New alternator 100amp fuse keeps blowing

[lolpartscar]

Hey guys, first post on the forums.

Bimmerfag/Subahoe here and I feel like I got in over my head with this one.

Owned 1408 for about 3 months now and surprise surprise the alternator went bad. So i got a new (reman) alternator from O'Reilly's (inferior, I know, but I'd rather keep replacing them for free under lifetime warranty than get a good one that will last longer with no warranty) and after the install it will not stop blowing 100amp alt fuses. As soon as I connect the battery it will blow. Connect ground first, it blows, connect power first, it blows. The amp is an "ultima" brand amp #15634. I already looked it up to make sure it was indeed a 90amp and it is. Everything is connected correctly, exactly as it was before before the old alt blew. The old alt was also a 90amp I'm assuming becasue the fuse that was in the alt spot was 100amp before I did anything. I don't know what is going on because everything worked correctly except the alternator before, and now I have all kinds of problems.

Car still starts and runs but the idle surge is worse now. It could just be the ecu resetting because I had the battery out for so long though. It used to just do it on startup and once the car was warm it would go away, pretty mild and I was going to get to fixing it once I had some time. Other symptoms include no clock, radio, glovebox light, door lights, dome light, or auto seatbelts. I found a fuse diagram that shows those being in spot #17 on the interior fuse box, but I haven't gone and checked it yet because I want to figure out this alternator fuse first.

I've searched a lot and not found anything like this except on some DSM forums, and none of the threads I found came to a conclusion. I don't usually like posting on any forums because I can usually find my questions already answered somewhere but with this I have had no luck. So please if anyone has had this issue before when replacing an alternator help! Otherwise I'm going to have to poke around with a multimeter or just sell the car... I don't really have money to pay someone to fix it but I do have my summer car that I wish could stay in the garage this winter but it might need to come out for DD duty if I can't figure this out.

Thanks in advance,
A stupid BMW guy

 

[cheekychimp]

Is the ground wire at the back of the alternator properly insulated? These are old cars and the wires understandably aren't all still in perfect condition. This sounds like a ground issue. That ground wire should be a ring connector that attaches to a bolt (post) and is secured with a nut. Check the wire insulation isn't frayed and that the wire isn't touching against the case and grounding itself.

 

[lolpartscar]

It appears to be connected correctly, the old one had a post with a nut like you are describing and the new one just has a bolt that goes through the ring connector and threads into the alt. the whole thing was covered by a red rubber cap that goes over the ring/bolt that I left in place. Sound right?

Any problems with throwing a slightly heavier fuse in there? say 110amp just to see if that works? I've seen amps for 4g63 cars up to 135amp so I'm assuming the wiring can handle it if it needs to. It'll probably blow anyway but if that works it'd be an easy fix.

 

[tektic]

If the fuse is breaking there is a short. You can try a bigger fuse. It may not brake, other problems will arise. Battery drain and fire come to mind as possible side effects.

Find the short.

 

[GSTwithPSI]

When you say amps for a 4G63, I'm assuming you mean alternator, right? Amperage rating for an alternator refers to the amount of current it can produce max. Your alternator monitors system voltage, and then the alternator produces the current required to stay at a target voltage (determined by the alternator's internal voltage regulator). You alternator won't produce 100 amps unless there's enough draw on the system to require that much amperage. I'd venture to say there's no way your system is drawing that much amperage.

You definitely DON'T want to put a higher amperage fuse in. The fuse isn't blowing because the alternator is producing too much current. It's likely blowing because you have a short to ground between the charging post on the alternator, and the positive post on the battery. The fuse is doing its job, and keeping your wiring from melting. You need to trace the positive side of the charging circuit, and find where it is going to ground. Look for a pinched wire, or some damage somewhere. Also, make sure the unit has a good ground.

Lastly, I couldn't tell from your post, but make sure you don't run the car without the battery connected. You should never run a car without the battery connected. You will destroy any alternator, new or old if you do so.

 

[lolpartscar]

Yes I mean alternator haha. I was just saying that I know the wiring can handle that kind of amperage from the alt because maniac sells replacements up to 135amp. I know that it won't do anything, and I know that its not the right way to do it. Just an offhand suggestion because I never thought replacing an alt would take me more than a full day or make me feel this dumb. I know it's a stupid idea, and even if it worked the real problem would need to be found ASAP.

Thank you for the diagram, at least now I have a picture of what I'm working with. I guess I'll be having fun finding the problem in all these oil soaked wires... I'm just gonna have to start at the alternator and work all the way back to the battery I guess. It has to be shorting somewhere along that route. Before I do that though I'm gonna go ahead and clean all the connections and replace them just to see if maybe that was it, but it's probably not. Have a couple more fuses showing up at the parts store tomorrow (I blew the 2 they had in stock... oops)

I'm not running the car without a battery, I may be a bimmer guy but I'm not THAT stupid. I was referring to the computer re learning the tune with the battery being disconnected for a couple days while it was on the tender and out of the engine bay.

If anyone has had this problem before and can tell me a specific place where the short might be happening that'd be great. If not I'll report back with my findings once I figure this out. Hoping the short is easy to get to and fix.

 

[GSTwithPSI]

Hey, you end your question with "A stupid BMW guy" and I gotta pull all the stops /ubbthreads/images/graemlins/cool.gif .

I've never had this issue specifically, but I did have a starter issue that was similar. Turned out to be a crappy ground. I'm pretty sure the alternator grounds through the case, so make sure all the mounting points are clean.

If I remember right, the charging wire is a thicker white wire. It traces down from the charging post on the drivers side, along the lower front core support in a wire loom. It then traces back up the passenger side to the fuse box under the hood.

You could disconnect the factory wire and run your own, to rule out a short to ground in the factory harness. Try and run a wire directly from the charging post to the fuse panel. Make sure it's heavy, I'd say at least 8 AWG.

 

[AnotherNewb]

Quoting lolpartscar:
...the old one had a post with a nut like you are describing and the new one just has a bolt that goes through the ring connector and threads into the alt.



You bolted you white wire to the case of the alternator? If so, you have shorted the battery directly to ground.

 

[lolpartscar]

All my wires are the color of burnt oil at this point haha. Maybe I shouldn't have ended my post like I did, I am pretty good with cars and working on them, just Mitsu retarded.I attached the wire that was at the back, to the back. I attached the wire that was in the front, to the front. Plug only goes in one way so I know I did that right. It's attached exactly as the old alternator was attached I guarantee that. Unless the polarity is switched on this reman alternator? I don't think that would be the problem either.

 

[AnotherNewb]

You have a dead short on the power wire. Figure out why. A multi meter or test light will be helpful here once you unhook the wires to the alternator, replace the fuse and reconnect the battery. If the fuse doesn't blow then, you hooked it up wrong.

 

[misterfixit]

Quoting tektic:
If the fuse is breaking there is a short. You can try a bigger fuse. It may not brake, other problems will arise. Battery drain and fire come to mind as possible side effects.

Find the short.



What he says. Look for crappy soldering or the live strap inside the alternator bracket out of shape.
put a meter onto the live post and see if it has low resistance to earth (case).

100A at 12v is ALOT of current. as said above, other stuff will be melting very quickly...

Rich

 

[quicktsi]

Curious if you had the new alternator tested. I have gotten bad ones before, new out of the box. If it can be tested, battery, alternator, starter, I test the new ones before I leave the store.