Alternator going on/off - help with troubleshooting

[superbepro]

Hi,

I recently acquired a stock 1978 280z, which has run pretty good until the last two weeks, when it has started to give me some electrical issues. It always starts normally and everything electrical is good on start-up. BTW, I have a brand new Optima battery (2 months old) and replaced all grounding wires on battery-engine-body with new ones while replacing battery (also did the positive one).

Anyways, now with some more frequency (in the last 2 days) after driving some miles, the Alt light in the Voltmeter goes on, and I immediately loose power to all gauges (tach, voltmeter, fuel, temp), lights (if they were on) and stereo (aftermarket with small amp, all on new high quality wiring), but my secondary tach still stays on, and a moments later the engine quits altogether, or actually the engine never quits running and the Alt light goes off and the gauges, lights and stereo come back on, and then a few minutes or miles later I get the same problem. I originally though that there was too much of a draw from the stereo , but the issue remains the same with the stereo system turned off completely. I suspect that the problem is with the Alternator (original as far as I can tell), but after reading some posts form this forum, I guess the voltage regulator might also be involved.

Before I go ahead with replacing the alternator and voltage regulator, are there any things that you would strongly suggest to me to check/inspect before going ahead with these replacements? Any tips on which components to check with a voltage meter will be appreciated.

As of right now, I am going to go over all my electrical connections on the engine bay to clean, remove oxidation/corrosion and replace any faulty or dubious wiring, fuses and connectors. I am tempted to have the fuse block mod to replace the fusible links in the engine bay as an added measure for lesser problems down the road. Does anybody in this forum fabricate these fuse-blocks for 77-78 280z?

Thanks for your tips/suggestions --- Raul

[superbepro]

I should add that until today, I had these issue with the Alt light going on with loosing power to gauges and lights, and a moments later loosing engine power only once. Today this happened 6 times in a 60 mile trip, with only 2 of those incidents loosing engine power completely (going at 60-70 mph), 2 incidents where the Alt light turned on and lost power to gauges and then light went off and recovered gauges without engine going off, and for the last 20 miles I ran OK on the engine at 65 mph (no hiccups whatsoever) with Alt light on and all gauges off, until I slowed down to 10 mph in town and then lost engine power. I pulled over, turned off ignition, waited 1 minute, and then the car and all electrical stuff ran OK until I got home 4 miles ahead. As you can imagine, I am not driving the car on the road until I solve this issue.

Raul

PS. Six weeks ago I moved to a quasi-rural town (Uvalde) some 70 miles west of San Antonio, and just south of the famous Hill country in Texas, where the weather is just great now in spring and the land/hills covered in green leaves and great looking wildflowers. I tried to enjoy my planned 200-mile trip around this area, but had to come back home after 60 miles (30 out and 30 back) due to these electrical gremlins with the intermittent Alt light on and engine cut-offs.

Edited March 25, 2012 by superbepro

[Zed Head]

Before you get too far in to buying (or trying to buy) new parts, you should take a little time and download the 1978 FSM, and read the Engine Electrical section. Try to understand how the coil and ignition module can have power to keep supplying spark to the engine, while power to those other components is cut off. Check your circuits with a volt/ohm meter, if you have one. Read up on the charging system so that you don't spend too much time trying to buy an external voltage regulator (78 doesn't have one).

Those are odd symptoms. What does the voltmeter show before and after the problem occurs?

[240260280z]

Is your battery and new wiring secure?

Batteries can slide and short against the body.

Edited March 25, 2012 by Blue

[SteveJ]

How are your fusible links? Take them out and do continuity tests on them. Look for corrosion around the connectors.

Also inspect the wiring harness in the steering column where it connects to your ignition switch. Look for signs of heat damage/corrosion. Consider buying a small IR thermometer to check the temperature of components: ignition swith, ignition module, etc., to find sources of overheating components.

[superbepro]

Before you get too far in to buying (or trying to buy) new parts, you should take a little time and download the 1978 FSM, and read the Engine Electrical section...... Those are odd symptoms. What does the voltmeter show before and after the problem occurs?

Thanks for the reply. I downloaded the FSM and will read all of the Engine Electrical chapter. The voltmeter has pretty much always read around 15 volts (hard to tell on that scale it has, which has ticks every 4 volts). To be honest with you, I did not pay much attention to what it read when the Alt light goes on (but I believe it stays put at around 15V). All the other gauges turn off when the Alt light turns on, except my auxiliary Autometer tachometer and the mechanical speedometer). The stereo actually only turns off when the engine dies (and now I have kept it off when driving).

I just went outside and check the battery voltage, it is 13.30V with the engine off. I started the car, and it runs fine, with all its gauges looking fine. I measured 14.48-14.50 volts at the battery with the engine running, and the alternator I read 14.63-14.65 volts. With the stereo on the battery shows 14.43-14.44V, and the alternator remains the same (unchanged at 14.63-14.65 V).

By the way, the only time I have seen the voltmeter gauge needle to change is when using the hazard lights (swings between 13-15V with each blink) and I also see a small decrease in the voltmeter anytime I press the brakes (it drops about 0.5-1V from its customary 15V or so).

I must add that this morning's ride when I had this intermittent issue with the Alt light on and engine cutting off sometimes, the ambient relative humidity was high, and I was driving in a rolling hills road (but not that steep). I kind of have the feeling that I have some loose wires/connects in the engine bay. I'll read the FSM chapter and check-inspect-clean as much as I can in the engine bay area. Two weeks ago I drove 380 miles without any problems, at 65-70 mph, and the stereo on at moderate volume (mildly hot day, flat terrain, no hills).

I'll keep posting what i find. Thanks. Raul

Edited March 25, 2012 by superbepro

[superbepro]

Is your battery and new wiring secure?

Batteries can slide and short against the body.

Yep, battery is pretty secure, and I have brand new terminals (with proper cover on +side) , plus new thick battery cables (gauge 2 I believe), and new thick grounds on engine-to-chassis and batttery-to-chassis. Also, on the stereo install (Alpine, Infinity and Kicker stuff) I used new, good quality wiring and fuses as recommended by the headunit and amp manufacturer.

Edited March 25, 2012 by superbepro

[superbepro]

How are your fusible links? Take them out and do continuity tests on them. Look for corrosion around the connectors.

I will be inspecting the fusible links (Some time ago I bought replacements from Courtesy Nissan, as well as their plastic covers), and will inspect and clean as many engine harness connects as I can. I d have this nagging feeling that corrosion and loose connection are giving me this intermittent Alt light and engine cut-off issue.