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how to check coil, distributor?


bledsoe's Avatar
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10-16-02, 09:25 AM   #1  
bledsoe
how to check coil, distributor?

Hi, '95 Cherokee, 115K miles, automatic. won't start. fuel pressure is perfect, I checked that. Now I need to figure out which ignition component is bad. This is my first time doing this. Can someone tell me the steps they would take to debug this problem? Am I right to:
1. check for spark by pulling a plug from the block, lay it close to a ground, watch for spark while my buddy cranks the engine?

then if there's spark there, how can I check to see if the distributor's getting juice? and then how to check the coil? after that?

One thing I noticed so far is that the main contact on the distributor(where the wire from the coil goes) is black. Could that be the problem? the other contacts(for the plug wires) are all clean.

Thanks!

 
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10-16-02, 09:43 AM   #2  
Joe_F
Start with the links and posts below in my signature file.

 
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10-16-02, 09:47 AM   #3  
bledsoe
Actually, I did, but the post doesn't go into specific details with regard to HOW to go performing these tests. Any advice?

Thanks

 
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10-16-02, 09:56 AM   #4  
Joe_F
Again, look at Autolibrary as instructed. The coil test procedures should be there.

If not, I suggest you get an Alldata.com subscription as it will contain the values of the coil and how to properly test it.

 
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10-16-02, 10:13 AM   #5  
Joe_F
Autolibrary has the procedures to test the ignition coil. I found it in a jiffy in two seconds.

Use the link as furnished by me below and let us know what you find.

 
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10-16-02, 12:33 PM   #6  
bledsoe
Oh ok, I thought you were talking about your "basics" post. sorry about that. I did find some good stuff at autolibrary, thanks. another question: how does the ECU factor into this problem? When starting, you have the battery providing power to the coil, then coil to the distributor, then to the plugs, correct? Where in this chain is the ECU and also crankshaft sensor? Thanks

 
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10-16-02, 12:37 PM   #7  
bledsoe
sorry guys, one last question: What does an ignition pickup do? I just saw a picture of one, but can't figure it out.

 
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10-16-02, 02:53 PM   #8  
rljsmith2001
The powertrain control module (what you call the ECU) uses an input from the crank sensor to tell the coil to send fire to the distributor cap which then goes to the appropriate spark plug. If you pull the spark plug wire, insert a screwdriver into the plug wire and place it so the blade of the screwdriver is near something metal for a ground but NOT touching. Have somebody crank the engine over and watch for spark, if you see spark it is working as it should. If you don't have spark, pull the coil wire off the distributor (should be the center wire in the cap) and do the same test. If you now have spark your problem is in the distributor cap or rotor button. If you still don't have spark then your problem could be either a faulty coil, a bad crank sensor or a problem with the PCM. You should get a professional to help you diagnose between the three.
As Joe always says "Diagnose it properly before replacing parts"
Good Luck.

 
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10-16-02, 02:56 PM   #9  
bledsoe
wow, exactly what I needed. Makes perfect sense. Thanks, I'll let you know

 
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10-16-02, 03:00 PM   #10  
Joe_F
Let us know what you find.

 
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10-17-02, 08:16 AM   #11  
bledsoe
here's the deal!

The plugs were soaked in fuel, plus they were all black, so that was the problem. I checked and found that there was spark getting to the plugs, so I knew the plugs were to blame. I replaced them and after trying a couple times(only because the engine was slightly flooded), it fired right up. Thanks for the help. Remaining questions:
1. How would you ever know if the spark was too weak? When I saw spark, I assumed that the distributor parts were Ok and that the plugs were to blame, but how could you tell if the spark was weak?

2. If I had needed to, how could I test to see if power is getting to the coil?

3. Also, I didn't have the tool to gap the plugs this morning, so we just threw the plugs in. Should I take them back out and verify the gap is correct? it is running ok....

thanks!

 
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10-17-02, 10:42 AM   #12  
rljsmith2001
Strong spark is blue, weak spark is yellow. Power to your coil is controlled by the PCM, you need a wiring diagram and a digital multimeter or a computer safe test light to see if the coil is getting powered up by the PCM. There are only two wires in the connector to the coil.
I would probably check the gap on the plugs, should be a label on the hood giving you the gap and the tool is fairly inexpensive.
Good Luck

 
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10-17-02, 01:12 PM   #13  
redneck
Black carbon filed plugs are a symptom of another problem! This is not normal--and most likely will happen again.

 
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