Two XJ issues - 210,000

Hi guys, first post!

I've got a '00 XJ, 4.0, AW4, NP231, 210,000 miles, with all sorts of problems. This is going to be my new project for the summer. I've got all sort of lofty plans for this thing, but first things first, I've got to get it running smoothly.

I haven't driven the Jeep all that much since May of last year. A couple trips to the beach, a couple loads of crap from the store, etc... Over the wintertime we had some snow, so instead of driving the car, I decided it was time to pull out the Jeep. As soon as the engine warmed to 210, I started experiencing very rough idle and a pinging / knocking noise from the vicinity of the bell housing. It eventually lost all power and stalled on the way back home.

Fast forward to February.

One buddy decided to attack the rough idle first. I've historically had an issue with a cyl. 3 misfire, that comes and goes with the temperature (heat soak?). First step was to replace the plugs and coil pack. Second step was to clean the throttle body. Third step was a half a can of sea foam in the tank, half a can into the engine via the brake booster vacuum line (?). Somewhere along the line, the rough idle got much better, but didn't go away completely.

Second buddy came over. We get the engine up to temp and put the transmission in gear to load the engine. The knocking noise came back immediately. He suggested that it may be the torque converter.

No MIL.

Just today I got the engine up to temp again to take some detailed notes:

- Cranks easily.
- Smooth idle upon cranking (engine cold)
- Revs to 2k smoothly, no noises. Held at 2k for a few minutes. Engine warmed to 25%.
- When going from 2k to idle, rough idle present. Must punch gas lightly to keep engine running.
- Revs to 2.5k smoothly, no noises. Held at 2.5k for a few minutes. Engine warmed to 33%.
- When going from 2.5k to idle, rough idle present. Could release accelerator completely, very rough idle, but engine stays running.
- When going from idle up, around 1500 RPMs, knocking starts emitting from bell housing area.
- Accelerated to 2k, knocking goes away.
- Decelerated from 2k to idle, must punch gas to keep engine running.
- Accelerated up, knocking present around 1500 RPMs.
- Engine now at 210
- Knocking present from 1.5k all the way through 2k.
- Repeat last step 10 times, same result

Torque converter? Flex plate? IAC? Injectors?

How can I narrow it down more without pulling the engine and trans? I need to evaluate the risk $$.


Thanks for reading!

Bueller?

So, I figure I'll attack the rough idle first...

The FSM indicates that I should look for vacuum leaks next. The leftmost vacuum line coming off of the intake manifold has some dry rot; I'm planning on picking up some line and fittings tomorrow to replace. It runs over toward the AC compressor.

Does this sound like an Idle Air Control motor problem to anyone? It idles fine when you crank it. By fine I mean that it sits right around 1k, but the engine is still vibrating. Again, you get it up past 1.5k and the vibration stops and runs smoothly. But after you start punching the gas, or better yet drive it around the culdesac, it doesn't to decel to idle properly and tries to stall. It does fluctuate a little bit, but doesn't track steady. I can keep it from stalling by punching the gas. If it does stall, it doesn't crank right away, and you have to punch the gas to get it going...

Thanks!

2000 XJ...could be cracked head or leaky head gasket. is there coolant in the oil or oil in the coolant?

Pull the front cover off the lower part of the bellhousing and check the flexplate bolts. With a bright flashlight inspect the flexplate for cracks while prying gently with a long screwdriver. Loose bolts or if the flexplate is cracked will cause that noise. Fairly common problem it seems.

Test the TPS sensor. A bad TPS sensor can cause odd idle issues when letting off the gas. It would probably also cause some strange shifting.

QUABOAG said:

2000 XJ...could be cracked head or leaky head gasket. is there coolant in the oil or oil in the coolant?

Click to expand...

I definitely have a leaky head gasket... You can see the oil seeping through. Reason #1 to pull and rebuild...

No oil in the coolant reservoir, haven't checked the oil.

lawsoncl said:

Pull the front cover off the lower part of the bellhousing and check the flexplate bolts. With a bright flashlight inspect the flexplate for cracks while prying gently with a long screwdriver. Loose bolts or if the flexplate is cracked will cause that noise. Fairly common problem it seems.

Test the TPS sensor. A bad TPS sensor can cause odd idle issues when letting off the gas. It would probably also cause some strange shifting.

Click to expand...

The TPS is pretty much the only sensor that hasn't been replaced in this thing since I've owned it... Good idea. I'll bust out the meter and test.

I've heard about the flexplate cracks and bolts. I have to pull the trans out completely to replace that, so it's looking like I'm going to roll everything into the engine rebuild...

A few observations....

Having to "tip in the throttle" to keep an engine going can be the throttle position sensor. I would definitely test it. They aren't particularly expensive to replace. More on the TPS below.

What you describe with the rough hot idle and cylinder 3 misfire is almost assuredly "heat soak". The 00-01 4.0 engines are the most susceptible to this. There is a TSB, but the fix is lame. Many have added hood louvers to lower engine bay temps and others have added an e-fan timer so that the e-fan stays on longer after key is turned off. SEARCH is your friend for heat soak.

The oil leak you are seeing could be the valve cover gasket, not the head gasket. Valve cover gaskets leaking oil is very common.

With an 00, you have the "infamous" 0331 cylinder head, which is prone to cracking between cylinders 3-4, especially with an overheat. So be SURE that all cooling system components are top notch. And keep a very close eye on that coolant reservoir as the #1 symptom of a cracked 0331 head is "unexplained coolant loss".

Good luck!
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The throttle position sensor is connected to the throttle shaft on the throttle body. It sends throttle valve angle information to the PCM. The PCM uses this information to determine how much fuel the engine needs. The TPS is really just a simple potentiometer with one end connected to 5 volts from the PCM and the other to ground. A third wire is connected to the PCM. As you move the accelerator pedal with your foot, the output of the TPS changes. At a closed throttle position, the output of the TPS is low, about a half a volt. As the throttle valve opens, the output increases so that, at wide open throttle, the output voltage should be above 3.9 volts. Testing can be performed with an electrical meter. Analog meter is best. You are looking for a smooth sweep of voltage throughout the entire throttle band. While slowly opening and closing the throttle, take note to the movement of the voltmeter needle. There should be a direct relationship between the needle motion to the motion of the throttle. If at anytime the needle moves abruptly or inconsistently with the movement of the throttle, the TPS is bad

You should have 5 volts going into the TPS. At idle, TPS output voltage must be greater than 200 millivolts. At wide open throttle (WOT), TPS output voltage must be less than 4.8 volts.. The best is to use an analog meter (not digital) to see if the transition from idle to WOT is smooth with no dead spots. With your meter set for volts, put the black probe on a good ground like your negative battery terminal. With the key on, engine not running, test with the red probe of your meter (install a paper clip into the back of the plug of the TPS) to see which wire has the 5 volts. One of the other wires should show .26V (or so). The other wire will be the ground and should show no voltage. Move the throttle and look for smooth meter response up to the 4.49 at WOT.

Perform the test procedure again and wiggle and/or tap on the TPS while you watch the meter. If you notice any flat spots or abrupt changes in the meter readings, replace the TPS.

The TPS is sensitive to heat, moisture and vibration leading to the failure of some units. The sensor is a sealed unit and cannot be repaired only replaced. A TPS may fail gradually leading to a number of symptoms which can include one or more of the following: -

NOTE: The throttle position sensor is also DIRECTLY involved with transmission shifting characteristics! It should be verified early in the troubleshooting process, when a transmission issue is suspected!

 Poor idle control: The TPS is used by the ECU to determine if the throttle is closed and the car should be using the Idle Air Control Valve exclusively for idle control. A fault TPS sensor can confuse the ECU causing the idle to be erratic or "hunting".
 High Idle Speed: The TPS may report faulty values causing the engine idle speed to be increased above normal. This is normally found in conjunction with a slow engine return to idle speed symptom.
 Slow engine return to idle: A failing TPS can report the minimum throttle position values incorrectly which can stop the engine entering idle mode when the throttle is closed. Normally when the throttle is closed the engine fuel injectors will be deactivated until a defined engine RPM speed is reached and the engine brought smoothly to idle speed. When failing a TPS will not report the throttle closed and fueling will continue causing the engine to return to idle very slowly.
 Engine Hesitation on Throttle Application: The TPS is also used by the ECU to determine if the driver has applied the throttle quicker than the Manifold Air Pressure sensor can read. The fueling is adjusted acordingly to cope with the sudden increase in air volume, however a faulty sensor can cause the ECU to ignore this data and the engine will "hesitate" when applying the throttle. In extreme cases with the engine at idle, a sudden application of full throttle can stall the engine.
 Engine Misfire: A fault TPS can report values outside the deined acceptable range causing the ECU to incorrectly fuel the engine. This is noticable as a slight misfire and can trigger the misfire detection software and/or Malfunction Indicator Lamp (MIL) light on the dashboard. Extreme cases can cause excessing misfires resulting in one or more cylinders being shut down to prevent engine and catalytic converter damage.

1. As suggested, pull the cover, remove the torque converter to flex plate bolts one at a time and clean them then use Loctite on them--unless you like doing this job over and over again. Torque to 40 ft lbs.

2. Now, check for cracks in the flexplate as described earlier--checking for cracks with the bolts loose is not going to be effective.

3. 4.0s with the distributorless ignition system need to run NGK V-Fire plugs.

4. If you have heat soak install a timer to run the aux fan for 5 minutes after the ignition is shut off.

5. If you have the 0331 head you may get a crack between cylinders 3 and 4, usually visible by locking into the valve cover. Even if you don't see a crack you could have problems. Check the coolant for oil and do a hydrocarbon test on the cooling system. Check the compression in the cylinders. Don't guess or just A**ume you have a problem with the head/headgasket.