I'm guessing electrical problem but this is odd.

If i turn the key to ON without starting the car...Gauge jumps to 0.
Fine, that makes sense.

Car turns on, needle flies waayyyy up. It points straight vertical.

It never did this before but the needle used to jump around a lot. Is the sender loose/bad?

Thanks in advance.

 

Yep, sounds like a bad sender. Just replace it, they go bad often, they're about $15.

 

Ok cool, where do I get one? Any auto parts store?

It's right above the oil filter, correct?

-Matt

 

The sender for your gauge, if it's a V8, is behind your drivers side valve cover.

 

What kind of car do you have? I thought you used to have a sig but maybe not.
It could either be a bell-shaped unit located next to the distributor or a cylindrical unit located above the oil filter depending on your engine and year. The bell-shaped one is available almost anywhere for $15 like RB said, but the other one I could only find at NAPA for $50.

 

It's a 1986 LG4 V8

 

Bell shaped, in between distributor and driver's side valve cover©

 

I just replaced this not too long ago (mine was a dummy light switch. yours will be a gauge sender, but it's the same principle). You're going to have to lift the distributor up a bit to get the sender out and the new one back in. So make sure you mark everything!! Mark the rotor to the distributor housing and the housing to the block. I made the unfortunate mistake of only marking the rotor, and had to set the timing.

All in all, it's a simple job. If you can't get the distributor marks to line up again, then the oil pump driveshaft that connects to the bottom of the distributor has most likely spun a bit (this happens pretty often in these situations). Keep a long-neck flathead screwdriver and flashlight on hand, so you can turn the shaft back to its original position. Keep us posted!

 

speaking of this "dummy light switch" I have this thing floating around my engine bay(tied to the heater hose right now) that looks like a light bulb socket but doesn't connect to anything...anyone know what this thing is? long wire coming from the driver side firewall...

-Matt

 

you know, i have about a hundred of those throughout my car. They're probably there for options that might've come with your car from the factory. I'm pretty sure the same wiring harnesses were used for multiple models. For example, I took off the top half of my center console yesterday, and there are two female connectors just laying next to the shifter (auto trans). I'm pretty sure they would be for a manual trans if I had one. If your car's fine, don't worry about it. You can pick up a Chilton's guide (or hopefully a model/year specific repair manual) and sort through the electrical diagrams.

 

its probably stuff that got taken out. A more detailed description/pic will get you a definative answer.

 

Might be a good idea to see if the wire is still attached to the sender before you head to the parts store

 

When I replaced mine, I didn't want to mess with the distributor so I got about a 1" long threaded pipe and a 45 degree female fitting 1/8" NPT and put it in that.