Rb20 wont charge.

[Gabes13]

I don’t like reading long posts, and Im sure others don’t also, so ill try to keep it simple. My rb wont charge
Background:
I did my swap (rb20 into s13) back in august ’10. It started up fine, but I had a little mishap when reinstalling the timing belt after the water pump swap. It has been garage kept, until this spring break (second week of march) where I was able to swap valve, miscellaneous gaskets and add arp head stud. Aside from the arp head studs, the motor is completely stock; side mount included. I referred to the fsm for all questions and triple checked my work.Motor started up fine and since then, I have put about 500 miles on the motor with no real problems.
Problem:
Tuesday, March 29, I try to start the car in the morning to go to class. I turn the key; car doesn’t start. The dome light worked, dash lights, worked, door/key chime et cetera, it just didn’t crank or start. I checked the voltage on the battery; 11.8v. I believe the fsm says the rb needs at least 12.5v to function. I wiggled my lower harness to see if something might have been loose sense the last time I worked on it; my alternator plug seemed loose. Thought that was why my battery voltage was so low. Plugged it in all the way tried again for the hell of it; nothing.
I pulled my bike out of the closet and took the battery to my closest Advanced Auto for a recharge. After the recharge I checked the voltage: 13.1v. Looked good. I plugged it up, turned the key, and the car started up fine; sounded better than ever actually. I checked the voltage again while the car was on: 12.5v I thought it was kind of weird so I raced the motor and the voltage began dropping ~0.01v veryyyy slowly. I thought my alternator was toast. Luckily I had my old single cam alternator with only a couple of hundred miles on it. Swapped alternators, turned the key, car started up fine, but didn’t sound as good as before. I checked the voltage while the car was on: 12.3v. Im going crazy now, double checking all the wires and plugs, no difference. I drive the car over to my nearest Advanced Auto to REcheck the battery. They hook up some multimeter on the battery, I start up the car. It barely turns on. Voltage is now at 12.2v but their multimeter showed the battery was making 500 amps; he thinks the battery is fine, and my alternator is toast. 2 alternators in one day? I thought it was kind of weird, so I had them bench test my old rb alternator. To my surprise, the test showed the alternator was GOOD! So now I’m really scratching my head. The test also gave a couple of suggestions of what else to look for. They were all lame, “check belt, tension, tensioner, et cetera” except for one, #1, check the circuit/battery light indicator.
The sales person that was helping me with my car said that some cars have a fuse link that connects the alternator to the check light on the dash, and if that’s blown, you’ll have an open circuit; ergo preventing you alternator from working.
What I’ve done/suspect:
Lower harness-
I checked the fuses in the engine bay, all looked fine. I also checked the voltage at the alternator post (marked “BAT.” On the alternator casing); emitted same voltage as battery, the ground wire is grounded onto the alternator by a screw (marked “E” on the alternator casing), so I don’t think my lower harness is bad. I haven’t checked the continuity on the actual alternator plugs, but will when the weather clears.
I do have a live wire coming from the fuse box. I couldn’t remember where it went since the chassis was motor less for a while between swaps. Right now it’s taped up, connected to nothing. When the weather clears, I’ll deloom the lower harness and really see what wires lead to what. Hopefully my problem is just a missing/misplaced wire.
Battery-
The battery is brand new. It has a “10/10” sticker on it and I bought about 2 weeks ago. Unfortunately, it’s a smaller battery from Advanced Auto. Crank amps are 500 and 370; I can’t remember the temp on each, but Ill look when I get back home. Reserve Capacity is 45 (I think). I think this battery may be way too small for the rb/240sx and could be draining more power than it can produce. I really don’t know much about car batteries, but I’m doing some research. The tech at the parts store swears it’s not the battery.
Fuse/Relay/ecm-
I’m not sure if there is a fuse behind the dash that is connected to the alternator, but Im going to look through chassis schematics to try to find out if I possibly have a broken circuit. Im also not sure if the ecu controls the alternator in any way, if so, possible fried ecu? Idk, I have to look up the pin outs again to make sure.
Any other help or suggestions would be greatly appreciated. I thought it was weird that I went 500 miles on this battery, and now it’s barely staying alive for 15 miles.Thanks.

[l0nestar]

Did you check the main 'Alt' fuse in the block in the bay (LHS)? It's a large fuse - 60 or 70A. I believe it is Green in colour on my DE. Also look inside your main plug to your alternator - make sure it's not corroded or gunked up. Make sure you have continuity in & out of your alt plug.

Check your surfaces for grounding and use star-washers on all bolts related to grounding.

[Gabes13]

Thanks for the reply lonestar. I did check the 75amp alt fuse; that was actually my first guess. I've blown it twice in the past by "grounding" a wire i thought was a "ground" (the same wire mentioned in my op actually) so it didn't look blown when I first checked, but I'll double check this afternoon.

But these star washers you mentioned, what are their significance? I think I've seen them before but didn't think anything of them.

[l0nestar]

When tightening star washers, they actually 'bite' into the surfaces. greater surface area for electron flow.
You will notice all of your 'important' connections use them (like your + and - lugs for your starter). I use them on all of my grounds. There are three main types - Internal, External, and Combination. Here is a pic of an external:


Here's a basic description from Wikipedia:

A toothed lock washer, also known as a serrated washer or star washer, has serrations that extend radially inward and/or outward to bite into the bearing surface. This type of washer is effective as a lock washer when used with a soft substrate, such as aluminum or plastic. There are four types: internal, external, combination, and countersunk. The internal style have the serrations along the inner diameter of the washer, which makes them more aesthetically pleasing. The external style have the serrations around the outer diameter, which provides better holding power, because of the greater surface area. The combination style has serrations about both diameters, for maximum holding power. The countersunk style is designed to be used with flat-head screws.

Apparently there is a fourth type..

[Gabes13]

Update: I got it working again it was just a ground :/ My explanation will just be for reference.


Yesterday, I was able to trade out my tiny battery for a larger one for no extra charge. This new battery has 700 cca @ 0 degrees f, 875 ca @ 32 degrees f, and a 130 reserve capacity. I turns over better, but still no charging.

I took out the lower harness to see where wires are going and with what signals. I noticed some random splices from the previous owner that will need some attention. I’m using my old ka harness, if I haven’t mentioned already.

This is the connector on the lower harness that connects to the fuse box by the battery tray.



It consists of 2 wires, one really thick white wire and one thick black wire. When I pulled the harness out today, I had the white wire on the alternator post labeled “BAT.”, it read 12.2v on and off the alternator post (same voltage as my battery currently).
If the white wire is indeed the power, then I believe this black wire is a ground.


White wire (power source)


Before I pulled the harness, I had this black wire connected to the alternator casing labeled “E”, which I believe is for engine ground. Before I pulled this wire, it had a voltage of -0.00v on the alternator and 0.06v off. I also noticed 2 splices on this wire from the previous owner; one close to the alternator spade (shown in blue in the picture), and the other further down the wire (looked like a ground for the neutral switch sensor; I didn’t deloom that far on the harness but will later for curiosity).

This is the alternator plug that connects directly onto the alternator.



It consists of one thick white wire and a thin white/red wire. The “white" wire is a power wire and the “white/red” is the signal wire for the dash. The "white" wire connects to another fuse box plug;That plug also holds a wire for the starter signal plug:



I noticed that the white/red wire had some random splice in it from the previous owner:



The "white/red" wire connects to another fuse box plug that also holds a wire for the "neutral switch" sensor on the transmission.

This is the alternator plug on the fuse box side; it has 2 wires, one really thick white wire, and one thick black wire (just like on the lower harness).



The white wire feeds somewhere into the chassis. I believe this is a power wire for the compatible alternator plug, and if that’s the power wire, then that should make the black wire a ground.

This is the black wire that connects to the fuse box connector.



This wire had a voltage of 0.06v. This was also the same wire that blew my 75amp alternator fuse twice back in august ’10 when I completed my swap. The voltage on this wire then was 12.5v (now it’s 0.06). When I pulled my original rb alternator the ground wire ("E" on alternator casing) and power wire ("BAT" on alternator casing) were both connected to the power post... doh, ergo charging my ground wire on the fuse box harness and blowing 75amp fuse whenever i tried to ground it.

I just put the really thick white power wire on the alternator post, ground lower harness on the alternator casing, and the ground on the fuse box side on the intake manifold, voila, charging. I just need to have my battery recharged, clean and tape up the harness and I should be good to go. Silly mistake, but whatev; you live and you learn.

[Gabes13]

My problem has come back. After I found out it was a ground, I took the battery to the parts store to be recharged, because the voltage reading was 12.2v. When I got it back the voltage was 12.3v. I thought it was a little low, but thought it was just my multimeter. Anyways, the car cranked fine and I drove it 25 miles to school. After school, it turned over a little iffy, but ran. I drove it 40 miles to a families house where it stayed for one day. The next day, today, the car turns over like crap. I would turn the key and nothing would happen for about a second or two and then the motor would crank over vveeerrryyy slowly. I drove it for 45 minutes, get home, park it, turn it off and try to turn it over again for giggles, nothing. Voltage is at 11.6v. I don't get it.

I'm thinking something is up with the battery this time. The older tinier battery I had was at 13.5v after I got it charged, this one was barely 12.4v after the charge. The sticker date on the battery reads 1/11.

Today I continued to removing some audio and viper alarm wiring I started removing from the swap. I thought maybe I had a short or some powersytic drain from those appliances. No fuses are blown, i'll go over my grounds again, I already put some star washes like lonestar mentioned.

extra: When the cars on, it stays on. It didn't sound well but it showed no signs of dying when on or waiting at stop lights. Idk if this is proof of a good/bad battery/alternator.

Also, When I turn the key to off, the car stays on for a second or two before actually cutting off. I don't remember it being like this when I completed my swap, and I only took notice before my first battery died. Idk if that is related to the charging problem, because when I threw my older 13.5v battery on after the alternator swap, the car turned on and off smoothly.

[Krazykouki]

Time for a new alternator.

[Gabes13]

The alternator only has a couple hundred miles on it, but I'm going to throw on the old rb alternator that tested "good" and see if that makes a difference.

I worked on the car a little this morning. The voltage was at 11.5v, just like it was last night when I finished diagnosing, so I don't think there's a drain. I looked in the cells of the battery. They looked a little low, but not drained, so I topped them off with some red wine. I then hooked up my some jumper cables to a car that had about 12.5v off and 13.9v on. my battery voltage went up to 12.8v. Car started up fine, but the voltage dropped to 12.2 when I turned the car on and sustained there. I turned on all the power accessories (head lights, high beams, a/c, defroster, dome lights etc.) and the battery voltage sustained at 11.8v. when I turned off all the accessories, the voltage went to 12.1v and slowly rose to 12.2v and sustained. When I turn off the car, the voltage drops to 11.8v, and won't turn on, just like yesterday.

Does this just mean the alternator is too small and cannot sustain or produce enough power the motor demands?

extra: Potential short; When I got the car up and running a couple of days ago, I sometimes noticed a hesitation at partial throttle. It reminded me of my tps problems that I had on my ka. I checked the rb tps yesterday and adjusted it to 0.46v but I could not get any continuity out of the plug.

Does this mean there is a short in the tps, and if so, could this cause a charging problem like mine?

[Yellow4g63]

I had a problem like that when I did my 1st RB20 install into a S13. I did something wrong with the wiring and the alternator was not shutting off after I turned the car off. It would just stay on and burn out and stop charging. I got lucky and had the shop that was rebuilding my alternator find the problem. After it was all fixed the voltage went back up till the fans came on lol.

[Gabes13]

hey yellow, do you remember where the bug was, eg. upper, lower, chassis harness etc?

[Yellow4g63]

I think it was something to do with the lower harness, it's been years so I don't remember that well.

[Gabes13]

Alright, so I had some time to work on the car today and I found out I definitely had a parasitic drain. When I checked th voltage on the battery (connected) it was at about 5.5v and slowly dropping about 0.01v every 30 seconds. When I disconnected the battery, the voltage would climb up to about 7.5v; a whole 2 volts more than connected. I found this interesting because my car would run at about 12.2v with the drain, so 2 extra volts would put me at about 14.2v-ish, which sounds legit.

I thought it was the alarm system or audio system, so I started pulling those fuses first; nothing. I pulled all the engine bay fuses; nothing. I started pulling the cabin fuses; nothing. I got to a 10a fuse, labeled "Room Lamp" and when I pulled it, my battery voltage started to climb back up to 7.5v.

I'm on my way to get this battery recharged and see if my alternator does it's job, but I have a question:

What is this "Room Lamp" Fuse? I thought it was the dome light, but my battery is way too low to work any accessories.

[Gabes13]

I poked around some wires this morning and continued to remove the alarm system components to clean up the rats nest. The battery voltage now reads 12.75v connected and disconnected.

On this plug, the white wire receives 12.75v, on or off. The black is a ground, and receives -0.00v on and off.

This white wire comes from the previous connector and also receives 12.75v on or off. I checked this voltage in the middle of the wire, at tip of the wire before the spade connector, and the spade connector and at the alternator post, still 12.75v on or off.

I also checked the the voltage on the white/red wire on the alternator plug, and when the car is running, the wire is emitting 12.75v.

extra: Just for curiosity i placed the positive node of my multimeter on the alternator casing, and and the negative node on negative battery terminal, and with the car on and running, the reading was -1.5 ish. Does this mean I have a bad ground or the alternator is not grounded?

After a couple of start ups with the car, the voltage on the battery dropped to 12.5v. I turned the car on and let it idle. While the car was idling, the voltage on the battery started to rise about 0.01v every 3-5 seconds. It got to 12.85v and just chilled there for a while creeping 0.01 very very slowly. Does this also mean I don't have a/enough grounds?

The alternator is receiving power, but I don't know if it's turning on. I heard you could check by placing a screw driver on the back of the alternator casing and see if it sticks like a magnet. I did that with every piece of metal I had and nothing would stick. Does this really mean the alternator is not turning on?

I don't think my problem is rb related anymore, but rather chassis wiring. I was wondering if a mod could move my thread to 240 tech or gen chat.

[Gabes13]

Alright, I have 13.99v now with the fans off. I was thinking that my motor had poor/little/no grounds, so I hooked up a 24in 4 gauge starter switch wire I bought 2 years ago but never used because it was too short. I bolted one end to the intake manifold and the other to the negative terminal on the battery. Turned the key, motor started up super smoothly, and bam, 13.99v on the battery.

I have to clean up the wiring mess I made now, but hopefully it will stay this way without problems.

[Jermaine7430]

For future note if your problem was fixed, a quick test of the alternator is to remove the battery cable while the car is running, if it shuts off its usually a blown fuse, if not that check the wiring, if that checks out you need an alternator. This will only work for 12v systems though because 24v systems have a alternator relay that only kicks on when there is enough battery voltage.

[Gabes13]

Thanks for the tip, but when researching my problem I came across multiple sources that said that was a good way to toast your alternator. When disconnecting the battery with the car on, multiple electrical components, including the alternator, are subjected to voltage spikes. Idk if that is true but I've read it many times.

The car is still charging and running fine so far. I'll be adding more grounds this weekend though.