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My 1980 z has died on me 3 times now. I've only had it for about 4 months. I know it is electrical because the voltmeter goes all the way down when it dies. Then, when I try to jump it, it will only run until I hit a red light and it idles. I've replaced the alternator and the battery but it did it again!
I was thinking I might have shorted out the alternator because the lady who sold me the car had the wrong battery in it and it burnt holes in my hood. Please help. I cannot figure out what is wrong or what I should do.
 

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It could be that your transistor ignition unit, or trignition unit, is shot. When this fails the car will die after warming up, for no apparent reason. I am not sure where it is on a 80. This is susp[ect if it occurs after the engine has tiome to warm up or if it has had power for a while. It happens because that is the failure mode of transistors, which are the devices inside the box.
 

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If you are pretty sure your problem is related to charge, there are a few things you can do.

#1 - Clean everything related to the charge system (doesn't hurt to do everything electrical).

a) Pull your bat terminals, clean them and the posts. When reattaching, seal the connection with either a clear coat like ignition sealer, or use plain old grease. This keeps oxidation from your connections.
b) Replace faulty battery cables. If at all suspect, replace them. While at it, clean the ends where they attach to the starter and block.
c) Check all grounds for good contact. If metal is rusty under the connection to a chassis or engine ground, remove rust and reattach.
d) Check and clean your connections at the alternator. Remove them all, and check that all terminals are shiny.
e) Check and clean all of your fusible links. All of the alternator current flows through one of them. If you have a bad connection here, not only will your battery not develope and maintain a good charge, your links and wiring will heat up due to the added resistance. When checking your links, verify that the connections are not only clean, but tight. If not tight, crimp them with pliers until they are. I'm not a ZX person, so this may not relate (don't know if you have the same setup as the early Z or not). Don't neglect the add on fusible links that are attached directly to the battery terminals. While not involved in charging, they should also be tended.

#2 - Have your system tested by a reputable shop. They can tell you if your alternator is outputting the correct amperage/volts at different rpms.
a) Batteries fail. Some batteries are much better than others. I recommend getting the best you can afford. While most all have warranties, it doesn't help when you have to keep taking the same battery brand back for a "free" replacement. Some fail very early in their life, leading you to think something else is to blame.
b) Very possibly your alt was damaged when the battery shorted against the chassis. A good indication of a failed alt would be no deflection of the volt meter when the car is revved above 1500 rpm. Z alts don't put out very many amps at idle. Some don't put out any below 900. Depending where you got yours, your mileage could vary greatly. Hopefully when the alt fails, you should see a red "charge" light on your dash. Have yours tested by a qualified shop before you rush out and replace it, though. Having a parts store test your parts isn't really the smartest thing. After all, they want to sell you a new one, and the "tech" that tests your alt may not know beans about it.
c) Test your fusible links to see if they have burned (opened electrically). This safety item is built in to prevent over current in the system. If burned, the alt can still power the cars vital systems, but your battery will not charge. When you idle, and your alt is no longer producing enough current, your car can die. Easy to check.

#3 Reduce your electrical load, or increase your electrical output.

a) Power windows, 3 power amps, toaster oven, etc etc, all draw their share of power. If your alternator is rated for 65 amps, and you have a hundred amp nut, sooner rather than later you will run out of juice. Cull any items you can live without, or limit their use during high current draw times (during a blinding rain storm at night). Have a look around and note what the current draw is for various devices. Headlamps, blower motor on high, rear defroster, transistor ignition unit, ECU, injectors. Start adding them up, and see where it all goes. Most of us will refuse to do without most of these, so this is a tough option.
b) Upgrade your alternator to a higher amperage unit. Later models use higher amp alts. Check the archives for specifics. You can use one of these later style Nissan alts with little or no modifications, but they are expensive. An alternative might be to investigate using a GM or Chrysler alt. This has been done by several people succesfully. Some are using units of 100 amps or greater. If you have aftermarket stereo equipment, this may be the answer to your prayers.

#4 - Do a maintenance "slow charge" periodically. Once a month or so, hook a battery charger up to your battery and charge it on the low setting (2 AMPS) overnight. This will bring your battery up to full capability, and make it much easier for your alt to keep it charged. If your battery is discharged, it becomes a load to your alternator, in effect becoming yet another power sink. If your alt is struggling to keep your car running at idle, and the battery is also sucking down what little it produces at low rpms, your problem becomes aggravated.

Your Factory Service Manual contains all the tests you need to find a charge problem. Please consult it or a qualified technician before purchasing new parts. Your problem is a common one, as many will attest. You can temporarily raise your idle slightly to try to compensate (say from 800 to 900-950). This will give you a little more amperage to work with. This is only a temporary stopgap, and your gas mileage will suffer because of it.

In order for the charging system to work, everything has to be right. As you can see from the above, just about anything can upset the balance.
 
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