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Unread 01-10-2010, 06:12 PM   #1
barlow
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1966 CJ5 
 
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drop in voltage and loss of starting

So, I replaced the brake switch and went to fire up my rig and it turned REAL slow and was unable to fire up? It would get to a slow rrrrr and not kick over. I even tried to jump it and was still unsuccessful. I had my battery load tested and it checked ok! Any thoughts on why my power to start has dropped? Thanks.

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Unread 01-11-2010, 06:26 AM   #2
Mike Romain
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The odds are high that you have a bad battery cable connection. Don't forget that those cables have two ends when you go to clean them.
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Unread 01-11-2010, 06:47 AM   #3
bobzoppa
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"The odds are high that you have a bad battery cable connection. Don't forget that those cables have two ends when you go to clean them."

Two more things
1st-- Grounds there's a list of grounds floating around the site-do a search- that should be added,If elec can't flow through and back to ground, things won't work. Make sure you get the main block to frame ground strap. For a quick test ground the starter from one of the mounting bolts to the frame with jumper cables.
2nd Pull the starter and have it tested
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Unread 01-11-2010, 07:24 AM   #4
barlow
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Thanks, I will give it a try and let you know.
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Unread 01-11-2010, 07:26 AM   #5
barlow
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Also, can I test the resistance by connecting the ohm meter on (-) battery and the (-) on the starter? Thanks.
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Unread 01-11-2010, 07:44 AM   #6
Mike Romain
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Quote:
Originally Posted by barlow View Post
Also, can I test the resistance by connecting the ohm meter on (-) battery and the (-) on the starter? Thanks.
Certainly and you can 'walk' the meter back to see where the resistance gets better. Sometimes it is even the cable to clamp connection on a battery cable which you can find by poking the meter probe into the cable as you 'walk' the meter along the circuit.

I normally use a booster cable from the battery negative to the part to verify the ground.
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89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
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Unread 01-11-2010, 07:50 AM   #7
barlow
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Thanks, I will give this a shot later along with the booster cable.
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Unread 01-11-2010, 08:10 AM   #8
jfwireless
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Looking at the resistance of the cables/connections with a meter is a good start, but many times these dirty/corroded connections break down under load, and you may not see that on a resistance test as you are not drawing much current with that test. I prefer to use the voltage drop test, put your meter on the 12 volt scale and measure across the cable while trying to crank the engine, see how much of a voltage drop you have across each cable or the starting relay(solenoid) contacts. You can also just go straight to the starter and see how much voltage is getting to the starter while trying to crank. Just use a couple of clip leads to the starter case(ground) and +12 volt terminal on the starter.

To check the battery just put the voltmeter on the two battery posts and see how much voltage you have when trying to crank, if the battery posts voltage drop significantly, that battery is toast. Make sure you try this test first on the battery posts, not the clamp connectors on the battery cables as these clamp connectors connection to the battery terminals can be the problem. You can check this by just putting one voltmeter lead on the battery post, and the other on the battery cable clamp connector, if you see a voltage drop, clean up that connection.

I also just feel the battery/starter cable connections after trying to start the engine, many times a bad connection will heat up. Be carefull, sometimes the connection can get hot enough to burn you.

Jim
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Unread 01-11-2010, 08:53 AM   #9
John Strenk
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Yes, I prefer the voltage drop check also.
I think the limit is 0.1volt per cable. So if you put you voltmeter across a cable from one end to the other, you should not see it rise over 0.1 volt when cranking.

The other way as described is to measure the voltage first across the battery and crank the engine. Say it drops to 11.55 volts. Then check the voltage at the starter motor terminal. The voltage there should be higher than 11.35 volts.

There are 3 cables usually to check. from (+) to Starter solenoid, from starter solenoid to starter and from (-) to engine block. I know some people like to attach the ground wire right to the bolt holding the starter to the block. This will surely put the power were it's most needed.
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