I'm been having some trouble starting the car lately... with the lights on, ill try to start, and it might but soon dies. sometimes it wont even turn over. i can hear the starter and the fuel pump priming. i can turn off the lights and itll turn over ... ill then rev it to 4-5 k, and it will stay running... the lights will dim when i start moving most of the time. how can i check if its the alternator or the battery that is bad?

 

start your car, take off the battery negative terminal...

if car stays on, batt is the problem
if car turns off, alternator is the problem

 

with fuel injected cars you are not supposed to disconnect the battery, it isn't good for the ecu i hear. get a multimeter and see how many volts your car is putting out when it is off, then when it is on. your car should put out around 14 volts when running.

 

DO NOT DISCONNECT THE BATTERY CABLE WHILE THE CAR IS RUNNING! You will fry the computer. This may have been an ok method for old school cars, but not computer controlled cars. Just take it to Autozone or Advance Auto, they have free starter, battery, and alternator testing.

 

ive got a voltmeter -- it should be reading 14v when running. what if it isnt? i still need to find out if it is the battery or the alternator. thanks

 

+ a million to not disconnecting the battery while running!

well, how old is your battery? the battery should read 12.65 volts while the car is off.

check the voltage thru the battery terminals while the car is running and see what it is. then, turn the car off and check in the same spot and see what it is. let us know what it says.

 

IT SHOULD BE STATED VOLTAGE IS NOT HIS ONLY CONCERN! voltage should initially be no less than 12.4 before startup and around 14.76 afterwards. this is due to the battery ONLY providing the charge to start the car and the alternator maintaining it. an alternator MUST be tested for not only voltage but also for amperage output AND diode pattern. take it in to an autoparts store as stated before, and have them test it. if the alternator is to be replaced, make sure that the battery is also then at a full charge when the new alternator is put in. and again, DO NOT do the ghetto *** "pull your battery cable" test.....misinformation will only cause worse problems than this kid's already having, anyone who said pull the cable gets a big

 

luckily i knew not to pull the negative while the car is running. thats a big no... now ive checked the battery while the car is sitting (not running) and while it is running. the readings are all correct. now what? i tanked up on gas today, and tried to start the car but it wouldn't do it. so i put it in neutral and pushed it out of the way ... got back in and it started right away it seems temperamental: sometimes it starts fine, sometimes it doesn't. sometimes it will start and idle correctly for about 2 seconds on its way out and it will die. the engine is strong... and i just swapped a new tranny in last weekend. frustrated, but i will test the battery in autozone -- and maybe the alternator, but thats a longer job. a friend of mine is having similar problems on his (nissan) sr20ve swapped NX and he thinks its the IAC (idle air control). could this be what it is? thanks for all the help... the car runs fine, but i don't feel safe having to rely on luck to start the car

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RS’R’ &raquo;</TD></TR><TR><TD CLASS="quote">i will test the battery in autozone -- and maybe the alternator, but thats a longer job. </TD></TR></TABLE>

i hope you are referring to replacing the alternator as being a longer job, as it only takes an extra minute to test your alternator after testing the battery. autozone has both a bench tester inside the store and a mobile teter for use outside, and each can test your battery and charging system. this all will be done for free. are you sure you are not having a fuel issue? just because you hear the pump priming does not mean that you are getting the necessary amount of psi at startup.....

 

good info. what i said was only to give you an idea of where to start, thats how i would start out w/customers cars sometimes if my machine was tied up. to find out for sure you would want to do what GRAF-FITI mentioned. if it is the alt, just make sure your battery is still good or you get a new battery if not bc if its not then it could kill your new alt.


edit: took me a while to respond bc i'm at work, that was supposed to go after GRAF-FITI first reply! lol

 

thanks again, this is great. GRAFFITI i didn't know they had a bench tester... i thought i would have to bring in the alternator i will do that tomorrow.

and the car does seem to run a little rich at start up if that means anything, but that just might be because the ecu doesn't regulate fuel at start up, yes?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by sabotage7 &raquo;</TD></TR><TR><TD CLASS="quote">
took me a while to respond bc i'm at work, that was supposed to go after GRAF-FITI first reply! lol</TD></TR></TABLE>

damn man, you work late! i manage an auto repair place out here, and we closed 45 min ago....hopefully you get paid well

to the OP, as sabotage and i stated, i will mnention this again as it is very important and often overlooked: either make sure your battery is fully recharged, and if this can't be done you should most deinately pop for a new battery

 

i will know more tomorrow, after i get battery and alternator checked at autozone. you guys are great help thanks

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GRAF-FITI &raquo;</TD></TR><TR><TD CLASS="quote">damn man, you work late! i manage an auto repair place out here, and we closed 45 min ago....hopefully you get paid well
</TD></TR></TABLE>

i dont do that anymore, i quit my job as manager of a parts store 3 yrs ago. i currently work for insurance, yay! but yes, the pay is well as i get paid extra for working late.

/offtopic

 

This is simple. Is your battery light on? If the answer is No then its the battery and not the alternator. While your car is running it should have around 13.5 volts if the battery is charging

 

wow bring it to honda they test it for free and they will also test for cca. bring to bramn honda and ask for ray i'll take care of you . no but really you can take the battery off while the car is running i do it almost everday how do you think we ( @honda ) change the battery and keep all your presets/radio code and time when someone comes in for a battery.

 

To test an alternator you need to do voltage drops across the s terminal and B+ cable , this is simply done by applying a multimeter to the one of the battery terminals and then to the terminals for the wires on the starter . You also should check to see if the bearing has a magnetic field , which it should . If all those pass get a tester check it at idle and at 2000 RPM , the amp clamp for a 4 cylinder should read anywhere from 100-150 amps .