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Doug, ASE Certified Technician
Category: Car
Satisfied Customers: 8535
Experience:  16 years automotive and OTR repair including specialized training from Toyota and Mitsubishi
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2000 Mitsubishi Eclipse: 3.0L automatic..output alternator..guage

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I have a 2000 Mitsubishi Eclipse, 3.0L automatic, with a thorny charging problem. I decided to go ahead with an upgrade to the electrical system, so I put in a high-output alternator and high-capacity battery, and I added a new cable between battery/alt. and a voltmeter guage. The problem began with the stock equipment, and it persists after the upgrade.

Symptoms: With a charged battery, the car starts perfectly. The voltage reads around 14V. After one to a few minutes, as the car warms up, the voltage falls to the battery 12.6V. At this point, the alternator output is only around 16A. Voltage drops in the cabling look good. The drive belt doesn't appear to be slipping.

I originally suspected the voltage regulator, but that got replaced with the alternator and the problem is still around. Now I'm thinking it must be either the PCM, or the cabling/connections between it and the alternator. The alternator side looks good, but I haven't been able to get at the PCM yet. I suppose the second voltage regulator could be bad, but what are the odds? :-)

Am I on the right track? If the voltage is falling with the alternator at such a low output, it has to be the regulator, PCM, or cabling between, right? Is there anything else to look at?

You are correct in that the only remaining suspect would be the PCM.
Having checked for voltage drop on the cable, you are left at alternator or PCM, providing you don't have any rodent issues etc with your wiring.

However I would strongly recommend you try installing a Mitsubishi alternator prior to replacing the PCM. Aftermarket alternators for Mitsubishi are notorious for intermittent failures, sometimes even being non-functional right out of the box.
I end up changing a brand new aftermarket alternator out about twice a month on these vehicles. The depressing part is that in most cases the factory unit is less or similar money to the aftermarket units.

I would replace the unit with either a new or known working Mitsubishi unit prior to investing in the PCM. The price difference is substantial, and for what it is worth, I have only time I have seen the voltage drive circuit fail in a PCM was after a catastrophic alternator failure (20+V charging voltage, melted have the wiring)..
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