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Tach is Dead.

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LKWTSI

15+ Year Contributor
601
9
Feb 7, 2008
Lake Wylie, South_Carolina
I have a 90 and did some cluster mod's to remove the OEM gauges and in doing so I cut some of what I assume were nonessential links on the flex connector on the back. When I didn't get my tach working, I figured I had messed up something, so I went and got another cluster, from a 93 and plugged it in, as I have been lead to believe the clusters are pretty much the same, it's the harnesses that are different.

So I plug it in and still no Tach signal. I've done all the troubleshooting I can and can't get a signal.

What I would like to know, is, I get a RPM indication on my logger, so is the signal for the tach' coming from the same source and if so, what might else be the cause of 2 dead tach's. If not, what might I have missed?

Thanks for the help.
 
90 year tachs are a little different than the rest. Here's a couple threads with some info. Look them over, if you need more info let me know. Basically the 90 has a noise filter it gets the signal from and the 91 gets it from the transistor unit by the coil pack. Unless you change you ecu, coil pack, transistor and maybe something else, you will need a 90 tach. Your logger (i think) gets the signal after the noise filter through the ecu.

http://www.dsmtuners.com/forums/newbie-forum/410779-90-model-dead-tach.html

Post 44 I put some pics there that might come in handy. ^^

http://www.dsmtuners.com/forums/420a-engine-management/418425-tach-signal.html
 
Thanks I appreciate the links, but I have pretty much read them all. :thumb:

Like I said, I've been told the actual cluster itself won't matter what year, it's the signal wire at the Tach Gate that seems to be the issue. I have both my 90 and the new 93 cluster sitting on my workbench and from what I can see the 2 feeds to the tach are identical, so the signal must join in some where on the harness/ECU and then go to the cluster?? That's my conclusion.

I pulled the noise filter and jumped the harness connector and still no indications on both clusters.

I did a ohms check on the filter and I'm getting a 2222ohm reading. I don't know if this is correct yet, I'm about to research and see what the reading should be or if my multimeter is lying or if the filter is messed up.

So at this point I have to assume I have a dead tach gate and I'm about to look up how to check that out.

Thanks for the input.
 
Thanks I appreciate the links, but I have pretty much read them all. :thumb:

Like I said, I've been told the actual cluster itself won't matter what year, it's the signal wire at the Tach Gate that seems to be the issue.

The 90 tach is different from the 91-94. They receive a different type of signal. The tach will NOT work on a 90 model dsm with the 93 cluster you have. Your 90 cluster may work and it maybe the signal that's the problem.

As discussed in many threads, the 90 cars generate their ignition pulse signal at the tach adapter on the bottom of the coil pack. That's why they have a 4 pin connector vs the 3 pin connector on the 91+ coils. The extra pin is the ignition pulse signal from the coil pack. That wire runs to the unique 90 noise filter where it splits, the unfiltered signal going onto the ECU pin 109 and the filtered signal to the gauge cluster to drive the tach.

On the 91 cars the ignition pulse signal is generated in the power transistor module and runs to both the ECU and gauge cluster. So the 91+ PTM has two extra pins, the ignition pulse signal and a power feed for the circuit that generates it. The actual ignition pulse signal is different between the two versions but I haven't scoped then to describe the differences and can just note that the 90 docs say it's an "OR" of the two coil drive outputs and the 91+ is a "NOR". The gauge clusters seem to be sensitive to this difference, requiring a matching meter to the type.

I'm sorry that I can't provide any additional information. The first thing I'd do is verify exactly what your running and how you have it wired including your ECU.

If you look closely at the tach circuit board inside the cluster it obvious they are different. 4th and 5th pics in my post.
http://www.dsmtuners.com/forums/newbie-forum/410779-90-model-dead-tach-3.html#post152755510

dsmpartout advertises them for 15 bucks.
http://dsmpartout.com/?page_id=10&category=15&product_id=533
 
Thanks for the info. All I can say is :ohdamn: I took some bad advice and wasted $25 on a 93 when I thought it would work..oh well. Thanks for the link to DSM part out never heard of that one before and I've ordered a 90 cluster.

Will post the result when it arrives.
 
Pretty much what everyone else has said. A 90 has to have a 90 cluster and a 90 cluster only.
 
Car is dead now, so 90 cluster won't matter!:cry:
 
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