Screwy Tach

B

BUBBA

Member
Joined
Jan 1, 2000
RO Number
2190
Messages
152
Last Spring after sitting all winter the tach on
the port engine was pegged.This was before the first start up and it never moved. I gad it replaced with a new tach and it instantly did the same thing. Why would a tachometer do this ??
 
+1 a bad connection or a bad sensor. I had this happen on diesels. The wire going into the Glendenning synchonizer tach was loose.
 
What kind of motor do you have it could be your ECM module. I helped a friend trouble shoot his and I ended up swapping the ECMs between motors and the problem switched to the other motor.
 
Any tach problem I have ever had was the ground wire.

Bob
 
Thanks Guys I will check the ground wire. Too old to be ECM's 1984 260 Mercruiser
 
Some of those tachs have a rotary switch on the back for 4-6-8 Cylinders. Sometimes cycling it through the choices a few times and going back to 8 may clean the contacts and put it back to work.
 
What j-d said. I have had this problem several times. I have even gone to the effort of removing the rotary switch and soldering a jumper wire in place when I could not find a replacement tach that matched.
 
While we're on the subject, my tach is a little jumpy. The engine is running smooth, it's just the needle has a twitch. What do you guys think?
 
Thanks J-D but this is with a brand new tachometer also tried resetting the rotary switch and did not fix the problem
 
quote:
Originally posted by CaptNCamille

While we're on the subject, my tach is a little jumpy. The engine is running smooth, it's just the needle has a twitch. What do you guys think?

Click to expand...

What kind of engines ?
If gas IB or I/O with older distributor, a warn rotor shaft and bushing-bearing will cause a "nervous" tach needle.

If you feel any side to side ( not rotation) play at all in the shaft, that would confirm it.
 
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