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Weird tacho issue

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Old Apr 13, 2017, 01:27 AM
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Weird tacho issue

So I just completed my 4G63T swap into my Lancer GSR 1800 (Aus built CC Lancer, similar to Evo III).
Ive done an Evo III loom swap, and am running an Evo VII ECU with Tephra V7.
Standard ignition system.
Car runs alright and drives fine.
The weird thing is the tacho, at idle, the tacho doesnt work, unless I set the idle above 1000rpm, below that it will just sit at zero.
Whilst cruising, tacho works fine.
Whilst accelerating, tacho works fine, UNLESS it knocks and the CEL flashes, if that happens, the tacho goes crazy and just bounces up and down.
After letting off the accelerator after boosting, above about 4500rpm, the tacho will just fall to 0 and sit there until you come back on the throttle.

This has got me completely stumped. I have no idea why it's behaving so weirdly, yet works fine whilst cruising.. I thought the tacho was just a wire from the ignitor to the dash?
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Old Apr 13, 2017, 05:10 PM
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Interesting (read weird) problem you have there.
I dont have an answer I would put money on, but am wondering if the old GSR tacho is looking for a slightly different pulse signal, eg a longer pulse (higher duty cycle) which is why it wont register at low rpm.

As to why it goes spaz on knock, thats totally weird.
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Old Apr 13, 2017, 09:47 PM
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Well, the even weirder thing is that I had the same ECU in the car running on the old GSR harness, and it bounced about a bit for like ten minutes after I did the ECU swap originally, and then never gave me any problems after that.

I put the Evo III harness in, and now it's just whacky.
I tried my old GSR ignitor, and that made no difference either.
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Old Apr 25, 2017, 07:47 PM
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installed boost solenoid and wound the boost up, now, the tacho doesnt work at all whilst accelerating at WOT. It just drops to zero and sits there until you back off..
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Old May 10, 2017, 08:53 PM
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UPDATE: Short video of the issue at idle..

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