Electrical dead

[ratsar_nx]

First off, a disclaimer:

My car isn't actually a Datsun, but I hope you can think of an '86 Nissan as a younger sibling to your dattos :P

 

I'm having issues with my car's electrical. Yesterday afternoon, I notided when driving that my choke was not opening up properly and also that my turn signals were acting funny and not staying lit for as long as usual in the "on" part of the cycle. I have the stock Hitachi carb so when the electric choke doesn't get power it won't open. Then, when I turned the car off, it wouldn't start again. I managed to get it started again by wiggling the positive battery terminal (which was badly corroded). Then, later as I was driving, I noticed that my dash lights were incredibly dim. I replaced the positive battery cable last night which did nothing and the problem continued to deteriorate. By the time I got home last night, I had hardly any dash lights, very dim headlights and barely visible tail lights.

 

Tonight, I replaced the negative battery terminal and got a friend to jump start me as I was only reading 10V across the battery terminals and it wouldn't start. It ran ok, although I had to give it a bit of gas at first to get it to run. I then tried the headlights again and found that it nearly killed the engine. I checked the voltage across the battery with the car running and found it to be only 4-5V. I also noticed that the choke was still not opening up and when I tried to rev the engine, the engine would just bog down and not rev up. I eventually gave it too much gas, which stalled the engine and I could not get it started back up. At this point, the voltage across the battery was only about 5V.

 

My suspicions are leaning towards the alternator. I checked the belt and the tension was OK, although it was too dark to get a good visual inspection of the belt. It felt fine and it's only about 2 years old with maybe 20,000KM (12,000mi) on it. I also didn't get to check the voltage coming out of the alternator because there wasn't enough light and I didn't want to reach around the back of a running alternator in the dark.

 

Does this sound like a bad alternator to anyone else? My only other suspicion is voltage regulator, but I don't know if the E16s powered Pulsar NX has an external regulator.

[az_rat210]

Datsun/Nissan switched to Internally regulated Alternators in 75 or 76. A car runs on the Alternator output, but Alternators are not intended to recharge a battery from Dead.

 

Replace the Alternator, but have a Full Charge put on your battery at the same time and keep an eye on it. A dying battery can cause an Alternator to burn out (not always, but it can happen).

[datsunaholic]

That's all the symptoms of a dead alternator. The choke relay is fed by the alternator's output (only on when the alternator believes it's turning) so that's why the choke won't open. The alternator light on the dash should have lit up under those circumstances, but in my experience they only light up when the diode trio goes bad.

 

 

Nissan switched to the internally-regulated alternator in '78.

Edited September 17, 2009 by datsunaholic

[ratsar_nx]

Thanks for the tips :)

 

It turns out that the alternator is probably not dead. When I pulled it out, the connectors on the BAT terminal of the alternator were corroded and almost fell apart. The boot covering the terminal was melted in places too. I replaced the connectors and put it all back together and it's been working fine ever since. I'll have to watch it in case it was because of some problem that was causing excess current drain.

 

I took the opportunity to open up the alternator and the brushes inside look fine too.

 

I took it into Partsource, where they tested it and it failed on the lamp test. The kid working there didn't realty seem to know how to operate the machine, but it could explain why my charge light never came on. The only dash light that was on without explanation was the BRAKE light, which apparently is wired into the same circuit as the battery light on the N12.

 

I figured the reason my choke was staying closed is that there was not enough power to heat the bimetallic spring in the choke so that it would open. The relay explanation makes perfect sense, I didn't realize there was a relay in there.

 

I'll keep an eye on my battery in case it is on its way out. I had a friend come over and boost me, letting it sit to recharge the battery a bit before starting my car again. The weather is going to get cold soon so that will be the true test of how well it works. Last winter, it was good enough to start the car a when it was around -30 to -40C out the couple times the block heater not working.

 

The only problem I have now is that I have to re-wire the oil pressure sensor because it's behind the alternator and the wire got disconnected when I was taking everything apart. Nothing can go perfectly, eh?

[deadmonkey]

Also, may wanna check for a current drain someplace. If there is a short, it will kill your battery. Hopefully the fuse box would take care of any shorts, but if something was jerry rigged then you never know.

 

From my knowledge of alternators (mostly from motorcycles), with the engine at around 3500 RPMs it should be generating over 12v across the battery terminals. For my motorcycle it is at least 12.4v But, if I remember from my old Chevy truck it is more like 13-14 volts.