Hey guys, new here.

Bought my WJ with 140k on it, now at about 152k. Fuel filter was whining in January, I assumed it was the regulator all gummed up inside, making noise, so swapped it out for a Wix (can’t recall country of origin but I know for sure not a China made filter). There was no ‘performance issues’, just the sound, and it went away when I swapped it out.


The end of February brought a new issue. I was on the highway and I felt what seemed like a slip or thud in the rear, and with it my speedometer started to dance from 60 to about 40 back to 60 again, though I was certainly losing power. Traffic moved around me. I floored it and it stopped. I went to auto store to get codes and I had a left rear wheel speed sensor malfunction come up. I swapped out the sensor.

Problem stopped for a few weeks and then it started becoming intermittent, and started bringing new symptoms (like stalling randomly when I come to a stop or rarely at an idle, But starts right up again)

Long story short, as of right now:

Changed fuel filter in January.
Swapped speed sensor late February/early March.

Issue became more frequent, speedo dance with the rear thuds STILL after changing the speed sensor (I thought that this was somehow ABS related, or was really hoping), intermittent stalling, and as of TODAY, same Speedo and rear problem (tranny is downshifting hard what it feels like?) but a new symptom came: fuel gauge dropped from about a quarter tank to empty, chimed and went back up. This happened twice.

WHAT IS THIS? It is driving me insane and my Jeep is my daily driver. I can’t afford to lose my rig or take it to a shop. I’ve thought of cleaning the throttle body, to swapping out CPS and TPS... to putting in a new fuel pump.

im planning on testing fuel pressure ASAP.

Does anyone have any ideas about what could be going on?

Here is a short vid of the speedo:
I appreciate your time

 

The issue you are having with your Jeep sounds highly likely the Crankshaft Position Sensor (CkPS) is faulty or failing. When the CkPS begins to fail in certain ways you lose the fuel and/or the voltage gauges. There is an easy to access location under the hood near the firewall with a pigtail connector for the CkPS. The next time you lose the fuel gauge, if it remains dead.. find this connection and unplug it. Go back and turn the key on and check to see if the fuel gauge comes back alive for you.


For further testing of the CkPS;

The Crank CkPS sensor is a type called a Hall effect sensor. There is no reliably accurate test available to test it for resistance. It is an on/off signal sensor based off measurements of the magnitude of a magnetic field. It's 5V

You can test it though. Turn the key on and hand crank it to see it provide 5V on/off as you rotate the crank by hand.

You can test it for ground and for power feed. Ground is less than 100 milivolts with key on, and also less than 100 milivolts with the engine on and running. If you pull the ASD relay, the ground will greatly increase if you test it while you are cranking the engine. It could read up to 200 milivolts You should probably see around 10 milivolts normaly.

The power feed is 5V. It is a shared power feed with the other sensors too, which is good to know. You should see a 5v reading on a DVOM with the key turned on. You should verify that the power feed to the CkPS remains at 5V while you are cranking it too, to be extra certain it is a good power feed. If you want to, just pull the ASD relay first to test it while you turn the key to crank it (it is safer with the ASD relay pulled). When doing this you could also hook up a scanner and be able to see the engine cranking RPMs between 100 - 500 RPMs while cranking. A bad RPM reading.. or, no RPM reading at all means the CkPS has totally failed.

Black DVOM lead to a good ground point (neg battery terminal works), and the DVOM red lead to probe the sensor for all the readings.

 

Whenever replacing the CkPS sensor it is highly advisable to only ever use a Mopar branded sensor. The aftermarket sensors fail quickly (sometimes within weeks), are faulty when new right out of the box, or provide poor performance in general.

It is such an important sensor to not use an aftermarket one for its replacement. It costs more when you have to replace it more than once like that, when it will fail.

 

It could be a multifaceted problem? A bad speed sensor was present and the CkPS. I would also recommend to test the Throttle Position Sensor (TPS). I say this about the TPS in addition to the CkPS. The CkPS sounds like a very highly likely reason for the issue.

The TPS has a direct link to the transmission shifting characteristics. By manipulating the application of throttle as something to help the poor running condition and your issue with the shifting characteristics makes me also question wether the TPS is showing signs of it beginning to fail in addition to the CkPS. Do you know how to test the TPS? It is very easy to test it to see what it may be able to tell you. I would also test the TPS if it were me.

I believe the primary suspect at this point is still the CkPS though.

 

Hey Noah,

I appreciate your replies. I went ahead and took your advice; I tested the CPS and ended up replacing it (man getting that bolt to thread off an extension was a nightmare).

I tested for resistance, and ultimately prongs B and C both had none (I even swapped the red and black leads around as I read somewhere else it’s a factor). I also checked for a 5v spike while the engine was being cranked and I did not have one at all.

The sensor cost me $150 at advance auto. I bought the TPS sensor as well but ended up taking it back because so far I have not had a single issue I was having before!

It’s strange that most failed or failing CPS sensors do not allow the vehicle to start, though mine really never had that issue, except for this past Friday. Friday brought All of the original issues and on top of it, I couldn’t turn over the Jeep after putterin to a stop.

With the transmission having been downshifting or trying to adjust the vehicle speed the speedo was showing (it always seemed like the speedo issues happened right before the tug in the rear) I’m hoping nothing back there is damaged.

Would you advise a full rear end service ?

Here’s to hoping this issue is indeed fixed and doesn’t come back to haunt me.

thanks!

binged

 

I am very happy to hear the good news that your Jeep is running well for you!

If you are asking about a transmission question or mechanical gearing structure or something when you said 'rear end', then I am definitely not your man. I have never tried to really understand a transmission. I acknowledge and express a lack of knowledge. I would do a full drain and re-fill of all the transmission fluid now if it were me though, and I was having transmission shifting issues. Especially, if it has been a long time since the last time? I use the passive flush method for transmission fluid replacement.

Has it been awhile since the last time the Jeep transmission fluid was replaced? Or, are there still issues remaining with how the transmission is shifting?

 

Since they are both required maintenance as it is.. I would drain and replace the transmission fluid and the differential fluids if it were anywhere near due time, if it were me.

 

I have noticed when I am cruising at about 60 mph there is a very faint, high pitched whistle type sound seemingly originating from the front of the Jeep. It’s hardly noticeable, but I surely did notice it today. And otherwise, the only other noticeable difference in performance since changing the CPS is a slight ‘rough’ idle (rough is hardly the correct adjective in this case) while stopped say at a light, and in drive. It’s not a bad idle, just kind of uneven at times, again very slightly. I’m curious if running the Jeep as I was might have damaged any other components, or perhaps the TPS is due for a swap as well?

 

As far as the transmission is concerned, I was planning on originally getting it serviced when the first issues started. It more than likely is due at this point. I’m not awfully familiar with the vehicles history but I think it was kept up on decently well.

I hope the CPS didn’t cause too much extra strain on the rear components.

 

I do not think it should have caused damages like those. If you do not know when they were both last done? I would start with checking the level and characteristics of these fluids. Smell the transmission to sense if it smells burnt, and look to see if it is very black or low? You could pull the plastic/rubber cap off the differential cover and look at the differential fluid.

It should probably be something to be done though on this old of a vehicle, if the known history is missing this information.

 

I'm sorry to hear that.

Aftermarket CkPS are a roll of the dice. Many are found to be bad out of the box, or fail in a few days, weeks, months. So, if your symptoms come back, get you to the dealer and shell out for the original part.

Many of the sensors on these beasties are just picky, and you are far better off paying for the real deal. The track record on the aftermarket stuff is just horrible.

 

Thanks for the post Blueridge. I actually did buy a mopar, that’s the sensor that cost me $150...
and turns out my issue did come back.

I’m not sure what to do now.

 

Hmmmm. Not sure on the 04, but I think you have a CAM Position Sensor where the distributor would have been on older models. Passenger side of the engine, near the oil filter. That sensor can give the same symptoms.

 

Yes, the Crank sensor controls ignition and the Cam sensor controls the injectors. The wrong or intermittent signals cause a cylinder misfire which will cause bucking.

 

It sounds like the sensor did test faulty prior to replacing it. Does the new CkPS test within specifications now after changing it out? It might have been the CkPS was something that was needing to be done.. and there is another issue somewhere to find?

Look over any of the wiring for anything obviously wrong about the CkPS. I recomend to look over the oxygen sensor wiring real closely too. A short at the oxygen sensor wires can directly effect the CkPS, to make it appear and act faulty. The CkPS and oxygen sensor heater element circuits are connected through the ASD (seen at the fuse in diagrams). Other members here have had classic CkPS issues and it turned out it was the result of a primary fault located at the oxygen sensor wiring where they found a short.