battery or alternator issue?!

[brittany behrends]

i bought a 98 GST spyder a couple weeks ago. Only has 74k miles on it. the previous owners did not drive it a lot over the last few years and it sat in their garage and all they did was start it up every month to let it run. i have driven the car everyday except for christmas day and then when i went to start it up friday, it wouldnt turn over just click. Replaced the battery Saturday morning and ran perfectly fine up until this afternoon. Ran errands just fine (got gas then groceries) but on my way home the radio would shut off for a brief second then come back in did this numerous times on my way home. also i was doing about 40mph and the rpms shot up and down between 1000 and 3000 a few times and jolted while the battery and break light came on for a bit then went off. So i let off the gas and slowed down a bit, that stopped and was the only time that happened on the way home. any ideas what could be wrong?

 

[Dsmkauai]

Check for loose or corroded wires from the battery to starter, and also the grounds. Also check the output voltage of your alternator.

 

[brittany behrends]

have not done anything concerning the alternator yet but the wires and connections were all spotless and really clean

 

[Dsmkauai]

That's good atleast. Sounds like Maybe the alt isn't putting out the proper volatage and it's causing the system to be underpowered.

 

[brittany behrends]

thats what i was thinking it might be. it starts up just fine though even in 20 degree weather

 

[jimsgsx]

Check your battery terminals and all wires running from them as well. Have the alternator tested at a autoparts store and go from there.

 

[97spyderman20]

I would lean to alternator as well. It could be over or undercharging. May need to be bench tested to get best results.

 

[simplejoe]

If your battery is new and your connection is good, then I'd run it over to advanced or somewhere to check your alternator.

 

[tindall2006]

Take a multimeter, put it on volts DC and put it on your batt. Should be anywhere between 12-13V. Start car, you should see the volts drop as the starter turns, then come back up. If the Alternator is charging you will see your votage climb and should be somewhere above 14-14.5 Try reving your car up to 2-3k and see if voltages increases. If it does odds are your alternator is fine and you have a bad ground or connection somewhere.

 

[keltalon]

Start the car and let it run get out of the car and disconnect the positive side battery terminal while the car is running and see if it continue to run if the engine stop then definitely the alternator is not charging if it continue to runs then you still need to take it and have the battery and alternator checked. I recently had a similar issue and found that the wiring harness that plugs into the alternator had a broken wire..

 

[92AWDHX40]

I have a similar issue low voltage on link battery is good so is altenator gonna check wiring next, ugg.

 

[keltalon]

I have a similar issue low voltage on link battery is good so is altenator gonna check wiring next, ugg.

Vick what fuel pump are you running?

 

[92AWDHX40]

the fp 255 hp its been working fine, got it on sale same specs as the walbro had a 255 but it was in my previous fwd dsm, for now next is the wally 450 so I can run e 85 gonna pull her in garage today to do some work on her.

 

[luv2rallye]

Start the car and let it run get out of the car and disconnect the positive side battery terminal while the car is running and see if it continue to run if the engine stop then definitely the alternator is not charging.

This is a bad idea because the alternator can load dump and spike the whole electrical system with >100v and even if it doesn't, the battery filters the alternator output and the AC ripple on the output will again flow through the whole electrical system. Both of these can damage the ECU and other electronics in the car.

 

[14b_gstky]

As mentioned check all connections. if that don't fix it get your alternator tested

 

[keltalon]

This is a bad idea because the alternator can load dump and spike the whole electrical system with >100v and even if it doesn't, the battery filters the alternator output and the AC ripple on the output will again flow through the whole electrical system. Both of these can damage the ECU and other electronics in the car.

If you don't mind posting evidence of this or some reference to this happening I like to read it, this is the first time I have ever heard of this. definitely don't want to be damaging the beast for sure.

 

[1990TSIAWDTALON]

It sounds like the field of the alternator is not getting "energized" which makes it start charging. From looking at the FSM Electrical book there diodes after the ignition switch but before the "L" terminal on the alternator. If they are bad then it won't energize so it won't charge. If you check the "S" terminal with a volt meter you should see battery voltage, if not then the fusible link is blown or it has a open circuit to the battery. This is right from page 8-126 "Regulated Voltage Test". I would check for battery voltage on "L" when the ignition switch is on and zero with the switch off. Then look for battery voltage on "S" at anytime according to the schematic. Just tryin to help since I have the complete set of FSM's. This is from a '90 Model FSM. Good luck and post back. Hi Vic, maybe this is what we have been talking about on the phone. I will try to post the diagram for all.

 

[jim95redgsx]

If you don't mind posting evidence of this or some reference to this happening I like to read it, this is the first time I have ever heard of this. definitely don't want to be damaging the beast for
sure.

http://en.wikipedia.org/wiki/Load_dump

 

[keltalon]

http://en.wikipedia.org/wiki/Load_dump

Thanks good read!

 

[1990TSIAWDTALON]

If this were a GM car I would run a wire from the battery to "S" and another one with a 12v lamp in line to "L" and see if it started charging but that is up to you for a test. The lamp acts like a resistor to energize the field and should be lit when the car isn't running and go out when it is running since it would see 12v on both sides of the lamp.

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[1990TSIAWDTALON]

I assume you have checked all of the fuses under the hood for an open circuit, I'm pretty sure there is a ALT fuse.