should my tach bounce?

[yeti]

should my tach, which is a 2888, bounce when I turn the keys on but not started. the needle shakes around 0. when I start itthe needle steadies until I rev it a little the needle is al over. the higher I rev it the worse it is. Could it be the position of the probe on the alt.? :confused:

[TimK]

We will need a little more information on your truck and tach. I don't remember tach's being a stock component for the 6.2L diesels. The two popular after market types are the ones that use a Hall affect devise with magnets glued to the damper pulley and the type of tach that connects to the one of the field windings in the alternator. There are a couple of other types out there besides these but I don't think they are as popular with our 6.2L.

TimK

[yeti]

ok, truck is an '82 GMC w/ a 6.2l. Tach is an Autometer # 2888. This has a "probe" that staps to the alternator. After hooking it up last night it didn't seem to work well. The needle would be stedy up to about 1000rpm. Anything above that it would bounce, 2k rpm and the needle would bounce between 1500 and 2500 rpm. After driving back and forth to work today it seems to work fine.

[gavio]

I have that tach in my van - was installed by previous owner.

It bounces a little around zero before I start it like you describe - began doing that when I installed an electric lift pump which apparently creates an oscillating drain on the battery.

After teh last time I changed the alternator, I had a problem where the needle would read up to about 1200, then stick until it would suddenly jump up to maybe 2400 - then read OK again after that. I realigned the probe on the alternator so it is centered directly over the gap between the front and back halves of the alternator and now it sems to read correctly again at all speeds.

Dunno if any of this will apply to you, but that's how it was for me....

Good luck!