Voltage Drop issue HELP!

[stravi757]

Hey guys

I am really struggling to solve this electrical issue and dont have enough knowledge to figure this one out by myself.

 

I had an alternator go out initially. I just replaced it as it was very old so It seemed normal that it was its day. a couple days later the replacement alternator goes bad too.

 

After poking around I put a multimeter on the battery to see if the second alternator was putting out any charge. the multimeter reading was odd. It will read 12.xx volts when you start the engine, then the reading will start jumping all over the place

7v, 3v 12v 8v It jumps constantly to random numbers ranging from 0.5v-12.5v and becomes more sporadic the longer the engine runs.

 

I thought I would start with bad grounding so I replaced both battery cables and the battery with a spare. no luck

 

I began replacing all kinds of parts since I have spares of EVERYTHING an nothing has fixed the issue

 

I have now replaced the entire wiring harness including the engine harness, efi harness, and main harness

fuel pump

alt

entire ignition system

starter

all relays

cleaned and doubled up grounds

removed/unplugged all accessories

and much more

 

 

I just keep getting this sporadic voltage reading that worsens the longer the engine runs, until the motor eventually dies(roughy 10 minutes).

 

I dont know what the next step to take is with electrical problems, you guys got any ideas where to start with a voltage problem like this??

Edited May 17, 2017 by stravi757

[Miles]

You didn't mention the basics:

 

• What year is your Z?  Wiring changes from year to year.
• What modifications have been made to the electrical system?
• Do you have the Factory Service Manual for your z?
• Have you downloaded electrical schematics for your Z?  Members have made some very well done schematics in color in pdf format.  Search.

[z240]

Simplify. Remove all ignition wiring to the coil. Disconnect the alternator. Run the engine with just the battery hooked up the coil + with a new wire. (Assuming you have points, you have to have that wire from coil - to the points too).

 

Watch the voltage on the battery now. If its going crazy still, its the coil. If not, start adding things back until you ID the issue.

[Zetsaz]

This sounds like a voltage regulator issue, and that's also the only thing I can think of that you haven't mentioned checking. Based on your profile image, it looks like you're in a 280 of some year. Either check/replace the voltage regulator, or follow the Atlantic Z guide to upgrade to an internally regulated unit.

 

http://atlanticz.ca/zclub/techtips/alternatorswap/index.html

 

The colors will be slightly different depending on your year, but the guide remains the same. 

I could be wrong but tha'ts the first thing that's coming to mind. 

Edited May 17, 2017 by Zetsaz

[stravi757]

Hey guys. Thanks for tips on what details you need.

 

My car is a 78 280z. Whole car is BONE STOCK, including wiring.

Yes I have the FSM, I have spent hours tacking down the wires on paper with the help of friends.

 

Z240-

I have simplified the system as much as I could.

I removed any unnecessary component that isn't needed to make the engine run.

 

I disconnected the alternator 

 

I only had things hooked up like the 

Fuel pump

Ignition system

EFI set-up

 

List of items ive swapped out with spares include/or new

Starter

Alternator

Coil

Transistor unit

Distributor

Efi harness

Ecu

Engine sensors

Fuel pump

Ignition switch

Main harness

Engine harness

Both battery cables

Battery

All relays

Fusible links

 

I have spent over 100 hours trying to figure out what the problem is and have gotten nowhere still. I have tried reading up on diagnosing electrical issues, but I am struggling to find information on what could be causing the voltage to drop sporadically. really been feeling defeated this past couple months.

Edited May 17, 2017 by stravi757

[NewZed]

I would put some better numbers on your description and don't use any "etc".'s  "I disconnected the alternator etc"

 

How long does the engine run before it dies (number of minutes)?  Have you tried another multimeter (maybe you just have a bad meter)?  Does the meter in the dash jump around like the multimeter does (78 has a dash volt-meter and an internally regulated alternator)?

 

Might be that you don't really have a voltage problem, just an engine that needs an idle speed adjustment.

[stravi757]

okay made a few changes to the post.

 

It runs for about ten minutes until it dies. when you start it back up after that, it dies quicker each time.

 

Yes I have tried different multimeter, and they read normal on my other cars

 

I currently do not have the dash board installed. But when it was a few weeks ago, the reading on the voltage gauge read steady at 12v(that was with the alternator disconnected)

 

There is definitely something off with the system electrically. Two alternators have died.

And also as the voltage reading begins to jump faster and faster on the multimeter, you can hear the injectors make a louder and louder humming noise that sounds like they are being starved of power.

I would put some better numbers on your description and don't use any "etc".'s  "I disconnected the alternator etc"

 

How long does the engine run before it dies (number of minutes)?  Have you tried another multimeter (maybe you just have a bad meter)?  Does the meter in the dash jump around like the multimeter does (78 has a dash volt-meter and an internally regulated alternator)?

 

Might be that you don't really have a voltage problem, just an engine that needs an idle speed adjustment.

Edited May 17, 2017 by stravi757

[Miles]

Swapping parts is not diagnosis. You are wasting time and money.

 

Learn how to use a voltmeter to diagnose charging circuits/battery. Shouldn't take more than ten minutes using a volt meter correctly.  Google it.

 

Verify that the battery and alternator are working by taking them to your local parts store.

[Miles]

Like this: 

 

[NewZed]

 the voltage reading was moving on the gauge from 12v

 

There is definitely something off with the system electrically. Two alternators have died.

 

 

You should probably study up a little more on electrical basics.  You might be killing your own alternators with improper wiring.  You're still having problems describing what's happening.  "moving on the gauge from 12" doesn't tell much.  Describing the problem is 90% of solving it.

 

 

Edit - seriously, all that can be pulled from your posts is that your alternator has quit working twice, you have odd readings on your meter, the engine dies after it wars up, and the injectors make a humming noise.  

 

Here's a question to ponder - how do you know the alternator has quit charging if the reading on your meter is jumping around?

Edited May 17, 2017 by NewZed

[stravi757]

Swapping parts is not diagnosis. You are wasting time and money.

 

Learn how to use a voltmeter to diagnose charging circuits/battery. Shouldn't take more than ten minutes using a volt meter correctly.  Google it.

 

Verify that the battery and alternator are working by taking them to your local parts store.

Thanks for the shared link, I watched a couple of that guys videos and another video On "voltage drop"

 

After watching the videos which were informative, including the one on "voltage drop" I still am not finding anyone describing the voltage reading I am getting on my multimeter.

 

Yea Im not proud of my parts replacement strategy, I know its not the proper way. But I do have spares of every part laying around, so I just gave it a shot.

 

 

 

You should probably study up a little more on electrical basics.  You might be killing your own alternators with improper wiring.  You're still having problems describing what's happening.  "moving on the gauge from 12" doesn't tell much.  Describing the problem is 90% of solving it.

 

 

Edit - seriously, all that can be pulled from your posts is that your alternator has quit working twice, you have odd readings on your meter, the engine dies after it wars up, and the injectors make a humming noise.  

 

Here's a question to ponder - how do you know the alternator has quit charging if the reading on your meter is jumping around?

 

I really need to work at better describing the problem forsure. Its honestly been a while since I have been on forums,  I am pretty rusty at describing in words what My problem has been. Ive done so many things, I guess I am struggling when I write, where to even start. So thanks for letting me know what errors Im posts descriptions.

 

To answer the statement you left me to ponder above. The alternator has not quit charging(although two have died). I have a old spare one in the car right now i just threw on. The battery reads 14.4V when running. But the voltage starts jumping all over the place. So the voltage will jump from 14.4 to 8v, It will go back to 14.4 then 10.7. It will just keep doing this and get worse the longer I run the engine, until the engine eventually dies.

 

When I disconnect the alternator, the battery reading goes to 12.6. The voltage will continue to jump as described above

 

I will make a video to show what i am trying to describe. 

Edited May 17, 2017 by stravi757

[stravi757]

[NewZed]

 

To answer the statement you left me to ponder above. The alternator has not quit charging(although two have died). I have a old spare one in the car right now i just threw on. The battery reads 14.4V when running. But the voltage starts jumping all over the place. So the voltage will jump from 14.4 to 8v, It will go back to 14.4 then 10.7. It will just keep doing this and get worse the longer I run the engine, until it eventually dies.

 

 

That sounds like a pretty significant short circuit somewhere.  The voltage drop would be from excess current flow.  Each time the short happens the voltage drops, and to go from 14 to 8 puts a big load on the alternator as it tries to bring it up to 14.

 

It might be that you just have a dangling wire somewhere that is bouncing around.  The high voltage when you start might be because the battery has capacity that is being used and the alternator can supply a charge on top .  As the short continues the battery dies and the alternator can't keep up with the short.  Does the battery get warm while this is happening?  And do you have to recharge the battery to restart the whole process?

 

If it's not a loose wire it could be an electrical component that shorts out more as it warms up.  The coil is a possibility.  I think somebody mentioned that.  Whatever it is should be getting hot as the current flows so touching things while the engine is warming up might find something.

 

Another thing to check is if you have replaced fusible links with regular wire, or wired something directly to the battery with no fuse.  If it is a short that's draining the battery that quickly, it really should be blowing a fuse or fusible link.  That's the other benefit of fuses, they tell you where the short is.

[stravi757]

That sounds like a pretty significant short circuit somewhere.  The voltage drop would be from excess current flow.  Each time the short happens the voltage drops, and to go from 14 to 8 puts a big load on the alternator as it tries to bring it up to 14.

 

So I am dealing with a wire shorting or a component shorting based off the reading for sure?

 

It might be that you just have a dangling wire somewhere that is bouncing around.  The high voltage when you start might be because the battery has capacity that is being used and the alternator can supply a charge on top .  As the short continues the battery dies and the alternator can't keep up with the short.  Does the battery get warm while this is happening?  And do you have to recharge the battery to restart the whole process?

 

I checked and changed all the wiring. I swapped out my main harness, EFi harness, and engine harness with very clean ones I had laying around, so there are no lose wires hanging around  I cant find any components that are getting hot while the car is on. 

The battery has not drained or needed to be recharged yet.

 

If it's not a loose wire it could be an electrical component that shorts out more as it warms up.  The coil is a possibility.  I think somebody mentioned that.  Whatever it is should be getting hot as the current flows so touching things while the engine is warming up might find something.

 

I started to eliminate  electrical components by swapping them with others I have but none of them seem to be the problem.

coil, dizzy, transistor, ecu, afm, dropping resistors, all fusible links, ignition switch, starter motor, fuel pump, all relays.

 

Another thing to check is if you have replaced fusible links with regular wire, or wired something directly to the battery with no fuse.  If it is a short that's draining the battery that quickly, it really should be blowing a fuse or fusible link.  That's the other benefit of fuses, they tell you where the short is.

Thanks for the response, Im going to continue to watch videos on tracking down short circuits, up my electrical knowledge! See If i can give some better descriptions to solve this.

Edited May 17, 2017 by stravi757

[NewZed]

Where are the leads connected?  Might be a clue.

[NewZed]

There's no significant drop in RPM when the meter reading drops.  The load on the alternator would jump, like it does when you turn on the wipers, fan and headlights, causing RPM to drop a bit as the engine strains to turn the alternator.  Seems more like you have an open circuit at the meter leads, or on the circuit the leads are attached to.