Tach reads high.
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Joined: Aug 2007
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Tach reads high.
Looking for help with tach that reads high.
Start idle is 1K on tach, with dial back timing light reading 860rpm. serial port connected to efi ecm, readout is same as timing light. Efi ecm is Haltech and harness. Dist. is a coil in cap GM type. it seems the higher the rpm, the greater the spread becomes. Had second tach tested at local instrument shop and it tested correct.
I'm using the same tach connection that was on the origional tac lead before conversion. it seemed correct.
Any ideas will be greatly appreciated.
Thanks in advance.
LP2V
'95 roller 302 +.020
Dart heads
hooker ceramic long tube
Edelbrock performer
Comp 260er
Haltech ecm
1000cfm throttle body
eagle/srp
aod
Start idle is 1K on tach, with dial back timing light reading 860rpm. serial port connected to efi ecm, readout is same as timing light. Efi ecm is Haltech and harness. Dist. is a coil in cap GM type. it seems the higher the rpm, the greater the spread becomes. Had second tach tested at local instrument shop and it tested correct.
I'm using the same tach connection that was on the origional tac lead before conversion. it seemed correct.
Any ideas will be greatly appreciated.
Thanks in advance.
LP2V
'95 roller 302 +.020
Dart heads
hooker ceramic long tube
Edelbrock performer
Comp 260er
Haltech ecm
1000cfm throttle body
eagle/srp
aod
Elder User
Joined: Apr 2009
Posts: 922
Likes: 1
From: San Diego
I was about to make an idiot reply, but the math works out to what you are saying Rogue.
Posting Guru
Joined: Aug 2009
Posts: 2,271
Likes: 2
From: Mexia, TX
I have a similar problem, my factory tach reads about 150rpm lower than my Sunpro tach did when I had it hooked up. I read somewhere on here about how there was a magazine article in like the 80s or 90s where they did a test, and found that various different brands of tachs all read differently, with the only truly accurate one being the computer-based one.
Perhaps you could try a different tach (maybe borrow one from a friend who has one?) and see if you get the same reading.
Perhaps you could try a different tach (maybe borrow one from a friend who has one?) and see if you get the same reading.
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Nero Morg
1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
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Jul 31, 2012 10:44 PM
