shift light

SickSix said:

So i installed a ford racing tach in my 89 mustang..its been there for monts now..but i was wondering when i installed it untill i got over 2k the needle bounces all over the place when its just idiling...i got it hooked up to my coil..has anyone had this problem...if im at high rpms is is very accurate with my stock tach its just buggin me

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Actually you're racing tach is the one that's accurate. The stock tach is buffered so that it doesn't jump with the idle rpms. Otherwise everybody would have their new mustangs back at the dealer complaining about a jumpy tach needle thinking their engine is screwed up. Our engines don't actually idle at a steady rpm, in reality it does jump around.

This buffering tends to put a lag in to the stock tach reading too.