98 JGC no spark from coil

[larrydm]

Hi everyone,

This is going to seem a lot like some of the posts that already exist but I can't find one that matches exactly what I am experiencing so please be patient with me on this.

I have a 1998 JGC Limited with the 4.0 inline 6 motor. It has 218k for mileage and up until now it has run great. It started running rough and backfiring and progressively got worse until finally it won't even start. I had changed the plugs, distributor cap, rotor and plug wires when it was running rough but it made no difference. Now there is no spark from the coil and no voltage feeding the coil. It turns over fine but won't start. I tried my coil in another jeep and it worked fine.

After reading many of the threads here, it sounds like my CPS may be bad except, I have 5 volts to the sensor and I am getting voltage readings as high as 4.5v on the signal wire from the sensor. I can hear the fuel pump start when you turn the key and there is plenty of pressure at the fuel rail even though I haven't actually measured it. I don't get any error codes. I would suspect the security system but on my previous jeep, it would start then kill a few seconds after when the security system was the cause. I have disconnected the battery and then held the key in the start position for a minutes as adivsed in one thread. I unlocked the driver side door to disarm the security system-just in case. All to no avail.

I would really like to fix this without throwing a lot of parts at it if soemone can make sure I am heading in the right direction. I have considered the PCM may be bad I readf a thread that said if it were the PCM, the check engine light would not even comes on when you turn the key but if you waited 5 minutes or more it would.

Any help woulfd be greatly appreciated,

Thanks

Larry

[reekor]

Check your ASD relay,

Originally Posted by larrydm

Hi everyone,

This is going to seem a lot like some of the posts that already exist but I can't find one that matches exactly what I am experiencing so please be patient with me on this.

I have a 1998 JGC Limited with the 4.0 inline 6 motor. It has 218k for mileage and up until now it has run great. It started running rough and backfiring and progressively got worse until finally it won't even start. I had changed the plugs, distributor cap, rotor and plug wires when it was running rough but it made no difference. Now there is no spark from the coil and no voltage feeding the coil. It turns over fine but won't start. I tried my coil in another jeep and it worked fine.

After reading many of the threads here, it sounds like my CPS may be bad except, I have 5 volts to the sensor and I am getting voltage readings as high as 4.5v on the signal wire from the sensor. I can hear the fuel pump start when you turn the key and there is plenty of pressure at the fuel rail even though I haven't actually measured it. I don't get any error codes. I would suspect the security system but on my previous jeep, it would start then kill a few seconds after when the security system was the cause. I have disconnected the battery and then held the key in the start position for a minutes as adivsed in one thread. I unlocked the driver side door to disarm the security system-just in case. All to no avail.

I would really like to fix this without throwing a lot of parts at it if soemone can make sure I am heading in the right direction. I have considered the PCM may be bad I readf a thread that said if it were the PCM, the check engine light would not even comes on when you turn the key but if you waited 5 minutes or more it would.

Any help woulfd be greatly appreciated,

Thanks

Larry

[larrydm]

Thanks for the reply. I checked the ASD relay. I can hear the coil working so I assumed it was OK. I switched it out with another coil just to be sure but it didn't make any difference. I did install a new CPS but that didn't work either.

Anyone else have any ideas?

Thanks

Larry