battery drain

[SteveJ]

3 minutes ago, Dolfinz said:

I got the replacement starter switch and installed it.  I also disconnected the blk/blu wire at the ballast resistor.  I checked voltage and now it's 8.5vdc at the connector to the resistor.  I also checked the voltage on the wht/red wire at the ignition switch and when trying to start and it drops from 12vdc to the 8.5vdc.  It appears that the supply voltage is dropping for some reason.  Any ideas of what could be causing this?  Can I just run a new wire to directly feed the ignition switch from battery power?  I'm also uncertain how the transistor ignition unit is related to the starting function?

There are two things that could cause the voltage drop

1. If the starter is turning and the battery is not good, you could see that kind of voltage drop. 
2. There is corrosion between the battery and the ignition switch. From the battery positive, you have a cable going to the starter. It goes out of the starter to a white wire to the fusible link and comes out of the fusible link as a white wire. There it goes through the shunt (for the ammeter) and comes out white/red. The white/red wire goes to the fusible link and comes out as white/red, going to C-5. From C-5 it goes down to the ignition switch. Lots of connections to get corroded. It measures fine with everything off, but when you try to power other things, the corrosion could limit the current flow and drop the voltage downstream.

[Dolfinz]

So here's what I'm getting.  Battery voltage in static state is 12.75vdc.  Voltage on white wires at fusible link when cranking 9.9vdc.  Voltage at wht/red wires at fusible link when cranking 9.75vdc.  Voltage on battery when cranking 11.4vdc.  Is this indicative of a week battery?  Definitely losing voltage elsewhere but what is considered acceptable?  Clearly losing nearly 3vdc between battery and fusible link and another .25vdc at wht/red after shunt.  Another 1.5vdc from fusible link to ignition switch.  Please advise.

[SteveJ]

Get some Tarn-X, dielectric grease, rotary tool (Dremel) with a small wire cup brush.

Here is a fusible link I replaced many years ago.

I put it in some Tarn-X for less than a minute, rinsed, and beat the water out.

Here is how the fusible link box looked when I took off the links.

Here's how it looked after some work with the wire brush.

I coated the terminals with dielectric grease and replaced the links.

Try that, and re-test.

[Dolfinz]

Ok, I cleaned the fusible link terminals, replaced the fusible links, replaced the white wire connection at the starter, replaced the positive battery cable and replaced the connections at the ballast resistor.  The voltages changed as follows.  Voltages under no load.  Battery 13.07, wht wire at flink 13.06, wht/red wire at flink 13.06.  Ignition switch on.  Battery 12.95,  wht wire flink 12.94, wht/red wire at flink 12.94, blk/blu at ballast 12.6.  Ignition switch at start.  Battery 11.25, wht wire at flink 10.9, wht/red wire at flink 10.4, blk/blu at ballast 9.1, coil+ terminal 7.5.  Coil wire at distributor seems to have decent spark as well as spark at the #1 plug wire but it's still not firing.  Keep in mind the engine was running without issue until we began troubleshooting the issue with the alternator not charging the battery when it was running.  All that's really changed is the new voltage regulator and ignition switch other than cleaning/repairing connections.  Looking for direction as to what to try next.

[Dolfinz]

I checked one more thing.  The wht/red wire at the ignition switch drops to 9.6 in the start position.

[SteveJ]

Well, at least the voltages are looking like you should be able to run.

Are you sure you have fuel at the carburetors? Have you tried starting fluid? Can you make a video of the spark? (I did that once to figure out that I had a wonky distributor.)

[Dolfinz]

I'm certain about the fuel as I can smell it when I'm testing.  The engine isn't firing at all so I doubt starting fluid would help.  A video of the spark where?  Coil wire to distributor or #1 cylinder plug wire?  You don't think the drop in battery voltage when starting is significant?  If it maintained 12+ it would raise the voltages everywhere.  7.5vdc at the coil is acceptable?

[SteveJ]

Place the end of the spark plug wire near one of the studs at the shock tower. Watch the video I made about a year ago. It turned out there was a lot of wobble in the shaft, causing poor sparking.

You expect a larger voltage drop during starting because the draw of the starter drops the voltage. For reference, on a good sized CAT generator with a 24VDC starting system, you can see the voltage dropping down to about 8 volts on starting. Of course that's an extreme example because the CAT 3516 is a 69 Liter diesel engine, so the starter is fighting against a lot of compression. However, the principle is the same.

[siteunseen]

It's an EFI car right?

If you smell fuel you have a cracked fuel hose somewhere or the cold start valve is fouled up. You shouldn't smell fuel on the EFI, 1975 and up.

I would take a plug cap off a plug, stick an appropriate sized Phillips head screwdriver up inside and hold it close to some metal while cranking the key/starter over and look for spark jumping from the screwdriver to the closest metal bolt head you can find. Turn off the lights and you may see it without getting a shock.

[Zed Head]

p.s. if I recall right it's a 74 260Z with carbs.  So many electrical problems it's hard to keep track...

Pull a spark plug and check for wetness.  With carbs, when you smell fuel it usually means that flooding/fouling has occurred.  Might be because you didn't have spark, maybe.  But even if you solve the spark problem, if it exists, flooding will still stop it from starting.

Edited November 20, 2021 by Zed Head

[Dolfinz]

Yes it's a 74 260z and the smog shi* was removed years ago.  Yes it has carbs and the mechanical fuel pump is going to provide fuel that I can smell as the air cleaner is off to facilitate the use of starting fluid should the engine fire.  I go back to the fact that the motor was starting and running fine 2 months ago outside the charging of the battery.  Now it won't fire.  I did have the choke partially on as well to ensure fuel getting to the carbs.  I have since shut it off.  I will let the motor sit and let the battery charge until morning as it's seen a lot of cranking due to all of the testing.  I will respond again after it has had time to rest.  As for the spark on the number 1 cylinder it is timely and consistent but I'm unsure if it is strong enough due to the voltage at the coil during starting.

[Zed Head]

Spark plugs on the Z engines are about the easiest you'll find anywhere to remove and inspect. If they're dry you'll know more, if they're wet you'll know more.  Why wait?