idosubaru Posted January 25, 2014 Share Posted January 25, 2014 (edited) Why does my 88 XT6 have 11.3 V at start up (@ alternator and battery) but return to normal after 5 minutes? At start up lights are dim, voltage low, turning on accessories makes everything dimmer and slow (wipers). After 5 minutes it's back to normal and everything is fine and I can turn on everything with no issue. plastic connector at the alternator looks new, i usually replace them and probably did at some point. alternator? voltage regulator? battery? Edited January 25, 2014 by grossgary Link to comment Share on other sites More sharing options...
naru Posted January 25, 2014 Share Posted January 25, 2014 Bad battery. Link to comment Share on other sites More sharing options...
idosubaru Posted January 25, 2014 Author Share Posted January 25, 2014 what confuses me is if it was the battery - the alternator should take over as soon as the car is started and car should run normal immediately, not after 5 minutes. for example, when you jump start a dead battery the alternator takes over and the car runs fine immediately after start up. but it runs fine at over 12+ volts after 5 minutes which means it should be charging the battery and it should act normal at the next start up....but it never does. i'll put the battery on a charger and see what it does. Link to comment Share on other sites More sharing options...
idosubaru Posted January 25, 2014 Author Share Posted January 25, 2014 (edited) battery tested 12.3 volts out of the vehicle, thoroughly confused now. weird it would test 11.3 volts while running in the car and 12.3 volts when i removed it (engine only ran for a minute or two). put the battery on a charger but i'm thinking it's the alternator Edited January 25, 2014 by grossgary Link to comment Share on other sites More sharing options...
naru Posted January 25, 2014 Share Posted January 25, 2014 It is 11.3V because it is drained down after starting the motor. If the battery draws enough charging amps,alternator won`t be able to keep the voltage up, Weakish alternator will not help. Battery has problems as evidenced by the 11.3V. 12.3 is crap too. Link to comment Share on other sites More sharing options...
SmashedGlass Posted January 25, 2014 Share Posted January 25, 2014 If you aren't getting around 14 or more with the engine running (accessories such as lights not withstanding, and you have not had a dead battery which required you to jump to start) there is an issue with the charging system. Link to comment Share on other sites More sharing options...
Loyale 2.7 Turbo Posted January 25, 2014 Share Posted January 25, 2014 Bad battery. Also I Believe it is a Bad Battery: It might lost part of its ability to maintain the proper Charge: Volts + Amps. The reason why it sends 12.3V outside the Car and 11.3 while connected to the car (Which is Normal) is due to the Resistance offered by the Wiring harness and certain devices, such like memory for the Stereo, etc... The same happens to the A-C to D-C transformers: in example a 9V ones will measure 11 or 12 while they're Unplugged because there is No resistance. So, I kindly suggest you to try to take voltage measures and behaviour, with Another Battery, and let us know the Results. Kind Regards. Link to comment Share on other sites More sharing options...
greg454 Posted January 25, 2014 Share Posted January 25, 2014 You should have around 14 volts with the engine running, even if the battery was bad. Sounds like alternator to me. Link to comment Share on other sites More sharing options...
skishop69 Posted January 25, 2014 Share Posted January 25, 2014 Sounds like the diodes in the regulator are on there way out. Diodes will pass less current and voltage when cold (a marginal amount less). As they 'heat up', the electrons will pass more freely and the current and voltage will increase. They will do this up to a point and level out. Again, the amount is marginal. Beyond this point you run into thermal cascade. More heat allows more current. More current means more heat. More heat allows more current.... You see where this is going. lol Generally though, when the regulator goes bad, 1 of the 4 diodes goes out and you see increased voltage (around 16) and a decrease in output current, hence no charging. There are two other possibilities. The field windings in the alternator are going bad. Same current flow principal applies here too. The other is the charge lead from the alternator has developed high resistance. Disconnect it from the alternator and measure the resistance from end to end. Realistically you should see around a half an ohm but up to 5 ohms is 'ok' depending on what manual you're reading. General consensus seems to be 3 ohms. It's not the battery. 12.3 is a normal, key off, static battery reading. Measure any car battery, and you'll get roughly 11.5-12.7 volts. They can't produce more voltage than that unless something has gone wrong internally. If a battery causes the charge reading to drop significantly, it is because it has a bad cell internally. In this case, every one I've seen like this will go dead overnight due to a high resistance internal short in the bad cell causing a slow drain. Loyale was right about the system resistance causing a voltage drop, but generally this only applies to older vehicles since the wiring wasn't quite as good a quality as current vehicles and over the years you end up with increased resistance in the terminal connections. It may be a minimal amount that by itself means nothing, but when compounded by the amount of wiring and terminals, it adds up to enough to cause a drop in voltage. Easy way to check is to start the car and disconnect the negative cable. Measure your voltage at the charge terminal on the alternator using the housing as your ground. You should see around 14 as the others have stated with everything turned off. Hook the cable back up and you may or may not see a drop. A volt or so is ok, but more than that and you'll need to start searching for the area of high resistance causing the drop. My Brat was doing the same thing your XT is doing before the alt went completely TU and I did the Maxima upgrade. After the upgrade, though, I did notice the system voltage was lower with the battery connected than without . Like a volt or so. Since I had several batteries lying around and the alternator was new, I swapped things around just to check and got the same results. It's normal as long as it's not a huge amount. The ability of the regulator to compensate for voltage drops is also somewhat dependent on the quality of the components int he regulator. Cheap components won't regulate as well so some people may see this drop and some won't, Lots of variables. Link to comment Share on other sites More sharing options...
bratman2 Posted January 26, 2014 Share Posted January 26, 2014 My Brat did a similar thing many years ago. I called it a lazy alternator and replaced it. May not be your problem but the alternator replacement solved mine. By the way I drove it like that for several months with no issues. I live in the sticks so it always had time to get up to charge, usually took about five miles. Link to comment Share on other sites More sharing options...
idosubaru Posted January 26, 2014 Author Share Posted January 26, 2014 swapped batteries and alternators with no change. ended up being the crank pulley separated. it wasn't visibly separated and the alternator appeared to be turning fine at idle. while revving the engine it didn't look like the belt increased speed, but it was so hard to tell i would have believed it if it was fine.so i drew a line across the face and after a few seconds i stopped the engine and the line separated.and i drew a line across the replacement pulley for the future!while working on it/replacing it - after running the engine a bit the pulley was very warm. i suppose the slipping created heat and after a bit of driving it would warm up enough to expand or stick the rubber back in place and that's why it would run fine after driving for a bit - it may have quit slipping at all or as much.thanks for the help guys! Link to comment Share on other sites More sharing options...
Loyale 2.7 Turbo Posted January 26, 2014 Share Posted January 26, 2014 You're Welcome! I'm glad to know that you solved the problem and reported back such non conventional issue, it will add good info to the USMB's Database for sure. Kind Regards. Link to comment Share on other sites More sharing options...
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