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Unread 06-12-2015, 06:34 AM   #1
Aethelwulfe
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2000 TJ Wrangler 
 
Join Date: Jun 2015
Location: Pittsburgh, PA
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Not the same ol' rough idle problem

So I have seen a few times on here that a lot of people experience a cold rough idle problem which sometimes presents with a cylinder 3 misfire. I am having kinda the exact opposite problem. When cold my (2000 TJ with the 4.0 I6 5 speed manual transmission) rig will run like a top, but after it warms up, the idle and oil pressure drop. The RPMs drop to 3-400 and the rig has no pull. If I ease the clutch out it will stall before it starts moving the jeep. The oil pressure drops to about 40 on the gauge, but the might just be a response to lower RPMs. This started after my girlfriend drove the jeep (with me in the car) and left the lights on, which killed the battery mostly. The jeep ALMOST started when we got out of the store, but couldn't turn over. Rig ran fine before that, and like crap after, but only when warm. Could this be a vacuum problem, or might the computer need reset? Is there another option? Also, not throwing any codes. Thanks in advance for the help.

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Unread 06-12-2015, 07:50 AM   #2
Jeepsr4me
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Need to verify the battery is good and strong... A weak battery will cause all kinds of issues..

And to clean the computer take the neg cable off and touch it to the + cable. Dont need to take both off just one...
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Unread 06-12-2015, 07:52 AM   #3
Aethelwulfe
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Thanks for the quick reply. The battery is fine, I had that tested. I will try cleaning the computer in about a half an hour.
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Unread 06-12-2015, 09:10 AM   #4
Jeepsr4me
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clean the terminals and check the cables for corrosion.
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Unread 06-12-2015, 11:03 AM   #5
Jeepster83
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Quote:
Originally Posted by Jeepsr4me View Post
Need to verify the battery is good and strong... A weak battery will cause all kinds of issues..

And to clean the computer take the neg cable off and touch it to the + cable. Dont need to take both off just one...
I agree with having a good strong battery but not with touching the cables in that order. I'd disconnect battery positive and touch it to the negative post/cable.
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Unread 06-12-2015, 11:49 AM   #6
Jeepsr4me
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Originally Posted by Jeepster83 View Post
I agree with having a good strong battery but not with touching the cables in that order. I'd disconnect battery positive and touch it to the negative post/cable.
Whats the ****ing difference on which one you take off? The neg post is farther away from body and way easier to get to..

Plus you stand a chance of touching the body while removing the +positive side without removing the -neg side 1st... So skip that and just take neg off and touch to the pos..
NOTHING WILL HAPPEN.... other than the small electrical charge in the computer will discharge....
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Unread 06-12-2015, 01:13 PM   #7
Jeepster83
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Quote:
Originally Posted by Jeepsr4me View Post

Whats the ****ing difference on which one you take off? The neg post is farther away from body and way easier to get to..

Plus you stand a chance of touching the body while removing the +positive side without removing the -neg side 1st... So skip that and just take neg off and touch to the pos..
NOTHING WILL HAPPEN.... other than the small electrical charge in the computer will discharge....
That small electrical discharge you see and hear can cause some expensive damage. NEVER disconnect positive first while there is an active ground for that circuit. The positive side ALWAYS has voltage whether there's a ground path or not. It's just not moving until there's a ground. Because of the direction of flow these steps should always be taken to prevent that small spark from happening. Fried computers happen every day because of someone doing what you suggested.

Also if you're trying to discharge the computer wouldn't you remove power from it? Removing the ground leaves the capacitors and whatnot charged. The easiest and safest way to clear the codes by means of discharging the computer is to disconnect battery positive then simply turn something on (or try to) like the headlights or even the dome light. Remain ing voltage is used up in a natural flow and there's no sparks anywhere to fry anything.
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Originally Posted by mrblaine View Post
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Unread 06-12-2015, 02:33 PM   #8
Jeepsr4me
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Nothing you said made any sense...
how can turning a light on complete the circuit? If you already taken the ground loose form the battery? The capacitor needs a ground to discharge or it just stays put.

What do I know.. I was a certified electronics tech on F18s and took that knowledge and worked in the communications industry for 8 years and dealt with way more COMPUTER electronics that you will ever see. I have been at ground zero of giant stacking stations of 1000's of cisco routers and millions of battery backups.
I know how to clear a minute charge in a computer..

Again touch the - cable to the positive and nothing will happen other than clearing of the charge and codes.
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Unread 06-12-2015, 03:28 PM   #9
Nee
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I agree with jeepster83. Always disconnect Neg ground first. I work on F-15 Eagles and part time automotive. Can always disconnect positive lead afterwards and reconnect ground to accomplish task without spark or fried electronics.
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Unread 06-13-2015, 12:07 PM   #10
Jeepsr4me
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Well that is exactly what I said to do... Neg off... no need to to take the + off at all.... for many reasons.

People get scared around batterys and electricity.. But they keep hearing bad advice on the forums.
once a battery has been disconnected from just one terminal the circuit is dead. so any of the wires can be touched and nothing will happen. Here with the computer it has some residual potential in it. Its looking for a way to ground.
It dont matter if you take both terminals off and touch cables then or if you do as I suggest. take - off and touch it to the + still attached to the terminal.. There is no voltage that can JUMP out of the battery.
I do this ALL THE TIME.... some people close their eyes affraid of the sparks... I just laugh..

I got a video of me doing it.. Nada happens...

Now if you got some punk *** stereo with HUGE capacitors.. Then watch out... Touching the cables together in any way will discharge those bad boys and it can be nasty.
but no voltage will come out of the battery and once the caps have discharged the sparks will stop..
I have a video of a normal set up no huge stereo.. Nothing happens...
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Unread 06-14-2015, 12:58 PM   #11
Aethelwulfe
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Clearing the computer work just fine. I had to take both terminals off anyway because of some strange way of wiring some random ground wire from the previous owner, but after clearing the computer, rig runs great again. Lesson learned, after girlfriend gets out of the driver seat, sit in the seat and make sure that everything is off... or don't let her drive it, but that might cause other problems that I would need to go to a different forum for advise. Thanks again.
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