1999 jeep just quit

[moily]

My 99 jeep died in the driveway the other day - it turns over but no spark and no start. So...I'm assuming it's the computer because there is no voltage to the coil input with voltmeter when key is turned on. But...I jumped a lead from the battery to the coil input, checked and got 12 volts on the output side of coil, but it still won't start. Why? Am I on the right track here by replacing the computer, or am I missing something.

[AlohaBra]

Originally Posted by moily

My 99 jeep died in the driveway the other day - it turns over but no spark and no start. So...I'm assuming it's the computer because there is no voltage to the coil input with voltmeter when key is turned on. But...I jumped a lead from the battery to the coil input, checked and got 12 volts on the output side of coil, but it still won't start. Why? Am I on the right track here by replacing the computer, or am I missing something.

Oh, you better check other things first....computers are not cheap.
If you read other posts, things like the TPS, CPS, and NSS go all the time. Actually, my ignition switch went bad on my 97. There are also relays and switches plus fuses that should be checked first.

[89ltd]

if your crank shaft sensor or your cam shaft sensor or auto shut down relay is faulty, the computer will not send any power to the coil.

[moily]

can I check the cps and other sensors with my voltmeter? any specs on what voltages or resistance readings I should be looking for? I appreciate your replies.

[AlohaBra]

Originally Posted by moily

can I check the cps and other sensors with my voltmeter? any specs on what voltages or resistance readings I should be looking for? I appreciate your replies.

YOU can check the CPS with an ohmmeter, but I would get a new one an replace it...it is known for shorting out because it goes over the top of the auto trans and then by the exhaust. Don't drop the screws into the bell housing. See other posts on CPS.

[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.

DIAGNOSTICS: 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.

REPLACING 4.0L inline6 CPS: the swivel socket and a couple of 8 inch extentions. then come from underneath left wheel (from behind left front wheel). more easier for people with small arms. also my suggestion is to stick a crumble newspaper page right undernneath sensor to block the bolt from falling in the hole. I was lucky the magnet on the sensor was still strong enough to hold onto the bolt. I could see it already.... a simply replace job turn into a major tranny dropping job or something and all I am is a shade tree mach.