Let me start off by saying I've searched what seems like every conceivable thread on this topic and I'm stumped.

Background Info:

87' Turbo II.
6 Month Old Battery.
Tested Working Bosch Alternator.

The Problem:

The battery is now draining overnight. I have suspicion that the battery isn't big enough for the 7, but I've checked the AC Delco website (I know, and I plan on putting a Red Top in it in the spring), and it say's that it should be just fine. The battery is a 35-5YR.

My troubleshooting has basically led to me cleaning up numerous grounds. The only one that I can think of is the starter ground that's left because it's a chore to get under the car and I haven't had that kind of spare time lately. I changed a cracked battery terminal, so now they're both fine. No fuses are blown, umm, that's about it.

The battery basically charges according to my revs. Idle (800), it sits about 11.7, (1100) is about 12.2, and normal driving it's 13.5. The second that I slow down, press the brakes, turn even the rear defrost on, it lowers. It's gone to the point now that I can't even start in the morning.

Any help/ advice is GREATLY appreciated. Thanks.

 

Is the alternator an S4 or S5? Secondly, your alternator might not be charging the battery as opposed to an electrical circuit draining the battery.

To check for amperage drain disconnect the negative battery cable. Turn the multimeter to the highest amperage setting, which is likely 10 amps. Place the Black meter lead to the negative battery post and the Red meter lead to the negative battery cable/clamp and tell us what you get. This test is done with all accessories off, doors closed and no key in the ignition.

 

It's the S4 Alternator (To my knowledge). I plan on upgrading to the FD alt. and putting a double sheave pulley on it, just for peace of mind, even though it is overkill.

So, I attempted to check the amp. drain. I'm decent with electrical, and know the gist of what's going on. I wasn't getting any readings other than the battery's voltage. I've uploaded a picture of the multimeter I am using and I think it's the reason why there's no reading. The DCA's section only goes up to 200Ma, and not 10A. Anyways, the reading I got was for DCV and it was 12.7.

Thanks for the quick response by the way.

 

What aftermarket things do you have installed in your 7? Aftermarket alarms, even when not engaged, are notorious for sucking up battery. Anything that has a constant "hot" connection would be a power leach suspect. If you have more aftermarket units (SAFC, sterio head unit, amps, HID lights, CD changer, etc), you have a growing army of potential leach's.

 

That's the thing, I don't have THAT many. Keep in mind I'm just spitballing so some of the suggestions might be a little ridiculous. Currently;

Potential Suspects:

- Turbo Timer.
- EBC? It's not even installed correctly (previous owner), so maybe the hack-job wiring could be the culprit.
- Fuel Cut Switch (Maybe not grounded?)
- Cobra Radar Detector. (Wired to Ignition)

Note:

- No Stereo.
- No Aftermarket Alarm (The stock one has a mind of it's own hah).

 

Your battery is the victim, killed by the alternator.
You should be seeing a steady 14.x V from idle on, regardless of the accessories.
Either the FD 100A or the more powerful Taurus alt should solve the problem immediately.

 

Edit; So, a new Battery and Alternator would be required? Sorry, just making sure.

 

Looks like the meter you have does not have a amps feature.

If none of the advice above works try this to see what is causing the problem. At the end of the day remove the output cable from the alternator. Reinstall it the next morning and see if the car starts or not. IF it starts I think that shows the alt was the problem (blown diode in the alt regulator...cause). Replace the alt or make sure the wiring to it is per the wiring diagram.

Batt still dead? Try at the end of the day removing the BTN fuse in the engine bay. Reinstall the BTN the next morning and if the car starts fine then the problem lies in one of the fuses on the BATTERY buss in the interior. One of those fuse would be feeding something all night long when it should not.'

Make SURE the key is in LOCK when you pull it out at the end of the day. Not in ACC.

 

You could also use a test light to tell if you have a battery drain. Ultimately, an ammeter would be the best option, but your multimeter only goes up to 200mA, which happens to be the max spec for battery drain. If you use a test light between the negative terminal and cable, you can see if pulling the fuses one by one will cause the light to go out. Once you find the one that makes the light go out, put it aside and install the OTHER fuses one by one. Do this in case you have 2 or more shorts. Once you find the culprit fuse, check wiring diagrams and see what's on that circuit.

More than likely, though, your alternator is weak sauce (as are all S4 alternators) and your battery has gone into overtime to try and make up for the lack of power at idle. Continual discharge and subsequent recharging of car batteries is bad... mmmkay.

 

Ok, so it's looking like I'll do some testing. The first thing I'll do is the BTN fuse, then the Alternator Cable. It's the green plug right (going off of memory)? If this fails, I'll have to invest in a test light and go that route.

In the end, the solution is looking more and more like the FD alternator. There's a guy locally that has every 13b part known to man x10, so I'm sure he can help me out with sourcing that piece. Nothing like an RX7 to swallow my spending money, but somehow I seem to love it more and more even after the countless hours under that hood. None of my friends seem to understand it, but that's because they don't have one!

I'll keep you guys posted on the results. Many thanks!

, Simon

 

What do you mean by "Green plug."

 

wouldn't putting a test light on to test for battery drain(instead of a meter) be counter productive?..as the light would need power to light up and drain what it needs to glow?.so it would light up anyways,.

 

I meant the terminal that plugs in at the back of the alternator. I just faintly had thoughts it had a green cover hah. My mistake.

 

The output wire from the alternator is the single Black wire bolted to the alternator thus no plug involved there.

 

The two wires coming from the "plug in the back" of the alternator is the "energizer" wire and the wire that talks to your idiot lights.

 

Think for a second. If there was no current flowing to a parasitic drain, the light wouldn't come on.

 

Ok, good that everything's cleared up. I'll get cracking on it tomorrow and post up the results.

 

Easy way to Clear up a power drain is to get a volt meter Hook it to the battery have someone watch the meter, While you Unplug each circuit (fuse) . when the meter ticks up then that is the most likely the circuit that is taking the power, I dont like to get into electrical problems. But i have done that in the past and it worked fo me, Just my two cents