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Tach underreporting RPMs

neilmcg

New member
"I have an '87 supra with

"I have an '87 supra with a 351w and VDO gauges. I've notice that the tach is reading low RPMs. The gauge is consistent, no fluctuations, just a continual low reading. Idle shows 300rpm and WOT is 3500 (should be 4500). I haven't touched anything. Any thoughts?
Thanks"
 
"The back side of the tach gau

"The back side of the tach gauge may look something like whats in the link below, If it does then you could try putting the arrow selector on the number that corresponds with how many cylinders you have.
If you have a 8 cyl and there is no number 8, try number 4. then you could check it against a external tach to see if it's working right and within range.

Here are some other examples the numbers could look like on the back side of the gauge.
A= 4 cyl.
B= 6 cyl.
C= 8 cyl.

Or
1 = 4 cyls,
2 = 6 cyls,
3 = 8 cyls...etc, There could be a few other setting also, But it will normaly tell you where to put the arrow.

Sometimes you can move the arrow selector on the back of the tach a few times and put it back on the setting it needs to go on, It may help reset everything.

Also sometimes just tapping on the front of the gauge will get it to work.

Check out this link so you know what to look for.
http://forums.iboats.com/attachment.php?attachmentid=43350&d=1263761013"
 
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