I chased this problem for weeks in my YJ. There are several things it could be.
1)..ASD Relay - Auto Shut Down Relay Yes it's under the hood in the main
.....fuse box. I pulled mine and checked it with a meter. Also check the
.....Power wires that goes to the blades on the bottom of the fuse box, where
.....the relay pushes in. Mine was loose and caused me problems every time I
.....would hit a bump. I would loose power for a split second and the jeep
.....would shut off while I was driving.
2) FP Relay - Fuel Pump Relay in the same fuse box under the hood. Also
.....check that relay with a meter and also check the power wires going to
.....the blades to the bottom.
**(tip)** there is a Horn Relay in the same box. Test the horn and then
...............swap out the relay with the auto shut down and the fuel pump
...............to check for operation.
.....a) both of these will not allow your Jeep to start and you will not hear
..........the fuel pump prime until these are working.
.....b) Have someone sit in the drivers seat and you get down on your knees
..........by the rear bumper. You should hear the fuel pump prime with a 2
..........second hum that is loud enough to hear.
.....c) Next if the fuel pump is priming, check the fuel pressure at the fuel
..........rail. Its up under the hood and has a small schreader valve that looks
..........like an air valve stem. Take a small screw driver and press the center
..........stem in. If you have fuel pressure, you will have fuel spray out. If
..........not, we are starting to narrow it down
3) CCS / Crank Case Sensor - You could also have a bad CCS. This is a
.....sensor that is on the top quarter of your bell housing at about 10:00
.....O-clock. This senses where your fly wheel is in relation to your motor.
.....If the sensor goes bad, your ECU can not see it and it won't start. It's
.....around $25.00 at any parts store and is extremely easy to replace.
4) Distributor Pick Up - This is located on the inside and at the bottom of
.....your distributor. This sensor goes bad often and won't allow the motor
.....to start. Your distributor has to be pulled and taken apart to get to this
.....sensor. Again, it's not expensive. I think it's around $34.00 dollars.
5) ECU / Engine Control Module - Sometimes your ECU's capacitors start to
.....go bad. These store the needed energy to power up your ECU when
.....starting you Jeep. When these go bad there are some tell tale signs.
.....When you turn your key on, does your check engine light come on and
.....does your buzzer sound? If not it could be your ECU. This is your Jeeps
.....main computer or Brain Box.
..........a) If your check engine light and the buzzer doesn't sound, turn your
...............key to the on position. Let it sit for 3-5 minutes to allow the
...............ECU's capacitors to store up enough energy to power up the ECU
..........b) After the capacitors build up power for 5 minutes, turn the key and
...............start the Jeep. If it fires up it's your ECU.
**(Tip)** A rebuilt ECU with your core is around $200.00. There are a lot of
...............write up's on replacing the capacitors in your ECU. The parts cost
...............less then $4.00 and if you can solder, you can fix this.
This is a good starting point to track down your No Start Problem.
John
