Tried a thread search, but couldn't find anything that describes my problem, so...

99 XJ, 4.0, auto, new battery. Starts and runs fine. However, at times I can be driving along and the engine dies for about a second, but then catches again and everything is fine. Other times, it might cut out for a few seconds and all the gauges go crazy and then the engine catches again.
Occasionally, it will be idling in the driveway and cut out and catch again.
I've taken it to a couple of places and had them hook up a reader, but there's never any codes. I thought maybe a battery short or something, but I put a new one in recently and the problem is still there.

The only pattern I can point to is that IT ALWAYS HAPPENS WHEN THE THERMOSTAT IS OPENING AND THE COOLANT TEMP IS REACHING ABOUT 212 ON THE TEMP GAUGE.
So, with that being said, is there some sensor(s) or circuit that kicks in or out right about that time in the warmup process?

Thanks everyone...

 

I had something like this. It turned out to be the cam position sensor. It was very intermittent and was not throwing a code. I finally gave in and replaced the cam position sensor and it cleared it. This was also on a '99 XK 4.0. If none of the sensors have been replaced it could any of them. All are pretty easy to replace but the crank position sensor is a little tricky.

 

You may want to find out what happens when the ECU goes into closed loop at operating temperature. See what is different, that might lead you in the right direction.

 

Bingo.

 

BlueRidgeMark: Bingo

I wanted to say something about open loop and closed loop somewhere in my post, but that's only because I've heard it mentioned before...not because I have any clue as to what I'm talking about

How would I check what happens when it goes into closed loop? Maybe I'm on the wrong track, but can I assume that when it hits operating temp, it goes into closed loop? If the temp sensor hits a certain temp, does that signal the ECU to go into closed loop? What might be causing the cut out at that point?

 

Polite bump, please... My main question at this point is:

How would I check what happens when it goes into closed loop? Maybe I'm on the wrong track, but can I assume that when it hits operating temp, it goes into closed loop? If the temp sensor hits a certain temp, does that signal the ECU to go into closed loop? What might be causing the cut out at that point?

Thanks...

 

You would need an OBD-II scanner to see what it's doing. When entering closed loop it will begin to consider input from the O2 sensors, but, as temperature increases in general, it changes programs and how much weight various sensors are given.

Don't forget to clean and tighten the battery cables

 

Thanks much, salad. I'll start there. I guess it's off to HF for a scanner this week... I'll see how it goes and post if I can figure anything out.

 

You might want to consider an OBD-Link, if you have a smartphone. I find mine very useful. You can log engine data to your smartphone or laptop, and then analyze what's happening later, or watch it in real time. That's far more than you'll get with an HF scanner.

 

OK, so a worthless update...or not...

Bought an OBD-II scanner and had it hooked up for quite some time. The XJ "skipped" a couple of times but never threw a code. Then, there were no issues for a while...until today (yeah, I know it's been months now).

Ironically, I was at NAPA picking up some parts for the XJ since I'm giving it to my relatives next week and I wanted it to be up to snuff. It had warmed up to temp, but I had been in NAPA long enough for the engine to cool down a bit. I had a stop just down the street on my way home. Long enough for it warm up and just get to operating temp again. As I pulled into the driveway AT AN IDLE (if that makes a difference), the XJ died and wouldn't restart (though I think my gauges still were active and the radio was still playing). I cranked it about a half dozen times and it wouldn't fire. I let it sit for about 5 minutes and she cranked right up. And, yes, I popped the hood and checked the battery terminals. They were tight.
Does this sound familiar to anyone? I hate to just start throwing parts at it, but as was mentioned above, should I start with a cam sensor, or...?
Thanks...

 

A "crank-no-start" condition diagnosis should always start by getting direction. The first 3 directions to check are Fuel, Air, and Spark. There are a few more, but 90% of the time, the problem will be on one of those 3. The first series of tests won't typically lead you to the cause directly, but will rule out 2 and allow you to focus on the correct one.

Testing for air on the XJ is the simplest and helps to rule out an Idle Air Controller that is failing to open during startup to allow a small amount of air for combustion. It can tested by starting while feathering the throttle a little. This will let a small amount of air through the throttle body whether the IAC is working or not. So if a startup behavior difference is observed, it can point towards the IAC.

Fuel requires a fuel pressure gauge, and noid lights or a good high speed test lamp. If pressure checks out good, the fuel pump is typically ruled out. Then the pulse circuit on the fuel injectors is checked to make sure that the computer is actually commanding the injectors to fire. Some people will use starter fluid at the throttle body to attempt to get the engine to fire. If it fires, you know that spark and air are present and that fuel is an issue. However, the fuel pressure and injector pulse tests will still need to be performed to determine which path to go down.

Spark can be tested for presence by either arching a plug wire to ground, or an actual spark tester. I prefer to carry an inductive spark tester (a small pen shaped tool that need only be placed against the spark or coil wire to create a small strobe if spark is present).

These are the first things to test for on any crank-no-start condition. They set direction, and guide the rest of the troubleshooting while cutting out additional unnecessary tests.

If all 3 of those directions check good (rare on a crank-no-start). Then the entire set of tests would be more like Fuel, Air, Spark, Timing (ignition), Timing (cam/crank relationship), exhaust, and compression.

 

Good info, jordan96xj. Thanks. One of the problems is that the issue is usually momentary and she'll crank back up.

I ended up replacing the crank position sensor and the throttle position sensor. Upon startup, it seemed to "learn" the idle, etc., and it's been running great. My plan WAS to give the XJ to my in laws this weekend, so I had the XJ detailed-including under the hood...And, guess what? Yes, you guys guessed it, they had to keep it overnight because they couldn't get it to start. Moisture issue in the distributor, they thought.

They bring it back this morning with the check engine light on. It seemed to run OK while it was warm. I couldn't get the check engine light to reset and the code was P0123, "Throttle/Pedal Position Sensor/Switch A Circuit High".
Oh yeah, did I mention the cruise control light will turn on, but won't engage/set now?
And that once the XJ cooled down, it'll start and idle, but once you hit the accelerator, it won't idle and you have to keep your foot on the accelerator or it will die?

Someone please tell me this is just a bad sensor I bought and this is an easy fix (or am I on the wrong track)... BTW, I did WD-40 the TPS to dispel any water. I also blew the connections out with air just to make sure everything at the TPS was dry. I can't give this to my in laws in this condition...can anyone help?

 

OK, so I might've answered my own question here. Short answer: My new TPS went bad 3 days after putting it on. Turns out I have a nephew who was able to walk me through testing the unit. Spec was supposed to be roughly .26-.95v at closed throttle. Mine was showing 5.22v on the center wire. I also had my OBDII tester hooked up and it showed the TP at about a wide open 96%. Installed a new TPS and preliminary results are good. TP shows about 18% at idle (a bit high) and it now idles fine at this point. Hopefully, all is well, but we'll see.
Thanks.

 

If you don't mind, which OBDII are you using. I have XJs ranging from '91-'98 and need a good code reader. Thanks.

 

I wonder if the detailers got your new TPS wet....................