Dying XJ on the way to Prom=Not Fun

Stats on the XJ:
1995
105xxx Miles
4.0
AW4
231
3" Lift
31" BFG A/Ts

On my way to prom last week my Jeep decided it didn't want to go. I'm driving down the road, no problems, everything's normal, when all of a sudden everything dies. The tachometer goes to zero, the speedometer goes to zero, the AC turns off, the radio turns off, no power steering. Literally everything shuts off. Well about 5 seconds later everything electrical turns back on but it won't start. It cranks, but won't actually start.

I pull over and look under the hood and the ground wire to the battery was disconnected. I fixed that and it started, but then died again within 100 feet.

Waited a few minutes and it starts again, only to die once more.

Long story short, my Jeep is still doing this. It will start and have no problems idling but when I start driving after just a little bit it'll die. When it dies everything shuts off, then come back on, crank, but won't start.
My dad and I have checked most of the connections and cleaned them up to no avail.
I have no idea what the problem is. Does anybody have a clue what it could be, or where to start? I need my Jeep back!

A few weeks back the "part time" light would come on seemingly randomly. Like I'd just be driving down the road in 2WD and it would come on. I don't know if that helps, but otherwise it hasn't been acting weird...

Thanks in advance, guys.

hmmm have you checked the alternator yet?

Not yet. We checked the battery and had good voltage there though. Would the alternator keep it from actually starting in this situation? It'll die, but it still cranks strong, it just won't start immediately.

Yes. If your alternator fails, your rig runs off your battery (which is why the reserve time is a good thing to look at when buying a new one) and when the battery runs out, S.O.L. Also, a lot of times the regulator is actually the part that goes out and it fails when warm, so your stuff will pass on a bench test when cold

Oh okay. Thanks! I'm gonna check that tomorrow.
What I still don't understand though is that if it is the alternator, why it will die, and it will crank but won't start. It seems to me that if it was the alternator, and it was just going off the battery, it would either not crank, or start immediately. Am I just wrong in my thinking? Lol. I'm trying to learn as I go here :thumbup:

That's real tricky, will it start at all or will it crank forever?

ok, you said that you had to reconnect the ground wire to get it to start up. and that you are still having issues. that leads me to venture to say its a grounding issue.

examine your grounds carefully. i dont mean just look at them. take the grounds off where they attach to. take some fine grit sandpaper or a wire brush and clean the underside of the ring terminals until they are shiny metal. then do the same to where they contact the sheet metal. if there is paint under the ground ring terminal, remove it. if your worried about rust/corrosion use a product called oxguard over the bare metal (it promotes conductivity and prevents corrosion where dielectric grease insulates and prevents corrosion). obviously hit the ground next to the battery, but also all the other grounds you can get to- the one by the battery, engine ground strap at the back of the driver side, i know theres more but i am having a brain fart. also, clean your batt terminals. speaking of batt terminals, if there is any exposed wire to the batt terminals then you WILL have green gremlins inside the wire. those are no good. if you find the gremlins, then you need to remove all the green, dark colored or corroded wire until you get to bright shiny copper. a lot of times you are then left with not enough wire to hook it back up to your battery. instead of just replacing, look into batt cable upgrades like the ones available from 5-90 (http://www.geocities.com/JeepI6Power/).

and since your at it take the time to clean the positive terminal on the batt and also the alt wire and terminal, and PDC terminals.

hth

is it possible that you have a broken motor mount and every time it starts, the engine rocks and pulls a ground connection apart on the block/ firewall?

Crank but won't start is not your alternator. Your issue sounds most like a bad connection or ground. If you really think you have all that covered, change the Crank Position Sensor. They are notorious for "crank - won't start" and "starts / runs / dies". And due to the intermittent nature, sometimes tests good, but changing it fixes the problem anyway.

Yes it will just crank forever. After cranking it several times and letting it sit a few minutes it'll start though.

We did look and clean up the battery terminals and connections that we could find, so I don't think those are the culprit although I could check again.

The more I'm looking around on the internet, the more it sounds like it may be the CPS. Sounds like I'll be taking a trip to O'Reilly's in the very near future :greensmok

A couple of questions...

When it does start, how long does it run?

Have you checked the codes?

When the Jeep just sits idling, it hasn't died. But It dies within a minute or so of normal driving. It happens whether the engine is cold or hot. If I step on the gas hard, the RPMs go up some, but kinda bogs/stutters then immediately dies.

I checked the codes and I have two: code 33 and code 35 which looks to be the AC clutch relay and the fan control relay. Both of which have been on since I bought the XJ about seven months ago..

My thoughts are CPS, or Throttle Position Sensor...

I don't know if there's a way to check them other than new sensors, I'll check in the 1992 FSM and see what I can find.

Look, life begins with the battery. Go back to basics--remove both cables and charge the battery overnight/24 hours. While it is charging, clean the cable ends and renew all of the grounds. Once fully charged take the battery to a chain parts store and have them load test it. If the battery is good, hook it back up and verify 12v across the terminals. Start the engine and check for 13.6+ volts, but less than 15 volts.

Your starter will crank with less volts than what it takes to run the electronics, which is about 9+ volts.

Here's what the FSM says... ( I haven't actually tried this yet, I don't have the tools.)

A basic test of the CPS is as follows...

Unplug CPS.
Place an ohmmeter across terminals A & B (When looking into the connector on CPS A terminal is on top, sitting on B & C terminals.)
The meter reading should be open, with no resistance. If there is any resistance, replace the sensor.

A basic test of the TPS is as follows...

With the ignition in the 'on' position, and the TPS still plugged in, check the center terminal wire (middle one) with a digital voltmeter. At idle (throttle plate closed) the reading should be greater than 200 millivolts, at WOT (throttle plate open) the reading should be less than 4.8 volts. The output voltage should increase gradually as the plate is slowly opened from idle to WOT.

Sorry I can't be more descriptive, it's straight from the FSM.

HTH!

TPS is best checked with an analog (needle gage) voltmeter, so that you can look for dead spots that the digital won't show.

With intermittant conditions CKP (crank position sensor) might check good when you test it but still be the bad part.