Intermittent Battery Warning Light (new alternator, new battery)

[N155@N]

Hi SAU,

Been having issues with my R33 GT-R. Battery warning light comes on at random times. Recently (1.5 months ago) had new alternator fitted, and new battery fitted (2 months ago). Car is used once a week and is always hooked up to a trickle charger.                                

Between the time I had the new alternator fitted and today, car was running perfect, i.e no warning lights. Was at a stop light and decided to give it a 1st gear pull. What ensued was the battery warning light turning on and my tune getting messed up (AFRs reaching 15.9 with no throttle input, misfiring etc). Kept cruising for a bit, then decided to pullover and shut car off. Once I got going again warning light was gone, only for it to come back after a couple of hundred meters of driving. It should also be noted this is at night, with lights, and radio on only.

I noticed that the warning light would turn off if I revved the car up aggressively (5000rpm+), at a stand still. Once revs dropped, light comes back on. However revving it up whilst moving would do nothing. Also when driving on bumpy parts of road, light flicks on and off, something must be loose right? I checked on the front and rear fuse boxes and everything seems to be plugged in. The high beams also struggle. The right side high beam comes on immediately while the left one has a little stroke before fully turning on. Oh and battery terminals are on nice and tight.

Any ideas?

I don't run any gear that would have heavy battery draw, and I get the car worked on by a reputable mechanic. In saying that, would it be possible for the alternator or battery to be malfunctioning this early in their lifespans? The car has traveled roughly 1000km+ since the new alternator was installed, no issues at all during that time. I will say though, the battery voltage while driving has never exceeded 13 volts, usually 12.x (with this new alternator). I think 14.x+ is the norm. Before I got this new alternator the voltage reading was around 10 to 11. 

When I got home I hooked up the trickle charger and it took a while for the light to go green (charged/maintaining). Usually after a drive, short or long, the red light on the trickle charger only lasts for less than 10secs, sometimes it goes green straight away. But today it took considerably longer than usual to go green, indicating the battery was not charging(?). 

Any and all help appreciated guys and gals, will have a chat to mechanic on Monday, however I thought I'd see if I could get quick help and fix straight away.  

[89CAL]

Ypu need to check some voltages with the car running I would say. Sounds like battery is dropping voltage

Have you checked your earth straps?

The voltage drop will be affecting your injectors which is why you are seeing leaner AFR's. Ive seen the same thing with supply voltage issues to my ECU (ECU was seeing lower voltage then was actually being produced)

Check (with a multimeter) the battery voltage at the battery and at the front relay box in the engine bay with the car running and report back

[GTSBoy]

Likely have a broken wire.  Likely the main one from the back of the alternator, but could be almost anything.

[N155@N]

Alrighty, went for a drive (car driving like shit due to the aforementioned AFRs/lack of voltage supply to injectors) hooked up multi-meter at different points of time and got the following results:

 

Car off: 13v front fuse box and rear (battery)

Idle: [NO warning light] 14.38v front and 14.25v rear

First time hitting boost (~15mins of driving): [Warning light comes on] 12.28v front and 12.3v rear

~30mins of driving: [Warning light still on] 11.87v front and 11.84v rear

Car off: 12.24v front and 12.18v rear

 

So just like when I first encountered this problem, the light comes on when I give it a hit on the throttle for the first time on a drive. I always let the car warm up before I play around. I'm not the most mechanically minded individual but could it be possible that hitting boost is causing some sort of surge? As I continued driving, the light would flicker on/off when I would increase throttle position... sometimes. Other times, even if I reach 7000rpm the warning would remain. Is it normal for any car to have a higher voltage reading after a drive than during the drive?

 

8 hours ago, 89CAL said:

Have you checked your earth straps?

Are you referring to the grounds? If you are, I only know of one (next to front fuse box). This looked fine in terms of tightness and contact. No idea where the other grounds are lol.

 

8 hours ago, GTSBoy said:

Likely have a broken wire.  Likely the main one from the back of the alternator, but could be almost anything.

If this is the case then do you think my mechanic will fix it (for free)? After all they did do the work and said it was new. Anyway is it possible to access this wire without lifting the vehicle (don't have the tools)? I had a look today and all I can see is a plug that attaches to the side of the unit. Don't remember being able to reach the back, or maybe I didn't try hard enough lol?

Before the drive I did a thorough check to see if any fuse/terminal was loose, and well everything was tight and properly contacting. What else should I check?

Thanks again guys

[GTSBoy]

It's going to have to go to a (decent) mechanic.  It sounds like the voltage regulator in the alternator is not doing what it is supposed to be doing.  The initial behaviour you report is basically normal.  13V at the battery, rising to 14.something at idle because the alternator is charging.  But the alternator should not allow the battery to go flat as you drive it, so it is not working properly.

[89CAL]

It doesnt sound like its charging properly at all.

Remove the negative cable off the battery and the chassis. Clean the terminals, cable lugs and chassis point to remove any paint/dirt/corrosion etc.

Check the cables on your alternator. Clean the terminals and lugs as well, check for tightness and contact.

Also with your meter you can do some continuity checks to make sure that there is low resistance from the Alternator to ground and engine block to chassis ground.

There is definetly a charging issue here though.

[N155@N]

Hi guys, finally have been able to check car again today (been very busy). Went for a drive again, refrained from giving it any stick, no battery light no charging issue (20min drive with two 'car off then car on' situations). The moment I accelerate hard, guess what, light comes on.

Had a talk with my mechanic, says its definitely a wire that's loose somewhere since I'm able to cruise without issue, without boost of course. Recommended just wiggling appropriate wires till I find the culprit.

On 10/27/2018 at 7:03 PM, 89CAL said:

Remove the negative cable off the battery and the chassis

I've gone and done this, battery terminal seems scratched up, cable seems fine no rust at all. As for the negative cable to the chassis, is this the one below the front fuse box? If it is, it looks fine, but I'll be giving it a clean soon.

On 10/27/2018 at 7:03 PM, 89CAL said:

Also with your meter you can do some continuity checks to make sure that there is low resistance from the Alternator to ground and engine block to chassis ground

I'm rather inexperienced, where exactly is/are the chassis ground/s?

As for checking the alternator cables, is it simple as reaching through to the back of the unit and checking if anything is loose? The mechanic says it could be any cable from battery to alternator, to fuse box, to engine, etc. How would I be able to check any of these? I should've asked him, but I felt he was a little busy. Would I be able to check all these cables/wires just from the engine bay, or would I need to go through interior (rear shelf/seat area) or boot?

[KiwiRS4T]

You need an auto electrician but for free go to a place that sells batteries and just tell them that your battery keeps going flat - they will check your alternator out put and battery and if you are lucky may find a (the) fault.

And if it was the mechanic that fitted your alternator consider getting another mechanic if he couldn't be bothered to  check his work.