1980 280zx Misfires Electrical?-Help!
 

My 280zx recently sat for about 8 months and, consequently, the battery needed recharging. I had to drive the car from one location to another. The Duralast (yes, I know its not the best) battery held just enough charge for me to drive the car a few miles before the Z began to misfire and behave as if it was not getting gas. It finally stalled and died; the battery was completely dead.

Fortunately, I had another battery, and replaced the original one. The car started up fine and ran fine. I put a brand new Duralast battery on the car about three weeks ago. I would go out daily and start the car and let it run for about 20 minutes. The ammeter indicated that the alternator was charging at about 14.4 volts at 2000 RPM. About a week ago, I began taking the car out for 40 mile drives each day. The Z started and ran great--all gauges appeared to function appropriately.

Today, after driving about 20 miles on a local expressway (at about 85 MPH), I noticed the car began to occasionally misfire. I slowed down to 60 and the misfiring became more frequent. I finally had to slow down and get off the expressway because the engine was misfiring, with loud backfiring, and barely running. I parked and allowed the car to idle for a few minutes, but the backfiring continued. Finally, I turned off the ignition. After about five seconds, I tried to restart, but the battery had gone completely dead.

Again, fortunately, I happened to have another charged battery in my garage. I called my wife and she brought it over. I replaced the battery and the car started fine and ran great back to my house.

My questions are these:

1. Why would the 280zx begin to backfire badly just because the battery was going dead? (I have concluded this is the problem after it happened precisely the same way twice within a month's time.)

2. Is it possible that the alternator is not recharging the battery, even though the ammeter shows that it is?

I think the problem is a defective alternator, but I would appreciate any constructive info someone might have.

Thanks

Problem Solved (I think)
 

I took my Z into Autozone and had the alternator checked. It is charging at a rate of 12.7 volts, even though my gauge shows 14.2-14.4 volts. Apparently, the gauge is off a little, and I need a new alternator.

Thanks for everyone's help.

w00t! Funny how things work out. :D

Z's are real voltage sensitive is why it began running funny as the battery discharged. You might want to put new battery cables on it also if they show any signs of corrosion around the terminals.

Thanks, rogerz. The battery cables look good and they are on tight.

I replaced the old alternator with a new Bosch and everything seems to be working fine now. BTW, it took awhile to get the old alternator off and the new one on. I took it out from the top, and that power steering pump bracket is a pain in the butt to remove and put back. The close quarters makes it difficult to get to the bolts--and realigning the bolt holes with the belt on the pump caused me some problems. You have to hold the pump/bracket, find the bolt hole, and then get the bolt to go in and align correctly or it will not thread. It didn't help that sweat was running down my arms and getting all over the pump. Ah, the pleasure of doing one's own mechanical work.

When I had to replace my alt i just took off the fan and dropped it. It worked out pretty well.

When I pulled out my alternator I pulled it from the top but i didn't remove my powersteering pump. I just pulled out and moved my charcoal canister and antifreeze overflow resevoir and I got it out fine. I have always had trouble setting tension on the alternator though so I bought this http://www.thezstore.com/page/TZS/PROD/PP1/10-2077. It's an adj. arm for the alternator. It won't work with stock size belt though, that or autozone kept messing up and giving me the wrong size. but looks great and makes it easy to adjust though.

Problem not solved!
 

Today, after a thirty minute drive, my Z began to sputter again. It died just as I pulled into my driveway and the battery was too weak to even run the radio. I replaced the battery AGAIN and the car ran fine again.

So far, I have ruled out battery, alternator, battery terminals, and alternator wires. There seems to be an electrical short that is causing the battery to discharge even when the alternator indicates it is recharging.

It looks like a trip to a good mechanic is in order.

Do your signal lights go really fast at higher rpm's? have you lost gauges and are things shorting out? my voltage regulator went bad a few weeks ago and my car was sputtering and backfiring on the highway like yours, everything started to short out. i put a voltmeter on the battery when it was running (cause it shorted my dash gauge) and it was running 18 volts at idle and 23 when i got it up to about 3 grand! I replaced the alternator and it runs great now.

oh nevermind, i read more and saw you already replaced the alternator, sorry!