I assume this is a bad ground?

rtstrack · #1 (**permalink**) 03-14-2009, 06:08 AM

Start the car up and while its at Idle the volt gauge on the dash reads a nice solid 14 (what it should read) but then as i get the car up to 3000 to 4000 rpms the needle will bounce down to 12 volts. When i take my foot off the gas the rpms obviously go down and the voltage gauge bumps back up to 14. So what the heck is going on here? Is the engine some how not grounded and then is my voltage gauge somehow grounded to the engine?

Ron61 · #2 (**permalink**) 03-14-2009, 06:20 AM

That is one possibility as when you rev the engine up it will torque a little and you could have a loose ground wire or strap that is then not making good contact. But the fact that you still read 12 volts would indicate that you still have some ground if that is the problem or the gage should read nothing if the ground was lost completely. I would check the ground wire for the gage and also the power wire where it attaches.

Ron

RICK LAKE · #3 (**permalink**) 03-14-2009, 06:37 AM

rtstrack Your volt gauge could have a loose wire or weak ground. I would start with the fan belt. It sounds like it is slipping at higher rpms. The fan belt could be glazed. You didn't say how many wires go to the Alt? Sanding the pulleys with 80 girt and adding a new belt is the easiest thing to do. You need to run a seperate volt meter to the battery and then the back of the ALT and go do your short drive and monitor this meter for voltage drops. As far as grounds, I recommend a min of 2 grounds to the motor and chassic. This means no paint on the connection and use start washers. If the car cranks ok, I don't think there is a starter or battery problem, it's just the Alt or Gauge. You are checking that with the road test. May sure the belt is not slipping. If your water pump gets a coolant leak and it goes on the belt, this will cause the same problem. Check the COOLANT level when cold. Check the weep hole on the pump for ANY discolor, wetness, or stain. If any is found, you need a pump. Rick L.

Paul F · #4 (**permalink**) 03-14-2009, 09:34 AM

It doesn't sound like a ground issue to me. A bad ground would make it bounce much worse, like to 0. It might be just the normal function of the voltage regulator.

Bryan Wilson · #5 (**permalink**) 03-14-2009, 11:24 AM

Quote:

Originally Posted by RICK LAKE

rtstrack Your volt gauge could have a loose wire or weak ground. I would start with the fan belt. It sounds like it is slipping at higher rpms. The fan belt could be glazed. You didn't say how many wires go to the Alt? Sanding the pulleys with 80 girt and adding a new belt is the easiest thing to do. You need to run a seperate volt meter to the battery and then the back of the ALT and go do your short drive and monitor this meter for voltage drops. As far as grounds, I recommend a min of 2 grounds to the motor and chassic. This means no paint on the connection and use start washers. If the car cranks ok, I don't think there is a starter or battery problem, it's just the Alt or Gauge. You are checking that with the road test. May sure the belt is not slipping. If your water pump gets a coolant leak and it goes on the belt, this will cause the same problem. Check the COOLANT level when cold. Check the weep hole on the pump for ANY discolor, wetness, or stain. If any is found, you need a pump. Rick L.

Agree with Rick. I had the same problem, went to auto electrician he tightned the fan belt and all was ok.
cheers,
Bryan