wire from the PTU to ECU pin 109 unless for some reason the tach is fed something from the ECU.

Edit: ^^That last bit, I suppose, is actually what you had been trying already, right? If so, I guess that doesn't work then.

 

[Chris2388]

I think I might have figured it out. After clicking on the link at the bottom of your instructions I noticed that my coil is actually missing the Tacho Interface. So I am now in search of one. I will post back my results once I find one. Thank you for your help so far.

 

[19Eclipse90]

Ah, yup. That would be a problem. Please let us know if that gets things going for you.

 

[Chris2388]

I definitely will

 

[Chris2388]

Ok so after replacing my coil with a proper 1990 coil which still have the tacho interface. My tach now works great.

Thank you for your help and good directions 19eclipse90