Tach has a life of it's own

[Smithcraft]

When I turn the key, and before the engine starts, the tach jumps. It's not like it's energized, sweeps and goes back to zero. It just starts dancing around, and it seems to be based more on the current draw in the dash items.

Once the engine starts, the needle works as it should(or at least the fluctuation is so minimal as to be not noticeable).

Any iDeas as to what is causing this, or if it really even matters?

Thanks!

SC

[ericem]

Thats sick does it sweep like new Subaru's? lol awesomeness aside. Do you have a ECU code? I think it is the cam sensor that is tied to the tach.

[Smithcraft]

Don't know if I have an ECU code...

SC

[SubaruNation]

i would roll with it that is awesome!

I want video!

edit: oh.. it DOESNT jump.

i get it.

if nothing seems wrong i would let it fly and dont worry too much

[asc_up]

Lol guys, he said that it DOESN'T do the sweep, don't get too excited.

[ericem]

When I turn the key, and before the engine starts, the tach jumps. It's not like it's energized, sweeps and goes back to zero. It just starts dancing around, and it seems to be based more on the current draw in the dash items.

Once the engine starts, the needle works as it should(or at least the fluctuation is so minimal as to be not noticeable).

Any iDeas as to what is causing this, or if it really even matters?

Thanks!

SC

[asc_up]

Lol dude you must have selective reading or something.

When I turn the key, and before the engine starts, the tach jumps. It's not like it's energized, sweeps and goes back to zero.

THIS is what it does.

It just starts dancing around, and it seems to be based more on the current draw in the dash items.

[Smithcraft]

Come on guys! Read the whole sentence!

Anyway, I didn't bother to notice when I went to work, but when I went to come home, I got in, turned the key and the tach started acting like a VU meter for the radio. After starting it again worked fine. I shut the engine off, and repeated the procedure, but the tach behaved.

SC

[asc_up]

Haha it's selective reading. Seeing what they want to see. Although, I can't necessarily blame them for hoping it said that.

The first things that I would check are the terminal connections on your battery (make sure the cables aren't loose) and the battery itself. Sounds like the amount of power it's putting out is causing an erratic reading from the tach, but once your car is on and the alternator is supplying the power, you're ok.

[Smithcraft]

This is just weird. It only does it at night, which either means a photonic reason, or a thermal reason(or both...).

I was maybe wondering if the battery might be flaking out, or maybe the alternator. But they were both replaced round about June or July.

SC

[asc_up]

Hmmm. Do you have your headlights and/or parking lights on when you try to start the car at night?

[Smithcraft]

I always have the headlights in the on position.

SC

[asc_up]

Does it do this when the headlights and parking lights are off?

[Smithcraft]

Don't know, but I'll check it tomorrow night.

SC

[Smithcraft]

Last night was pouring cats and dogs, and more cats, so I just ran and jumped into the car to get going.

However, it was only drizzling this evening, so here is what I did.

Open the door and sit down.
Turn off everything(couldn't turn off the radio as it has to be on to be turned off! ).
Turned the key. The radio came on, and the tach behaved. Turned the radio off.
Turn on the Defrost/Heat. Tach comes to life. Turn on the radio and the tach had a great time! Turned the HVAC off and the tach died down but not completely.

So I think it's in the HVAC controls!

SC

[Legacy777]

Could be a bad ground somewhere....