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#1
RacerDad

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Today I replaced the starter on our 99 SM to correct slow starting speed and a overcharging condition (16.2v).  I replaced the starter with a new reman Denso unit.  Once it was installed, the cranking speed was much higher.  However, once the car was running, the battery voltage started at 17.2v and just continued to climb until I shut the car off at 19.0v.  I reinstalled the the old starter and the battery voltage was steady at 15.8v.

 

Things I have checked or replaced over the past year.

 

1. New reman Mazda alternator (mid-season) to replace failed NAPA one

2. New cutoff switch (last year)

3. Tested system with alternate PCM

4. Tested system with alternate instrument cluster (charge light functions normally)

5. Checked continuity between alternator signal wires (Grey and Grey/Red) and PCM

6. Voltage drop checks between battery, cut off switch, alternator, starter, fuse box, and PCM. All less than 0.5v with car running

7. Ground locations for torque and general condition

8. Alternator belt tension

9. Battery (last year)

10, Battery terminals

11. Connectors at the starter, alternator, fuse block, and cut off switch

 

What am I missing?  How can a starter cause the alternator just overcharge that quickly?  Any thoughts on how to correct this?

 

BR



#2
Ryan Roberson

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Check the main relay and main fuse.  Both can be working, but the resistance could be driving the ECU to drive the alternator to increase output.

 

replace to check.



#3
Steve Scheifler

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You lost me at replacing the starter to (in part) solve an overcharging issue. So to your question of how a starter can do that, my first reaction is “it cant”. It sounds more like a defective reman alternator.
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#4
RacerDad

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You lost me at replacing the starter to (in part) solve an overcharging issue. So to your question of how a starter can do that, my first reaction is “it cant”. It sounds more like a defective reman alternator.

Sorry about that.  Replacing the starter was to correct a slow cranking condition as it would do this even with a fresh battery and low voltage drops on the power and ground circuits for the starter..  Also, the car's voltage typically runs high (15.8-16.2) but stays steady.  This higher voltage has been the same no matter which alternator, PCM, or instrument cluster I use.  However, when I installed a new starter yesterday, the voltage started at 17.2v and climbed quickly at idle until I shut the car off.  Reinstalling the old starter brought the voltage down to 15.8v and remained steady.



#5
RacerDad

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Check the main relay and main fuse.  Both can be working, but the resistance could be driving the ECU to drive the alternator to increase output.

 

replace to check.

 

Thanks.  Just finished checking these.

 

80A Main Fusible Link: 0.5 ohms

EGI Main Relay: Coil Side - 639 ohms, Load Side -   0.2 ohms

Voltage Drop (with car running) from starter to fusible link: 0.02v (Battery: 16.1v)

From alternator to fusible link: 0.05v

Across link: 0.01v



#6
Jeff Wasilko

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What does your battery voltage read with the car off? Wondering if you've got a bad Voltmeter....



#7
RacerDad

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What does your battery voltage read with the car off? Wondering if you've got a bad Voltmeter....

 

12.3v after the car sits for about an hour.






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