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Discussion Starter · #1 ·
So long story short I was trying to jump my jeep in a hurry because I was late for work and hooked the cables up backwards. :facepalm: (luckily my friends truck wasn't harmed)
The next day, after replacing the battery (surprise!) she won't start.

Here is what i know:
Its a 1999 4.0L with a three speed tranny.
It sounds like it really wants to start if you crank it for about 5 seconds. It's definitely getting fuel, in fact it smells very strongly of gas after trying to start it.
It has spark, I checked this by placing a plug on the manifold while turning it over. but the spark seems less uniform than I would expect. (although i don't really have anything to compare this to)
Which makes me think it might be a timing issue. that being said I know nothing about timing or how to fix it.

Short of replacing random sensors I don't even know where to start troubleshooting this. can anyone give me a clue? any help would be greatly appreciated!
 

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Check the fuses in the fuse block under the hood. I'd look close at number 6 but probably check them all
 

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Check the grounds

If you really have a brisk crank a spark at the plug end on the boot and good fuel rail pressure and clicking injectors it would start so figure out where you missed one of those thinks

My guess is no spark but it could be no injector pulse

Also is check engine light on and any codes
 

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I'd guess that you might have fried a couple of electronic sensors and maybe the PCM.

Try pulling the codes and see what you come up with.
 

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Guys this is why I keep a bottle of red fingernail polish. New battery get +painted red, top off plus cable gets it to. Just an idea to share.
 

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Discussion Starter · #8 ·
I guess i forgot to mention i had checked the fuses and didn't find any that had been blown. I don't think it has any fusible links.
No check engine light, a friend of mine has an OBO-II reader that didn't come up with any codes.
 

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Discussion Starter · #9 ·
Check the grounds

If you really have a brisk crank a spark at the plug end on the boot and good fuel rail pressure and clicking injectors it would start so figure out where you missed one of those thinks

My guess is no spark but it could be no injector pulse

Also is check engine light on and any codes
I'm not sure where to check the grounds, I don't know much about electrical workings.
What do you mean clicking injectors/injector pulse? I'm almost positive its getting fuel, the smell of gas is quite strong.
I visually verified that the plugs (at least the one i pulled to test) are creating spark.
How would I check for the other things?
Also I plugged a house hold OBO-II reader in but it didn't show any codes.
Thank you for taking the time to help me!
 

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Discussion Starter · #10 ·
Guys this is why I keep a bottle of red fingernail polish. New battery get +painted red, top off plus cable gets it to. Just an idea to share.
That is a good idea!
The sad part is I have subs! The extra lead should have been a dead giveaway!
 

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All TJs have a fusible link between the alternator and battery. Do you have and know how to use a multimeter?

The Fusible Link is not actually a fuse, it's a short length of dark green smaller gauge 10 gauge wire spliced in between a pair of larger gauge black/gray 6 gauge wires connected between the alternator and power distribution center. Check for continuity across that wire. Or with the engine off, check to see if there's any battery voltage on the alternator where its heavy charge wire connects to. Even a dead battery should show some voltage and if the fusible link is good, you'll get that same battery voltage at the main charge wire connector on the alternator.

Then check Fuse #6 inside the Power Distribution Center, that's a 30 amp fuse and it's right in the middle of what could have blown.

Edit: I was trying to rush the edit time and just now noticed it's at least trying to start. Can you temporarily disconnect your existing battery and swap in a known good battery? Connecting a jump start battery without disconnecting the main battery can cause odd symptoms so for this test, it'd be good if your existing battery was not connected at all... just a known good battery.
 

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Discussion Starter · #12 ·
All TJs have a fusible link between the alternator and battery. Do you have and know how to use a multimeter?

The Fusible Link is not actually a fuse, it's a short length of dark green smaller gauge 10 gauge wire spliced in between a pair of larger gauge black/gray 6 gauge wires connected between the alternator and power distribution center. Check for continuity across that wire. Or with the engine off, check to see if there's any battery voltage on the alternator where its heavy charge wire connects to. Even a dead battery should show some voltage and if the fusible link is good, you'll get that same battery voltage at the main charge wire connector on the alternator.

Then check Fuse #6 inside the Power Distribution Center, that's a 30 amp fuse and it's right in the middle of what could have blown.

Edit: I was trying to rush the edit time and just now noticed it's at least trying to start. Can you temporarily disconnect your existing battery and swap in a known good battery? Connecting a jump start battery without disconnecting the main battery can cause odd symptoms so for this test, it'd be good if your existing battery was not connected at all... just a known good battery.
Yes I have a multimeter, but i only know how to use it for a few things.
Im not sure how to check continuity or what that even means honestly.
I imagine its a way to check if a circuit is broken?

I checked all the fuses, including the ones in the glove box just to be sure. none of them seamed to be blown.

I replaced the battery the day after the incident because the old one was toast. So all the efforts I've made to troubleshoot this problem have been with a new battery. is that good enuff? or should I try the battery from my chrystler?

Thank you for your help!
 

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Yes I have a multimeter, but i only know how to use it for a few things.
Im not sure how to check continuity or what that even means honestly.
I imagine its a way to check if a circuit is broken?

I checked all the fuses, including the ones in the glove box just to be sure. none of them seamed to be blown.

I replaced the battery the day after the incident because the old one was toast. So all the efforts I've made to troubleshoot this problem have been with a new battery. is that good enuff? or should I try the battery from my chrystler?

Thank you for your help!
Continuity is a way to make sure that electricity can flow through something. That "something" may be a wire, a fuse, etc.

To check a fusible link, you put your multimeter into continuity mode. This is sometimes indicated by a symbol with an arrow pointing to a vertical line.

You then take the leads and put them on either side of the fusible link. You'll usually get a beep and a 1 on the display of the multimeter if the circuit is good.

You should check continuity of fuses too since it's not always possible to visually verify if a fuse is blown. I don't know about our mini fuses, but the larger style blade fuses had little metal parts on the back side that you could check continuity off of so you didn't even have to remove the fuse to check them.

So same concept there. Touch two sides of the fuse with your multimeter in continuity mode and look for the indication on your multimeter.

If you want to see what the multimeter should do as a test, just touch your leads together. Then you'll know what to expect.
 

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Your meter has a couple positions on its selector dial labeled Rx1, Rx10, Rx100, etc. and those are the setting you check continuity with. To see what they do, select any of those Rx settings and then touch the leads together. It'll show 0 Ohms on the display which means zero resistance or more simply, that there is "continuity" between the leads... in other words, a connection.

Rx1 is the setting you'd use for most continuity checks, like is a wire making a connection or not. A '0' means no resistance which means a good connection.

Those Rx1, Rx10, etc. settings are only for use on circuits that are shut off, don't try a continuity check on a circuit that is turned on.
 

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Discussion Starter · #16 ·
OK, so I checked the all the fuses with my multimeter they all seem to be good. I'm not sure how accurate this meter is (harbor freights, go figure), it never zeros out even when touching the two leads together. but it did give a similar reading on the fuses as touching the leads together, so I think there good.

I haven't had much luck finding the fusible link, it appears to be one large wire but I might be looking in the wrong spot. does anyone have a picture?

Jerry, you mentioned I could check the connector to the alternator as a way to check if the fusible link is good. how would i do this? just pull the connector and put a lead on two of the terminals?

Sorry for my lack of knowledge, but thank you all for trying to help me.
 

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Use your multimeter to measure the battery voltage. Then move the multimeter's red lead to touch the main/heavy output lug on the alternator. If the fusible link is good, you'll see the same voltage on the lug on the alternator. Zero voltage on that heavy alternator output connector while the battery shows at least some voltage would indicate a blown fusible link. Engine should not be running for this test.

The fusible link is just a smaller diameter wire spliced into a larger diameter wire, it would be covered by some heat shrink tubing and the fusible link itself would probably not be easily visible.
 

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Discussion Starter · #19 ·
Use your multimeter to measure the battery voltage. Then move the multimeter's red lead to touch the main/heavy output lug on the alternator. If the fusible link is good, you'll see the same voltage on the lug on the alternator. Zero voltage on that heavy alternator output connector while the battery shows at least some voltage would indicate a blown fusible link. Engine should not be running for this test.

The fusible link is just a smaller diameter wire spliced into a larger diameter wire, it would be covered by some heat shrink tubing and the fusible link itself would probably not be easily visible.
OK. so I've checked the alternator in the manner you described. It seems the fusible link is good, the voltage was the same as the battery.

What do I check next?
 

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And to confirm, you have physically removed and checked every one of the fuses inside the power distribution center in the engine compartment?
 
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