Just_exploring Posted November 16, 2016 Report Share Posted November 16, 2016 Just purchased a 78 620. Truck ran fine charge light was on but dim. Truck broke down on highway and brand new mechanical pump failed. The part store did not have the right pump so I had to install an electric pump. Drove 200 miles and had to jump it every 50 miles or so.I took the battery and alternator to the store and had them tested the alt passed and the battery failed. I put everything back together wired the pump correctly. The charge light is still on. Now the issue I'm having in the alt is not making enough power at idle but if you rev it up it is good will even overcharge. If you use the lights it is not charging enough even while revving. I've cleaned all wiring and fuse block. I'm going to add grounds from battery to body and body to frame. Any thing I should check? Quote Link to comment
datzenmike Posted November 16, 2016 Report Share Posted November 16, 2016 Battery failed.... did you replace it? 1 Quote Link to comment
Just_exploring Posted November 16, 2016 Author Report Share Posted November 16, 2016 Yes the battery was replaced with a new one. 1 Quote Link to comment
Doctor510 Posted November 16, 2016 Report Share Posted November 16, 2016 AND ... Quote Link to comment
datzenmike Posted November 16, 2016 Report Share Posted November 16, 2016 ...... I put everything back together wired the pump correctly. The charge light is still on. Now the issue I'm having in the alt is not making enough power at idle but if you rev it up it is good will even overcharge. If you use the lights it is not charging enough even while revving. I've cleaned all wiring and fuse block. I'm going to add grounds from battery to body and body to frame. Any thing I should check? How do you know it is 'over charging' with the lights on? Do you have a volt gauge? Engine off 12.6 volts Engine on 13.8-14.5 volts charging normally. Just ground battery to engine (check clean the negative battery cable to the head behind the fuel pump) and the body sheet metal. 1 Quote Link to comment
banzai510(hainz) Posted November 16, 2016 Report Share Posted November 16, 2016 if it over charges then the volt reg is bad. I dont know YEAR when the cross over from external volt reg to a internal type(inside alternator) find a cig lighter battery alternator monitor that plugs in. They work really good and dont drain the battery Equus makes one. uses diodes lights to me the alternaot works untill you put a load on it. NAPA cheaks mine and they load it down. then you can tell 1 Quote Link to comment
datzenmike Posted November 16, 2016 Report Share Posted November 16, 2016 '77 and older are external regulator, '78 and on, the regulator is in the alternator on all Datsuns. . Quote Link to comment
Just_exploring Posted November 16, 2016 Author Report Share Posted November 16, 2016 Sorry guys it is a 1978 620. ¤when the truck is at idle with no accessories on it is under charging. ¤when the trucks rpms are raised it is charging and sometimes goes into overcharging. ¤with any accessories on it is under charging even with raised rpms. I'm using a battery/alternator tester as my multimeter is mia. So I don't know the exact voltage. Quote Link to comment
racerx Posted November 16, 2016 Report Share Posted November 16, 2016 get a VM and test it, they are really cheap or borrow one. I think it's your VR. 2 Quote Link to comment
DanielC Posted November 16, 2016 Report Share Posted November 16, 2016 If you do not know the exact voltage, you do not know if it is under or overcharging. Quote Link to comment
Just_exploring Posted November 16, 2016 Author Report Share Posted November 16, 2016 This is the tester I'm using tells you if it is over or undercharging...... Quote Link to comment
datzenmike Posted November 16, 2016 Report Share Posted November 16, 2016 Brushes may need replacing or one of the diodes is bad. I assume the belt is snug... able to deflect the belt about 1/2" between pulleys with strong thumb pressure? and the belt is not glazed and in good shape??? Quote Link to comment
Just_exploring Posted November 16, 2016 Author Report Share Posted November 16, 2016 ¤not running 12.33 ¤running at idle 12.60 ¤running with throttle 13.20 ¤running with lights 12.28 ¤running with lights and throttle 12.21 The belt is brand new and the tension is good. Any ideas? Quote Link to comment
Lockleaf Posted November 16, 2016 Report Share Posted November 16, 2016 That's definately not charging well. If it's internally regulated, take it off and have it tested on a bench tester at oreilly or auto zone or where ever. Sounds like regulator failure, as mentioned Quote Link to comment
Just_exploring Posted November 16, 2016 Author Report Share Posted November 16, 2016 I had it bench tested at oreilleys and it passed. Is there anyway to test the alternator on the truck while it's running? Quote Link to comment
Lockleaf Posted November 16, 2016 Report Share Posted November 16, 2016 Yeah, they can do that there too Quote Link to comment
Just_exploring Posted November 16, 2016 Author Report Share Posted November 16, 2016 I hooked the voltometer up to the alternator and it was At 13.20 I put the positive on the feed wire and the negative on the negative battery post. Quote Link to comment
banzai510(hainz) Posted November 16, 2016 Report Share Posted November 16, 2016 yes you can load test it by putting on your lights and take another reading. then add the heater another reading. If load down still at say 2k rpm and drops under 12.5 and lower I say alt is bad. key is when you ask O rileys to test you ask them t Load test it???????? IMPORTANT hopefully you bought a pump that's under 4 pound pressure Quote Link to comment
DanielC Posted November 16, 2016 Report Share Posted November 16, 2016 13.20 is a little low, especially considering you checked the voltage at the alternator. I like to see 13.5 to 14.5 at the battery. you lose voltage as current travels through a wire. The more current, the greater the voltage drop. So, if you are driving at night, headlights on, heater on, wipers on, 13.2 volts at the alternator could easily be too low to charge the battery fully. I am guessing on a cold Wyoming morning, you would like the battery fully charged. The general though on this forum is you are better off getting a used OEM Nissan alternator from a junkyard, than a rebuilt one from a chain auto parts store. 1 Quote Link to comment
Just_exploring Posted November 16, 2016 Author Report Share Posted November 16, 2016 The pump has a min pressure of 3 lbs and max of 5 lbs. I'm picking up a new alternator at oreillys tomorrow. The truck needs to run and drive so my fiance can get back and forth to work. Hopefully that will get it on the road until I can go hunting at the salvage yard or convert to a more reliable alt. Thank you all for your help and I'll let you know if the new alternator fixes it! Quote Link to comment
datzenmike Posted November 17, 2016 Report Share Posted November 17, 2016 If you have an original alternator save it!!! Have it rebuilt properly laterand you have a much better spare. Those $60 ones are... Quote Link to comment
banzai510(hainz) Posted November 17, 2016 Report Share Posted November 17, 2016 just a reminder make sure the batter cables are good clean and NOT Cracked. Quote Link to comment
Just_exploring Posted November 18, 2016 Author Report Share Posted November 18, 2016 Despite all the snow i was able to swap the alternator out. Everything is working properly now! 1 Quote Link to comment
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