2003 Jeep Liberty Sport, 156 K miles, Check Engine Light, and Engine knocks

Check engine light has been on for months now. First occurrence was when driving, and car started to knock as though I was shooting 50 cal machine guns. Stopped vehicle, shut off, and upon restart, engine ran smooth. Now, almost every time after engine has been running a while, and I am going on a down slope, the check engine light starts to blink, and engine starts to miss. Took to my mechanic, and so far, I have been told and have replaced, Fuel pump, Spark plugs, coils, and wires, cam sensor. Latest and most recent with promise that this has to be it, I replaced engine computer. Sighs, has not fixed the problem

perhaps you should try a different mechanic?

Thanks, I did try but they had said much the same steps to take. I am putting more into fixing this than the vehicle is worth.

2003 Jeep Liberty Sport, 156 K miles, Check Engine Light, and Engine knocks

The thread title says it all, time to quit throwing money at this and start shopping for a replacement.

I would not throw in the towel just yet.
Just to clarify something regarding the knocking.
You refer to a flashing CEL and running poorly going downhill but no mention of knocking.

Do you mean uphill and is there knocking present even if downhill?

Is knocking always present with the poor running and flashing CEL?

It’s hard to find a good diagnostician these days. A lot of under skilled mechanics are all to willing to just throw parts at a problem. Maybe the best would be if you could leave it with the mechanic and they can drive it until the problem occurs. What codes are set when the engine begins missing?

I do believe the Jeep Liberty engine is well known for having problems with the valvetrain

Expensive problems

As the others said . . .

Find a new mechanic. If he confirms the car will need expensive repairs, start shopping for the next one

It seems the “Powertech” V6,is not known for longetivity.

Concur w/other, good idea to start looking for a replacement. But in the meantime …

A machine gun or firecracker sound could be an exhaust leak rather than an engine knock or pinging. A valve problem could cause an exhaust leak back into the intake manifold, which would make a similar sound. As the problem can be made to go away by rebooting sometimes, it might be a valve timing problem. Has your shop done a compression test? An intake manifold vacuum test?

For the missing problem, both fuel pressure and spark tests (including spark timing) would be the place to start. Does this vehicle have a crank position sensor? Those tend to be problematic from the reports we get here, not on that vehicle in particular, but generally.

Compression test wet and cold
Fuel pressure test
Which cylinder is misfiring?
Swap coils . . . does the problem move?
Swap plugs . . . does the problem move?

If compression is bad on a particular cylinder only, you need to determine if the problem is top end or bottom end. Since I’m a cynic and believe in pattern failures, I believe it’s top end in this case

Once the knock starts, it continues on even grade and up grade until I can stop the car and restart. I can travel for some time, with no knocking, but once it starts, I cannot clear without actually stopping the car and restarting. As to codes, I will have to get them again. Thanks for all the input!


If the engine had a mechanical issue, the “knock” wouldn’t quit happening after a restart–it would be there all the time, or at least there after the engine warms up. It sounds like the knock may be the noise from the engine missing on one or more cylinders, but more info is needed.

I had a pinging problem occur when the spark plug gap had grown too wide. I realize the OP has new spark plugs, but might be worth it to double check the gap is correct.

Offhand and wild guessing a bit, I tend to think this could be a valve train knock or a spark knock. The latter could be caused by a faulty knock sensor, EGR system fault, or possibly poor fuel quality. There may or may not be codes set by problems with a knock sensor or EGR fault; especially if any EGR fault is caused by clogged passages.

You are a victim of “shotgun” maintenance. You need to find a good, independent mechanic to actually find and fix the real problem. This is made even more difficult because the early Jeep Liberty’s have a bad reputation when it comes to reliability. The fact that your Liberty has managed to make it to 156K is almost amazing.

We need to hear the sound to make a better guess.