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View Full Version : tach is bouncing around 2000 rpm



ehummelman
02-28-2012, 07:47 AM
Everything worked fine before I had to pull the engine up (not out) to replace the oil pan. To do it, the grounds off the back of the heads and the distributor wires (it's an HEI) had to be disconnected. Now it's bouncing like I said. Common sense tells me it's a loose ground or maybe tach signal wire but I've tightened them up, at least the ones I can find.

Any other reason this could be happening? Maybe coincidentally something in the HEI went bad? Any clues or things to trace down would be great. Thanks!

Modo Innovations
02-29-2012, 06:26 PM
Everything worked fine before I had to pull the engine up (not out) to replace the oil pan. To do it, the grounds off the back of the heads and the distributor wires (it's an HEI) had to be disconnected. Now it's bouncing like I said. Common sense tells me it's a loose ground or maybe tach signal wire but I've tightened them up, at least the ones I can find.

Any other reason this could be happening? Maybe coincidentally something in the HEI went bad? Any clues or things to trace down would be great. Thanks!

Have you tried backing off a little on the grounds and twising the connector a little on the bolt as you tighten back up as to maybe re-establish the ground? If that doesn't work, did you change any of the wire routing...maybe moving the tach wire close to a hot wire that could be causing an interference?

ehummelman
03-02-2012, 08:43 AM
Thanks Shannon. I had noticed that one ground strap had come off at the crimp so I resoldered it and connected it back up. The screw into the firewall is a bit loose which may be the culprit. I need to replace it with a bolt so I can tighten it down properly. It's just weird, everything was fine before, now it doesn't like me. If it's most likely a ground problem, I can figure that out. I was more curious if it could have something to do with the HEI. I have no problem buying a new module or even a new distributor if that will fix it, but don't want to just throw money at a problem without nailing it down first.

ehummelman
03-07-2012, 09:45 AM
seriously? No one has ever had a tach that jumped around?

Booger
03-28-2013, 08:11 PM
I've had several SunPro tachs that, eventually, went bad jumped around, but that stuff is cheap junk. I wouldn't run anything but an Autometer, now.
The insulation on one of your wires might be chaffed.