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Topic Review (Newest First)
11-26-2008 11:12 AM
Jerry Bransford The alternator only puts anything out when it detects a non fully-charged battery's lower voltage but it will never put out more than its rated capacity and thus won't be harmed by jumping a larger vehicle. This "never jump a larger engine" rumor is, from an electrical/electronic point of view, nothing more than an old wive's tale. First, the current drawn by the other vehicle you're jump-starting primarily comes from the battery, not the alternator. Remember that if your battery isn't low, you could jump-start another vehicle without even your engine running so it's coming purely from the battery... though of course it's always best to have your engine running since the other engine may need some extra time cranking to get it running. And even then, you may need to remain connected to the other Jeep so it can remain running as modern Jeep alternators don't put out any power if the battery is dead... which means if the other Jeep's battery is completely dead, its engine would die if you removed your jumper cables too soon.
11-26-2008 02:05 AM
flounder35 is it possible, working on the "never jump a larger engine" theory, that the alternator produces larger amperage and when charging the battery on the larger engine, passes the larger amperage through the jumper cables and to the wires coming off the smaller battery, frying the computer? I'm not very mechanically inclined but I believe there are different ratings on alternators. I'm interested in not only the how of a fix or problem, but the why, if I understand that, I do very well. Any thoughts?
11-24-2008 04:10 PM
Jerry Bransford There's some hand-wringing type of info in this thread based on hearsay and half-truths. The Jeep and its computer is nowhere nearly as sensitive to problems that can conceivably (!) occur from jump starts as some have claimed. Generally speaking, simple jump starts are not going hurt anything, whether you are the "jumpee" or the "jumper". Saying the computer will be damaged by jump starts is a gross exaggeration. Heck, I've been jump started and given jump starts MANY MANY times on my tired old '97 TJ and never a problem.

Winter102265, how long did you disconnect the battery's negative lead? And have you checked that both of the air bag fuses are intact? It's possible one of the two air bag fuses have popped for whatever reason unrelated to the jump start and it just needs to be replaced. Having one of the two air bag fuses popped still leaves both air bags in operation, they work fine if either fuse is intact. Each of the two fuses provide back up for the other so only one is really needed for both air bags to be fully functional.
11-24-2008 03:38 PM
jtalar Sound to me like you fried the brains of the operation....I was taught to NEVER jump a vehicle that has a bigger engine, in most if not all cases the larger engine has a larger battery, and you could potentailly fry your batt or worse, which seems to have happened here.
11-24-2008 03:28 PM
horn Jumpstarted a neighbour recently and found out that the positive and negative pole of the battery are the other way around as on my other (european) cars. So I got a spray of sparks when I put the red wire on the negative pole...
CHanged it immediately but today I found out I fryed the battery. Did start more difficult over the last week and yesterday didn't do anything anymore. Only ABS light stayed on. Jumpstarted it this morning with the 911 and drove it to the battery/tyre shop. Killed the engine and never got it started again. The checked it and found out that the battery was fryed. Put in new battery and everything worked like a charm again. ABS light is out also.
07-08-2006 09:06 PM
amerijeep I know the local Jeep dealer pretty well. I'll give him a shout Monday and see what he says.
07-08-2006 10:29 AM
bluvikng That is exactly what I was thinking last night after showing this thread to the other guy that said his Jeep would not start after jump starting someone. I even asked the wife if she had used her jumper cables, and she said she had. No ill effects have been noticed on our wrangler. I have also used the winch many times, and have never suffered any ill effects. I would think that the spike of electricity would increase significantly when winching someone. I will have to find out more about this. It does not make sense. ??????????
07-08-2006 10:25 AM
bzserv5057 I have heard this pertaining to all newer vehicles with CPU's, sometimes if the conditions are right a spike can occur, espically jumping a larger engine. Was told this many of moons ago, but never paid much attention to it. Well I guess they are right now.
07-08-2006 09:46 AM
Texapple I don't understand.......
wouldn't there be "voltage spikes" when using a winch or air compressor, etc? Someone educate me
07-06-2006 03:19 PM
bluvikng Oh man.........that sure is good to know. Sure hope he was kidding, but that hardly seems something to joke about.
07-06-2006 11:51 AM
amerijeep A dealer told me awhile back that you shoule never jump another vehicle with your Jeep, because it will damage the computer. The Jeep cpu is apparently sensitive to voltage spikes.

I can't say that's what happened or even if the dealer was right though...
07-06-2006 11:47 AM
winter102265
Airbag light came on after jump start

Used my '97 Wranger to jump start another vehicle and every since the airbag light has been on. I disconnected the neg bat cable but problem still exists. Any ideas what may be the cause?

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