Time to come out and admit retarded mistake

[osama1234]

Ok, so i connected the battery backwards. I'm justifying it on the fact that i dont have a hood strut, and have to hold the hood up with my back (i'm afraid of using a stick, that it may fall, the result of which would be a lot more painful than holding up a hood for an hour)

I hooked it up backwards, and noticed the smoke coming from the Junction Box near the battery and disconnected the battery (just so you know, i didn't turn the key at all)

So the ALT 1.25B fusable link melted, and the radio/cdplayer fuse blew. So i got a new fusable link and replaced it. Car started up fine, but the voltage with the car idling was 17 volts, and Emergency Brake, Battery and Brake lamp warning lights came on. I dont remember exactly, but giving it gas or some scenario turned those warning lights off. I didn’t give it much thought, I mean a car with some power is better than no power, and hell it even started, I called it a day.

Next morning battery is flat, so i figured the diodes blew in the alternator, which turned out to be the case. The alternator was shorted with only 4ohms thru it. So i took the alternator wire out, the current dropped from 4 amps to 0.025amps (both with the car turned off). So clearly alternator was fudged. Got a new alternator and installed it.

Now is when it gets more challenging for me. The car starts fine, it even goes fine. Its just that there seems to be times when the 3 warning lights (emergency brake, battery, and brake light blown) come on. It happens more often when idling, and giving it gas makes it go away (unless I have car lights on).

Also mostly (but not always) when brake depressed or brake+clutch depressed, the voltage drops to 12 volts, and if I don’t take action like clutch a couple of times or turn off the front+rear lights, it slowly keeps dropping. Turning off all the lights, or pressing the clutch a few times tends to bring the voltage back to 14. (I can turn the car-lights back on, and the warning lights stay off)

I’m quite baffled, I am guessing the ecu is has some short that occurs only under certain circumstances, but the thing is the car runs fine otherwise besides the warning lights + voltage drop which seems to be from alternator not charging battery (which my theory explains by a short in the ecu). I think it’s the ecu, as it’s the only thing that I think would have access to all these variables such as the clutch battery/brake/handbrake lights.


So the question is can the ecu be fried, even when the car seems to function fine otherwise (engine wise).

Thanks a ton for reading all that, and any help.

 

[BlackMKIII]

The EFI fuse should blow before the ECU gets fried. I've seen it happen before, though. Try and borrow someone elses ECU (Same year/trans/ortions if possible) and see what happens. Just try not to fry theirs, too.

 

[ms07s]

Here is one if you need one and don't fear ebay.....they range on there from $10-100.

http://cgi.ebay.com/ebaymotors/1986...017QQitemZ270198250144QQrdZ1QQsspagenameZWDVW

 

[MK3.0dudeman]

use two vice grips on each shrut and it will hold your hood up just fine

 

[mkIIIman089]

LOL, kind of funny this same thing happened to me... except it was not my end of the jumpers that got hooked backwards.

I blew the Alt fusible link also, just haven't had a chance to research anything past that with the holidays.

 

[Jostar]

get the battery checked, Autozone does that for free, i think the battery is going bad.

 

[jdub]

It's not the ECU

Check the wiring harness that connects on the back of the alternator..one of the wires goes to the dash combination meter (it's yellow w/ green stripe on an '89). Make sure you didn't fry it. Also check actual battery voltage with a multimeter when it drops like you described.

 

[cuel]

Wouldn't be surprised if the battery is shorted.

http://www.batteryfaq.org/ (link courtesy Jetjock)

 

[p5150]

since the alternator connects directly to the battery and the voltage regulator is built into the alternator, my bet is that you fried the v/r inside of the alt.

Change your alternator.

 

[KicknAsphlt]

I agree with changing the battery. It's most likely damaged and is drawing too much current from the alternator to fully power your system at lower engine speeds. When you stab the throttle, the alternator spins faster, providing more current to the whole system...so your lights go off. Think of it as similar to running an underdrive pulley setup. When the alternator turns slower, it doesn't produce enough current at lower engine speeds, so your battery doesn't get fully charged and your dash lights come on...but when you pull the RPMs up, it's able to provide the necessary current, and your dash lights go off.

 

[Justin727]

Got a new alternator and installed it..

he has a new Alt. btw for those that missed it.


check the wiring that goes to the engine bay fuse box. could have slightly fried those as well and one may be either burnt and because of it causing a loose connection

 

[pogoism9]

if hes got lights coming on, its probably a good idea to inspect all your grounds. I dont care how you slice it, your car is old, the wiring is not as tough as it used to be. Could have shorted as well. I used to have an 86 MR2 and had similar problems with dash lights coming on, I had a ground wire that was hanging on by a thread

 

[osama1234]

Thanks, i was waiting to look at the car before posting, but my flashlight burned out so i guess i will just give an update.
As many of you pointed out about the battery, i've replaced it another battery from another car and its still the same. I will be checking the wire from pin 2 of alternator to pin 20 of connector A1 in kicker panel junction box 3 to see if its continuous. (as jdub said). And after that the ground for the dash. I'm semi reluctant to take apart the dash, as its something i know i wont be able to put back together as aesthetically pleasingly as it right now.

A question about alternators in general tho, those three wires that come out of the back (IG,L,S) , are they supposed to provide 12 volts each when the car is running? I haven't been able to find info on that in any of the manuals i've been reading. And while at it does anybody know, why the 15A to engine connection from alternator is needed.
http://www.cygnusx1.net/supra/Library/TEWD/MK3/manual.aspx?S=Main&P=042

 

[wiseco7mgt]

Thanks, i was waiting to look at the car before posting, but my flashlight burned out so i guess i will just give an update.
http://www.cygnusx1.net/supra/Library/TEWD/MK3/manual.aspx?S=Main&P=042

did you put its batteries in the wrong way?:biglaugh:

 

[KicknAsphlt]

did you put its batteries in the wrong way?:biglaugh:

 

[IJ.]

did you put its batteries in the wrong way?:biglaugh:

LOLing here

 

[cuel]

Lol

I emailed Bill from the battery link I put up earlier, out of curiosity as to what would happen to the battery specifically in this case. He wrote this back:

"It is impossible to predict exactly what will happen every time a battery is connected or jumped with reverse polarity because depending what electrical devices were "on-line" at the time will produce different resistance; hence, a different current load is on the battery and every vehicle is different, as you well know. The health, State-of-Charge, performance and temperature of the battery are also contributing factors. But generally, fusible links, fuses or circuit breakers, design to protect the wiring and electrical/electronic accessories, can open ("blow"). The locations of these protection devices can be found in the vehicle's owners manual. Other damage can include, but not limited to, charging system (alternator or voltage regulator); emissions computer (and other electronics or computers due to voltage surges or spikes); bulbs; electrical wiring; or the battery. If electrical problems still exist after testing and replacing all of the open protection devices, I highly recommend having a good auto electric shop troubleshoot them.

In osama1234's case, the ECU would be the next thing I would test after the charging system was repaired or replaced.

All of my work is in in the public domain and can be freely quoted. Attribution is not required but greatly appreciated. The only references I have to batteries connected with reverse polarity is in last paragraph of Section 6 and in Section 14.4 in the Car and Deep Cycle Battery FAQ on http://www.batteryfaq.org/.

Kindest regards and Happy New Year,

BiLL....."

Oh yeah, you might want to check that flashlight as mentioned above

 

[jetjock]

Interesting thread. I'll refrain from comment (too stunned by the hood strut remark) other than to say the 15 amp IG line supplies power to the regulator for field excitation. S is the sense line and L is lamp. Normally all will have 12 volts when referenced to ground with the engine running.

 

[blackturbona]

i didnt reverse polarities on the battery, but one day my car was doing the exact same thing as u mentioned, osama, when u got ur new alternator did they happen immediatly or did they take a bit? i still havnt found the answer to my problem so i sadly cant give good input

 

[osama1234]

Ok, so i finally gave up on testing things on small hunches, and decided it was probably the alternator.
Turns out, the alternator people say it is the problem and the cause is 'delayed excitation', something to do with a (regulator?) chip.
Looking back it makes sense, i mean the car was telling me with warning lights the charging system was screwed, but i kept on wanting to find a leak in the car when under electrical load.

@blackturbona: If its happening constantly, its most definitely your alternator, if its periodic like mine... i guess it could still be the alternator.