Resolved 1G Gauge Cluster testing/diagnosing

[CrackedDSM]

Hey guys, I waited to make this thread after I reached the end of my rope. Well, reached that point today.

Quick background: 91 Talon TSI AWD. The gauge cluster will show lights, but the tachometer has never worked according to previous owner. It has a weird hybrid of 90 interior harness and 91 engine/chassis harness.

Attempted fixes:

1) Ran a wire from tach signal wire from ECU, directly to pin 11 (white wire) on the dash harness plug that plugs directly into the cluster. No tach still.

1a) Looked on back of gauge cluster and saw that the lead for "TACH" screw goes to pin 12 on dash harness, ran wire to pin 12 instead. No working tachometer.

2) Ran a wire from tach signal at ECU directly to screw on back of gauge cluster that says "Tach". No tachometer still.

3) Fully unplugged gauge cluster and kept fix #2 wired up, and ran a ground wire from ground to "GROUND" screw directly next to "TACH" screw on back of gauge cluster. Still no tachometer. Doesn't even flutter or twitch. Nothing.

I've searched and searched, and have no clue what the problem is. I am getting RPM signal at the ECU (duh), and it's the same exact wire I'm tapping into. It worked for a giant autometer ricer tach.

QUESTION OF THE THREAD:

How can I test the gauge cluster independent of the cars chassis harness and see if it's working? Is there even a way to do this without plugging the whole cluster into the dash harness? I'm honestly at my wits end. I really don't want to buy another gauge cluster, pop it in, and have the same exact issue so I'd really like to know if there's a way to test the cluster by itself.

As always, appreciate all the help fellas.

 

[1990TSIAWDTALON]

You don't happen to have a 90 engine harness that needs the tach filter do you? It is only on the 1990 model wiring harnesses. It has a "L" shaped connector IIRC and it is close to the knock sensor plug, in the same harness. Some folks have tried a jumper wire on that connector to get it to function but I run the actual tach filter on mine.
Just something you can check.

 

[CrackedDSM]

You don't happen to have a 90 engine harness that needs the tach filter do you? It is only on the 1990 model wiring harnesses. It has a "L" shaped connector IIRC and it is close to the knock sensor plug, in the same harness. Some folks have tried a jumper wire on that connector to get it to function but I run the actual tach filter on mine.
Just something you can check.

I thought about that, but there's no plug on the engine bay harness for the filter itself. And from what I've read, without the filter the needle will at least jump around and move.

This one has rigor mortis. Stiff as a board. It ain't goin' nowhere.

Edit: I actually was looking at a couple of your posts when I did the "tach" thing on the back of the gauge cluster. I saw that that worked for you so I gave it a shot. It was worth a try!

 

[1990TSIAWDTALON]

Could it be that the instrument itself is just plain bad? I have a dash with a bad speedo but a assumably good tach in it. Maybe try a different dash as a test?

 

[CrackedDSM]

Could it be that the instrument itself is just plain bad? I have a dash with a bad speedo but a assumably good tach in it. Maybe try a different dash as a test?

That's the idea for sure. I'm HOPING it's just the dash that is bad, but before I spend the money on a replacement, I want to see if there's a way to test the current dash. Like, apply 3v here and ground this pin, and something should happen. That kinda stuff. I can 100% afford to throw parts at it until it fixes it but it just feels wasteful.

 

[CrackedDSM]

Update: Ended up just buying a used cluster from Performance Partout. When it gets here, I'll update the thread on if it fixes the issue or not.

If it doesn't, I guess I'll be manually tracing the dash harness to see what the issue is. UGH.

 

[1990TSIAWDTALON]

Nate will treat you right! I would have sent you my tach to test if you needed it. I have several dashes. Crossing fingers that is all it needs is a swap out!

 

[CrackedDSM]

Nate will treat you right! I would have sent you my tach to test if you needed it. I have several dashes. Crossing fingers that is all it needs is a swap out!

It's actually John that owns it now, Nate retired. But he's the man for sure! Appreciate the help/advice. Will definitely update when have the new cluster. I just have this bad feeling it's not gonna fix the issue. And I really really don't want to have to crawl under the dash or pull the harness.

Quick question: if I provided a ground and a signal wire directly from the ECU to the back of the cluster and the Tach still doesn't work, that definitely means the cluster is bad right? I mean, I don't get what else could be causing the issue unless the tach needs a power source too and it's not getting it. However the lights on the cluster work, so does the oil pressure gauge, and all the lights. If it wasn't getting power, nothing would work right?

Idk. I'm mystified, and more than a little nervous in just swapping the cluster and would love either some reassurance or someone to drop some knowledge on me.

 

[1990TSIAWDTALON]

I am assuming that a factory tach works the same here, but all aftermarket tachometers require a 12v positive, a ground and a signal from the coil(s) with the light being optional.

 

[19Eclipse90]

The tach does not get its signal from the ECU. On the 1990, it gets it from the tach gate on the coil pack. On the 1991-1994, it gets it from the power transistor unit.

So running a wire from the ECU to the tach will tell you nothing about the condition of the tach.


What PTU and coil pack are you using?

Is the engine harness matching or something that was modified to work with the PTU and coil pack?

Do you know if the cluster is a 1990 or 1991+? (I’m assuming that it’s unmodified and has the gauges that belong in it.)

 

[steve]

Thank you Brian, I was going to mention that after reading the posts so far. I don't see any indication that the source has been checked.

The ECU RPM is derived from the CAS signals. The Tach input is used by the ECU to verify that the coils are firing not as a source for RPM information.

When I wanted to test Gauge Clusters I put together a 555 circuit to generate pulses to feed the tach input. It's been way too long for me to remember the exact circuit and values but today I might just whack together a simple Arduino and transistor to do the same with some code to vary the pulse rate and width.

 

[CrackedDSM]

The tach does not get its signal from the ECU. On the 1990, it gets it from the tach gate on the coil pack. On the 1991-1994, it gets it from the power transistor unit.

So running a wire from the ECU to the tach will tell you nothing about the condition of the tach.


What PTU and coil pack are you using?

Is the engine harness matching or something that was modified to work with the PTU and coil pack?

Do you know if the cluster is a 1990 or 1991+? (I’m assuming that it’s unmodified and has the gauges that belong in it.)

Thank you Brian, I was going to mention that after reading the posts so far. I don't see any indication that the source has been checked.

The ECU RPM is derived from the CAS signals. The Tach input is used by the ECU to verify that the coils are firing not as a source for RPM information.

When I wanted to test Gauge Clusters I put together a 555 circuit to generate pulses to feed the tach input. It's been way too long for me to remember the exact circuit and values but today I might just whack together a simple Arduino and transistor to do the same with some code to vary the pulse rate and width.

Sorry fellas, should've mentioned in the first post. It's a 91 coilpack, 91 PTU, and 91 gauge cluster. The interior harness(like plugs at the ECU) have wire colors that are from a 90 harness, but the engine bay harness is a 91 as it doesn't have any spot for the tach filter, and a few other differences like it has the 91-94 ISC plug and etc.


So would running a wire from pin 109 to the back of the gauge cluster not actually work? Should I run a wire from the PTU to the tach instead?

 

[19Eclipse90]

Or check continuity on the wire, as the problem could still be in the PTU and a new wire isn’t going to fix that. Pin 4 of the PTU to pin 12 of D-05 dash connector (driver-side connector).

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[CrackedDSM]

Or check continuity on the wire, as the problem could still be in the PTU and a new wire isn’t going to fix that. Pin 4 of the PTU to pin 12 of D-05 dash connector (driver-side connector).

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Well that makes sense. This is my short week so I have this weekend off entirely. I'll do that this weekend. I do have a spare PTU from the PO, and so far legit every spare everything I have had, I've had to use. So it wouldn't surprise me. Wonder if it's related to the random dying issue the car has right now when idling.

Appreciate the hell out of the help guys! I'll keep the thread updated.

 

[CrackedDSM]

Or check continuity on the wire, as the problem could still be in the PTU and a new wire isn’t going to fix that. Pin 4 of the PTU to pin 12 of D-05 dash connector (driver-side connector).

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Updating the thread, this was the problem. I tested continuity for pin 4 on the ptu to the cluster, and nothing. Ran a quick ghetto wire from the ptu pin 4 to the cluster, and Tacho works great.


I’m ecstatic don’t get me wrong, but now I’ve gotta figure out why continuity is broken. I need to just buy all new harnesses for this thing man.


Regardless, thanks a million! So stoked to have a working tach now.


Edit: the more I think about it the more I think I seriously need to just get a full 1991 harness for the engine and trans and cluster. Looking at the coil pack plug someone has cut it off and butt connected this one on. So it may be a full 90 harness someone converted. Terribly.