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Unread 10-07-2009, 06:13 AM   #1
Reverb
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1988 YJ Wrangler 
 
Join Date: Dec 2008
Location: NY
Posts: 600
diode on the alternator

Hi all,
my Yj won't turn off after it's been running. I've put a switch inline to the power for the distributor/fuel pump so i can turn it off.
I've read that it's a common problem and i need to put a diode inline with the alternator.
Anyone know what size diode and where on the alternator??

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Unread 10-07-2009, 06:24 AM   #2
Alfons
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1992 YJ Wrangler 
 
Join Date: Jul 2005
Location: Ontario, Canada
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Quote:
Originally Posted by Reverb View Post
Hi all,
my Yj won't turn off after it's been running. I've put a switch inline to the power for the distributor/fuel pump so i can turn it off.
I've read that it's a common problem and i need to put a diode inline with the alternator.
Anyone know what size diode and where on the alternator??
The first thing I'd do would be to make sure the key switch was working - it it "cuts" the power, the engine should stop. A lot of things need a good steady source of DC power to keep the engine running (including the computer).
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Unread 10-07-2009, 06:37 AM   #3
Que89YJ
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1989 YJ Wrangler 
 
Join Date: Apr 2008
Location: Detroit, Michigan
Posts: 14,564
Pull the asd relay and see if power drops. I just spent a week with Rebuild rookie troubleshooting the same type of problem. The question is wether power is going to the system through the relay or after the relay. Disconnecting the alternator will tell you if you need the diode or not. The diode stops the alternator field from back feeding. Do both and post back
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Unread 10-07-2009, 07:01 AM   #4
Reverb
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I'll give it a shot. Do I have an ASD relay on my 88 4.2?
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Unread 10-07-2009, 07:33 AM   #5
Que89YJ
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1989 YJ Wrangler 
 
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I didnt see that. Are you nuttered? Do the alternator first.
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Unread 10-07-2009, 08:04 AM   #6
Fernando
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1987 YJ Wrangler 
 
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Location: San José, Costa Rica
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Hello

If you have a 4.2 your fuel pump is mechanical, I do not know what you mean by cutting power to the distributor, I guess you have tapped on the line that provides power to the coil, the distributor itself has no power, or maybe you interrupted the connection between the distributor and the ignition module.

You need to install this part

Radio Shack part number 276-1103.

There is a brown wire coming off the alternator, this is the battery charge wire, you need to install the diode to prevent the current from flowing back from the battery to the alternator, diodes have a "side" to them so make sure you install it the right way, you can test this with a multimeter and I know there are marks on each side but can't remember now what they look like, just use the leads of the multimeter to check for continuity, one on each side, when you get a good reading you know you have identified the flow direction.

I did this on my YJ when I installed my MSD ignition box, I do not know why a stock YJ would have this problem, the MSD runs on so little current that a few volts coming back from the battery to the alternator were enough to keep it running.

Use proper soldering when attaching the diode and when you are done cover everything in shrink wrap.

If you need help I can take a picture of the wire but later today when I get off work

Good luck!
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Unread 10-07-2009, 10:07 AM   #7
Reverb
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Sorry I should have updated my profile - Currently running a HEI distributor and an electric fuel pump. I will get that diode and install it - I kinda like the kill switch I have in there so will probably leave that as an anti theft device.

thanks all for the help.

EDIT: 1A rating is enough for the diode?
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Unread 10-07-2009, 10:12 AM   #8
Fernando
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1987 YJ Wrangler 
 
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Location: San José, Costa Rica
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Quote:
Originally Posted by Reverb View Post
Sorry I should have updated my profile - Currently running a HEI distributor and an electric fuel pump. I will get that diode and install it - I kinda like the kill switch I have in there so will probably leave that as an anti theft device.

thanks all for the help.

EDIT: 1A rating is enough for the diode?
This is the part number recommended by MSD, should be fine, mine has worked flawlessly
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Quote:
Originally Posted by JeepHammer
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Unread 08-24-2013, 03:20 PM   #9
superj
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1987 YJ Wrangler 
 
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Location: corpus christi, texas
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This diode fix works great on the 76 cj5 we bought two weeks ago. I know this thread is from many moons ago, the info is still relevant as the diode part number is the one I just bought and installed and now the cj turns off properly
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