Help me with BATTERY DRAIN (RB20DET)

[Cpt_Impossible]

So the car is a 1990 Nissan 240sx Coupe with an RB20 swap. I had a Nismo FPR in the car and messed with it without having a gauge on hand and blew the fuel pump fuse. Trying to start the car afterward while tuning the fpr with a gauge, I drained my Optima Yellow Top battery. Now, once I get the battery all charged up, I can start the car and it drives just fine. All the accessories work while the car is on, Stereo doesnt stall the car or anything. But when the car sits overnight, the battery drains. The most recent example is yesterday I turned the car off and battery tested 11.8 volts. Today at the same time, it tests a flat 10 Volts.

It will continue to decrease until it hits about 4.2 volts then it just sits there. I took out the relay for the fog lights and AC since those arent on the car anymore but that didnt help, I removed the fuses for power windows and the fog lights, but it still goes down. I tested the battery when the car was on and it tested 13.8 Volts so the Alternator seems to be charging it and after a drive the battery is near 12 again while off. All of the accessories work fine when the car is on so I think the alternator is working just fine.

I started testing what voltage the fuses under the hood were seing with the car off but the car is only at 10V right now. Of the fusebox on the passenger side (the one thats half relays half fuses) All of the fuses are getting the same 10v as the battery except the 10amp fuel pump and 10amp eng-control which are only seing 1.1v.

Any direction on what to check would be great.
Modified by Cpt_Impossible at 11:03 PM 8/3/2006

[180sxmonster]

check the alternator output.... when the car is on and see how much voltage the alternator is putting out.... maybe youll get somewhere with that.... if the battery is low and then charged up and is low agian... check the alternator to see by anychance that might be the problem....maybe the battery was being drained before the car was off and sitting.... check the alt...

[Cpt_Impossible]

Well, after driving the car around for like 15 mins and using the headlights and stereo and Efans and everything, the battery tests fine. Its only after sitting around that it starts going down.

*Also, while the car is on, it reads 13.8 rather than 11.8V like when it's off.
Modified by Cpt_Impossible at 9:37 PM 8/3/2006

[anumeric]

Take you car around for a drive for about 15 mins or so. Then park it and let it sit for about 30 - 40 mins. "This helps if you have a quick disconnect" Disconnect the negative battery cable from the post and hook up a amp-meter in series inbetween the negative battery cable and negative battery posts. So now current basically runs through the meter. Set the meter to DC amps and it should show you how much of a parasitic draw there is on your battery. Start removing the fuses one at a time until you find out what circuit or circuits is causing the draw. If you pulled all the fuses and the meter still shows a draw, look at the wiring diagram in the FSM and find and test the fusible links. Hopes this help to point you in the right direction.

Wei

[Cpt_Impossible]

OK, I'm getting two versions on this now. Some people are saying do it on the positive side, some on the negative side.. which is it?

I tried it on the positive side with the meter set to 2000m Wehn i pull the cable apart, the meter shoots up to 1 and stays there. Im assuming that means its over 2000m. So I started pulling the big fuses first. Pulled the 75amp alt fuse and it still shot up to one. Then I pulled the 30amp "anti skid cond fan" and tested it and when I pulled it away I got "0.00"

[Cpt_Impossible]

***Correction***

Oh and the tester is at 200m, NOT 2,000m

I retested the same thing on the positive and negative side, at 200m and it still jumps up to one, not zero with the 30a anti skid fuse out so it musta been a glitch with the meter. So I continued down the row.

-Pwindow (is gone)-Ret Mirror (no change)-Eng Control 25A (dropped down to 23m)
Modified by Cpt_Impossible at 10:18 PM 8/3/2006

[anumeric]

Hmmm, I have always done this on the negative side. I correct myself, set the meter to the 10A setting with the black lead to the COM port and the red lead to the 10ADC port. Try it again in this setting.

[Cpt_Impossible]

I edited the above post with a small update. Does this mean my ECU is not grounded properly?

[nism0240]

ive been having the same problem with my car lately. still trying to find the culprit. my battery drains about 3 volts every night......sigh

[anumeric]

Do you have the meter set to amps or volts? with the meter leads pluged into the correct ports? It should give you some sorta reading before you even pull any fuses if there is a draw on your battery. When you start pulling fuses leave them out, once you get to the right fuse you'll know, the reading should drop by a pretty good amount. If the meter is still giving you a reading of only 23mA it shouldn't be a problem since anything less than 50mA is considered ok, draw from stuff like clocks, alarms, etc. Then you battery maybe bad and not be holding a good charge. But Optima's going bad are pretty rare. But I have seen it happen. Someone correct me if I'm wrong.

[anumeric]

Forgot to add that the black lead needs to be already touching the post and the red lead already touching the cable. Even before you take off the cable from the post. Basically never opening the connection. The red lead is never to lose connection with the cable during the entire test, same goes for the black lead and battery post. Much easier with 2 people or with leads that have alligator clips. This will give you a accurate reading on how much draw is on batery with the car off. Sorry stuff is much easier to explain in person than with posts. lol Keep us informed so we can help find the source of the problem. I'm sure that having to recharge the battery everyday must sux.

[Cpt_Impossible]

Ya, I did the test correctly, I had already read up, just switched over from the pos to the neg to reflect your input.

So with all the fuses in, the meter set on DCA at 200m climbs rapidly and reads "1" and wont go any higher. When I take out the fuse marked "FL25A ENG CONT" and do the test, it climbs to 23m and stops. If I am correct, that is 0.023Amps and is right where it should be.

From what I have searched quickly, that fuse having problems could be the starter, alternator, or ECU or any wires connected to them which means a whole lot of searching tomorrow.

The battery has drained some from all my testing and turning things on, but right now it's at 8.36volts we will see what it is at when I get off work tomorrow if it continues to drop with the "25A eng cont" fuse out.

[Cpt_Impossible]

So, after retaping all the wiring on my ecu main harness, i found a couple holes on a grounding wire.

BUT..... when I tested the battery drain, I discovered that I was doing it all wrong. My multimeter does not have aligator clips, so I was pinching the probes in place and discovered that all I was really doing was measuring how great a ground I can make when I lean on the car. Once I found this out, I redid the test on each fuse at the battery.

The problem I found is that everytime I thought that I had found the fuse, if anything else changed, the test would show over 200m again! Even after I undid the change!

So here I am sitting with the only fuse in the box being the 75A alternator fuse, and Im still testing over 200m!

At this point I am getting really frustrated so any help would be great. My friend suggested I test the amps at each fuse terminal rather than at the battery so I did and what I found was that of the fuses on the passenger side next to the battery:

P/WIND (over 200m)ENG CONT (over 200m)IGN SW (over 200m)

EVERYTHING ELSE (<or = 0.03m)

I dont even have power windows and I dont get how the fuse is drawing over 200m when the car is off.

[tyrannix]

i bet a previous owner did a hackjob install on something (alarm, radio, whatever) and tapped the first wire they found. (my shell had the stock radio plug cut, taped and sitting, with home speaker wire going to the doors, andpos, gnd, acc all coming from the kickpanel fusebox... just wire stuffed in with the fuses

and did ou do the swap, previous owner, shop, or random person?

i would pull the dash and examine that harness

CJ

[Cpt_Impossible]

A shop did the swap. Alarm was done by cartoys and previous owner did the speakers and CD head unit.

The battery drain is a recent thing. I meesed with so much stuff trying to get the car to run after I messed up the fuel pressure.

So where I stand now is if I take out all of the fuses in the passenger side engine fuse box EXCEPT the alternator fuse, 4 fuses are drawing over 200m.

Eng ContPwr WindIgn SwAlarm inline fuse

Even with all four fuses out, all four of those terminal sets test over 200m (the limit of my multimeter)

[Cpt_Impossible]

K, I just tried unplugging the ECU and retesting those fuses and even with the ECU, unplugged from the harness, they all still show over 200m.

[Cpt_Impossible]

K, when I unplug one of the ECU relays, the eng control fuse goes back down to normal current draw. Also, when I unplug the smaller of the two harness plugs on the Seatbelt computer in the center console, the pwr window fuse acts normal.

[Cpt_Impossible]

This first pic is showing the relay that if disconnected will make the ENG Cont 25Amp fuse read normally.

This is showing all the fuses I have removed from the box and the battery is still showing over 200m of draw.

This third pic is of my wiring harness.

Something I find odd about my harness is that there are several thicker wires containing thinner wires that are wrapped in an unshielded wire. It just spins around them and then splits off by itself into the brown plug that seems to house all the ground wires. There are about three wires like this. Is that normal? I cannot tell where the unshielded wires begin because I dont want to cut too far back where they dissapear. I have no experience with ECU wiring but this seems odd to me.

[Cpt_Impossible]

Still plugging away with zero progress. Even with ALL of those fuses out as shown in the pic, the battery is being drained too much. The only one that I can take out that stops the drain is the 75 amp alternator fuse.

Does this mean that this is my culprit? I would think that since the alternator kinda powers everything that that doesnt narrow it down much.

[180sxmonster]

i think you just need a new battery .... sounds like you might just have a dead battery cell.... over time, battery do go out too.... they last roughly 4-5 years which is a really good battery.... cheap ones last 1-2 years...

you gotta start out with the basics... you cant just jump yourself into bigger mess... take your battery to a service center to get the battery tested....at least testing the battery first you know thats not the problem....

[Cpt_Impossible]

Ya I guess Ill give that a shot. It a 1.5 yr old Optima Yellow top. If its the battery Ima be really pissed cuz those are $175 and its just past the warranty point.

[anumeric]

if your pulling the fuse for the alternator and it stops the drain then that is def. the problem in my opinion. Check the ground and power connections going to the alt. and if that doesnt do anthing then it may very well be something internally bad with it. But it never hurts to have your battery tested either.

[Cpt_Impossible]

OK, so I did some more cleaning, found a grounding strap that wasnt attatched, cleaned and reattatched all the grounding straps on that side of the engine. Took off both single wires on the alternator and cleaned the connections. Took off the positive cable and cleaned up the connection on the starter. Some notes about the draw test though:

-The alternator fuse only cures the problem when all of the other problem fuses are pulled so I have to have the Alt 75A, the engine control 25A and the ign switch 30A pulled in order for the draw on the battery to go down.

I noticed that the thick black single wire going to the larger of the two terminals on the alternator had some scarring so I taped it up.

The main concern I have right now is I found two small wires in the alternator harness that are clipped and sticking out. One is tan, the other is black.

First pic is of all of the wires:

Second pic is of the two wires in question highlited.

Anyone know if these are anything important?

[Cpt_Impossible]

I tried disconnecting the main lead on the alternator and testing, and it is still drawing too much from the battery.

[180sxmonster]

removing the power to the alternator will only cause the charging system not to charge properly and is only going to drain the battery some more..... another thing that i have found was.... diconnect the negative terminal and put a test light between the battery post and the negative terminal... if the test light lights up, then you have a short....

[Darshand]

I actually had the SAME exact problem...on my John Deer Lawn mower :S. All I did was replace the battery and she was good as new x_X.

[Mez_DK]

hes gonna be pissed if its just his battery!

an example of this situation is the ipod battry, after so long of recharging the battery just lays down.

[oki_bum]

just for reference, what should the battery voltage be when the car is running? Mine says 12.8

[amolao]

Should be 13 volts or higher when charging, Cpt Impossible, you are doing the right things, let's check the facts: Is not the alternator and something is draining your battery. If there was no problems before the FPR, and assuming that there are no shorts (by taking most of the fuses out you are basically isolating anything like that...) maybe you want to try a new battery. Buy a cheap one year battery for now and have a battery charger available to continues the test. If you present battery have a bad cell is not going to charge or maintain the charge. Im not really sure if the tester is giving you the right diagnostics and I think you should keep it simple. Hopefully this helps, I feel your pain Bro....good luck

[Cpt_Impossible]

So I went back to the shop that did the swap to get my power steering lines and talked to him about it I guess from the symptoms its a bad alternator. Battery holds a charge fine as long as I disconect it at night.

Hes gonna get me a spare alternator here in a few days so it should be all good. He said the fact that my ecu light stays on is a good indicator that that is the problem.