Possible Electrical Problem?

[chaseincats]

Hi guys,

So something odd started a few days ago.  I drove the car to and from zcon this year and it was perfect (about 1200 miles in total) then I get back and of course theres some sort of gremlin that was waiting for me (but luckily it hid for the duration of the trip haha).

I was driving today at highway speed (70ish) and the tach jumped from 3.4k to 4 and then later in the drive jumped from 3.4k to 6 (the engine speed didnt budge, just the tach).  All of those hops were only for a split second and I've never seen it do that before.  I noticed also sitting at highway speed a couple of times I felt the engine power diminish for a split second and then come back.  The car will also overcharge when driving at highway speeds for 30 minutes or more (at least it does according to the voltmeter as it reads maybe 15ish volts instead of the 13ish it reads when cold (those numbers are very abstract of course since its just a needle)).

I took a look at the clear cone fuel filter that sits between the pump and tank and that looks clean.  I jiggled the cables by the coil too but everything seems solid.

 

Any ideas?

-chase

[Patcon]

Chase

what ignition are you running? Points, Pertronix, 280zx, MSD?

A voltmeter while idling will tell you if the 13volts at idle is really 13 volts. Hard to check at speed

[chaseincats]

2 hours ago, Patcon said:

Chase

what ignition are you running? Points, Pertronix, 280zx, MSD?

A voltmeter while idling will tell you if the 13volts at idle is really 13 volts. Hard to check at speed

It's the stock electronic 280z ignition to my knowledge.  The only difference is it has an ignition coil that apparently required the ballast to be removed by the PO.

Edited July 27, 2019 by chaseincats

[Patcon]

The ZX distributor has a small black box on the side of the distributor body with plugs on top of it

[chaseincats]

3 minutes ago, Patcon said:

The ZX distributor has a small black box on the side of the distributor body with plugs on top of it

Ya - i quickly removed that edit after I scampered to the garage to look.

How was the PO able to remove the ballast without changing to a ZX distributor (there is an aftermarket coil on there named "Jacobs p/n380672" https://www.ebay.com/i/283558856457?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=283558856457&targetid=595069534683&device=c&mktype=pla&googleloc=9026920&poi=&campaignid=1689799120&mkgroupid=66574332155&rlsatarget=pla-595069534683&abcId=1140466&merchantid=6296724&gclid=EAIaIQobChMI8oa58JbW4wIV6f_jBx0T7w82EAkYASABEgJD-fD_BwE)?

Edited July 27, 2019 by chaseincats

[Zed Head]

1978 280Z's don't use the ballast.

The 15 volts is concerning since the 1978 cars have an internally regulated alternator.  Should only go up to about 14.3 or so at most.  High voltage can mess up your other electronic parts.

The tach jumping is a sign of a failing ignition module or a failing tach.  Sending out extra sparks, that the tach can see but don't affect the engine.

Probably want to check the alternator first, getting the voltage right might make the other stuff right.  Like Patcon says use a voltmeter at the battery, don't trust the dash gauge.

[chaseincats]

40 minutes ago, Zed Head said:

1978 280Z's don't use the ballast.

The 15 volts is concerning since the 1978 cars have an internally regulated alternator.  Should only go up to about 14.3 or so at most.  High voltage can mess up your other electronic parts.

The tach jumping is a sign of a failing ignition module or a failing tach.  Sending out extra sparks, that the tach can see but don't affect the engine.

Probably want to check the alternator first, getting the voltage right might make the other stuff right.  Like Patcon says use a voltmeter at the battery, don't trust the dash gauge.

Alright, I'll give it a test the next time the gauge is looking high.   Do I just put the probes on the pos/neg battery terminals to test it?  I'd think that would tell me what the battery is at rather than how much juice is being thrown into it, no?

I also noticed a weird phenomenon - the temp gauge will sneak up (not too high) when I start using a lot of voltage (cabin fan, headlights, etc).  The temp gauge goes up almost instantly which wouldn't make sense, right?  Sounds again like something electrical, again this could be due to it overcharging?  When it has been overcharging (according to the gauge) in the past, I've put the headlights on to lower the voltage gauge - is this helping at all? 

[Zed Head]

The battery terminals are connected to what the alternator is putting out.  It's the right place.  Make sure to rev the engine while measuring.  Slowly bring up the RPM until voltage stops rising.  If it just keeps rising, over 15, you have a regulator problem.

[chaseincats]

1 minute ago, Zed Head said:

The battery terminals are connected to what the alternator is putting out.  It's the right place.  Make sure to rev the engine while measuring.  Slowly bring up the RPM until voltage stops rising.  If it just keeps rising, over 15, you have a regulator problem.

Is it common for internally regulated alternators to overcharge?  I thought this was an externally regulated issue.

[Zed Head]

1 hour ago, Zed Head said:

The 15 volts is concerning since the 1978 cars have an internally regulated alternator. 

Alternator failure is common.

You might be using the wrong FSM.  You're looking for ignition ballast and external regulators on a 78.  Both not there.

[chaseincats]

6 minutes ago, Zed Head said:

Alternator failure is common.

You might be using the wrong FSM.  You're looking for ignition ballast and external regulators on a 78.  Both not there.

Gotcha, I'll give it a look and report back.  It might be good to grab a new one anyhow - I have an oreilly's re-manufactured one in there.  This one should do, right: https://www.amazon.com/gp/product/B00KY0CN0Q/ref=ox_sc_act_image_1?smid=ATVPDKIKX0DER&psc=1?

[Zed Head]

That's just a reman.  Premier Gear and Hitachi are not the same company.

Your Oreilly alt should have a lifetime warranty.  Should be in the system under your name if you bought it.