240dan

Just got it running, '71 datsun 240z with an '02 LS6, I used a '00 camaro ss wiring harness, computer and alternator. The problem is the alternator constantly charges at about 30 amps. The regulator is working (adjusts to loads) but always returns to about +30 on the amp gauge. I bought a new alternator and the problem is unchanged (battery is good too). I've read that the previous ecms require a resistor but the 99+ do not. Any ideas?

Pop N Wood

iTrader: (1)

Did you measure the voltage being put out? You should have 14 to 16 volts at the fuse box when the engine is running. If the voltage is OK then you probably don't have an alternator problem.

Also try fully charging your battery before you run the engine. Maybe the battery is just drawing the juice.

If you have the alternator hooked up through the PCM then you don't need the resistor.

How are your engine grounds hooked up?

There is a chance your ammeter sucks. Once you figure out what is going on you may want to consider swapping in a voltmeter from a 280. I did that on my 240 and it worked out well.

One last thing, where are you powering the computer from? 240's split the fuse box and power half the circuits off the alternator side and the other half off the battery side. The thing that connects the two sides is the ammeter. If you hooked the computer to the battery side then the ammeter will be measuring the computer amps.

240dan

Ok made a little progress this morning, but I'll answer your questions first (I appreciate the help).

Voltage to the fuse box and battery is about 14.1 but can drop to 13.5 with all loads on. Battery is an optima red top, it tests a bit low at 12.0 volts but passes load tests and will easily fire the engine with all loads on. I borrowed another optima which tested at 12.6 volts and got similar results. So the battery may be a contributor but not the problem.

My harness grounds at the stock location, behind the left cyl head. I have several grounds behind the right cylinder head that run to the chassis, ecm, fuel pump, etc. The battery is behind the passsenger seat and is grounded to the chassis.

I believe the ammeter is good and at least reasonably accurate, the car was running and driving in December with the old six cyl using this exact charging setup.

The ecm orange 12+ is connected to the common on the 240z fuse box (upgraded MSA version). The pinks (ign hot and injectors) are on the battery side, relay activated.

This morning I ran an additional wire from the battery + to the alternator. That seemed to bring everything back in line on the ammeter. Not sure why this is needed on the new setup and not the old though.

Pop N Wood

iTrader: (1)

I'm not familiar with the MSA fuse box. I assume it hooks in just like the stocker. If that is the case, then what you are seeing makes sense. My guess is the ammeter is just showing the 30 amps worth of load you added to the the battery side.

Like I described above in our 240’s the battery side of the fuse box gets power from the alternator side via the ammeter. Thus any load you hook to the battery side of the fuse box is going to draw current from the alternator through the ammeter. EFI draws a lot of current. Just look at the fuse sizes for things like injectors and O2 heaters.

By running a wire from the alternator directly to the battery you are essentially jumpering out the ammeter.

If I am right then there might be nothing wrong with your electrical system.

If you want the ammeter to give you some idea of a failed alternator you need to move the pinks to the alternator side of the fuse box.

Switching to a voltmeter is a worthwhile option. The back half of a mid 70 280Z voltmeter gauge mounts directly to the 240 front. That allows you to splice the fat wires that went to the back of the ammeter together. If this is all you do then you still have battery current coming into the car and through the dash to flow back out to the battery. This puts a lot of heat through the connectors. Here is a picture of what my dash connectors looked like after 35 years of carrying battery current before the upgrade.



A better solution is to run the alternator wire to a common terminal under the hood and run a wire from that to the battery. You can then connect the two 10 gauge wires from the fuse box (from the alternator and battery sides of the fuse box) back to this common terminal. That way you no longer charge the battery through the dash and you have 2 fat wires feeding the reduced fuse box load instead of just one.

On my car I added a 4 fuse distribution block up near the radiator and used that as the common terminal. I got it from a car stereo place. It is nice because it allows me to run a 4 gauge wire from the alternator. I am using one of the fuses to power the radiator fan relay, one to the battery and the third for the two fat wires headed to the fuse box. I am running a Denso alternator and carb so my alternator hook up is slightly different. The alt voltage sense wire is connected to the fuse box and the alternator charge wire is connected to the idiot light on the 280z voltmeter. The voltage is now regulated right at the fuse box and a charge light is a nice thing to have.

240dan

I think the jumper wire to the battery has done the job. All loads now register through the ammeter. I like your idea though and will probably do a little re-wiring in the future.

Pop N Wood

iTrader: (1)

I think the jumper wire is just supplying the current to the EFI that use to flow through the ammeter. Not a problem, car should run fine, but youi may have effectively bypassed the ammeter so that it no longer gives a postive indication that the alternator has failed.

You may want to run a test where you disable the alternator and see what the ammeter reads. With a good alternator the ammeter should show a slight current into the battery. With the alternator off it should show a strong current flow out of the battery.

One way to do this would be to run the car with the alternator belt off. You could also disconnect the small plug on the back of the alternator, that should keep it from charging, but I'm not sure if that would hurt anything. I know you should never run an alternator with the power lug disconnected so don't do that.

240dan

Not all loads are passing through the alternator but the alternator is charging (on the low side but charging) I like your idea of the block under the hood and use both white wires to supply power to the fuse box so that will probably be coming soon. Thanks for the help.