electrical failure

carpenter_jai · #1 07-05-2006, 12:23 AM

I hate hot weather, it messes cars up... It got up to 35 (95 F) today, and you know how it is when it's that hot, you just want to hide from the heat, but today my car is not cooperating. I drove to work without any problems or signs of problems, but when I went to start my car after work, I had nothin. Not even enough electricity to make the dash lights come on.

I checked belts which were fine, tried to push start it, and it wouldn't start that way either. Got a boost and it started fine. While I still had the hood up, I noticed a ticking sound coming from the relay box. I then did some errands, and it was fine for a while, even shut it off, and it started again, but on the last leg of my trip home, the radio stopped working. I even had the hand brake up a notch to turn off the running lights, and there was still no electricity.

The alternator is a rebuilt that I put in two years ago. I have the belt on very tight, could that have worn out the bushings inside? Any bright ideas out there?

Jai

hot_sd · #2 07-05-2006, 12:40 AM

Doubt if it is the alternator bearings - if they are worn you will probably get noises like scraping noises and if it is really bad it may lock up but you will have all sorts of other symptons like the belt sqealing or the engine starting with a jolt. I would start by removing and cleaning out the battery connectors. Also it would be handy to get voltage readings off the system. Can you get a hold of a multimeter. Check the voltage when the problem happens and see if there is anything. The voltage with the ca turrned off should be close to 13V and above 14V when it is running (the alternator will produce a higher voltage than the battery in order to get current to flow to it). That would be the first things to check.

geozukigti · #3 07-05-2006, 11:22 AM

Metros have a habit of toasting the wires that go from the alternator, to the fuse/relay box. If you remove the relay box, check out the wire coming from the alternator. It'll be the 8ga white wire connecting to the bottom of it. If that wire is toast, you won't get a charge. Personally, I ran a 4ga amplifier cable from my alternator, straight to the + battery terminal with a 60a in-line fuse. It won't be bypassing anything at all really, just the fuse in the fuse box.

carpenter_jai · #4 07-05-2006, 12:04 PM

Alright, here's an update. I popped the hood this morning and checked the battery. Terminals are clean. Voltage read 2.09 v. I don't know much about electrical, but I know that's nothin. Once again, I was unable to push start, which has always worked in the past. I got a boost from a helpful driver. Checked again, had about 11.5 v and dropping. After only 3 or 4 minutes it was back down to 9.8 v. I got back in, let off the hand brake, and low and behold, that little draw from the running lights stalled the engine. Checked voltage again, this time 1.77 v. Does this sound like a battery that won't hold a charge, a kaput alternator, or like Alan says, toasted wire, which I'm heading out to check right now?

Jai

carpenter_jai · #5 07-05-2006, 01:24 PM

Is this white wire in the relay block or the fuse block? Most of the wires are white each with a different coloured stripe. I can see no obvious problems. Would the wire be burnt where it comes into the harness, similar to the headlight wire problem?

Jai

hot_sd · #6 07-05-2006, 04:16 PM

Once it has started the state of the battery should not really have an effect if the alternator is working correctly. Such a voltage drop sounds like a short somewhere, the alternator not working correctly or even both. Could be a shorted diode in the alternator - if the output rectifier has a diode that has broken down it will not be able to hold reverse bias and will short current to ground. May not be a dead short depending on what has happened to it. If this is the case it may have also killed off the battery.

Things to try - take the battery out, charge independently and then load test. This will confirm if it is the battery. Then you can start and run the car with the alternator disconnected for a few minutes. If the voltage holds it could be an alternator problem.

carpenter_jai · #7 07-05-2006, 04:29 PM

How does one load test?

Jai

hot_sd · #8 07-05-2006, 04:35 PM

There is a special tool for that. Actually all it is is a large resistor with a fairly large power rating which provides a load to the batt. Here in the US you can take it to some auto parts stores and they will perform the test for free. Maybe you can do that in Canada. If not you can buy one at a place like Sears but I think it may be around $50. You can probably get a used one for cheap on ebay but if you want it fixed soon that may not be an option.

The easy option is to test it on the car - disconnect the alternator after charging, turn on the headlights and what how the voltage behaves.

bansheetaz · #9 07-05-2006, 05:10 PM

it needs a new battery.

carpenter_jai · #10 07-06-2006, 12:07 AM

My friend came by tonight and gave me a boost. Voltage reading was 14.09 while her battery was hooked up, and it dropped to 13.86 when I removed the cables. The voltage was very slowly dropping. I let the car run for about 15 minutes, and at the end it went down to 13.36. Took off the negative cable, and the battery read 12.36. The good news is, I was able to turn on all my electrical devices, with the battery out of the loop, and it ran fine.

Sounds like I have an intermitent problem, the kind that are hard to diagnose. In the morning I will check the battery voltage again.

Anybody know what to make of this?

Jai

hot_sd · #11 07-06-2006, 12:24 AM

Assuming friends car was running, the 14 something volts would be normal - actually it should be higher but possibly the extra load would have brought it down somewhat. However, if the voltage drops into the 13V region it sounds like the alternator is not charging. The 12 something volt on the batt is low but if the alternator was not charging and the car was running off the batt then that would explain it. If one or more of the diodes are shorted then it is possible that i could drain the batt when it is off and not charge correctly when running. An oscilloscope should quickly prove what's going on with the rectifier circuit although that's not an easy option.

Also I would insepct the electrical wiring for any evidence of shorted connections.

hot_sd · #12 07-06-2006, 12:27 AM

As an additional suggestion - you can try leaving the batt connected as well as disconnected overnight on 2 different occasions and then check the voltage in the morning. This will help confirm whether there is a drain on the batt.

carpenter_jai · #13 07-06-2006, 01:18 AM

Is it possible to yank the altenator and replace the diodes? Are they just basic radio shack finds?

I checked the wiring as well as one can without cutting off all that tape. I couldn't see anything wrong.

Thanks for the ongoing advice everyone!

Jai

hot_sd · #14 07-06-2006, 01:50 AM

Never had any reason to take the recitifer out of an alternator to date but I would suspect it is probably an off-the-shelf semiconductor item. If you are going to take the alternator apart you can test the dides before replacing them using the multimeter. They should conduct one way and not the other. If they conduct both ways then they are toast. However, sometimes the semiconductor junction can become damaged such that they will look OK with a small amount of current generated by the multimeter but will break down in the presence of a larger current. I would test them before replacing.

Another possibility to try and track down the problem is to try unplugging various devices overnight including the alternator and other items such as radios to see which may be the culprit. I would suggest the batt is charged and then loaded - either with the tester or in the car with the lights on - to rule it out as the problem. I cannot find it at the moment but I did have a document with the various voltage reading using the car to load the batt - I believe I got it off the web somewhere.

carpenter_jai · #15 07-06-2006, 09:19 PM

I went to part source today (Canadian version of Autozone I would guess) and had the alternator and battery tested. Load test showed the battery to be at 2 per cent health, but I think it is wrong, as I was able to drive all day with many starts and not one problem.

The alternator passed as good with 14.11 volts. I asked to test it one more time with some of the electrical components on, and this time it read 0 volts!

Anybody know why it would be exactly 0?

I went to the pick n pull and got an alternator. Is there any way to test it off the vehicle to see if it is good?

Jai

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