Courage

Hello everyone. I'm really struggling to figure this one out.

I have a stock 4.0L XJ that died suddenly while driving and hasn't started since. It didn't spit or sputter; it just shut off like I turned the key. Now, it just cranks and cranks, but won't start.

I have replaced the crankshaft position sensor, as well as the camshaft position sensor. I checked the fuel pressure with the Schrader valve on the fuel rail a few times and it seems to be fine, so I think the fuel pump is in decent shape (it should be noted that I did not get a pressure reading; I simply pressed the core of the valve and had a helper turn the key). I have spent a bit of time searching for rubbed or grounded wires, but have yet to spot anything.

I recently replaced the spark plugs and the coil pack (less than 5,000 miles ago). Plus, I find it unlikely that all of them would lose spark simultaneously.

It's possible that the fuel injectors failed, but, again, it seems quite improbable that they'd all fail at once.

At first, I wasn't able to pull any codes, but after disconnecting and reconnecting a few sensors and the battery, I finally pulled a code for the throttle position sensor (P0122, Control Unit: 18). I don't know if it was caused by my sensor checking or just that disconnecting the battery, cleaning the terminals, and reconnecting it prompted it to take a once-over of everything.

I have had trouble with heat soak causing a rough start after hot drives in the past, but this was on a cold day and I recently replaced the heat shielding for the injectors. It definitely did not overheat.

Any tips, suggestions, or advice would be greatly appreciated, as this is my primary vehicle (I have a CJ5 too, but that's also out of commission) and I have been forced to borrow family members' vehicles.

Thank you all in advance. I look forward to discussing with and learning from you all.

-Courage Grell

Roler

Welcome to the forum
The automotive Jeep equivalent of Heartbreak Hotel haha

Trust me when I say, whatever your problem with the XJ is going to be, its not unique and others had it before you. With 5000+ pages of approximately 20 threads each, I'm sure there will be an answer to this problem.

But back to this issue
If you have a crank, no start situation , you will have to do some diagnostics first imo. There is simply too many possible causes and your replacement of CPS and CAM obviously have not solved the issue. Not sure what sensors you put in (quality or chinesium?), but nothing more frustrating than putting in bad parts that turn out to be faulty right out of the box (you'll be chasing the issue for ever)
You say injectors/sparks unlikely to fail all at once; yes maybe on an individual level, but what if for example the PCM didnt provide ground to fuel injectors all together, causing them ALL to not work all at once?

You said unlikely that all spark plugs would fail, but have you actually CHECKED you HAVE spark?

If you want, there is help in narrowing things down. It seems you had a bit of catastrophic failure with the XJ shutting down (was it whilst driving?), which needs to be sorted.
Systematic approach is key and some testing from your end will be needed. Rule things out by testing, not assuming. The same thing with new parts that you put in; how ****ty it might be, keep in mind that replacement parts might be faulty right out of the box. So testing and narrowing things down is key. Otherwise you will have every man and his dog fire his ideas at you and you'll be in the woods in no time.

Crank but no starts are common, and a systematic approach will most likely bring your cause to the surface.

So first I'd suggest (if you want):
1)Test for fuel with a gauge
2) test for spark
3) let us know the the results.

Just trying to make it as effective as possible for you

Good luck

Courage

Thank you. I'll start with those. It did die while driving. I appreciate the objective response.

The crankshaft sensor is from O'Reilly's and the camshaft sensor is from AutoZone. I went with the middle ground price options. Not the cheapie, but not top tier $100 sensors.

-Courage Grell

fb97xj1

Just an observation.

Stick with Mopar on the crank sensor. Yes, they cost more, but aftermarket (crank sensor, cam sensor, TPS, etc.) is questionable, i dont care who makes it. The XJ is a fussy beast when it comes to engine management. Fuel pressure must be checked with a gauge. You can have fuel in the rail, but the pressure can be way off. Heat soak can happen even on a cold day. The 4.0L puts out lots of heat. Cramped engine bays, and pre-cats if equipped, build heat. Lots of it. The injectors are right in the line of fire, namely 3 and 4. A shield helps, but heat soak is still possible. This can affect the crank sensor as well.

My knee jerk reaction for a dies while driving and a crank no start is a failed crank sensor. But thats just a guess.

Dirty grounds can cause all sorts of issues as well. Check the wires and cables for corrosion, too. And of course, check the battery voltage. Just because.

Courage

Thank you for that input. Due to my work schedule as a trucker, I was forced to take it to a local mechanic for the first time. They found that the crankshaft and camshaft sensors were not synchronized. Also, a relay was fried and a couple fuses blown.

Hopefully that'll be the end of it, but if not, I'll go around and clean all of the grounds to start.

I have always done my own work on my vehicles, so this was a little hit to the ego for me, but I'm happy it's solved. I'm also glad to have found this awesome online community and appreciate the lightning fast responses!

Thank you gentlemen for your help. I'll try to post an update during the next couple weeks about how it's running.

-Courage Grell

Courage

(I should rephrase that: I have taken it to a tire/alignment shop, but this was the first time I've had any electrical or engine work handled by someone else)

It also gave me a chance to have the alignment handled once and for all. After lifting it 3", I took it to a tire/alignment place and they did a poor job. I've been driving crooked for the better half of a year. XD

-Courage Grell

Courage

It seems to be running great now. Thank you for your advice, folks. My positive battery cable had some corrosion under the red insulation. The fuse for the fuel pump was also blown. Couple other minor issues as well. I might have to replace a short length of corroded wire as well, but it is working for the time being.

Thanks again!
-Courage Grell