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Charging issue, charges fine when i give gas

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eclipsek17

15+ Year Contributor
130
5
Aug 1, 2004
All over, Arizona
One problem after another with this thing and it is always some weird problem that takes forever to figure out it seems like. So I just put in a new optima red top battery about 2 months ago, just swapped the alternator today, fuses appear to be ok, but for some reason the car is only charging when I give it gas. Right now the battery is sitting at 12.4 volts, start the car and at idle it is 12.1 - 12.2 volts, then if i hold rpm anywhere above 1100 then it reads 14.5 volts.

Any idea of why this would happen? Also this is the 4th alternator in about an 8 month period. Voltage is the same at battery, at fuses, and at alternator. Oh and I just put a new belt on it as well.
 
Belt is really tight, still doing it. Was doing it with the last alternator I had in too. I am able to drive it around, but if I am in traffic too long or at idle too long its starts pulling from the battery and wanting to die unless I give it gas. If battery was relocated to the rear should I increase the size of wires coming off the alternator? I have like 0g or one size up from that for the battery wiring to the distribution block I installed in the front of the car. I guess that doesnt make sense though, because I am seeing the same power at the alternator.
 
Remember that on a 2G the ECU can control when the alternator actually generates current.

I'd look up which wire from the ECU is used and monitor to see if the ECU is telling the alternator to stay off at the time.
 
I think I swapped to the 90 amp alternator a while back when I relocated the battery.

I was trying to find a wiring diagram for the alternator, but they are all just the basic parts of the system, fuse, relay, battery, etc. Doesnt the ECU also have the voltage regulator in it as well? I have a black case ECU from a 98 gst in right now, just swapped ECU like 2 or 3 weeks ago because my old ECU was fried and was causing misfire.
 
The voltage regulator in Mitsubishi powered DSM's is internal to the alternator on both generations. On a 2g the ECU can turn the alternator on or off via the G terminal on the alternator. If the G terminal is grounded the alternator is turned off and the output voltage is limited to 12.3v

Since you've swapped various parts it's hard to say what might be going on. You can measure the G terminal and if it reads higher than 0v it's likely not the issue.
 
Is that supposed to be like a 5 volt reference circuit just to turn the alternator on or off then? Or is it a 12v circuit? If it is a 12v circuit, would it hurt to make a regulated bypass for it?
 
The Alternator provides the bias voltage for the G terminal. The ECU pulls it to ground. You could try disconnecting it. The FSM doesn't say what the nominal voltage is on the terminal when the ECU isn't exerting control.

I'm expecting you just have a bad alternator but trying to make sure nothing is overlooked.
 
I thought alternator also, but I just had it warrantied because I thought it was that, but I still having the same issue with the one I just put in. Wouldnt be the first time I have gotten bad alternators brand new, but I am just thinking how unlikely it is also.
 
Something is drawing from your battery then. Could be you need to get a test light and do a "draw" test. Find out which circuit it is perhaps. Make sure your cable ends are tight and you have the correct gauge wire going to both the starting and charging systems. Go back and add a few more grounds, make sure the alt pulley is on tight; verify that you cannot spin the pulley by hand. Make sure your battery is fully charged before you install any further alternators. Try to borrow or temporarily buy another battery just to rule that out if you come up all good on all the other checks.
 
What color wire is the G terminal?

Already did load test, no issues with battery and alternator works perfectly after rpm is past idle a litttle. Have a new optima red top battery with 1000 cca and it is ran with gauge wire I have on it is bigger than what most people have used when relocating battery to rear. If you cannot spin pulley by hand, then that would mean the pulley is locked up.
 
I have been and still am driving the car everyday with no issues, but the voltage on the system always drops to battery voltage when the car is idling. A couple of times, after sitting in traffic too long, I noticed the car losing power from running off just the battery too long, but have just gave it gas and brought rpm up to charge it. Normal idle is at 800 rpm as well right now, this is when i am having the issue.
 
What I remember from Auto tech school years ago is that the the Alt does not charge at idle speeds. The magnetic field generated in the field coils would load the engine to a point it would stall, so the battery provides the power to keep the car running at idle.

Now your batt may be to small to power the car for extended idle periods. What is the CCA rating of the batt?

Also check the resistance of the batt cable from the alt out put, and from the batt to the fuse box.

Also if you have a sound system with some big amps, that will draw the batt down faster at idle.

How long can you idle before the car starts to stumble?
 
Bogus, I think you are remembering the old school GENERATORS that don't charge at idle. Mine always charges when it is running, idle or hi rpm. Excuse me if I am wrong as I have been before, but I think that is correct. Back in my day at the shop I learned a lot from, (1978-79ish) the cars with generators would only charge if revved up, the alternator cars used to charge at all times, that's where the wonderous idea :cry: of pulling off a battery cable and see if the car still ran deal came from. Please correct me if I am mistaken.
 
Does the voltage go up if you turn on your accessories ( a/c, headlights etc.)? I'd also do a voltage drop across the cable and check the output at the alternator with a meter. I've ran through 3 aftermarket alternators in a row at work before. Napa ones seem to be the worst.
 
Neither my Rangers, nor my Tbirds charge at idle. all 1985-1996

Generators were back in the 50's and older.

Pulling the pos batt cable was to check if the alt put out, but the car had to be brought up in the RPM to do so. But if you do that on an EFI car you can send a voltage spike to the ECU and fry it.

I went to school in 1993-1995, and that is what I was taught.

I say grab your DVOM and check another car, one about the same age as yours and see if the alt is putting out at idle or not.
 
I just printed this off the all data site. You should be able to zoom in to see it better. This is the way Mitsu wants the alternator tested if you wanna try it there way to rule the alternator out.
 

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Neither my Rangers, nor my Tbirds charge at idle. all 1985-1996

Generators were back in the 50's and older.

Pulling the pos batt cable was to check if the alt put out, but the car had to be brought up in the RPM to do so. But if you do that on an EFI car you can send a voltage spike to the ECU and fry it.

I went to school in 1993-1995, and that is what I was taught.

I say grab your DVOM and check another car, one about the same age as yours and see if the alt is putting out at idle or not.

I'm an old GM guy and my Camaros all charge at idle, but good to put this out their. In GM models they had generators into the 60's and when they switched to alternators they still had an external regulator which may not charge at a slow rpm but all of my 3rd gen's charge as soon as started and we run aftermarket gauges so I can see it as soon as they fire up. Good to know info on both. Thanks!
 
Bogus, the car used to charge at idle. The voltage when a car is running should be between 13.5 and 14.5 volts. There is no way this battery is too small for the car, I have a 1000cca optima red top battery.

Fastfred, I will try the print out from all data you provided and see what I get. All data I am using didn't have a checklist type thing like that, which version of all data are you using? Also, I've been driving the car around for a few weeks now and only time I see issue is at idle in traffic. I am about to drive home soon though, which is about 20 miles, I'll hook up my power probe on the way how and see if I see anything with voltage when headlights are on. I don't have ac,, no radio or speakers at all, car is close to gutted. Have removed boxes of stuff from this car.

Can someone tell me which color wires are which letter terminal on the alternator.
 
Alldatapro. I can get the wire colors you need tomorrow when I get to the shop. I actually pulled that flow chart from the starting/charging section under symptom diag. Skip down to the big box on the left and start with that one. You can check the resistance on the +/- cables too, but I like voltage drop testing better.
Just as a reference, I came home and started my car tonight just let it idle since its up for winter and I had 13.1v with an oddyssey battery mounted in the trunk. 65 amp alternator.
 
The color of wires would help a lot if you can get them for me.

As I was driving home I checked the voltage regularly and when I was going through town it was between 13.9 and 13.7, highway was 14.0 and 14.2, and idle at stops was 12.7 and 12.9. When I got home I turned headlights off and voltage went from 12.9 to 13.6, that was first time I noticed that. Then I let car idle for a while with lights on and voltage began to drop from 12.9 to 12.6 then I held room at 3000 rpm for about 20-30 seconds until voltage read 13.5 again.

I think I got another bad alternator from orielies, but I would like to check wiring first, because I did do a wire tuck, relocation of fuse box, and just put in a new (used) ecu. I just want to make sure nothing with the wiring, ecu, or relocation of anything is interfering with the charging system.
 
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