Voltage issue?

[Bambam91]

Hi all

 

I'm having some issues with my 720 ute.

Whilst driving, the battery light flashes and the engine coughs, splutters and on occasion backfires. Unless I have the high beams on. Then the engine runs perfectly.

 

My head unit will also stop playing music unless I turn the high beams on.

 

I'm assuming this would be a voltage regulation issue?

 

If so, is there any way to test the voltage regulator? I'm assuming the voltage regulator is inbuilt with the z24 alternator?

 

Cheers, Mat

[banzai510(hainz)]

have you ck the voltage with a meter at idle low beam then high beam. See if it shows anything weird.

 

Yes the volt reg is in the Alternator on newer rigs.

[Bambam91]

today the issue seemed to disappear. ute ran perfectly. took some measurements today anyway.

 

Voltages all take from the battery terminals. Taken in the following order:

Engine Off: 13.04vdc

Engine Off - High Beams: 12.20vdc and dropping

Turned High Beams Off

Engine Running: 14.20vdc

Engine Running - High Beams: 13.70vdc dropping to 12.40vdc

Engine Running (high revs) - High Beams: 12.56vdc

Engine Running High Beams Turned off: charging up to 14.20vdc and then stable.

 

As i said the ute ran fine today, and also did not display a flashing battery light.

If the issue happens again i will take some readings.

[banzai510(hainz)]

engine running with High revs I think it should be higher voltage unless you got the heater and wipers on at the same time.

 

unless you got all 100watt lamps and Roo lights also

[Bambam91]

 

engine running with High revs I think it should be higher voltage unless you got the heater and wipers on at the same time.

 

unless you got all 100watt lamps and Roo lights also

 

Yes that was with all lamps and two spottys as well.

 

It all looks normal to me. Well see if the issue pops up again.

 

Cheers anyway.

[datzenmike]

Make a good ground connection between body sheet metal and the battery ground. There should be one on the 720 ground wire to the motor. See if loose/ missing/corroded.

[dreadsiren]

as well as the aforemetioned ground wires make sure your fuseable link wiring is clean and tight fitting, had same gremlin a while back and had to make my own harness piece for replacement as it fatigued all to heck. check your pigtail to the alternator as well, bad wiring equals random gremlins :)

 

here is a schematic for most 720's electrical, its also a semi complete workshop manual so it comes in handy :)

the next page shows exacly where the problematic link is as well

 

http://asavage.dyndns.org/nissan/display1.php?Path=720/FSM_1984&db=Nissan&table=720_FSM_1984&Page=20-005

 

hope this helps!

[Bambam91]

the issue has returned.

 

i took some measurements again, they are as follows:

 

Engine Running: 17.7vdc

Engine Running - High Beams: 14.20vdc

Engine Running (high revs): 18.3vdc

Engine Running (high revs) - High Beams: 17.0vdc+

 

im assuming the voltage regulator is the cause?

[datzenmike]

The alternator has a built in regulator.

[Bambam91]

 

The alternator has a built in regulator.

 

Yes I am aware of that. But I'm assuming the voltage regulator that is built into the alternator is stuffed?

[datsunaholic]

Sounds like it.  I had one spike to 20V once.  Caught it in time; could have fried everything electronic.

[nerdistmonk]

just make sure it doesnt climb over 24 volts or you can sign off on the engine computer at that point, they designed the electrical systems in these trucks to take up to 24 volts if needed and only for a short period (jumper cables).

 

Im assuming the 720 has some sort of computer if its newer than 1983, they have a relay to protect them but it wont protect it if the truck is running and the voltage slowly climbs. The computer doesnt have any sort of fuse from what ive seen, just relays and a direct link from ignition switch to battery (with fusible link). The relays open only when the truck is off, so if its on and running it allows the voltage to enter it directly.

 

Also too much voltage will screw the battery up.

[Bambam91]

is it possible to wire in an external voltage regulator? would that work?

[wayno]

is it possible to wire in an external voltage regulator? would that work?

 

Seems like it would be easier to just buy a new alternator, your time has to be worth something, and you would have to buy a new alternator without an internal voltage regulator to use an external voltage regulator anyway.

[permanentslacker]

I had a similar issue in my 84. It turned out that the diodes in the alternator were bad. I replaced that and my truck ran normal again. I also put a cheap 20 dollar voltage regulator in line with my battery and the truck idles smooth as ever and all the spitting and sputtering went away too.

[Tinman]

Do yourself a big favor, get an original alternator and call it a day for the next 20 years.  Rebuilds are junk. 

I went through this secenario 3 times in a row with rebuilds after my original finally went bad.  After the 3rd rebuilt I got an original and have had no issues since.

 

Cheaping out on these trucks is the fastest way to make them unreliable.

[Bambam91]

so i installed a new alternator today, started the ute up, checked the battery voltage, 13.5vdc. high revs got to 15vdc and no higher. here i am thinking ive finally sorted it.

go for a drive with lights, stereo, aircon, anything and everything electrical turned on. ute runs perfect yet still has the batterty light on. pull up to the house feeling pretty chuffed with myself, turn the ignition off, and the ute keeps idling.

i flick the ignition on and off, this does nothing. just keeps idling. after about a minute of it idling, it finally turns off.

i start it again, it starts first time with no problems. idles nicely. turn ignition off, and the ute turns off. very strange.

 

now when i check the battery voltage it sits at 13vdc. no higher. high revs it sits 13vdc. on idle with lights on it sits at around 12.7vdc.

[Tinman]

Did you check the fusible links at the battery?  It's also possible that your ignition switch is either getting flakey or coming loose from the back of the lock.  It's only held by a screw.

 

Also pull and reseat the big plugs under the dashboard.  Corrosion never sleeps.

 

It's something stupid simple.  Just have to find it.

[Bambam91]

 

Did you check the fusible links at the battery? It's also possible that your ignition switch is either getting flakey or coming loose from the back of the lock. It's only held by a screw.

 

Also pull and reseat the big plugs under the dashboard. Corrosion never sleeps.

 

It's something stupid simple. Just have to find it.

Fusible links? Where are they located :p I don't see them.

 

I pulled and reseated every plug I could find. Didn't solve the alternator issue.

 

The ute hasn't kept running since last night.

 

I've found that if I bring the ute above 4000rpm the alternator jumps to 15vdc and sits around there even at idle. Until I turn it off and start it again where it'll sit at around 13vdc.

[Tinman]

The fusible links are attached to the positive battery cable, right past the post connector.

 

And you could have another bad alternator as well.  If it's a rebuilt, don't be surprised.

 

But the first thing to check is make sure the grounds to the engine, body and battery are good.  Then measure at the small plug to the alternator, you should get 12v with the ignition on one of the wires.

 

This is the field wire which the alternator needs to run.

 

Sorry, I don't remember the colors without digging out the service manual.  But I can if you need it.