Jeeper  Adventures Under the Hood  Jeeper

Tricked Ignition

This is what the ignition looks like after being modified to look like the pre-1983 wiring. This modification to later CJs was made famous on the Internet most notably by John Nutter, and is commonly referred to as "The Nutter Bypass," or "The Nutter Mod."

Modified Ignition

The solid-state ignition module is located under the washer reservoir.

A length of wire must be added to extend the violet wire from the distributor to the ignition module.

The distributor vacuum advance hose is moved from manifold vacuum to ported vacuum. You should add a tee here because ported vacuum also operates the EGR valve and charcoal canister purging.

The stepper motor on the Carter BBD is unplugged. The metering pins should be moved forward to the full-rich position before unplugging it. To accomplish this, and assuming the stepper motor is working to begin with:

  1. Create an air leak somewhere by unplugging a vacuum line. The metering pins should move forward to the full-rich position.
  2. Turn the engine off.
  3. Unplug the stepper motor.
There is discussion and disagreement about whether the metering pins should be fully forward, or more toward the middle. In my own personal experience, placing them fully forward makes the engine run a little stronger, but placing them more toward the middle improves gas mileage somewhat.

The timing must be set differently since the computer no longer controls it.

  1. Disconnect the vacuum advance hose at the distributor and plug it.
  2. Set the timing to 8 degrees BTDC.
  3. Reconnect the vacuum hose.

A Trick

Your buddy borrowed your timing light and never returned it? Here's a trick I learned from my brother. The timing can be set to surprising accuracy with a vacuum gauge. Hook the gauge to manifold vacuum and run the engine at curb idle. Rotate the distributor clockwise to retard the timing. Now slowly rotate it counter-clockwise to the point where you just reach the maximum vacuum reading. Back off (clockwise) until the vacuum drops by 1". Lock the distributor down. Timing can be set to ±1° using this method.

Note: With no distributor signal input, the computer does not know the engine is running, and remains asleep. In this state, the input sensors and controlled devices have no function. The idle speed controls, BBD stepper motor, and the Pulse Air system do not work.

Looking at it another way, if the computer has been taken out of the loop and no longer functions, the only things that do work are: