Another hard start thread...

Ok, I've been searching (on here and under the hood) for a while so I thought I'd post up since I'm not finding an answer.

96 4.0 auto, 190,000 kms

A couple weeks ago, I hopped in and turned the key. All it did was crank, didn't even try to catch. Weird, since it's been dead-reliable for a couple years now. I crank again and after several seconds it starts to sputter then reluctantly starts. Takes a couple seconds to smooth out, then all's well. Idle was fine, performance was fine. It did it again the next day but then the problem went away for 2 weeks.

Now 2 weeks later the problem is back and worse than ever. I also started getting a brief stumble when pulling away from a stoplight and seem to be running slightly rougher (or maybe it's just my imagination).

Now the only way to start it is by holding the gas pedal to the floor. If I don't, all it does is crank. I can smell fuel and hear the pump running. It only takes a second or two to fire with the pedal held down. Once it's running, it idles fine. But give the gas pedal a stab and it stumbles, then revs, then holds the revs high for a second, then very slowly returns to normal idle.

Just did the basic tuneup - plugs, air filter, throttle body cleaner, wiggled connectors, inspected distributor cap/rotor/coil/wires. No effect.

Vacuum leak? Haven't found one yet but I'm going to keep looking.
If it had a carburetor, I'd blame the choke.
CPS? TPS? How do I test those with a multimeter (how's that for a newbie question)?

I'd really appreciate any advice or direction - I'm planning to take it on a road trip up north this weekend to a buddy's cottage and hit a trail or two.
Thanks!

Didn't get any further last night. Had to hold my foot to the floor to get it started and move it. When I got in it this morning, it fired up no problem and has been running great since.

My mechanic suggested crank position sensor or cam position sensor but scratched his head about the pedal-to-the-floor cure.

Doesn't seem to matter whether it's hot or cold.
No CELs.
I'll try pulling codes tonight.
Should also do the fuel filter, I suppose.
Can't be fuel pressure if it runs fine most of the time, right? But I suppose the pump or regulator could be on their way out, creating sporadic pressure levels.
O2 sensor? I already replaced the one just ahead of the cat.

Could it actually just be the weather? We've had record rainfall this summer.
Bad gas? That always sounds like a myth to me. But I filled up with higher octane this morning figuring it could only help.

I know all this stuff has been discussed ad nauseum but I'm just going to keep updating this thread and hope that it helps someone else some day.

Jeep ran great all day today.

I pulled the codes:
12: Battery disconnected (I've also read that this might just be a code to indicate that the codes are coming?)
17: Engine running too cold
55: End of code

http://go.jeep-xj.info/HowtoECUcodes.htm

Haven't disconnected the battery in ages so maybe I have a bad ground and it's affected by the wet weather.

Not sure I believe the 17. Thermostat seems to function properly and temp gauge reads fine. I'll be grabbing a new thermostat to have in the truck just in case.

Picked up a new crank position sensor for the heck of it. I'll hopefully have time to install it this weekend. From the sounds of things, it's not if your CPS will go bad, it's when.

Heading up to the cottage tomorrow afternoon. Fingers crossed.

It's nearly a week later and the problem hasn't returned. Made it up to the cottage and back without issue (3 hours each way). Ran great.

I kept the tank above half-full and ran 91 octane. I'll let the level drop down and see if the problem comes back. If it does, that could indicate a fuel pump related issue.

I'll be installing a new CPS, thermostat, water pump (starting to make some noise) and belt. Will pick up a new fuel filter as well. I'll also be cleaning all the grounds.

Ran the tank down below 1/8th and the little low fuel light came on. The hard start issue still hasn't returned. We've also had a lot less rain lately, so that might still have something to do with it. Haven't made any repairs yet, I was hoping the symptoms would show up again before I go changing variables.

If you're thinking this is becoming a pointless thread, I'm starting to think the same thing.

Try the coolant temp sensor. It's about 25 bucks. The sensor thinks its way to cold and tries to overcompensate with gas and floods itself. When you open the throttle it doesn't give it more gas it gives it more air, that's why it tries to run. Maybe a bad or corroded connection.

That makes sense. It totally seems like it's flooding. I'll do that repair for sure. Thanks for the help!

Update:

XJ was running fine until a couple days ago. Then she died on me yesterday as I left work. Seems to only happen before the motor has warmed up to operating temp., backing up dfete91's theory of an issue in the coolant temp. sensor circuitry. The result being running too rich for too long at startup? Restarting with my foot to the floor still works, so she's flooding.

I'd picked up a coolant temp sensor from Napa for a 96 XJ for $17. But when I went to install it last night, I noticed it wasn't the right part.

The Napa computers don't seem to know that some (or all?) 96 XJs came with the updated engine found in 97 and later models. If you have a 96 XJ, the correct coolant temp. sensor is actually listed as a part for a 97 and costs $50. Nice.

Anyway, I'll be installing it this weekend. But pulling the connector and wiggling it a bit has the truck running like a top again. Could've just been dirty contacts. I found a procedure for testing the sensor so I'll do that before replacing it. Go to page 3 of this pdf from Wells Mfg.: http://www.wellsmfgcorp.com/pdf/Counterpoint2_2.pdf

Ok, sorry to resurect this old and semi-pointless thread yet again. But after one month, the symptoms haven't returned. All I did was clean the contacts on the original coolant temp sensor (located at the thermostat housing). That seems to have fixed the issue. Never did replace the sensor, so I now have a backup, I guess.

Just wanted to follow up and let anyone know who's having intermittent issues like mine to check all their electrical connections. It can save a lot of time and money.

10 points to dfete for suggesting the coolant temp sensor - thanks!

Lock it up.

hey i got a 96 4.0 with 190k miles on it and i'm gettin almost the same symptoms as you and im tryin to figure it out, my sister is drivin it now and my dad wants to get rid of it so it doesn't leave her sit but i wanna keep it since he had it since 10k and i got it at 134k lol anyways can you maybe try and take a pic of where the sensor is you cleaned so i can try this, my only other thoughts on mine are a clogged cat or O2's.