Author Topic: Tachometer shuts off... (Read 4762 times)

Mopar44o · « **on:** January 25, 2009, 03:39:14 pm »

So sometimes My tach will not work. It used to be once in a blue moon when i first started the car it would be off and the oil light would be on... But as soon as I started moving it would be fine, both tach and light.

But today while driving it shut off and the oil light and battery/generator light both came on...

I drove for 5-10 mins and the tach started working intermently... When it did work the warning lights shut off but when it stoped the lights kicked in... Is this a ground wire or could it be a sensor or something?

Mopar44o · « **Reply #1 on:** January 25, 2009, 06:36:37 pm »

How can I test my alternator to make sure its still powering the car while running. If I gotta live with warning lights and no tach for a while thats fine but i wana make sure the alternator is at least working....

Vincent Waldon · « **Reply #2 on:** January 25, 2009, 06:43:50 pm »

The alternator charges the battery *and* drives the tach... so if it's having problems (and thus the battery light comes on) you can expect the tach to stop working as well.

To test the voltage output of the alternator:

1) with the engine off, connect a multimeter to the battery and turn the key to the ON position. The BAT light should come on and you should read somewhere around 12.5V, assuming your battery is charged.

2) now start the car and rev it once past 3000 RPM... the BAT light should go out and the battery voltage should jump at least a volt to 13.5 or more.

The fact that your BAT light and tach are intermittent suggests that there is in fact a problem with the charging system... most common issues being a loose alternator belt, worn brushes, or a bad voltage regulator. The brushes and voltage regulator are one assembly that can be removed and replaced with the alternator in the car.

Smokey Eddy · « **Reply #3 on:** January 25, 2009, 06:54:27 pm »

Quote from: "Vincent Waldon"

The alternator charges the battery *and* drives the tach... so if it's having problems (and thus the battery light comes on) you can expect the tach to stop working as well.

To test the voltage output of the alternator:

1) with the engine off, connect a multimeter to the battery and turn the key to the ON position. The BAT light should come on and you should read somewhere around 12.5V, assuming your battery is charged.

2) now start the car and rev it once past 3000 RPM... the BAT light should go out and the battery voltage should jump at least a volt to 13.5 or more.

The fact that your BAT light and tach are intermittent suggests that there is in fact a problem with the charging system... most common issues being a loose alternator belt, worn brushes, or a bad voltage regulator. The brushes and voltage regulator are one assembly that can be removed and replaced with the alternator in the car.

What about the oil light though? how is that connected to the issue?

Mopar44o · « **Reply #4 on:** January 25, 2009, 07:00:36 pm »

Quote from: "Smokey Eddy"

Quote from: "Vincent Waldon"
The alternator charges the battery *and* drives the tach... so if it's having problems (and thus the battery light comes on) you can expect the tach to stop working as well.

To test the voltage output of the alternator:

1) with the engine off, connect a multimeter to the battery and turn the key to the ON position. The BAT light should come on and you should read somewhere around 12.5V, assuming your battery is charged.

2) now start the car and rev it once past 3000 RPM... the BAT light should go out and the battery voltage should jump at least a volt to 13.5 or more.

The fact that your BAT light and tach are intermittent suggests that there is in fact a problem with the charging system... most common issues being a loose alternator belt, worn brushes, or a bad voltage regulator. The brushes and voltage regulator are one assembly that can be removed and replaced with the alternator in the car.

What about the oil light though? how is that connected to the issue?

Ya its weird cause all the warning lights shut off when the tach works...

Assuming the battery is 13.5 then the alternator is charging my battery right? Which means there is some issues with the tach wiring I guess?

Smokey Eddy · « **Reply #5 on:** January 25, 2009, 07:02:34 pm »

yeah but loose tach wires wouldn't cause the oil light and battery light to turn on, surely.

Vincent Waldon · « **Reply #6 on:** January 25, 2009, 07:08:29 pm »

Yeah it's weird that the oil pressure light is involved... I've seen this once myself many moons ago and just assumed that the dynamic oil pressure system was being confused by the wonky tach signal. Didn't see it enough to confirm my theory.

Rabbit TD · « **Reply #7 on:** January 25, 2009, 08:13:47 pm »

Quote from: "Vincent Waldon"

The alternator charges the battery *and* drives the tach... so if it's having problems (and thus the battery light comes on) you can expect the tach to stop working as well.

To test the voltage output of the alternator:

1) with the engine off, connect a multimeter to the battery and turn the key to the ON position. The BAT light should come on and you should read somewhere around 12.5V, assuming your battery is charged.

2) now start the car and rev it once past 3000 RPM... the BAT light should go out and the battery voltage should jump at least a volt to 13.5 or more.

The fact that your BAT light and tach are intermittent suggests that there is in fact a problem with the charging system... most common issues being a loose alternator belt, worn brushes, or a bad voltage regulator. The brushes and voltage regulator are one assembly that can be removed and replaced with the alternator in the car.

Is the voltage regulator the problem most of the time when these alternators fail and they all seem to eventualy and probably from vibration would be my guess. I've bought a few alternators for these cars and have always wondered if it was just the regulator which don't really cost that much and are pretty easy to put in {just 2 screws} and you could carry a spare with you :roll:

Vincent Waldon · « **Reply #8 on:** January 25, 2009, 08:29:11 pm »

My personal experience as been that by the time the brushes/regulator go the commutator is worn to the point that a rebuilt alternator is required anyways.

Having said that, an extra regulator/brush assembly is one of the spare parts in my "long trip" toolbox... there's a first time for everything. :wink:

Rabbit TD · « **Reply #9 on:** January 25, 2009, 09:13:41 pm »

Quote from: "Vincent Waldon"

My personal experience as been that by the time the brushes/regulator go the commutator is worn to the point that a rebuilt alternator is required anyways.

Having said that, an extra regulator/brush assembly is one of the spare parts in my "long trip" toolbox... there's a first time for everything. :wink:

I'm thinking about carrying the whole damn alternator if I come up with one for a spare that's any good.

farkman · « **Reply #10 on:** January 27, 2009, 09:26:58 am »

Mopar44o

I had the same type of problem a few months ago. Take a look at the thread I started. I had the same problem of the oil light coming on.

Get your alternator tested to see if it's working. Replacing the voltage regulator didn't help me because something inside the stator got melted which caused it to not charge at all. Got a rebuilt alternator and everything's golden now.

Mopar44o · « **Reply #11 on:** January 27, 2009, 02:13:08 pm »

My alternator was tested and its pooched... So its getting replaced now