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Mt Goat 02-20-2011 04:59 PM

2000 Jeep Wrangler engine issue
Having trouble with my 2000 Jeep Wrangler. Last week my jeep battery died after returning from town. I had to leave my head lights on for about 5 minutes, but right after I went to start the Jeep and it wouldnt start. Not sure if it was a battery issue or alternator ? I decided to pull the battery from our other car, the Jeep started fine. I took the ground wire off the battery, engine kept running fine. Two days later the other battery still in the Jeep goes dead, if I Jump start the Jeep it starts fine, but died as soon as I took my foot off the gas petal. So I go buy a new alternator. with the new alternator installed I jump start the jeep, it starts right up, BUT again will only stay running as long as I keep my foot on the gas petal. If I take my foot off the gas petal the jeep instantly dies. No sputtering, just dies, like I turned the key off.

If its an alternator shouldnt the new alternator keep the engine running after the engine is started ? or can a completely dead battery still cause engine running issues ?

Anyone have any possible ideas on what might be the problem ? any help would be of great help. As of late if I didnt have bad luck I wouldnt have any luck at all.

Jerry Bransford 02-20-2011 05:08 PM

The engine won't run for long with a completely dead battery, the alternator requires +12v from the battery which is called an "exciter voltage". The alternator will continue putting power out for a short time until its magnetic field collapses if the battery is disconnected.

An engine won't even run very well if it's near dead after jump starting the engine. Odds are very good your battery simply needs to be replaced which can be verified by having an auto parts store do a load test to it. The TJ's alternator rarely fails.

And it's "pedal", not "petal". :)

Mt Goat 02-20-2011 05:35 PM

Jerry thanks for the information. The first battery I though might be older and need to be replaced but the second battery I pulled from my other car ands its only a couple years old. After two batteries I figured it was the alternator.

I always thought that once an engine was running that if the alternator was good you could disconnect the wires from the battery and the engine would still run ?

Jerry Bransford 02-20-2011 05:40 PM


Originally Posted by Mt Goat (Post 1069241)
I always thought that once an engine was running that if the alternator was good you could disconnect the wires from the battery and the engine would still run ?

That is only true with some alternators, although it is true with all generators that vehicles used to use many years ago. But the type of alternator the TJ has absolutely positively requires +12v from the battery for it to work.

herbie 02-20-2011 06:00 PM

charge the battery fully and do a proper load test, also check the alt output or have it tested as it could also be a field regulation problem

Zack93 02-20-2011 06:07 PM

Go to autozone and they test both of them for free, and help you get the right ones, and the stuff you need ;)

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