He is right, somewhere around 10-20% charged @ 12.1vdc. At that level when you crank the starter the system might be seeing in the 8-10 volt range, not enough to power the electronics. Typical problem with these jeeps, is the battery temp sensor goes bad. Even with everything working right, they still tend to undercharge, but either something is really amiss with your charging system or the battery may have seen better days. Just replaced one in a montego, it was also 12.1.

 

ok I’ll have it on the charger over night. It’s definitely discharged but not dead. Also this happened with a battery that sat only 1 night. I doubt it’s the battery but if I can’t get up to 12.66 from 12.1 or so then I’ll buy a new one.
Any idea what the voltage should be on the coil pack plug. I have 11v on the power wire and intermittently on the other 3 but no power getting to the plugs. I’m assuming through testing and process of elimination it’s the coil pack.
I’m unable to find where the voyage is supposed to be.
Thank you for the replies

 

cant help on the coil situation

be aware that once freshly charged, even a dud battery can often read above 12.6V. This is called a "float charge", and is almost meaningless.

to eliminate this, they need a bit of discharge, (ie headlights for 2min).. or to sit for a few hours

excessive cranking will obviously discharge a battery, as per normal. If they wont hold over 12.5V for a few days (without any discharge), they are bad

any battery over 3yrs old should be considered suspect, especially if it has run flat a few times

 

Well now, I say if he charges it overnight and in the morning disconnects it and lets it sit an hour and it's still under charged, time for a new battery. Went through this just last week.
As far as the coil pack goes, you should be able to check that with an ohm meter. Are there any diagnostic codes? You may have bias B+voltage at the coil but if you have no signal from the pcm it wont fire. With key on you have the bias voltage so I think the ASD relay circuit is ok..the usual suspect is the crank sensor, which you replaced, twice, followed by the cam sensor. Also the harness to either of those.

 

 

If no access to a scanner you can do the key trick and count the flashes to get the codes. It might very well be the coil pack if the other cyls are firing.