Resolved 90 Dead Tach with 91+ ECU

[dugan33]

I've read a lot of articles on this issue so I know I'm not alone, but I really wanna make sure everything gets hooked up right. I got a 1992 ECU with ecmlinkv3, a 90cas, what looks like a 91+ power transistor and I'm not sure what coil pack probably 91+ also.

This car had this hacked wiring when I got it and the tach never worked. I tried jumping the noise filter and that's all I did -> following this http://www.dsmtuners.com/threads/90-model-dead-tach.410779/.

I plan to jump the white wire previously ran from other owner to pin 4 on the power transistor, but is that all I have to do? I hope someone with more knowledge or experience can look of this heres all the pics I could take of my wiring mess.[DOUBLEPOST=1415870208][/DOUBLEPOST]I ran across I piece of info that seems like gold for me and others with this issue. http://www.dsmchips.com/pdf/tachadapter.pdf I just need to know that the tach adapter is.

 

[19Eclipse90]

The correct wiring for a '90 is pin 3 of the ignition coil to pin 2 of the noise filter. Also at pin 2 of the noise filter, the wiring exits and goes to ECU pin 109. The length that goes from pin 2 of the noise filter to ECU pin 109 should be shielded and the shielding grounded. Pin 1 of the noise filter is the one that goes to the tachometer. That wire should be shielded somewhere along its length and that shielding should be a ground.

A '91+ is much simpler. Pin 4 (white wire) of the power transistor unit branches to run to both the tachometer and ECU pin 109.

So since you're CAS is still the '90 version, I'd assume that the control harness is still a '90, aside from any modifications made to the coil or PTU? Does the power transistor not have a white wire at pin 4? Is that white wire a straight-through, single wire, nothing attached or branched off?

 

[dugan33]

It does have a white wire at pin 4 on the 91+ PT. Someone previously soldered that wire to the white wire from the 90 coil wiring but since i have a 91+coil i dont think that did anything. Today I resoldered the wire from pin 4 on PT 91+ to a white wire going straight to the 91+ ECU. After doing this my tach still doesn't work. I left the white wire from the harness that used to go to the 90 coil taped up unplugged. I don't have the bracket on the intake manifold or a noise filter. I found a black plug on my harness that i believe went to the noise filter that I jumped according to obsidians tech article.

 

[19Eclipse90]

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's trick, 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.

 

[dugan33]

Sounds like a plan. I probably won't mess with it til I get it back from Boostin performance December 2nd. My buddy should have a few 91+ Tachs. Too bad I liked my 90 tach with the 5mphs.[DOUBLEPOST=1416116095][/DOUBLEPOST]What's strange is with the wiring it has now ecm link reads my rpms perfectly fine.

 

[19Eclipse90]

It isn't necessary to change the complete gauge cluster so the 5mph-incremental speedometer can stay the same. The tachometer is the only gauge that should be changed. A '91+ tach is a direct swap into the '90 gauge cluster.

If Link is reading the RPM, then the ECU is getting the proper signal. But if a new wire was run from the PTU to the ECU and only to the ECU, the tach won't get the signal.

 

[dugan33]

Link was getting the signal before and after me hooking up pin 4 from ptu to ecu

 

[dugan33]

Ok, got my 91 gauge cluster in and the ecu is getting a signal from the 91 pt like it should. Now comes the question of how the hell do I split the signal and run it to the tachometer? The cluster is well really clustered and I don't know where to run my wires to from the power transistor. How is this done regularly on 91+ dsms? This diagram from the 92 electrical service manual shows it being split I just don't know how to run my wire

 

[19Eclipse90]

Isn't there already a white wire at pin 12 of the driver side cluster connector?

 

[dugan33]

I didn't check. I didn't really look beyond the cluster I figured I would find the signal wire in my engine bay. But pin 12 of the gauge cluster connector you say? Since I have a 90 where does that wire run I'd rather tap into that end. I'll have to find a pinout of the cluster connector too.

 

[19Eclipse90]

It runs to the noise filter on a '90. The diagram is the exact same for the '91+ (shown below) except where it says "Power Transistor (2.0L DOHC Engine)", it says "Noise Filter (2.0L DOHC Engine)" on the '90. This is why I outlined what I would do in that previous post -- the signal is sitting and waiting at the noise filter terminal and should simply need a jumper to connect it to the PTU signal, so long as the wire to pin 12 is still in place -- why it would have been removed is beyond me.

For S's and G's, you can check continuity with pin 12 (going to the tach) of the dash connector (that's D-05 encircled below) to pin 1 of the noise filter connector on the harness (the terminal of the connector with a single wire going into it). If that is there, the jumper trick should work.

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[dugan33]

The noise filter harness, or what I think is the noise filter harness is jumped and only has 2 pins. I'll check continuity behind the cluster and I'll run another wire into the engine bay if I got no continuity. Thanks for your help

This is what I looped. Is this the right harness for the noise filter?

What pin here do I test left or right?

 

[19Eclipse90]

This is what I looped. Is this the right harness for the noise filter?

I can't tell because of all the tape. It's pretty simple. Whatever connector the white wire from the PTU runs to is the connector that needs the jumper. I imagine you've probably got the right one.

What pin here do I test left or right?

I thought I mentioned this earlier but I guess I didn't. The driver's side connector.

 

[dugan33]

So yes I confirmed my looped connection with the three white wires is the noise filter plug. See first upload.

I got the voltage meter out and found that I still wasn't getting continuity from pin 5 of ptu to the gauge cluster pin 11 or maybe 12 I just tried each one til I got continuity.

That continuity did not occur until I bridged pin 4 off the 90 cas wiring. Pin 4 was already unplugged because I have a 91+ ptu and cas.

Pin 4 cas must be bridged to pin 5 ptu to get signal to both the ecu and tach. Pin 5 also has to be extended to pin 109 as following this write up on 90 to 91+ ignition system conversion. http://www.dsmtuners.com/threads/1991-1994-ecu-swap-into-a-1990-dsm-ignition-wiring.302812/

Following this write up alone wasn't enough to get signal to my tach. I got a 91+ cluster and bridged pin 5 ptu and pin 4 of cas. The cas pin 4 wire is what runs through the looped noise filter and then to the tach gauge cluster pin 12.

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[19Eclipse90]

Congrats.

However, I'm concerned that what you've described for people may be misleading. First thing’s first, do you by chance mean COIL PACK when you're saying CAS?

 

[dugan33]

WHOOPS!! Ya just sub coil pack plug for every cas spot . I hope they will see from the video and pics I'm working with coil pack plug

 

[19Eclipse90]

I didn't even watch the video and the pics are hard to tell much of anything from, especially that the coil is involved. Let me continue to clarify for everyone else.

In addition to everything saying "cas" instead of "coil pack", there is no pin 5 on the '91+ PTU. The tach signal comes from pin 4 of the '91+ PTU. For all those with a '91+ harness or pigtail, this is the white wire. The wire that was "unplugged" at the coil due to the '91+ coil swap was actually pin 3, also a white wire. That is the wire that runs to the noise filter connector on the '90 vehicle. Without this connected to the PTU pin 4, the tach would never receive a signal, even with the jumper in place. This is why I mentioned, with the original wire at ECU pin 109 back in place,

...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's trick, 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.

I could have sworn, for the longest time, that ECU swap article covered that. I see now it only mentions running a straight wire from the PTU to the ECU pin 109 but never splitting to/for the tach. That's an issue I'll look at addressing. Anyway, glad you finally got it figured out.

Edit: The reason that article doesn't mention this is because it keeps a '90 coil pack and gauge cluster. The tach signal still should be fine if it is there to begin with. It's when you get away from the '90 coil pack that this other wiring bit is needed.