just wondering if any one can help:i have a very good condition d21 2.5d 4x4 pick. but the battery light and water in diesel filter light stay on 
is it a problem with the alternator? they both dim when engine is reved...anyone any ideas? please!d21 alternator
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d21 96
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- Location: uk cheltenham
d21 alternator
hi.. im a new boy on this site so hello all just wondering if any one can help:i have a very good condition d21 2.5d 4x4 pick. but the battery light and water in diesel filter light stay on is it a problem with the alternator? they both dim when engine is reved...anyone any ideas? please!
just wondering if any one can help:i have a very good condition d21 2.5d 4x4 pick. but the battery light and water in diesel filter light stay on is it a problem with the alternator? they both dim when engine is reved...anyone any ideas? please!-
rlaggren
- Posts: 541
- Joined: 17 years ago
- Location: San Francisco
To take on electrical issues you'll need at least a digital volt meter - available from HD or Lowes for about $20. Or anyway something to measure voltage fairly accurately (like w/in 1/4 volt or better).
When using a meter you want to make sure it's not lying to you (or that you're not messing up). Sharpen the points on the two probes and make sure they are plugged into the meter firmly. W/the motor off test across the battery terminals themselves (not the connections there-to. You should see about 12+ volts but the actual value doesn't matter. What you want to do is try this a couple times, wiggling the probes, putting the meter down in different positions, switch it on and off a couple times..., etc and just make sure that reading never changes at all. If it does, something about your test set up is going to really confuse you down the line - so figure out how to make the thing work right now, beforehand. Paint, dirt, rust etc on the parts you're testing can make it hard to get the real reading so when you're testing something be patient, try a couple different ways of placing the probes and make sure you're getting the correct reading. Some fairly expensive decisions follow on this stuff so it'd be nice to have the correct data.
1) See what the alternator is actually doing. Measuring across the battery connections (on the ends of the large wires, NOT on the actual battery posts) you should see 13.8 to 14.8 volts with the engine running; revving the engine should raise the voltage up to about 14.8 (yes, you need 3 hands). If it is less or more, something isn't right. You can do it again, this time touching the actual battery posts to see if the connection between the large battery clamps and the battery itself looks good; s/b w/in 1/10 volt of the previous reading; the connection between the actual battery wires and the large clamps is a little harder to verify - you can leave it 'til later..
2) If it doesn't look right at the battery, try again between the alternator output terminal (usually a large post on the back of the alternator with a heavy wire going to it - careful this is always live) and the alternator body (case or frame); this eliminates all the wiring and just tests the alternator. S/B 13.8 to 14.8. If not start thinking about fixing the alternator. If there is a substantial difference from the battery end, 1/4 volt or more, somethings bad with your wiring. Rule of thumb is you lose 1/10 volt at each connection, but you really don't want to lose more. The connections are where you start looking - see below.
3) If the test at the alternator looks good, measure again between the alternator output post and the head or some bracket that solidly attached (metal to metal) to the engine. Should read essentially the same as the alternator - if not then the ground connection has failed somewhere between the alternator case the where you put you ground probe. Keep going, "stepping" further away from the alternator with each probe (hot and ground) until you find a problem; back up a little and make sure it repeats itself. If so you've narrowed down a bad connection somewhere between the point w/good readings and the point w/bad.
I'm not familiar with the wiring of your truck - the above is just a basic reality check for your alternator function to get you started locating the problem. There are people here w/a lot of experience and they've discussed electrical problems a lot. Use the SEARCH button and you can get some good info right now. Could be your problem has been nailed town before or you could get some good ideas.
Also, our host makes a point of asking people to put their vehicle and location (eg. city) into their PROFILE. This saves a lot of time when it comes to answering questions. The other standard advisement is to get the FSM (Factory Service Manual). You (or whoever you get to work on your vehicle) will quickly require info that's available only from the FSM; having it on hand can easily save you $20-40 worth of time an frustration.
Good luck. Rufus
When using a meter you want to make sure it's not lying to you (or that you're not messing up). Sharpen the points on the two probes and make sure they are plugged into the meter firmly. W/the motor off test across the battery terminals themselves (not the connections there-to. You should see about 12+ volts but the actual value doesn't matter. What you want to do is try this a couple times, wiggling the probes, putting the meter down in different positions, switch it on and off a couple times..., etc and just make sure that reading never changes at all. If it does, something about your test set up is going to really confuse you down the line - so figure out how to make the thing work right now, beforehand. Paint, dirt, rust etc on the parts you're testing can make it hard to get the real reading so when you're testing something be patient, try a couple different ways of placing the probes and make sure you're getting the correct reading. Some fairly expensive decisions follow on this stuff so it'd be nice to have the correct data.
1) See what the alternator is actually doing. Measuring across the battery connections (on the ends of the large wires, NOT on the actual battery posts) you should see 13.8 to 14.8 volts with the engine running; revving the engine should raise the voltage up to about 14.8 (yes, you need 3 hands). If it is less or more, something isn't right. You can do it again, this time touching the actual battery posts to see if the connection between the large battery clamps and the battery itself looks good; s/b w/in 1/10 volt of the previous reading; the connection between the actual battery wires and the large clamps is a little harder to verify - you can leave it 'til later..
2) If it doesn't look right at the battery, try again between the alternator output terminal (usually a large post on the back of the alternator with a heavy wire going to it - careful this is always live) and the alternator body (case or frame); this eliminates all the wiring and just tests the alternator. S/B 13.8 to 14.8. If not start thinking about fixing the alternator. If there is a substantial difference from the battery end, 1/4 volt or more, somethings bad with your wiring. Rule of thumb is you lose 1/10 volt at each connection, but you really don't want to lose more. The connections are where you start looking - see below.
3) If the test at the alternator looks good, measure again between the alternator output post and the head or some bracket that solidly attached (metal to metal) to the engine. Should read essentially the same as the alternator - if not then the ground connection has failed somewhere between the alternator case the where you put you ground probe. Keep going, "stepping" further away from the alternator with each probe (hot and ground) until you find a problem; back up a little and make sure it repeats itself. If so you've narrowed down a bad connection somewhere between the point w/good readings and the point w/bad.
I'm not familiar with the wiring of your truck - the above is just a basic reality check for your alternator function to get you started locating the problem. There are people here w/a lot of experience and they've discussed electrical problems a lot. Use the SEARCH button and you can get some good info right now. Could be your problem has been nailed town before or you could get some good ideas.
Also, our host makes a point of asking people to put their vehicle and location (eg. city) into their PROFILE. This saves a lot of time when it comes to answering questions. The other standard advisement is to get the FSM (Factory Service Manual). You (or whoever you get to work on your vehicle) will quickly require info that's available only from the FSM; having it on hand can easily save you $20-40 worth of time an frustration.
Good luck. Rufus
82 Maxima wagon
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