No power to Coil

My jeep doesn't have any power going to the coil. Check for obvious things.

I saw Alfman with a similar situation. The mechanic has been working on this

problem for about two weeks now and I really need my Jeep back.:doh:

The guy you're working with is not a mechanic. What's your year and I guess engine.

It's the Crank position sensor.

replace it and drive on!

nw-xj-scott said:

It's the Crank position sensor.

replace it and drive on!

Click to expand...

X2

He said "My jeep doesn't have any power going to the coil", not "no spark". Two different issues.

Checked the latch relay? I think that was the source of the problem over on the other thread.

lawsoncl said:

He said "My jeep doesn't have any power going to the coil", not "no spark". Two different issues.

Checked the latch relay? I think that was the source of the problem over on the other thread.

Click to expand...

Don't throw parts at it without testing! (Sorry, my pet pieve.) Lawsoncl has a good point. I believe that the normal funtion of a coil is to have 12 volts going to it. A spark is fired when the ground side of the coil is interupted. In other words, the spark triggering system does not stop juice from getting to the coil.

1992 4.0L Where does the power to the coil come from?

This is a temperature issue because it will start when it 40 degrees out.

winterbeater said:

The guy you're working with is not a mechanic. What's your year and I guess engine.

Click to expand...

1992 4.0L

nw-xj-scott said:

It's the Crank position sensor.

replace it and drive on!

Click to expand...

Crank position was replaced because it was cracked in half.

turkman182 said:

1992 4.0L Where does the power to the coil come from?

This is a temperature issue because it will start when it 40 degrees out.

Click to expand...

If you've got a voltmeter, check for +12-volts on one side of the connector. That is fed from the Auto ShutDown (ASD) relay which is controlled by the engine computer. The ground side of the coil is controlled by the computer.

Temperature dependant could be the coil, although they usually get bad when hot. Swapping or even just tapping on the relay might sort things out for ya.

The ASD relay (through the PCM) needs some pulsing from the CPS to actuate (or it's beens said also from the sync sensor). In normal function the motor stops and the ASD relay opens.
An easy test is to check the fuel pump relay, it should close for a second as soon as the key is turned to run then open, then close again along with the ASD relay while the motor is cranking.
If the ASD relay and the Fuel pump relay don't close during cranking, it's most likely a sensor or the wiring.
If the relays are closing, but still no spark, it's likely a fuse and/or a harness problem.
You can do a key test and check your MIL codes, if you can't check your MIL codes, it is often a short in the CPS or the sync sensor. A shorted 5 volt sensor supply, can kill the MIL code function.