720 Charging System Issue (z24)

[Jdm720]

A while back, the voltage in my truck ('84 720) would drop down to ~12 every now and then. When this happened, I would get no power to anything when the engine wasn't running. I was unsure of what was going on, so I dropped the alternator real quick and took it to get tested, passed.

 

The issue then disappeared for a few months. Recently, it started happening again. I then continued on with the research. I was led to believe that maybe one of the fusible links may have blown. Checked em out, all seemed to be fine (maybe I should've replaced them anyway, but I didn't)

 

So I was back up at 14V, no issues. Within the past week, back down to 12V, and my truck feels like it's running out of gas and not getting enough fuel. Research led me to believe that the fuel pump relay is shutting off the fuel pump since it's being informed that the alternator is not charging.

 

Last night, I went out for some delicious ice cream. After dropping off the lady, my voltage is slowly dropping, my driver's side HID goes out, and fuel is cutting out intermittently. I was running off of what was left in my battery reserve. Barely made it home. Proceeded to do a few hours of research, continued this morning. All alternator connections are tight, I double checked fusible links, resistance, my charge light in the cluster is functional..... Then I checked this.

 

 

When running, at ~12V, I get the same readings at the oil switch, acc, fuse... BUT not at the alternator, I would only get between 5-6V. 

 

Is the reading at this connection supposed to be the same as at the battery...? Or am I somewhat onto something... The battery is now dead, took it out and have it charging at the moment, but I didn't get a chance to get a reading at the alternator.

 

I don't believe my fuel pump relay to be an issue aside from the charging system problem, at least not at the moment.

 

What do you guys think..? Even after I get my battery charged and back in, and after checking output at the lower terminal of the T on the alternator, I'm not sure of what else to check... Alternator has been tested twice and passed, (yet for some reason I'm still iffy about that), and the battery is brand new (also took in to get tested with the alternator to be safe)

 

On top of that I just sold my last other car yesterday, and called off work today to try and fix her..

 

(BTW, alternator is a 50 amp)

[banzai510(hainz)]

when its 12volts are you running the heater headlights and wipers by chance.

 

or does it do it with load or no load? if loaded down then the alternator is weak and works when theyre is NO LOAD on the system.

 

if a fuseable link blown you would have no power to the fuse box

 

 

sorry I dont know the later trucks

Datsun mike will be better suited to awnser.

[racerx]

yep..fuseable link gone then no power..what about play on alt. belt?, how about ground? voltage regulator?

[banzai510(hainz)]

volt reg will be on alternator. so I assume the alt was load tested at the shop he took it too.

Key is LOAD TEST.

[racerx]

forgot it was 80s truck....thank you for pointing that out.

[Jdm720]

when its 12volts are you running the heater headlights and wipers by chance.

 

or does it do it with load or no load? if loaded down then the alternator is weak and works when theyre is NO LOAD on the system.

 

if a fuseable link blown you would have no power to the fuse box

 

 

sorry I dont know the later trucks

Datsun mike will be better suited to awnser.

 

Just charged the battery and threw it in the truck right now, I get this when warmed up, running, with no load (all lights, blower motor, wipers, etc. off)

 

 

And this is the reading I'll get at the lower T connection at the back of the alternator.

 

 

As well as here.

 

 

Grounds all seem to be good, belt is tight enough. (replaced belts a few months ago when one started squealing)

[Jdm720]

Also, voltage was slowly dropping, signifying that the alternator was not charging at all. Drove the truck around the block, same issue with the fuel cutting out, then parked it. Was unable to start it again as the voltage had gone a tad too low.

[racerx]

Take the alternator to another parts store and have them check it out.  This happened to me before when Autozone said alt was good and had Kragens checked it out and was bad.

[Jdm720]

That's what I've been thinking.. I'll drop it again and try to get a ride. (mine was tested at Autozone as well)

[Jdm720]

Took the alternator to O'Reilly's, Failed

 

New one should be in around 3:45. Once I get it installed I'll post the results.

 

Thanks for the tip racerx, I don't think I would've gotten it tested again this soon since I did have it tested twice, after all.

[Jdm720]

Installed the new alternator, and bam

 

 

Also no more fuel delivery problems, or clicking from that relay on the passenger side.

 

Mission accomplished, problem solved, lesson learned. Do not go to Autozone. 

Fortunately, O'Reilly is opening a new location literally less than 2 minutes away (and that's in walking distance!)

 

We're back in business~

[Jdm720]

Spoke too soon.......

 

Got 12V all the way home from work, fuel cutting off in the higher gears. 

 

:huh: 

[racerx]

Try changing relay, my wagon would not charge..many moons ago forgot which forum but was told to change it and charge held up. Battry would drain.

[Jdm720]

Which one..?

[racerx]

DAng that was soooooooooooooo long ago.  I think it was my headlight...kept draining my battery and at same time, auto parts store said that alternator was good then took it to another one and was bad.

[Jdm720]

Ok, I've gone to a couple yards, no 720's in sight.. May visit a few more in the next few days..

 

Decided to change my fuel filter, and no more fuel cut-outs in the short time I drove it to pick up some hose clamps. We'll see if it acts up again.

 

Voltage hasn't dropped yet... 

 

 

On a different note, the oil light in my cluster started turning on intermittently.... All of this happening right after I sell all of my other cars.. I think my truck is lonely.....

[racerx]

see if the wire to oil sending unit has good connection, mayb you have to mess with the connector. wire to my gas tank connection was loose and sometimes it would read fuel and sometimes it would not.  Sounds like a connection issue.  I would check your oil, maybe reading okay.  bTW what where you looking for at JY for your truck, thought Autzone carries relays for that year.

[Jdm720]

I'll go over all that as soon as I can.. Went to fill up, then I got no crank whatsoever... My buddy helped me push start it, got home. Turned it off, and was able to start it back up no problem... Once, and only once... *sigh*

Why...

 

I usually go in hopes of finding something.. Anything, for my truck. 80% of the time I find one, they've already been stripped.

[racerx]

Maybe bad connection somewhere and bad ground..check to make sure connections are solid.

[banzai510(hainz)]

so was this part alternator fix???????? as you didnt have 13 volt before and then you did.

 

soon as it went to 12volts going home ai would ck the fuse box for a popped fuse as most likely your just reading across the batter at 12. then if you put the lights on Im sure it will go down in voltage.

 

Im not a 720 expert.

 

ps autozone and O rileys are the same far as im concerned. I got a started from them and lasted about 3 weeks.

[Jdm720]

So far, when running, I haven't gotten any voltage drops.... 

 

Problem is, I need to get it running first. Just got home and going over everything. Setting the oil light aside for now. 

Still no crank (wasn't expecting it anyway) Starter connections look good. Before inspected the starter further, I decided to check out the connection at the ignition switch. This is what I found. 

 

When in the "start" position (while connected to the switch, of course), I get power output from terminals #4 and #5 (Please correct me on the numbering if I'm wrong, using Haynes).  These two.

 

 

Problem is, there is no wire to receive the output at #5..... What goes here...? What would it lead to if it was there....? Where are you mystery wire....

 

 

Meanwhile I'll go over the starter again... 

[datzenmike]

Only 4 wires to/from the ignition switch.

 

Black/Red stripe is the start signal to the starter solenoid.

Black/White is power from the fusible link at the battery positive terminal

White/Blue is the power to the coil in START and  RUN key positions

White/Red is power to the fuse box in the ACCESSORY and RUN positions

[Jdm720]

Thanks Mike, that cleared some things up for me.

[Jdm720]

So I get power to the starter, yet it does not engage. Supplied power to the solenoid with a power probe, same results. Pulled starter, tested outside with separate battery, no engagement. Shit.

 

Gonna take it to get tested one more time and hopefully that'll be that.

 

Also, discovered that I have a bad connection at the oil pressure switch. Will get back to that...

[Jdm720]

Starter passed the test. 

 

I performed a few more and it works sometimes.. Sometimes it doesn't...

 

It occurred to me after the reinstallation that I should've just bought the new one... Ahh.. Tomorrow.