No voltage on primary side of coil

Tiny
BREDMONDSON1
  • MEMBER
  • 1994 JEEP CHEROKEE
  • 4.0L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 400,000 MILES
I get no spark from coil. No power to coil. Everything else works fine, except when I turn the ignition key to start my oil gauge meter doesn't register.
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Monday, May 31st, 2021 AT 3:36 PM

26 Replies

Tiny
ASEMASTER6371
  • CERTIFIED MECHANIC
Good evening,

The power for the ignition coil comes from the auto shutdown relay.

I attached a wiring diagram for you to view and also the location of the relay for testing.

https://www.2carpros.com/articles/how-to-check-wiring

With the key on, there should be 2 powers to the relay. You need a voltmeter to do this check and verify. The relay is a common failure.

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Roy
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Monday, May 31st, 2021 AT 4:36 PM
Tiny
BREDMONDSON1
  • MEMBER
The only thing that baffles me is that I checked all relays before and they were all good. I eventually started the engine and it went about 10 feet and shut off. Then, it wouldn't restart.
Do you think the ignition switch might be causing everything?
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Monday, May 31st, 2021 AT 6:41 PM
Tiny
ASEMASTER6371
  • CERTIFIED MECHANIC
How did you check the relays?

Yes, the ignition switch provides power to the auto shutdown relay but this needs to be confirmed. You need to do the test I suggested by checking for powers at the relay.

Roy
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Monday, May 31st, 2021 AT 6:44 PM
Tiny
BREDMONDSON1
  • MEMBER
I'll re-check tomorrow. But I tested the relays under voltage to check the contact connection. I also checked the resistance. I really do hope you are right.
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Monday, May 31st, 2021 AT 6:53 PM
Tiny
ASEMASTER6371
  • CERTIFIED MECHANIC
The ECM is what grounds the relay for it to provide power to all the components.

Roy
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Monday, May 31st, 2021 AT 7:08 PM
Tiny
BREDMONDSON1
  • MEMBER
Okay, I replaced the shut down relay. Nothing changed.
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Tuesday, June 1st, 2021 AT 9:47 AM
Tiny
ASEMASTER6371
  • CERTIFIED MECHANIC
You needed to check for power to the relay. You need 2 terminals with 12 volts with the key on.

Roy
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Tuesday, June 1st, 2021 AT 9:53 AM
Tiny
BREDMONDSON1
  • MEMBER
I checked it, I didn't get a click. So, I went on and replaced it.
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Tuesday, June 1st, 2021 AT 10:06 AM
Tiny
ASEMASTER6371
  • CERTIFIED MECHANIC
Again, do you have 2 terminals with power with the key on?

Roy
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Tuesday, June 1st, 2021 AT 10:15 AM
Tiny
BREDMONDSON1
  • MEMBER
I don't follow you on that one. Clue me in, please.
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Tuesday, June 1st, 2021 AT 10:19 AM
Tiny
BREDMONDSON1
  • MEMBER
I don't know which terminals you are asking about.
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Tuesday, June 1st, 2021 AT 10:29 AM
Tiny
ASEMASTER6371
  • CERTIFIED MECHANIC
Remove the relay and with a voltmeter or test light, see if 2 of the terminals have voltage with the key on.

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

Roy
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Tuesday, June 1st, 2021 AT 10:46 AM
Tiny
BREDMONDSON1
  • MEMBER
I tested the 87 and 30 terminals with a light and got no voltage.
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Tuesday, June 1st, 2021 AT 11:07 AM
Tiny
ASEMASTER6371
  • CERTIFIED MECHANIC
Pin 30 needs power all the time. I attached a diagram with the fuse that controls the power for that pin. Check that fuse for power on both sides.

Pin 87 will only have power when the relay is energized.

Roy
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Tuesday, June 1st, 2021 AT 12:05 PM
Tiny
BREDMONDSON1
  • MEMBER
There is power at the pin 30. The fuse had power on both sides.
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Tuesday, June 1st, 2021 AT 1:16 PM
Tiny
ASEMASTER6371
  • CERTIFIED MECHANIC
You just stated there was no power to 30? Please clarify.

What about 85 or 86? One of those has to have power as well.

Roy
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Tuesday, June 1st, 2021 AT 2:39 PM
Tiny
BREDMONDSON1
  • MEMBER
I stated that there is power on pin 30. I also checked the resistor; it had power on both sides.
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Tuesday, June 1st, 2021 AT 2:42 PM
Tiny
ASEMASTER6371
  • CERTIFIED MECHANIC
Your response:

I tested the 87 and 30 terminals with a test light and got no voltage.

I need to know if there is a second voltage at 85 or 86.

Roy
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Tuesday, June 1st, 2021 AT 2:45 PM
Tiny
BREDMONDSON1
  • MEMBER
With switch "off", I got no power. With "on" I got power.
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Tuesday, June 1st, 2021 AT 3:05 PM
Tiny
ASEMASTER6371
  • CERTIFIED MECHANIC
At what terminal do you have power with the key on?

Roy
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Tuesday, June 1st, 2021 AT 3:12 PM

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