Exarth

I have a 02 trans am, just replaced the alternator and battery is only about 4 months old and tested good. Well the car dies when the positive battery cable is disconnected. I changed the alternator 2 days ago because the car died and had to jump battery and such. What could the problem be? Or should the car die when it's disconnected from the positive side?

The Outlaw Kid

iTrader: (1)

I've seen somebody twist the post on the back of the alternator while tightening the nut down and it ruins the alternator. Is it possible that you did that?

They should stay running when you remove the battery. I've actually undone a good battery while the cars running and swapped in a drained battery to charge it back up.

luigiandme

iTrader: (2)

What's the voltage on the dash read while running?

Double check your wiring. Wiggle test and check that post on the back of the alternator mentioned above.

Fiveliterbtr

Unless you want to replace the PCM or other electronics, I don't recommend disconnecting the battery while running on a computer-controlled vehicle...the battery acts as an insulator. The PCM *may* be shutting the car down to protect itself from the voltage spike that you're creating by removing the insulator. On old cars, yes, if the car died when you disconnected the battery, the alt was bad...but that theory can't be used anymore with a PCM that has over-voltage protection, which most do.

Exarth

Wires seem fine but I'll check again today and it runs at about 15 volts

The Outlaw Kid

iTrader: (1)

Makes sense, but I've done it so many times I'm afraid I might have to learn that lesson the hard way. I tend to do that often.

On another note I dropped a wrench and it got stuck between the posts, quite the spark show. Melted the wrench and the positive terminal on the battery and everything was fine. Everyone says I got lucky on that though.

To me 15 volts seems high, but it might be fine. Report back after you've checked the wires.

chrysler kid

iTrader: (14)

Mine died when I forgot to connect it tightly. Just don't disconnect the battery

Fiveliterbtr

Speak of the devil, on the rarity that this happens, had an 01/02 Caravan today that came in that cust. replaced the alt on himself...and had some issues afterwards. No locks, no radio, no heat, engine light random stuff...fixed the heat, locks, and radio with various blown fuses...engine light was a P0601 - internal PCM memory checksum error...fried the computer...and with this post still fresh in my mind, we got it out of him that he checked the alt the old fashioned way I don't know what PCM's have over-voltage protection and which don't tho.

15 volts is pretty high...esp. if the OP is using the dash gauge, as most of our volt gauges typically read low. A DVOM btwn ground and the pos. directly on the alternator would be the most accurate reading.

LS6427

iTrader: (2)

Does the battery stay charged if you just use the car normally......?

I'm wondering if the exciter wire is broke or messed up.......

.

The Outlaw Kid

iTrader: (1)

Man that's gotta suck. Do PCMs always throw codes when they die? I know they "get confused and just give up" (best way I know to describe it). I'm sure there are over-voltage protections in some PCMs but I wouldn't know where to begin to figure out which ones do and which ones don't.

I agree, my dash gauge typically reads 10 volts. But when you put when you put a DMM on like you said it reads around 13 - 14 volts.

dailydriver

Yes, IS there any code thrown (or ANY type of dash light) when a PCM is fried, or is that just not possible since all codes originate from the PCM??

LS6427

iTrader: (2)

NO......when my PCM fried I got no SES list or codes......but it was shutting things off and on randomly like my MAF, TPS and IAC. It wigged everything out and NO codes or lights.

Pop the two tops off, Look at the pin rows, look for any burnt pins. Tell tale sign its burning up on the inside.

.

dailydriver

I had the two connectors off, and ALL of the pins looked fine.
I even straightened out the red gaskets before putting everything back together with the correct torque setting.

Has ANYONE found those gaskets sold all by themselves, WITHOUT having to buy a whole new PCM????

Fiveliterbtr

Depends on the severity of the failure...the Caravan I referenced had ZERO apparent problems (after fixing the blown fuse stuff), but had the P0601 code that kept the engine light on, even after reflashing...so it was a hard internal fault of some sort. Being in the aftermarket, I work on way too many different makes to know the deep down workings of their PCMs, unfortunately. Would be a lot easier to explain being at a dealer, with years of make-specific training.