1986 Nissan Z31 300ZX issues

Hoping I can get some other people's experience. I've messed with Z31s before, but it's been a while.

So, my car died a couple of nights ago, and my dumb butt accidentally reversed the jumper cables on my already dead battery. (It was dark, and the positive terminal had a black cover on it and the negative had a red cap on it.)

It started smoking pretty bad, and when I realized what I had done I mentally slapped myself. The only apparent damage I had done was melt the wire on the fuseable link for the battery.

I changed it out with a spare. Connected the charger in the correct manner, and it started.

For all of a few seconds. So, my dad and my sister's boyfriend come out and start trying to tell me what to do, which pissed me off as I don't really care much for my sister's boyfriend, and I didn't ask for any help especially not to be told what to do. So, I told both of them to bug off, and I let it sit in his driveway.

So today, I waited until the weather was a little better and it was daylight and I start going back over it.

Here's what I found:

All of the fuses are good.
None of the cables are melted or damaged.
The battery will charge up to 13.5 V
The car will crank/turnover, fire up, and then die.
The battery doesn't hold a charge. It will completely flatline after three to four attempts to start.

I don't have any diagnostic tools, but I believe that it's most likely the alternator that got screwed up when I reversed the jumper cables.

Another thing I believe might be wrong is that the ECU got screwed up. I don't know for sure as both LEDs come on when the key is in the on position, but I can't run any ECU self-checks since the car won't stay running.

I just want other people's inputs, because my dad is giving me a hard time about my car sitting in his driveway, and keeps trying to tell me that it's just flooded and I won't let him or my sister's boyfriend touch it since they already started poking around on a car that they're not familiar with and I caught them spraying a bunch of starter fluid into my oiled air filter, and it wasn't even flooded.

1986? Bro, get a new car.

a reply to: KKLOCO

why?

Keep wrenching on it. I have a 2000 300z 2+2 turbo that I bought new. It stays in the garage and I'll likely never sell it.

Check with the Nissan forums, you're more likely to get the right answer there.

a reply to: AutomateThis1

Nice! 300ZX Got pics?

Wouldn't happen to have a volt meter by chance? Chances are, you fried your alternator. Your ECU might be ok.

I changed it out with a spare. Connected the charger in the correct manner, and it started.

Changed out the battery? If not, start there first. You could have done some internal damage to the battery, even if it holds a charge, doesn't mean it has enough amps to continue running, especially if you fried your alternator. Autozone or similar places will test both for you free. That is, if you live in the states.

If you had a volt meter, even a cheap one, you could test your connections all the way back to the alternator and beyond, if you know what you're looking for.

If it were me, I'd focus on the battery then the alternator. I wouldn't think you'd have to go back further than that.


Seriously though... Pics! I never had a 300ZX. I did have a 200SX with a few minor mods. Currently running a 15' WRX STI with stage 3 cobb including deletes. I put a little better than 300hp to the road.

originally posted by: Anathros
Keep wrenching on it. I have a 2000 300z 2+2 turbo that I bought new. It stays in the garage and I'll likely never sell it.

PICS! Bruh!

a reply to: AutomateThis1

You either blew a fusible link, ECU/MAIN relay, or fried your ECU. If there's power going to the relay after the ignition switch is turned on, then either the computer control relay or ECU got fried. You need to get your hands on a diagnostic tool to check the codes. It's the only way to know for sure.

a reply to: AutomateThis1

Replace the battery, and double check all you fuses.

If not, you may have fried the ECU. There's plenty of 300 clubs online that can help you out.

a reply to: AutomateThis1

Get a new battery, the replacement is bad.
Volts don't mean much. Run it by a battery place if you can and load test it.
Amps under load need tested, not volts.
Leave all the other crap(alternator and ecu) alone until you can load test it. Reverse polarity won't hurt much besides the battery and charger.
Thank me later.

a reply to: AutomateThis1

Shooting from the hip, here ...

My guess is you fried the diodes in the alternator. Take it to an auto parts store and they will be able to check it for you.

An 86 probably has an OBD1 computer. If the alternator checks out, disconnect the battery to clear the codes in the computer. Reconnect the battery, start the car and let it die. Turn the ignition off. Then turn the ignition key on, off, on, off, on, off, on, off, on (that is four times and leave on.) The computer should then flash the check engine light with a series of trouble codes, like five flashes, pause, two flashes for 52.

You should be able to find the trouble codes online to point you in the right direction.

a reply to: StallionDuck

Thanks everyone for the input so far. I don't have a multimeter. I wish I did. Those things are handy.

I've had several Z31s, and I used to have a bunch of pictures, but I lost them all when I deleted Instagram.

If I had a trailer I wouldn't have had to leave it in my dad's driveway, and I could just bring the whole turd to get the system checked out.

The battery being damaged is a possibility I thought of. The reversed cables were on there for probably about 30 seconds. Long enough to do damage.

I definitely think that the alternator is fried. Knowing my luck the battery and ECU are as well, but I gotta do one thing at a time for the moment.

I'll start with the battery since it's the easiest. If that doesn't resolve the issue I'll swap out the alternator. IF that doesn't work I've got an '87 ECU I could put in. I'd just have to tweak it since it's for a turbo.

Either way, non or the parts are too expensive, and truth be told the car needed a new battery and alternator anyways.

To KKLOCO. I refuse to buy a newer car. I've only done so once, and it wasn't worth it.

To HalWesten. I've checked the forums and I've seen things come close to the specific thing I'm asking, but just different enough to not answer what I'm looking for.

And man those forums are old lol. I don't think anyone still posts on them.

Back to StallionDuck.

Let's see.. my first car was an 87 Z31 only one owner. Bought it new when it came out. Kept it garaged, and basically never drove it. It was NIIIIIIICE. Sadly I totalled it when I fell asleep at the wheel.

The second one I bought was an 84 50th Anniversary. Real thing, not a fake. I got pissed off at it, and gave it away for a pizza.

The car I bought after that was a 2017 370 Nismo. I sold it because it was too expensive to make it go faster.

So, I went back and bought an 87 Z31 turbo. I raced it to death. Ended up knocking the pee out of it and frying the electronics.

I wanted to buy something more mundane and reliable, but my dad insisted on me buying the current one I have. So, everytime something goes wrong with it I give my dad grief about it.


Now my dream car would be a 240z or 280z. Those things are so sexy when they're fixed up. I want to fix one up put a beast sounding engine in it, put some fender flares on it, paint it black. Some nice rims.

So nice. One of these days I'll make it happen.

The thing you need to look at is why it died in the first place, before you connected the charger wrong.
Probably the only damage that the reverse polarity caused was the fusible link you already replaced, that is why they have those to minimize damage to anything farther along the line.
What was it doing prior to dying?

It tries to start, assume the ecm is working for now. You need air, fuel, and spark to keep an engine running. The fact it's trying to run means your getting some spark. Start by checking fuel flow and if it's been setting the condition of the fuel.

a reply to: AutomateThis1

Just bite the bullet and save for a Skyline. The 300s and 240s were built as cash cows.

The diodes in the alternator could be fried, pushing the power to ground and away from the ignition. In a honda the diodes are in the fusebox instead of the alternator. I am guessing, I have never worked on a Nisson.

ATS hasn't been letting me upload pictures for a while now either.

a reply to: RazorV66

I left the lights on

a reply to: Jason79

Fuel system works. Fuel pump is working, fuel injectors are working, and spark plugs aren't fouled. There's no rough idle.

It starts, idles like normal for a second or two, and then dies.

a reply to: strongfp

They're nice cars. I'd buy a 2000 or a R32 if I ever had the chance.

The truth is I'm a diehard Z guy. I don't care what anyone says; I like the L28. I used to have one I restored and kept it in my garage until someone gave me a good amount of money for it.

I like the VG30E/ET/DETT

I like the classy look of the 240-280z, I like the retro 80s look of the Z31s, the Z32s were bad little cars. I like the electrical dashes in the Z31s. I like the cockpit feel of the Z32s.

I used to build racecars. So, they weren't pretty. They were made with the knowledge that there were going to be bumps, scrapes, and collisions.

But, I've seen some really nice sexy ones.

A buddy of mine had a Z32 that he put an LS engine in and that thing would haul ass.

My second 87 Z31 could take on slightly worked up 350Zs.

They're solid cars, and even though they tend to be run down when bought, if you find out where they need some love you can make them last a long time. The VG30E and VG30ET are strong. It takes a lot of neglect and abuse to destroy one beyond repair.