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Topic Review (Newest First)
12-08-2010 03:29 PM
Garyk Time to invest in a new battery
12-08-2010 01:09 PM
bjwalsh Sorry for all the noob posts, I'm new to this stuff. I've been doing some googling on this and found some posts on other forums suggesting a drained (or bad) battery could cause the alternator to output the full 90 amps, which blows the 50 amp maxi fuse. My battery is definitely low. Any idea if putting it on a charger first would avoid blowing the fuse? Seems strange that a drained battery could cause that.
12-08-2010 02:19 AM
bjwalsh Am I over-simplifying this? The alternator is supposed to be computer-controlled. Is is possible the computer (wherever that is) is faulty and not controlling the amperage from the alternator?
12-07-2010 09:39 PM
bjwalsh I'm starting to think that maybe I did get the wrong alternator. I examined the test report that came with it and it says it's a 90 amp alternator. The output at 2500 RPM is 63 amps. Since the fuse is only 50 amps and I don't see anything that would be stepping down the amperage it seems logical that the alternator is putting out too much power.

BTW, the fuse blows when I rev the engine.
12-07-2010 09:08 PM
bjwalsh
Quote:
Originally Posted by NAVYCHIEF View Post
where was the fuse located? by brake pedal or under the hood?
Under the hood. According to the wiring diagram the alternator is connected to that fuse.
12-07-2010 08:44 PM
NAVYCHIEF where was the fuse located? by brake pedal or under the hood?
12-07-2010 08:19 PM
bjwalsh Replaced the alternator (old one had lifetime warranty, so free!). Unfortunately didn't fix the problem. Finally decided to check the fuses (should have done this first, but I'm still learning). The one labelled "ALT PWR 2" was blown. Thought I had found the problem, but replaced the fuse, started it up and minute later - pop. Fuse blown again.

I'm pretty sure I got the right alternator. So perhaps a grounded wire coming from the alternator?
12-07-2010 01:08 AM
bjwalsh
Quote:
Originally Posted by hannahuffster View Post
incorrect - 12* Direct battery input to PCM was disconnected within the last 50 key-on cycles -- and doesn not trigger check lamp.
Good to know. Had it in the shop not too long ago to replace the fuel pump, so that would explain that code. Battery is perfectly clean. Looking like the alternator. Going to replace it tomorrow.
12-06-2010 06:51 PM
hannahuffster
Quote:
Originally Posted by ISUSteve View Post
12 is the start sequence, but you hardly ever see it listed.
33 is normal if you have no ac.

is your battery and terminals clean
incorrect - 12* Direct battery input to PCM was disconnected within the last 50 key-on cycles -- and doesn not trigger check lamp.
12-06-2010 06:34 PM
ISUSteve 12 is the start sequence, but you hardly ever see it listed.
33 is normal if you have no ac.

is your battery and terminals clean
12-06-2010 05:36 PM
hannahuffster I would guess the alternator. If the battery is starting the jeep is is probably ok.
12-06-2010 04:30 PM
bjwalsh
Quote:
Originally Posted by hannahuffster View Post
You got a 55 at the end too right? I always get the ac clutch when I trouble code mine (and I have not AC too). I would say that 47 is the trouble...
Yes, got the 55 at the end. So looks like either the battery or alternator then. This all started after running out of gas and running the headlights and emergency lights off battery while waiting for AAA. First time I ran the battery that low.
12-06-2010 04:13 PM
hannahuffster 47** Battery voltage sense input below target charging voltage during engine operation. Also, no significant change detected in battery voltage during active test of generator output. -- will trigger check light...
12-06-2010 04:11 PM
hannahuffster You got a 55 at the end too right? I always get the ac clutch when I trouble code mine (and I have not AC too). I would say that 47 is the trouble...
12-06-2010 04:09 PM
hannahuffster I get right @ 13 mpg on my 93 2.5 with 33" bfg km2's & she runs like a top...
12-06-2010 04:09 PM
bjwalsh
Quote:
Originally Posted by NAVYCHIEF View Post
i had the same thing happen. i took the alternator apart and cleaned the armature with emery cloth and reassembled it. never had that problem since. been about a year. haynes manual has directions on how to take it apart. what code are you getting?
Ok, I checked (and re-checked) the codes. Some weird results. Here's what I got:

12 - ?
33 (Air conditioning clutch relay) - strange since I don't have an air conditioner
47 (Battery under voltage) - expected

I thought maybe I had screwed up the first couple codes, but got the same numbers when I checked again.
12-06-2010 12:54 PM
bjwalsh
Quote:
bj, the codes are read by following the proceedures in my first note above. all you do is turn the key on and off as described above and count the number of times the light flashes. when i did mine the flashes indicated 41 which is the field voltage of the alternator was low.
Sorry, didn't read far enough. That's very handy to know. Will check the codes tonight. Thanks for the info.
12-06-2010 02:20 AM
wranglerYJnewb
Quote:
Originally Posted by bjwalsh View Post
@NAVYCHIEF: Don't have anything to tell me the code. Will look into servicing the alternator if nothing else comes up. Thanks.

@hannahuffster: No, not running rough. Checked the belt - it is nice and tight - no play or slack. Was hoping for a little better mileage with the 4 cylinder. My 4 cyl. toyota truck gets 19 MPG.
hmmm i have a 93 2.5L and she gets consistently 16.5 mpg ... I did th 20g mod and get around 325-335 miles a tank
12-06-2010 02:06 AM
NAVYCHIEF bj, the codes are read by following the proceedures in my first note above. all you do is turn the key on and off as described above and count the number of times the light flashes. when i did mine the flashes indicated 41 which is the field voltage of the alternator was low.
12-06-2010 12:17 AM
MikeMTJ It won't ever get 19 mpg. I get 13, and my engine only has 57k on it.
12-06-2010 12:12 AM
bjwalsh @NAVYCHIEF: Don't have anything to tell me the code. Will look into servicing the alternator if nothing else comes up. Thanks.

@hannahuffster: No, not running rough. Checked the belt - it is nice and tight - no play or slack. Was hoping for a little better mileage with the 4 cylinder. My 4 cyl. toyota truck gets 19 MPG.
12-05-2010 10:55 PM
hannahuffster Is the motor running or idling rough when the voltage (it is reading alternator volts not the batteries volts) meter is reading low? If the motor is running rough it will most likely be reading low voltage because the alternator is turning slower than it should be. check for slack / play in your new belt. Does it sqawk or squall like it is slipping?

hey over 13 mpg aint bad in an old jeep...
12-05-2010 10:53 PM
NAVYCHIEF i had the same thing happen. i took the alternator apart and cleaned the armature with emery cloth and reassembled it. never had that problem since. been about a year. haynes manual has directions on how to take it apart. what code are you getting?
12-05-2010 10:47 PM
bjwalsh
Battery gauge low, check engine light on

I have a 91 Wrangler, approx. 175k miles. Recently replaced the fuel pump and belt. Just ran out of gas (to my dismay discovered I only get about 200 miles on a 15 gallon tank, but that's beside the point). Now the "check engine" light comes on after a few miles and the battery gauge is showing pretty low. Checked the battery with a multimeter and it shows 12 volts. Not sure what to check. Alternator? Any help would be appreciated.

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