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Old 04-25-2006, 03:08 AM   #1
azjoe_02
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Alternator Issue?

OK guys, I have a 98 Mitsubishi Montero Sport. (~135k, 3.0L, 6cyl, 2wd) I replaced the battery a couple days ago because it would not start. I read the voltage and only was getting ~10.0 volts. So then it would start but would bearly hold an idle. (sputtering, then would eventually stall) My daughter informed me she drove it to "extreme E" on the gas gauge. So I thought she clogged the fuel filter. So I replaced that. But it still stalls out at idle (oh well the fuel filter needed replaced anyway). When I start it, the RPM's go up to 2000 or so then drop to the regular 800, then it sputters below 500, then stalls out. I can drive fine as long as I can keep moving. At a light I need to keep my foot on the gas a little (RPM's @ 1k). Other times I can stop at a light and have no sign of stalling at all. So anyway...The lights that come on at the stall (or almost stall) are the oil, battery, A/T and brake. Since this started happening at the same time the battery died I checked the battery again and was surprised to see it only at 11.9 volts at 2k RPM's. I thought this was a little low esp for a brand new battery. So I think the alternator is bad. I read the voltage at the alternator (red wire to the alt body) and it is reading 11.9v also at 2k RPM's. Is this a low or weak alternator? And could this somehow be causing the stalling? HELP!!!
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Old 04-25-2006, 07:04 AM   #2
thongsai
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yes that is low.. it should be around 13.5-14.5
u will need to properly diagnose the charging system b4 you should condemn the alternator
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Old 04-25-2006, 01:58 PM   #3
azjoe_02
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Quote:
Originally Posted by thongsai
u will need to properly diagnose the charging system b4 you should condemn the alternator

Can you tell me how to do that???
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Old 04-25-2006, 02:17 PM   #4
glagon1979
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Quote:
Originally Posted by azjoe_02
Can you tell me how to do that???

get a volt meter, put the negative wire on the negative post and same with the positive. keep an eye on what the meter is reading. if it slowly decreases, it is the alternator. be sure to check all connections to the alt and the battery to make sure they are tight.
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Old 04-25-2006, 08:13 PM   #5
thongsai
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well u gotta check those wires going into the alt. on the cars that i worked on, they all had 12v goining into to thru various circuits.. yours may vary. get a wiring diagram!!
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Old 04-26-2006, 09:20 PM   #6
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Quote:
Originally Posted by tbaxleyjr
most of those circuits are 12V.

You are right on the money on check and verify before buying parts. - an initial check of the electrical system is see if the battery approx 12.5V. If not, it needs to be charged before doing much else. with engine on should read 13.5 - 15V both w/o major loads and with lights and AC on. Much deviation (1/2 V) would indicate a possible bad voltage regulator.

OK it died after work last night. As I was waiting to turn a corner. I got nothing at all, just clicks when I tried to turn it over. Once it was pushed into a parking lot, I read the battery and it was like ~11.1 or so. I got a jump to start it and read the voltage from the alternator and it was now 11.4v - down from the 11.9v it was before. So I removed it and had AutoZone bench test it twice, both times it was no good. Bought a new one and installed today, along with a freshly charged battery. I also changed both terminals at the battery (they were pretty corroded). One I trimmed back because the corrosion had started down the stranded copper line. Started it up and I drove it home. As I pull into my driveway...It stalled!

I recheck the alternator (at 2k RPM's A/C on) and it is reading 14.5v. Beautiful right? At the battery I get (same 2k RPM's A/C on) the same 14.5v.

I am now noticing that the battery, brake and the A/T lights are much dimmer than the oil, check engine and other lights when the key is in the "on" position. I have checked the fuses and all are good. I even pulled the 100A fuse that is screwed into place. Do I need to reset the computer?

So, a recap:
1. Replaced dead battery
2. Repalced fuel filter
3. Replaced low output alternator
4. Replaced both battery terminals
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Old 04-27-2006, 12:25 AM   #7
Wally
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You might like to grab that multimeter and test the chassis straps and terminals for above zero resistance connections.
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Old 04-27-2006, 01:50 AM   #8
azjoe_02
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Quote:
Originally Posted by Wally
You might like to grab that multimeter and test the chassis straps and terminals for above zero resistance connections.


Can you shed some light as to were those might be? I have had a lot of trouble finding a manual for this yr/make/model. I tried Haynes and they said they don't have one and neither does chilton. So I am figuring these out as I go. Thanks for the help.
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Old 04-28-2006, 03:59 AM   #9
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OK, I think I fixed it. The idle adaptive memory was erased when my battery died. So I had to clean the throttle valve. Thanks to everyone who helped.
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