Shadowx775

So I've had a hell of a time trying to figure out whats wrong with my electrical system on my 93 Rx7 FD.

The first thing that happened was my passenger window stopped working. I figured since it wasnt budging at all, that it was the motor or regulator. So I tried to replace it. But the window was all the way down, and if anyone has had to take that out before when its all the way down, you'll know my sadness. Anyways, I found a junked rx7 and replaced it, was in good condition. But it still didn't work, yet when connected to driver side, it worked just fine. So I figured it was either something wrong with the switch, or wiring. So I used a volt probe and tested the wires and switch, and both sides were getting voltage when going up and down on the window switch. So then I was stumped. But around that time, I went to turn the car on, and the car wouldn't start. The battery was pretty much dead. So I bought a new battery, and the window was working. So I put everything back together, and drove home, and noticed the headlights were dim. When I got there, I tested the window again, and it went down, but stopped working again. I then sat there for 20-30 min to give the battery time to charge. The window then went up just fine.

So my question is what is wrong? Could it be there is a short, or a crossed wire, or something causing it to lose voltage when powered off?

Thanks!

ploplen

Are you losing voltage during standstill? Then something is draining the battery. Are all lights of when you leave the car? (Including the light in the trunk)

or

Are you losing voltage while driving? Then I would suspect the alternator.

CrimsonPride

iTrader: (11)

To see if you are draining the battery when the car is off you can remove the negative terminal from the battery and the slowly reconnect it and see how big a spark jumps between the post and the terminal. Usually none or either only a very small spark will jump because of clocks, etc. pulling a small load. If there is a bigger spark something in the electrical is pulling the battery down. If this seems inconclusive, you could set up an ammeter between the negative terminal and the post to see how much current it draws with the car off.

If above seems ok you could run a check on the alternator output. Most parts stores can do this with the alternator still on the car.

ploplen

Can measure the voltage across the battery and see if it increase to 15-16 V when revving the engine to 2000-3000rpm, Otherwise the alternator (or maybe it's wiring) is bad.

Close the doors when checking for draining, otherwise the lamp at the ignition will illuminate. (And maybe something else, know my car drains 0.1A if the door is open)

moconnor

iTrader: (14)

Have you gone through the diagnostic procedures in the Body Electrical Troubleshooting manual? It is in the stickies.

CrimsonPride

iTrader: (11)

Never tried this. Is this a good enough check? When it is checked on the car I think the checker unit draws a lot of current and sees if the alternator can keep up. What does your suggestion check/not check, if I can understand this I might want to use this test in the future when need arises.

ploplen

To charge a battery you need to apply a voltage that is higher than the battery voltage. If the alternator can not produce a higher voltage, it can not charge the battery. The voltage produced by the alternator is speed dependent so you need to rev the engine. If you want to know that it can deliver current also, just turn on the radio, fans, ac, rear window defroster, wipers, etc.

But I think, if the alternator brakes, it brakes good. For example when my broke both some diods were fried and a winding was broken, then it can deliver neither voltage or current. I don't see how it could brake so that it delivers voltage but not current.

Shadowx775

I'll try out some of these tips this weekend when I have some time, and will let you all know the results of what I find. I like the terminal arc idea for when its not on, but if I do get a big spark, how do I go about figuring out whats draining it, other than the obvious lights and stuff? I also like the volt test of revving the engine to see if the alternator is working. But what is the range of a bad alternator? If its 15-16v its good, but does that mean if its 14v, I should replace it?

I also went to the auto hobby shop today, and asked a mechanic there for advice, and he said that the next time it wont start, I should pull the fuel line out and crank it, and check for fuel coming out, and if it doesn't then there is a problem with the fuel pump. Anyone validate that? And would that have an effect on the electrical devices?

Shadowx775

Nice timing on that post ploplen lol

ploplen

Lets see if the timing is different this time...

According to the workshop manual the output should be 14.1-14.7 V during idle.
So when revving it should be some volts higher, 16-17.

If something is draining the battery I would start pulling fuses and then reconnect them one at the time while checking if the draining reappears. That way I would know over which fuse the draining is. Next thing to do depends on which circuit that is draining the battery.

linnadawg

iTrader: (14)

I dont know where you get 16-17 volts from? If youve ever charged a 12v battery and charged it higher then 15 volts it has the possibility to explode. You see slight changes in alternator output no matter where the gas pedal is. When your idling the voltage should be 13.5-14.5v . With the car off the battery should be about 12.5v. If you hold the voltmeter on the battery and the numbers steadily drop look for a glove box light on or something of that nature. If you have a key off drain and cannot find it slowly pull one fuse out at a time until the steady drop goes away. Then you know what circuit is being effected. Get your battery tested before you waste your time with anything else.

linnadawg

iTrader: (14)

Reading through this makes me want to pull my hair out. You do not have a fuel pump problem it is electrical. Test your battery first. Then test the alternator. Check your battery cables. Make sure you have proper grounds. No corrosion on terminals. Make sure the connections are tight. Do the key off drain test if necessary. If your battery is no good it will steadily drop as well with the key out so make sure it is good before you start.

ploplen

lol, Thought battery voltage + 2-3 V, but battery voltage is not 14V

ploplen

Well, not according to the workshop manual, 14.1-14.7V

linnadawg

iTrader: (14)

Battery voltage with the alternator running is around 14 volts. Stop trying to argue with someone who is ase certified in electrical. Your arguing off a basic misunderstanding and uneducated speculation. Hook up a voltmeter to your battery and rev your engine and let me know what you find!

ploplen

oooh, the one and only educated person! How could I ever have argued with you...

Hell linnadawg!

Shadowx775

Not to be mean, because I really appreciate you giving me tips, but if you're going to say you're educated, it's a bit hypocritical when you misspell "Hail"

ANYWAYS, back to topic, I may have found a problem. I was checking my battery and looking for anything wrong with it, and found a wire hiding behind it, just chillin'... I think its probably the grounding wire for the positive terminal? Am I right or talking out my ***?

Here's a picture for a visual.

linnadawg

iTrader: (14)

It says in your sig that youre not a good mechanic. If your not sure what your talking about its better to just not give the advice. You could make someone start spending all kinds of unnecessary money and become even more frustrated their car isnt fixed.

Anyways that red wire is probably for an audio system that was in the car or an alarm. Look for an accessory in the car that is not working any longer if your concerned about it. It is not stock incase you were wondering.

Shadowx775

So to test what it is, connect to positive on battery and see what happens? Always like making sure when it comes to connecting things to the battery...

linnadawg

iTrader: (14)

I would try to follow the wire and see where it goes. If its been ripped out and left dangling it could be touching a ground and short when u connect it. Never know though

mike_merryguy

iTrader: (8)

sounds like a weak alt to me, if you are driving and the lights are dim and you have a new battery, when you stopped the window went down but not up then waited 20 min and the window went up...

if the alt is WEAK but not dead it may be hard to find out, you should remove it and have it tested, I know that autozone and kragen will do that for free but i don' tknow what shops in OKI will, maybe the hobby shop has alt tester...

also make sure the switch on the DS door is in the ON pos, if its OFF the window won't work, it requires power from DS to work b/c the main switch is over there... just like the power lock on the PS side runs off the DS door...

its wierd but that the way it works, also my PS window switch works when it wants to sure there could be the same prob with the DS switch if thats the one you are using...

Shadowx775

I like the sound of a weak alt... Sounds right, I just didnt know they got "weak" I thought they just up and died... Either way, I'll get it looked at, and if it is broke, just found a rx7 identical to mine that I can take parts from ^.^

mike_merryguy

iTrader: (8)

well its basically dead just providing enough juice to barley keep a charge not enough to run the car with lights and stuff on, I had an FD alt in my FC long ago and it worked for months but the lights were dim and the brake lights made them dimmer and then when I supercharged the car I had the alt tested and it was pushing like 12.1 volts LOL