New alternator... 15V


Gold Member
Username: Iufan4lifeul

Post Number: 1125
Registered: May-05
I just had a shop put on a stock 85 amp mitsubishi alternator. After they put it on the car died twice while idleing. After I had driven it about 50 miles, the check engine light came on. The car has had a rough time idleing and sometimes dies while idleing. Also, when I first start up the car the voltage is about 12.5V for several minutes (when the alternator isn't on), when it comes on the average voltage is about 15-15.3. It used to stay at about 14.4 until the bass hit, which is when it would drop. What do you think causes these things?

Gold Member
Username: Iufan4lifeul

Post Number: 1126
Registered: May-05

Gold Member
Username: Basshead86

Google is your Friend, FL

Post Number: 4061
Registered: Aug-05
how long was the batt. disconnected?????

b.c while i was having my HO put on the computer reset itself....b/c of a lack of power for an extended period of time...and my car wouldn't ahrdly idle right either.

how soon after the car was started was it driven????

i startd my car up and immediately backed in out of the shop and drove down the car's comp couldn't set everything at a steady my car's comp setting's were all screwey.

take the neg. batt. wire off for like an hour to an hour and a half...the comp should reset itself.
then reconnect it and start the car up and let it idle for about 15 mins...

then drive it slowly for about 20. the comp should set everything up correctly.

ORRRRR... you have a bad alt. or they fu**Ed something up. :-)

Bronze Member
Username: Makmillion

United States

Post Number: 100
Registered: Apr-06
Do what Muddy said, only, after you reset the computer by disconnecting (-) drive it 20-30mph for mph for 15 minutes, then on the freeway at 55mph or so for 15 minutes.

I had this problem in a few different cars and this ALWAYS fix it.

Good luck.

PS: Unless it is the alt. which isn't likely because your electrical system will only take in so many volts at which point it's wasted power.

Gold Member
Username: Basshead86

Google is your Friend, FL

Post Number: 4066
Registered: Aug-05
better advice after the reset mick. :-)

Gold Member
Username: Iufan4lifeul

Post Number: 1127
Registered: May-05
It used to be that the car would run off the battery for about 5 minutes, then the alternator would kick on. Now, just tonight, I was driving all of the way home with my audio system blasting for about 1-2 minutes and the alternator never kicked on. It should have. Its going to the shop that did the work tomorrow.

(Before the new alternator, it would run a 14.4 at idle constantly, the alternator was constantly running)

Silver Member
Username: Troy81

Tavernier, Fl Us

Post Number: 793
Registered: Mar-06
uhhh, your alternator doesnt "kick on" its constantly running that is the only reason the car runs your car wouldnt run without an alternator, how tight is the belt? try tightening that, try reseting the comp. like they said above, if not then its prebably the alternator, or they did something wrong installing it
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