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Old 03-24-2013, 11:50 AM   #1
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Problem with my 4.0

This just happened within the hour of this post. I went out to get coffee and for some reason the battery was dead. I brought my other car over and jump started it, I went and came back. The battery died even though it was a 10min drive, which I though should be enough to recharge. Started it again took a longer route and drove home it drove fine till now. WHen I got home I turned it off and turned it on again to make sure the battery was fine. This is when it all started. The engine had a hard time cranking and took a while to turn over. Once it did it would idle VERY low almost stalling at neutral. Oil pressure also drops a lot. And my biggest fear is the knocking noise, that goes away when I give it a bit of gas.
Its a 4.0 5spd 2000 Wrangler with 157k
Short version:
Battery died twice , jump started twice.
Tried to restart the engine had a hard time cranking but eventually turned over.
VERY low idle at N. If in gear it stalls and dies. Low oil pressure.
Knocking noise at low idle but goes away with a bit of gas.

What could it be? Its sunday so most places are closed and I don't want to risk stalling it in traffic. Any help appreciated.

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Old 03-24-2013, 12:02 PM   #2
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What could it be?
For some reason, I would suspect that you might have a battery problem.

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Old 03-24-2013, 12:23 PM   #3
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I'm no engine guru by any stretch but I hope your right. I'm going out to buy a new when I my sis comes back so I can take the other car.
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Old 03-24-2013, 12:24 PM   #4
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Easy solution would be to park on a downhill grade... you won't need a jump then. Otherwise, you have either a bad battery or your alternator is not kicking out enough juice to recharge or maintain voltages. My money is on the alternator due to the low idle and knocking. Giving it more gas on idle increases the overall volts coming off the alternator just enough to get it going.

Put your battery on a charger for a few hours and test the voltage. Should be 11.9 or higher with a voltmeter. With the engine running, test the volts from the alternator, it should be roughly 14V. Anything below 12V and you have a bad alternator.
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Old 03-24-2013, 12:25 PM   #5
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First thing I would look at is any corrosion on the battery cables. Second thing would be to run to a local auto parts store and have them check the battery for free. Third would be to have them check the alternator. It is one of those three.
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Old 03-24-2013, 12:28 PM   #6
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My bet is on the alternator, but running down an old battery can be the final nail in the coffin as well. You may need a new alt and battery. As posted above, have them checked at an auto parts store.
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Old 03-24-2013, 12:33 PM   #7
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First thing I would look at is any corrosion on the battery cables. Second thing would be to run to a local auto parts store and have them check the battery for free. Third would be to have them check the alternator. It is one of those three.
Ok I will be trying that. Can someone explain why the knocking happens at low idle? I've owned 3 4.0s and never had this problem or any other problems for that matter. I have only very basic understanding of an engine but don't understand how low idle causes the knocking
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Old 03-24-2013, 12:41 PM   #8
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Ok I will be trying that. Can someone explain why the knocking happens at low idle? I've owned 3 4.0s and never had this problem or any other problems for that matter. I have only very basic understanding of an engine but don't understand how low idle causes the knocking
As you previously stated the oil pressure drops down with low idle. Could be that or could be some kind of spark knock. First and foremost I would pull your battery cable and hit the cable ends as well as the battery posts with a wire brush. This seems to be a very common fix to this problem.
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Old 03-24-2013, 01:08 PM   #9
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As you previously stated the oil pressure drops down with low idle. Could be that or could be some kind of spark knock. First and foremost I would pull your battery cable and hit the cable ends as well as the battery posts with a wire brush. This seems to be a very common fix to this problem.
I'm just about to head out. I'm getting some new wire brush a new diehard battery and go from there. This isn't the first time I've had problems with the battery so I decided I'm just going to replace it. But I will try cleaning the contacts just to see if that was the problem. I don't have the money for a new alt right now so I hope its not that. Will report back once I get done. Thank you everyone for your inputs.
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Old 03-24-2013, 02:40 PM   #10
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So I'm back and it turns out it was the battery. So I replaced it with Autozones duralast gold. I don't know how true this is but my friend that works there tells me they are made in the same factory as diehards. Plus he got me his employee discount which came out to be about half of diehard. The diehard does have a nice set of aux posts and also they have 50more cca. I'm a bit skeptical but I trust him, Ill have to see how it holds out.With a 3yrs warranty(same as diehard) in addition a 2yrs prorated warranty. He also said he recommends replacing the alternator soon so with the money I saved I'm ordering a mean green alternator. Its a pretty penny but rather upgrade than replace. Thank you everyone. I'm glad I'm not looking at a new 4.0
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Old 03-24-2013, 03:41 PM   #11
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I scraped the mean green idea. Doing some reading they don't seem to be worth it. Decided to just go with OE alt.

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