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jdm>usdm
05-14-2012, 03:48 PM
Whats up guys. I'm having a hell of a time with this. Hoping someone can provide some helpful info.

The car is a 1990 240 hatch with a SR.

I went to start my car and saw my turbo timer was reading around 11.7V immediately after start up. I had to rev to around 3k rpm before the volts rose at all, and then it read about 13.6-13.7V or so (and yes, I am positive the belt was not slipping). It would normally run around 14.3V at idle, so I thought the drop in voltage was weird. I began to drive it and a little after half an hour of driving I observed the volts steadily dropping, all the way down to the high 11's. By that point, the fuel pump wasn't getting sufficient power and the car was starting to stumble from lack of fuel. I had to pull off the side of the road and my car was pretty much dead.

After getting the car back to my house the next day, I pulled off the old alternator and had it tested. It failed across the boards, so I put on a new one. After installation of the new one, I'm having to rev the engine, once again, to around 3k rpm before the alternator seems to do any recharging. Only then does it read around 13.6-13.7V, just like the old one!

I'm afraid if I drive it like this, it will kill the alternator, which is what I believed happened to the old one. What would cause the alternator to not output the proper voltage? I had the new one tested, and it was outputting around 14.5V, so I know I should be seeing somewhere around that.


Cliff Notes:

-Old alternator died
-New one was put on, outputting less voltage than it should
-Old alternator output same amount of voltage as the new one shortly before it died.


Could there be something completely unrelated to the alternator that could be pulling power while it's running? I still have the stock wiring supporting a walbro 255 pump. Would a solution be to rewire the pump?

Help would be greatly appreciated.

JDMRIDDAZ
05-14-2012, 03:52 PM
Are all fuses good?
Also is ground on alt good
I would check voltage output at alt to see if its good then backtrack from there

jdm>usdm
05-14-2012, 05:15 PM
Are all fuses good?
Also is ground on alt good
I would check voltage output at alt to see if its good then backtrack from there

The 75 A fuse is good. The ground is also good.

I just discovered that when I remove the plug from the back of the alternator, the volts jump up around 14.5V, where they should be. As soon as I plug it back in, they drop to 13.6V. So something must be going wrong where that wire from the plug joins back into the other wire that runs to the battery.

fliprayzin240sx
05-14-2012, 05:22 PM
Is it a new alternator or another used one? Get it tested...

Nikeboy355
05-14-2012, 05:27 PM
Or maybe the plug to the alternator is bad... These old cars have corroded connectors over time...

MrChow
05-14-2012, 07:55 PM
Look up the big 3 and get it done. Also have you actually let the battery charger up? Not a small 10 min drive.

Wookie384
05-14-2012, 08:42 PM
If I remember correctly alternators don't charge at idle, it will charge after it passes a certain RPM. I would however check the battery, maybe it's on it's way out (Ex: wasn't capable of holding a charge, etc...) and that killed the alternator?

Taylor008
05-15-2012, 12:19 AM
You could have a big short sucking all your juice. Make sure your wheel didn't rub through the harness under your fender.

jdm>usdm
05-15-2012, 10:50 AM
Is it a new alternator or another used one? Get it tested...

It was a re-manufactured one for a dohc ka. I actually already had it tested and everything looked perfect.

Or maybe the plug to the alternator is bad... These old cars have corroded connectors over time...

Ill take a closer look inside the plug. If it looks bad, I'll just snip the plug and resort to blade connectors.

Look up the big 3 and get it done. Also have you actually let the battery charger up? Not a small 10 min drive.

The big three? lol

And yeah, I dropped the battery off at an Advance and had it re-charged.

If I remember correctly alternators don't charge at idle, it will charge after it passes a certain RPM. I would however check the battery, maybe it's on it's way out (Ex: wasn't capable of holding a charge, etc...) and that killed the alternator?

I just find it weird that it use to charge at a much lower rpm, like around 1300 rpm or so. Now I have to rev it to 3.

You could have a big short sucking all your juice. Make sure your wheel didn't rub through the harness under your fender.

I had to situate my harness to try and prevent this. Maybe it's not doing the job anymore. I'll have to take a look. Good suggestion.






And thanks everyone for the reply! I really appreciate it.

jdm>usdm
05-15-2012, 02:44 PM
Well, the harness under the driver side fender was cut into by the wheel again. I just pulled the fender off and got all of the individual wires taped back up. Went to start the car and nothing changed.


Im beginning to wonder though, maybe the old alternator had a bad regulator which is why it output around 14.5 V. Since that is what my new alternator outputs with the regulator plug unplugged, maybe it should be running around 13.7V instead.
Doing some research now to find what the output is supposed to be around.



EDIT: Just found in the FSM that the regulated output voltage should be 14.1-14.7V. So the regulated 13.7V that I have now is too low.

projectblak
05-16-2012, 07:13 AM
I had a similar problem awhile back couldn't figure it out for anything.. Went through 3 alternators, and same junk my volts would drop and car dies.. Then looked at my alternator feed line that goes to the fuse box and connects to the blue 100 amp fuse, the previous owner had chopped all the lines to those fuses, maybe take a look there and see what's going on... Turns out my original alt was just fine..

riptor
05-16-2012, 07:25 AM
When i had thiss issue...it was my 75 amp alt fuse...i changeb it and it worked for like 3 weeks..im havin the same prob tho...where is this 100 amp fuse AT? Ive been thru them all..Nd dont see Nything thats rated thAT high.

JDMRIDDAZ
05-16-2012, 07:34 AM
ok i just had a bad alt on my sr
and a bad lower harness to chassis
the 2 pin plug on alt is
wht=12v constant
wht/red=ign signal
with out the wht/rd wire alt will not charge or at least this is wat hapened to me
i had to match pins for alt,reverse,speedo,..since i had some strange lower harness that pluged but no wire color matched

projectblak
05-16-2012, 09:21 AM
I'll take a pic of my car when I get home and show u

MrChow
05-16-2012, 06:26 PM
The big three? lol

You think I'm joking?? (http://bit.ly/LU1wLX)

There youtube videos and what not. The 12volt community have been doing this for years. This has fix every single car i've worked on that has any problems with battery,charging etc.

It's help my sr20 car idle a lot even with big ass fans, hid and a higher power system. This also helps cars without them also.