Coil/coil wire

Tiny
DANNY CAIN
  • MEMBER
  • 1999 JEEP CHEROKEE
  • 4.0L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 200,000 MILES
Vehicle wouldn't start so we got a new coil, when we plug the coil into the wire there is no power, but when it is unplugged there is power. Don't know what it is or how to fix it.
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Monday, May 13th, 2019 AT 2:10 PM

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Tiny
CARADIODOC
  • EXPERT
I'm not clear on where you're taking voltage readings, but if it's on the primary side of the ignition coil, there should only be 12 volts there for one second when you turn on the ignition switch, then it will go back to 0 volts. The 12 volts should come back during engine rotation, (cranking or running).

For this type of circuit, use a test light, if possible, instead of a digital voltmeter. The test light can be more accurate in finding some problems.

Another test is to back-probe any injector through the rubber seal. This will be the dark green / orange wire at the ignition coil or any injector. In particular, we want to know if the 12 volts comes back during cranking. If it does not, you won't have injector pulses or fuel pump either, so you don't want to waste time with the ignition coil.

The test points are shown in the first, third and fourth diagrams.
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Monday, May 13th, 2019 AT 6:13 PM

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