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Discussion Starter #1 (Edited)
There are plenty of "my Jeep won't start" threads on here, with various causes.
Switch that tells the computer an automatic is in park and the clutch pedal switch on the manuals seem to be common culprits, but for those with intermittent probs and issues where you get it towed to the dealer and it fires right up- this may be whats happening.

I'll start with:
CHECK YOUR BATTERY!
and by that I mean load test it, swap it out or hit it with a charger really hard for awhile, not just put a meter on it and think "ok its got voltage, what's next?"

Everyone knows what a weak battery acts like, and how to check it with a voltmeter, etc.
But the Jeep computer TIP start deal can make it tricky to diagnose!

My Jeep, like 4 or 5 times since I got it has refused to start - turn the key and get a "chunk" sound - not the typical click of a dead battery clicking a starter relay, but the CHUNK of the starter engaging and just barely starting to turn the motor over and immediately kicking back out. Kick it a few times and it would fire right up - no slow crank or anything just spin and go like nothing was wrong, plus the interior lights would just barely dim.
So I'm defintely NOT thinking battery.

Well it was - here's what I think was happening.
The computer checks for sufficient voltage to start the motor, battery starts getting toasted and is holding a surface charge - check it with a meter and it shows sufficient voltage but as soon as there's a load (like the starter engaging) the voltage drops immediately below the required amount and the computer kicks the starter out.
The battery isn't completely toast and holds plenty of amps, just at a lower voltage than the computer will allow the Jeep to try to start at.
Bump it a few times and maybe you'll catch it where it doesn't quite drop enough and the battery puts out the amps to start it right up, but just barely above the threshold for the computer to let it try starting.
check it with a meter and with no load, the voltage shows good.

Mine did this and then wouldnt do it again for months, then finally it did it again - I got the video and 5 min later it spun right up, then the damn thing stranded me the next day.
I bumped and bumped and bumped - called a buddy for help, the second I hung up with him on his way, it cranked right up.

Anyway, I know I'm hell on my electrical system - 14+ lights, winch, etc - I know I need to go dual battery, just gotta find the $$.

Bottom line is these things are very sensitive about battery condition, and sometimes a bad battery condition is really hard to diagnose.

I have a video of the "chunk" sound so you can hear what I'm talking about, I'll insert it as soon as vimeo is done processing it so you can hear what I'm talking about - its not the typical dead battery "click" of a starter relay.

YouTube - IMG_0111.MOV
 

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here I was expecting pictures of a jeep on fire as the solution. lol

I agree with you though - my experience with the JK so far has been that it is super sensitive to the battery health like any other CANBUS equipped vehicle. Very little room for variation basically.

We were winching a broken TJ up a hill for about 30 minutes one weekend with a petrol JK manual with an electric winch. No dual battery system. All was good for the first 5 min until the TJ hit the steepest part of the hill. As soon as the winch loaded up the JK's idle changed and it'd start to run rough and very rich exhaust smell. Sure enough after the winch effort we had all sorts of lights on the dash. Wound the winch in and got it back to camp just not running right. Had to go through a full computer reset (someone consulted the internet and found a reset procedure, as simply disconnecting the battery did nothing) to clear all the warning lights and to make it run properly again.

Despite my CRD having a 180A alternator I'm not about to tacking extra electrical gizzmos to it! :bawling:
 

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My 07' is doing it now. Has been for about a month. Advanced Auto has a 800 amp battery that seems good, 3 year war. Whould you use that, or go Optima?
 

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Discussion Starter #5
My 07' is doing it now. Has been for about a month. Advanced Auto has a 800 amp battery that seems good, 3 year war. Whould you use that, or go Optima?
If you're still on the stock battery with an 07, it has outlived most!

make sure the advance warranty isnt prorated.

I've heard a lot about optimas quality being dodgy lately.
I used to be fan, anything I had that needed a battery got an optima, but not so much in the last couple of years.
My stock battery gave up, I went to walmart and bought their $77 MAXX because of their 3 year free replacement policy.
Not prorated and they dont give you crap, battery has problems, they give you a new one.
 

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Thanks. I did the Wal-Mart MAXX. The warrantee is what did it.
 

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good info there and with the vid. Ours did that about 2 months ago but since I didn't have the hood up not sure if the sound was "exactly" the same as the vid. I would have to take the key out, back in and it would fire up like normal. Hasn't done it in a while though since but with the 08, and a winch on there now I'm sure we are due for a battery before too much longer!
 

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my first battery died within 18 month. now a yellow top within a year.

the JK kills batteries i think.

i think the reason it clunks is due to the tip start system. it must check to see if the battery can complete the cycle and if not, abort.

my yellow top has a full charge, but only shows 180 CCA...
 

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***** This is good info.... BUT THIS WONT SOLVE EVERY "MY JK WONT START ISSUE"

However view the video for comparison... If you hear that "chugging" sound like in the video it is the battery. If you just hear a click... it may not be the battery.

I know this because when I this issue a year ago, I got myself a new battery, then a new starter, then checked ALL my electrical's (took DAYS)... and the problem was with the factory computer. (search for related threads for solutions).
 

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One Battery not being mentioned here is "Braille" I currently run one of the ultra light batteries in a summer toy, without issue, its a sealed design, half the size of an OEM battery, half the weight at 21 pounds and has performed flawlessly. I think it would make a perfect dual battery setup as I believe 2 would fit in the OEM battery tray.
 

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Interesting info on the Braille battery site. But looking at the reserve capacity of their lightweight batteries, even a dual-battery setup using their largest model would only equal the reserve capacity and runtime of the better Group 34 alternatives at twice the price. But the small size would make mounting as an auxiliary remote battery for a fridge and camping lights easier. Their endurance batteries have high CCA but reserve capacity is only slightly higher than Optima, and the same as Odyssey.

Looking around, it seems to me the Sears Diehard Platinum. 880 CCA and 68A/134min reserve capacity is better than anything else I've found. The $189 price makes it affordable.

Even though my JK is only 4 months old I've managed to kill the battery 3 times by running the stereo and small (14qt) Engel fridge for as little as 2 hours (hey, I like my cold beverages on a hot day).
 

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Had to go through a full computer reset (someone consulted the internet and found a reset procedure, as simply disconnecting the battery did nothing) to clear all the warning lights and to make it run properly again.
How about posting that procedure or a link here? Definitely sounds like useful info.

Despite my CRD having a 180A alternator I'm not about to tacking extra electrical gizzmos to it! :bawling:
I wonder if that alternator would fit a 3.8L LHD. Would like to upgrade my 140A stock unit, but haven't found any replacements.
 

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Discussion Starter #14

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Man i love this site, you guys (and girls) talk about everything, i haven't had this problem with my 07 but i don't have anything cool like lights or winch (yet) but if it starts i know to go for info, thanks
 

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Mine's doing it now too.....

Hey Venom,

My stock battery from my '08 had been acting whacky at random too...after it stranded us last week, I immediately put in an optima redtop....

just this morning, it wouldn't start for a few attempts, then cranked over like there was nothing wrong.....

SO,

could my accessories be vampire'ing juice from the battery? Or confusing the canbus....? Not much, just a winch and a cb...

Im also running the poison spyder led brake/tailights, and they seem to store a tiny bit of energy in them...they blink when you open the doors....


Im totally cornfused!

any thoughts guys?

Is there a single battery saver solution?... I don't need a dual setup...
 

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Hey Venom,

My stock battery from my '08 had been acting whacky at random too...after it stranded us last week, I immediately put in an optima redtop....

just this morning, it wouldn't start for a few attempts, then cranked over like there was nothing wrong.....

SO,

could my accessories be vampire'ing juice from the battery? Or confusing the canbus....? Not much, just a winch and a cb...

Im also running the poison spyder led brake/tailights, and they seem to store a tiny bit of energy in them...they blink when you open the doors....


Im totally cornfused!

any thoughts guys?

Is there a single battery saver solution?... I don't need a dual setup...
While I'm researching this I stumbled across a few things....

1. It could be water in the rubi swaybar disconnect connector (ill have to check it out later)
2. The CanBus system might be aborting the start due to the TIPMs system being gay
3. I should blow this thing up.

I'll post what ever I find out....
:beer:
 

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As I'm sure you guys already know, the OEM battery in the JK is pretty terrible. It has a tendency to die at the worst times with no warning.

At the very least, upgrade your single battery to a Odyssey/DieHard Platinum, or a Optima Yellowtop.

For the ultimate in peace of mind and extra capacity, you can't beat duals! :smokin:

 

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red top DEAD

I have a red top that I bought back in May for my 07. Replaced the original and now this thing is giving me problems. It was a little slow starting the other day so I charged it and now today it's dead. Yesterday it started fine, today just dead. I have a winch and CB but the winch is the only thing hooked up, cb runs through a cig plug which isn't hooked up. Could the winch be draining it some how? I think I probably just have a bad battery. I bought from a shop in Costa Mesa called RPM. They haven't had any in stock for a replacement battery for 2 days so I guess my warranty is worthless. I think the wal mart deal is what I am gong to do. Just because they will have one if I have more problems. Duals in the near future... very near. Anything else that would be a constant on that I'm not thinking of? Anything weird with these new Jeeps? Thanks for any input....
 
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