2G Bad Alternator?

[TatarSauce]

Hey there! I own a 1998 Eclipse GST and while driving the other day I noticed a loss of power over time, so I immediately think bad alternator. I was making sure the wires were all good before ordering one and noticed a dangling black and yellow wire in between the alternator and oil filter. Could this be the problem? I can't seem to find a wiring diagram anywhere but I'm assuming it plugs into something. Here's a pic of the wire.

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[luv2rallye]

Oil pressure idiot light pressure switch.
- https://www.dsmtuners.com/threads/o...ge-loose-hanging.264198/page-3#post-151588699
- https://www.dsmtuners.com/attachments/altoilsensorsharness-jpg.68187/

 

[AWD-Tony]

Alternator has a fat connector and a power cable. I see coolant on your oil cooler. It's very common for power steering pump leaking onto the alternator.

 

[TatarSauce]

Ok that's what I thought. I put a new alternator in it but it's still not charging. Could the idiot light be causing this? Otherwise I'm guessing it's a wiring issue or another bad alternator. The fuses look all good. I have put a new cig lighter and radio in and blew several fuses with the cig lighter wiring. My dimmer switch still doesn't work either but the gauge lights are working. I feel as if I just fried a wire somewhere that's causing all of these electrical issues.

 

[luv2rallye]

The dash alt charge light must be working for the alt's field coil to have power (or the alt won't work). Does the dash alt charge light come on when the key is just turned to Start?

 

[TatarSauce]

It does but it's faint. It's not as bright as the other lights thar come on. I put after market led lights in it and that was one of many that didn't come on so I put the old ones back in and it now works but isn't very bright.

 

[luv2rallye]

You must NOT use an LED light for the dash alt charge light!!! It MUST be incandescent. Same for the dash turn signal indicator (in fact that may be your whole front turn signal problem - the LED is probably clamping the front turn signal bulbs to the LED's voltage making them not work).

 

[waltah]

I don't think having a bulb in the socket is required for the alternator to get field current -- there's a resistor across the bulb isn't there? That's what that's for.

That resistor may be in a package labeled 'generator field relay' on the diagram. But it's now just a resistor.

The ight doesn't have to be bright at all.

Interesting that LEDs don't work for the turn signals. That's gotta be a polarity problem and might depend on the brand.

Put a voltmeter on your battery. After starting with no other loads should get up around 14.4V for a while. Eventually back down to around 13.5. After running a while (without other loads) and you turn off the car voltage should be around 12.2. These numbers assume a healthy battery. An alternator that will do this is unlikely to be a problem.

 

[luv2rallye]

Yes the generator relay is there as a backup to provide field current if the charge light is burned out or not there.

Also note that often the generator relay is destroyed on these cars which then means the charge light must be there and working. Internally the generator relay is a resistor in series with a diode. However the generator relay is in parallel with the charge light and a different diode.

So if the charge light is an LED instead of an incandescent bulb, that MAY cause problems due to having just the LED charge light (diode) in series with another diode, all in parallel (or across) the generator relay. Voltage clamping may result instead of letting the voltage float across the incandescent light bulb as it should.

Of course if the LED has an internal resistor of its own, it may work. Or it may not due to now having 2 diodes in series instead of 1. I can't say for sure as I've never tried it.

 

[TatarSauce]

Ok this is what I've done. I put a new alternator on to no avail. After I did every test possible. The grounds are all good across the car, and the positive terminal on the alternator itself is reading battery voltage so there is no wiring issue as far as that goes.

I assume the fat connector is working since the battery light now comes on after I swapped the bulbs and that fat connector is just to the voltage regulator anyways.

After all of this, I ordered another alternator and put on as I figured just two bad alternators. Still nothing.

I can drive the car around but if I use turn signals and brakes too much it will eventually die and I can't take it out at night since the headlights draw to much power.

I'm lost for answers here.

I will again mention I jerry rigged a new cig lighter in and the wiring in there I don't think is correct as my gauge lights come on but my dimmer switch doesn't work at all. I'm wondering if that may be causing a problem but even when I unplug all of those wires the voltage stays the same.

I really don't know anything else I can do. I was thinking of taking it to a mechanic but I figure they'll just do everything I did and then just swap the alternator and say it was just bad. I have a gut feeling it's not the alternator at all and is just a problem with the wiring somewhere but I'm not 100% it's that either.

I also checked the fuses and I'm getting battery voltage through them too so I really don't know what else to do.

I also rule out bad battery as I get 13.1v fully charged but when I start the car it goes down to 12.5v or so and slowly declines.

 

[waltah]

While a competent mechanic should be able to track this problem down to the real issue (not just "You need another alternator" which will not fix the problem), at least the first steps are simple. You can do this faster, cheaper, and right.

Before heading into diagnostics I would check all the fuses and links in the block in the engine compartment. It's five minutes work and when you've had short-circuit problems a blown fuse or fusable link (big fuse) is a frequent result. Some of them could have non-obvious effects. If all are okay then ...

1. By replacing the alternator twice you have almost eliminated the alternator as a source of your problem. It is likely a charging system problem but not the alternator.

I also rule out bad battery as I get 13.1 v fully charged but when I start the car it goes down to 12.5 or so and slowly declines.

2. These numbers do not sound good. If you are saying battery voltage is 12.5 with engine running after starting that is plain wrong -- the alternator should be charging at a pretty high rate then and voltage should be around 14 depending on battery condition.

3. Your next step is to pin this down as either a charging circuit problem or a regulation problem.

I just checked on my '95 GS-T. Battery is fully charged and near new so I turned on the headlights for a minute to discharge it a little. Right after starting the battery voltage was 13.8. With an older battery it will be higher -- up to 14.4V or so. If you're saying yours is 12.5 at that time, that's too low -- that's 'not charging at all' or very close.

Next check: Hook the positive side of your voltmeter to the big screw terminal on the alternator and the negative side to the battery '+' terminal. Start the car. In the test above my car shows 0.34 volts there -- the drop caused by charging current flowing from the alternator to the battery.
BE CAREFUL -- your hand will be near fans, belts, and hot manifold and you'll be leaning over a running engine.

"There are old mechanics and there are bold mechanics ..."

Then check with the positive side of the multimeter to the battery '-' terminal and the negative meter probe on the alternator frame. That voltage is well under 0.1 volt on my car.

If either of these voltages on your car is much higher than the numbers above then with the battery terminal voltage low (12.5 and goes down you said) then you have a charging circuit problem and it is in the circuit (wire) with the high number.

If both of these voltages are lower than mine then you have a regulation problem: Your alternator and wiring are likely okay but the alternator isn't trying to charge your battery.

Report results and we'll go from there.

 

[pauleyman]

Ok that's what I thought. I put a new alternator in it but it's still not charging. Could the idiot light be causing this? Otherwise I'm guessing it's a wiring issue or another bad alternator. The fuses look all good.

Meaning you actually tested the fuses for continuity? Or you just looked at them?
Particularly the 100 amp ALT fuse under the hood?
If you didn't look at the ALT fuse you need to and you need to actually remove it (it's bolted in) and test it with a meter.

I have put a new cig lighter and radio in and blew several fuses with the cig lighter wiring. My dimmer switch still doesn't work either but the gauge lights are working. I feel as if I just fried a wire somewhere that's causing all of these electrical issues.

 

[TatarSauce]

Yes I tested them with my multimeter and they were reading battery voltage on both sides and the grounds that are connected to them are also getting a good reading.

 

[waltah]

Meaning you actually tested the fuses for continuity? Or you just looked at them?
Particularly the 100 amp ALT fuse under the hood?
If you didn't look at the ALT fuse you need to and you need to actually remove it (it's bolted in) and test it with a meter.

The reason I didn't suggest taking the link (ALT fuse) out to check it is that it'll get checked along with wiring and connection resistance when the voltage drop is tested. If there's much over 0.35 volt then that link should be freed and specifically tested.

The usual inexpensive ohmmeter cannot meaningfully test continuity of the charging path because the resistance is (ballpark) 0.01 ohm. If a bad connection raises that to 0.1 ohm you'll get almost no charge but both those numbers will test as '0' on the ohmmeter.

 

[TatarSauce]

waltah this was helpful. I have tested the post on the old alt and it just read battery voltage but I will try on this one.

Also I did test the big plug that goes into the regulator and with the car not running two of the plugs read battery voltage, and then one of them read 1.8v or so and the other was just 0v so I would guess that's ground, but the other one I thought was a bit weird.

When I turn the car on all of them read 0 so it seems like the computer has recognized an error but won't reset itself to let the alt charge.

 

[steve]

Knowing the wire colors of which ones are measuring which would help.

On a 2G alternator there are 4 wire on the big regulator plug. Two run to the ECU to control charging and tell the ECU there is a load on the engine from the alternator and the other two are the normal sense and field wires. This diagram doesn't show the 2G "alternator relay" that is in parallel with the charging warning light. Those two provide current during initial startup of the alternator for the field coils (to make magnetic field in the coils) before the alternator can self-power the field. The Sense line is so the regulator can read the voltage back at the battery.

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[TatarSauce]

The white and red wires are showing battery voltage and the other two don't show much but the green shows 1v when car is off. When car is on all of them show no voltage. Could this be an ECU issue?

 

[waltah]

The white and red wires are showing battery voltage and the other two don't show much but the green shows 1v when car is off. When car is on all of them show no voltage. Could this be an ECU issue?

Well you've got another level of symptoms there. Just to start with the red wire has to be at battery voltage -- it tells the regulator the actual voltage at the battery so the charging rate can be set properly. I would check that #5 fusible link first; if that's not it then something else between the battery and the plug is open.

 

[T bags]

X2 on a fuse or stuck relay. Try pinging with a dvm to see if theirs a breakage in the wire

 

[TatarSauce]

Where are the fusible links located. I'm only asking so I can try and limit the amount of electrical tape and wire sleeves I have to pull off.

I've tested the fuses with a volt meter and they read battery voltage so there's not a break there. I didn't think it was the fuses because they don't look burnt or broken anyways but I tested them to be sure.

Thanks everybody by the way for the help. This problem has really been driving me nuts lately, but I think I'm getting close to the problem. I have a feeling it's just a broken wire or link somewhere.

 

[Mello]

Under the hood in the engine compartment with the normal blade fuses. They're the bigger, square things that look like a fuse but the ratings are large like 100, 80, etc.

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