Tach acting weird

[matdand]

Terex 750 with about 100 hrs. Everything works fine, tach reads good, autofeed works fine. Only issue is when engine is at idle, tach reads zero.

I don't use this chipper, the guys just told me about it today. I know they swapped the throttle switch not long ago, but not sure if it coincides with this issue. They also tightened the clutch belt, but again not sure about the timming.

Is this a non issue?

 

[tc262]

It’s likely a speed pickup that’s miss adjusted.

 

[matdand]

I started acting weird again, I'm thinking something is dirty or frozen during the cold.

Do you know where the pickup would be and what it looks like?

 

[flyingsquirrel25]

I started acting weird again, I'm thinking something is dirty or frozen during the cold.

Do you know where the pickup would be and what it looks like?

Many times the pick up is on the alternator. Not saying that’s where it is on the terex but that’s where I have found them before. It’s normally just a single wire attached separately to the alt, apart from the voltage regulator. If the machine is as new as it sounds you should be able to find a wire schematic and follow the wires back to the sensor.

 

[craneguy1]

Mag pickup mount to side of clutch housing or near flywheel end of motor?

 

[evo]

I’m having a similar issue in reverse. Tach reads fine to 2k rpms then bounces around a bit. Would a failing alternator cause this, also having minor symptoms of a weak battery (but it’s also been cold)

 

[flyingsquirrel25]

I’m having a similar issue in reverse. Tach reads fine to 2k rpms then bounces around a bit. Would a failing alternator cause this, also having minor symptoms of a weak battery (but it’s also been cold)

If the pick up for the tack is in the alternator a failing alt could cause an issue. My 2070 morbark had a tack issue and it wound up being a bad connection on the alt wire. I just cut the end off, crimped a new ring on and reconnected and all was good. A slipping alt belt could also cause fluctuations, had that too with cheap automotive belts.
Try a multi meter on the battery when running. If it’s charging 13-14 volts the alt should be ok. Shut it down and watch to see if the battery voltage falls off past 12 and change. If so the battery is probably tired.