'99 XJ HELP!

I have a stock '99 XJ Classic at 120,000 miles, I got it around 75,000 miles. I have been good about changing fluids and basic tune ups. My issue is strange and I have no idea what it could be so here I go.

- went to start up on a cold and wet Saturday morning and it would crank and crank and crank but no start. would start to fire and then quit and just kick out a cloud of black smoke. I thought it was CPS, so I changed it, and nothing. My brother (who is a Jeep guy too) said to take off the air intake off the throttle body and jam something under the throttle to keep the butterfly valve open and try to start it. That worked and the Jeep kicked out a lot of crap and it ran fine. I changed out the spark plugs with Champion RC12ECC

- I had an issue with the engine feeling like it would suddenly drop RPM's and seem like it was being choaked when I pushed further on the accelerator pedal. Took the Jeep home and changed out the MAP sensor and TPS. Put in a lot of HEET and Lucas Fuel Treatment to help with extra cleaning. Put a fuel pressure tester on it and saw 45-49 PSI when starting and running.

- I was driving on the interstate christmas eve with my daughter in the back and when I got down to about 1/4 tank I got poor performance, almost no zip and very delayed response. It seemed like the engine kept wanting to go lower and lower RPM's until it would just die. I was able to start right up and when I put it in drive it would die under a load by pressing down on the accelerator pedal. I finally got a code, OBD2 p0171, system too lean. So basically it's like I have low fuel.

- I have put in a lot of SeaFoam and it's running fine now, I notice the problem come back when I get low on fuel.

- Now I'm having LONG cranking times in order to get started, 5-6 cranks, but use to be 1-2 cranks.

BUT WHY? I am keeping a lot of fuel in the tank for now but want to try to figure out why this is happening.

Is it a bad pump? Fuel Regulator? Check valve?

EGR Valve?

Somewhere else I found talk about the IAC (Idle Air Control) on the throttle body.

Can somebody give me some advice here, I'm going bananas.

A P0171 can be caused by quite a lot of things.

You should re-verify fuel pressure when the vehicle is symptomatic if that is possible, as marginal fuel delivery is still in play here.

Also to consider would be a vacuum leak somewhere which is futzing with the mixture.

There is no EGR system on a 99

Never hurts to review tuneup hardware when symptomatic. You mentioned you put in plugs, but what about plug wires, distributor cap, rotor. Even if not related, replace if it's been a while

The upstream (before cat) oxygen sensor itself could also be faulty. Oxygen sensors have a finite lifespan of between 100k and 150k. They don't last forever.....

The extended crank time you mention. Is this happening ONLY when engine is cold, ONLY when engine is hot, or all the time. Devil is in the details. If it happens only when cold, you could have a failing check valve in the fuel pump assembly, in which case it is not related to your other problem.

Without all of the other details, my first guess would have been the ignition coil wire.

I fiddled with sensors and ECU's on my vw daily driver for 6 months before finally taking a step back and changing the coil wire. That fixed all of my issues. In your case, it sounds like there is a link to the fuel system, but wires are cheap. It's worth a shot. Did the plugs look to be fouled when you swapped them?

thanks fellas, I appreciate your help with this.

today it started and ran just fine, go figure

I have not replaced the distributor cap and rotor or looked at them, replaced them about 35,000 miles ago, as well as replaced the ignition coil with an Accel coil that should be a bit hotter than stock (so it says)

so basically I'm not sure if I simply have something floating in my tank and when I get low on fuel it covers the fuel intake thus causing the P0171 Error (system running lean)
OR
if this is an actual problem with my fuel pump assembly and or injectors

I saw a thread on another site saying to hold a piece of paper up against the tail pipe to see if it sucks up the paper, to test for bad valves, I will try this today

How many O2 sensors are there, where are they, and how do you replace them? Never did them before.

I see one sensor on the manifold just next to the throttle body assembly, looks like a spark plug, is that my O2 sensor? I see one down by my CAT and is that the other O2 sensor? Are those the only two on a '99 XJ ?

When I pulled out plugs about 500 miles ago all the plugs looked fine, I did notice that the part where it sparks from the porceline to the metal gap was rounded over and on the new ones was flat, so they had a bit of wear (what's that called by the way)

My 96 would do this, it would run fine and then magically run like total crap and bog heavily under acceleration and sometimes would even let you drive faster than 15mph and then stall.

My 96 was throwing this code obd2 0171, It turned out to be multiple things. I replaced the filter and within 2 weeks it was all fouled up again. So with this said I pulled the tank to see what the heck was going on and it looked like a sunken ship. I shot gunned it and replaced the tank, lines, pump,sending unit, and new filter, and ran that bgk44 or w/e through it after and all problems have been gone for nearly a month and the issue has never been repeated.

Check your fuel pressure though to verify its a Fuel sending issue

On a 99 you have one on the headers which is the only important one, and one on the cat but that only functions to verify the cat is working.

My father in-laws Buick did the same thing when he got a bad load of gas...turned out a bunch of other people did too and it got traced back to the gas station. So, after many complaints, and threat of lawsuits, the gas station flushed everybodys fuel tank/system, filled them with good gas for free and gave them a second fill for free and everybody was happy... in any case, either way it sounds like a fuel pressure or fuel quality related issue... get a $15 fuel pressure gauge and own it for good so you can test pressure when if/it happens again.

Could be a bunch of things....off the top of my head...take a look at your ECT (coolant temp sensor) located in the thermostat housing. If you have a Multi meter you can test it, if not try to unplug it and run with out it for a little while and see what happens. Warning: the coolant fan will kick on and run constantly.

I would be interesting in knowing this also.

The extended crank time you mention. Is this happening ONLY when engine is cold, ONLY when engine is hot, or all the time.

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How many O2 sensors are there, where are they, and how do you replace them? Never did them before.

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2 one before the cat and one after

I see one sensor on the manifold just next to the throttle body assembly, looks like a spark plug, is that my O2 sensor?

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No that is yur IAT Intake Air temp sensor

When I pulled out plugs about 500 miles ago all the plugs looked fine

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What color and did that smell like gas?