post #1 of Old 07-12-2011, 03:58 PM Thread Starter
CLNinja
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Voltage issues

Havnt posted here in a while...especially asking a question about my own jeep ..

So my jeep has been sitting for a while , ive been doing some axle work and some power steering work and whatnot and basically i also just dont drive the jeep as much anymore since i have a new DD and the Jeep is just a toy.

I started up the Jeep ( after putting in a brand new battery ) and started it up and it didnt fire right up like it used to but it fired up and idled and ran just fine so i started to drive it to my parents house to do some work to it. well i noticed that the voltage guage was registering very very low.. in the red .. so i kept driving and almost to my parents house check engine light came on ( didnt check it ) i assumed it was because of low voltage. I took the battery back and replaced it with another brand new one ( just exchanged it with another, had only been a week so they swapped it out. )

voltage guage still registers very very low... but it seems to run just fine after it gets started up

im using a new kind of bettery that ive never used before its the Duralast Platinum .. supposed to be the same type of battery as an Optima. maybe its the battery... i dont know... i have a 5.9 alternator in the Jeep so i dont think the alternator is the problem but who knows..it is used after all

any ideas? im gonna get my alternator and bettery checked when i have time but i figured id ask here for ideas in the meantime


Matt
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post #2 of Old 07-12-2011, 04:01 PM
XOFMOT
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Does the voltage read low when driving say on the highway..2000 rpms or so??
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post #3 of Old 07-12-2011, 04:08 PM Thread Starter
CLNinja
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reads low while driving at 45mph or so .. thats the highest ive taken it like this... revving the engine or driving does not effect where the needle sits, it stays in the same spot very very low on the gauge

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post #4 of Old 07-12-2011, 05:05 PM
sebian
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After you get the charging system checked, check your body and block grounds to make sure they are clean and secure. If the grounds are ok, then probably looking at a new PCM.

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post #5 of Old 07-12-2011, 10:15 PM
onyx
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i would check your ground regardless of the batt the alt when running should be at atleast 12 if not id check the alt but check the voltage regulator in the pcm first
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post #6 of Old 07-12-2011, 11:02 PM Thread Starter
CLNinja
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i have a Mopar Performance PCM so i hope thats not what it is.... those are expensive and hard to come by


if thats what the problem is.. then ill be switching back to a stock PCM

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post #7 of Old 07-15-2011, 10:43 AM
onyx
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at advance they have bdu ones for 131.99
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post #8 of Old 07-15-2011, 03:51 PM
rooster51
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I would sure investigate and rule out the used alt before even considering a PCM. Your symptoms are not high on the list of bad PCM symptoms. Be sure to check the alt pully for function also.
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post #9 of Old 07-15-2011, 05:59 PM
JeepOrvis97
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Not to question the obvious but have you checked the volts with an external volt meter? Maybe the gauge is bad???
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post #10 of Old 07-15-2011, 06:12 PM
jeep210
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If you can use a voltage meter you can do some testing. With engine running, test the battery and it should read in the range of 13-15 volts. If it is reading 12 volts or less the alternator is not charging.

Now, with engine off for these tests, test the battery for voltage. Then test for voltage on large terminal on back of alternator. You should read the same as battery voltage. If you read battery voltage, then the cable from the alternator to the battery should be good. Check that it is clean and tight.

If you do not read battery voltage at the alternator, then you have a fault in the cable going to the battery. There is an inline fuse on this cable.

Finally, start the engine and have some one rev it up a bit. Now test for voltage on the alternator large terminal. You should read 13-15 volts. if it is charging.

Hope this helps and good luck.
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post #11 of Old 07-17-2011, 09:56 AM
onyx
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also look for any melted or stiff wires that feel brittle sometimes over time the wires will harden and crack like plastic allowing contact
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post #12 of Old 07-17-2011, 10:51 AM
98mopar
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You will need a voltmeter. With the engine off the battery should read around 12.4 volts. With the vehicle started and nothing else on (lights, radio, ac, ect) should read right around 14.5 volts. If not then you have an issue. First check battery terminals. Check for loose cables, or corrosion, or frayed ends. Then check your grounds. Also check your alternator fuse. Also check all your connections at your alternator. After all those things you find no faults, then you probably have a bad alternator.

--- 1998 ZJ 5.9 Limited - 4" lift, 31 x 10.50 15, Jet chip, Kenwood Excelon everything, current DD
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post #13 of Old 07-17-2011, 06:26 PM
onyx
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ive never had an alt go from working on a car if there was a jolt to the system you can kill the pcm
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post #14 of Old 07-17-2011, 06:28 PM
onyx
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nothing like the oops when someone connects positive with neg somewhere with a wrench or crosses wires and it costs you $$$$$
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