HELP! My car eats tachomters!

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Hi all. I drive a 1993-1997 AE101 Corolla with a 20V Silvertop swap. The instrument cluster is stock (although I'm still looking for a Corolla GT cluster), however my car eats tachometers.

It starts out fine, then at some point you notice the rpms at idle reading slightly lower than usual. For example, at cold start-up on mornings, it's usually in the 1100rpm range, instead it reads the first notch below the one (which is like what, 800rpm?). Then you notice that it's not redlining the way it used to (better still, you HEAR it redlining but it's not reflected on the tach).

Now it's reached the stage where cold start idle is the first notch off the zero (which is like what, 200rpm?). This is the 2nd tach I've had with the same symptoms in a year!

Now the car has automatic transmission, so I'm not even close to considering bolting an external tach like the rice boys do on their A/T grocery-getters.

The only thing that isn't stock on the engine is that the coil is an MSD Blaster SS instead of the stock coil, but that's been there almost 3 years now and I question whether it would start killing tachometers at this late stage in the game (the first tach that was changed last year, came with the car 4 years ago).


Where do I start checking to troubleshoot this?

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Okay, after driving it around and monitoring it since I posted this, I've deduced that the tach is reading just about half of what it should read. It's hitting high revs as normal, just that it's not being reflected on the stock tachometer.

Is there a resistor or diode that I should've wired in, or is it simply tough luck I managed to get a bad replacement tach that died a year after the original one died (after 16 years)?

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LOL NO RESPONSES?!?!?!

I guess this forum isn't as hardcore tech as I thought!

I found this http://www.mindspring.com/~jayk3/toyota/tachmod.htm

Will update if it works.

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Okay, so it can't work

The AE101 tachometer is completely different from that unit in the article and there's no adjustment to be made anywhere.

It was suggested that maybe the stock tach simply wasn't designed to be swung that high that fast and that the second unit was possibly on the way out anyway so it didn't live very long, so my best bet is to scour the junkyards for a GT instrument cluster with a 9000rpm tachometer and hope that I get one with some life left in it.

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Okie, managed to get my hands on another stock AE101 instrument cluster with less than 49,000kms on the odometer so hopefully it'll hold out while I'm looking around for a GT tachometer or one from a BZ Touring wagon.