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Old 02-13-2011, 02:47 AM   #1
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Default tach and ms way off?

I've always noticed that my tach was a little off at idle. about 200 rpm or so. No big deal right? so it idles at 850 rpm verified by snap on timing light with tach and that is what MS reads as well. but my tach reads 1k. I was just going to re time the needle so that it matched, but tonight I was doing some in boost tuning and noticed that the higher the revs the farther off it is. I have hard limit fuel cut set at 7200. anyway I do a third gear pull and look down to see my tach passing 8,200 and no sign of a rev limit at all. so I pull to the side of the road and verify the settings and then check my log. it read 7k. thing is when I was running the stock ecu it was dead on and fuel cut was right at 7200rpm.

so in short
idle 150-200 rpm high
7k 1200 rpm high

anybody come across this before? is it one of those things I need to fiddle and **** with a voltage range in mt config somewhere?
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Old 02-13-2011, 05:33 AM   #2
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Originally Posted by dynokiller90 View Post
anybody come across this before?
Yes.

Quote:
is it one of those things I need to fiddle and **** with a voltage range in mt config somewhere?
No.


The factory tach is a pretty simple analog instrument, and they're known to sometimes be inaccurate. I can't say that I've ever personally seen one as far off as what you're reporting, but it wouldn't surprize me. I would tend to trust the display from your megasquirt, as it's based on a fairly accurate crystal-driven reference.
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Old 02-13-2011, 11:20 AM   #3
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At 3600rpm my tach reads 3900 rpm

at 7000rpm my tach reads 7500rpm.

at idle it's accurate though!
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Old 02-13-2011, 11:43 AM   #4
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at 7200 my tach reads 8200
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Old 02-13-2011, 12:39 PM   #5
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Same issue here. It was the same with Emanage Ultimate as well.
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Old 02-13-2011, 01:27 PM   #6
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thanks fellers. I do indeed trust the MS display as it and my timing light are two peas in a pod. I think I'll still try to re-time the needle at idle just so it's not quite so far off and live with the ricer points on the top side.
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Old 02-13-2011, 02:11 PM   #7
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at 7200 my tach reads 8200
ditto
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Old 02-13-2011, 02:14 PM   #8
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No issues here.
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