Harbison

Battery ran down while removing headliner due to dome light left on. Sat for a week before I noticed battery was dead. Charged battery. Cranks but won't start. Someone suggested holding gas pedal down. (Relearn idle?) Did that, no change. I replaced the Crankshaft Position Sensor a couple of years ago. After cranking on it a couple of seconds, gauge goes from 12v to 10v but goes back up to 12v when you stop cranking. Tried it with battery charger, with jumper cables. Just cranks but won't start. Been very reliable up until this. Any suggestions?

awg

I would test for spark, and fuel pressure at the rail...does the fuel pump whir for 2-3 secs when the ignition key is turned to "on" position?

if your battery is old & suspect replace it

country2

my 2000 when this happens I got to keep holding pedal down and keep trying it sometimes it may take 10 secs or so cranking maybe and then still got to keep it revved up for a while till it relearns. How long did you let it crank?

dave1123

Take the battery out and get it fully charged and load tested. With a marginal battery, the starter may be pulling all the power available and not leaving enough for the computer to function while cranking. JMHO.

BlueRidgeMark

X2.

And while you are at it, clean up those battery cable connections. All 8 of them.

DFlintstone

Holding the petal floorboarded is what you do if it's flooded. It cuts off fuel and provides max air.

country2

Yup, but on mine to get it to crank after removing battery/clearing the computer that's the only way. If you don't hold gas down it won't catch and run.

dzywicki

I learned the hard way that XJs do not like a marginal battery. I have a '99 that I accidentally ran the battery all the way down. I put a charge on the battery and it still wouldn't start. Tried to jump it and it still wouldn't start. I was finally able to get it started but it wouldn't stay idling unless I kept on the throttle. Pulled the battery and put a full battery tender charge on it and still wouldn't idle. It started and ran perfectly fine prior to the battery killing so I didn't go down the parts cannon path. Did some searching and found a lot of threads saying the same thing about a a marginal battery. Got a fresh replacement and it started right up and idles perfect. I have used a battery tender on many different batteries after they had been run down and never experienced anything like I did on this XJ.
Had the same thing happen on my '98 due to the dome light. Same process, same replace the battery and everything is good to go again. Wouldn't have beleived it unless it happened to me, twice.

dave1123

Look at it this way. The PCM has a voltage regulator in it that changes the 12v supply to 5v. If it doesn't get 12v in, it won't output 5v for digital switching.

Waynerd

Don’t hold the pedal to the floor otherwise it shuts down the injectors. Instead just hold I t down a little maybe even just tap it a few times. If it still doesn’t start then the battery is really gone.

Kind if off off the topic but I figure it’s a good time to tell a story. I bought a 91 c1500 in the December ‘18. 4.3 with 239,000 miles. It was sitting for a year. Charged the battery, changed the oil and put some gas in it. Drove it home. To this day I can let it sit for a month and go out and fire it up without a jump even. Still has the same battery that sat dead for a year. Lol. When I went to get it I said there’s no way that battery is going to take a charge. I’ve never been so wrong.

I guess it doesn’t have near the amount of electronic components of a Cherokee so I would assume that’s why. But I wouldn’t even think it would retain enough to crank the engine.

dave1123

Okay, but it's a Chevy! My 89 350 was the same way. Always cranked! The TBI was a problem sometimes.