No spark

[tnolan19]

I have a 1988 4.0L. I do not appaer to have any spark. I have installed a new cap and rotor. Any help here?

[89ltd]

test or replace you crank position sensor.

[JDusen4211]

if there is no spark coming from the distributor, check to see if there is spark coming from the coil. if there isn't, then check the voltage at the coil. it should be relatively the same voltage as the battery. to check the voltage, the key must be in the run or start positions. if there is no voltage or extream differences, then go back through the ignition system all the way to the computer by checking the voltage at each component. use a wiring diagram to indicate places to check. hope this helps.

Originally Posted by tnolan19

I have a 1988 4.0L. I do not appaer to have any spark. I have installed a new cap and rotor. Any help here?

[jdsalas]

this just happened to me. there is a good possibility it is the CPS (crank position sensor. When you look through the forum you will see no spark with everything working usual ends up being the Crank Position sensor (CPS). The jeep will not start if this has a problem. There is a wiring harness that follows the fuel injector rail and comes back out behind the throttle body. One of the connectors from that wiring harness goes back and down to the transmission. If you follow that wire to the end you will see a black sensor near a open in the transmission with flywheel with teeth. this is secured by two bolts. Now, the connector has three wires, left, middle, right. with a ohms meter check the middle wire to the battery ground the reading should be less than 5 ohms. If higher than the wiring needs repair or replacement. If OK than turn the ignition on but don't start and voltage probe the middle wire with one of the outer wires (middle and left or middle and right) to find out which one is giving out over 5 volts. next voltage probe between the middle wire and the one that did not have voltage and with the probes connected have someone crank the engine, the voltage reading sould be alternating between 0.0 and 5.0 volts or averaged out to 2.5 in some voltmeters. The book (chilton) says if the voltage reading is not as specified above the sensor maybe faulty. Which is the conservative way of saying it's broken and you need to replace it.

[wwwildman]

I would check the Camshaft position sensor first. This is otherwise known as the pickup coil. For your year, if it is the pickup coil, you will have to take the distributor out to change the pickup coil. Advance sales the part for for about $50.
To test the Crackshaft position sensor, use an ohmeter to check the resistance of the CPS. You can also disconnect the connector to the CPS and check for voltage across the leads while cranking. Voltage should be between .2 and .8 volts.