Need suggestions for engine misfire (potentially sensor related)

[primetime4]

Hello All...

I have owned my 2001 TJ auto with 4.0 since new and despite some of the issues with occasional leaks (RMS, valve covers, radiator), the engine has always run like a top for over 20 years. Truthfully, the only time I have ever experienced the check engine light was for an EVAP code. Within the past 2 months, the engine finally would not start which after some research here turned out to be a bad crankshaft position sensor.

The problem is there are no factory MOPAR CPS sensors available. I placed a few orders at places like moparpartsgiant which were quickly canceled and an ebay search also turned up nothing. I ended up installing an NTK unit that is labeled as Made in USA and everything seemed to be working great until last week. As a weekend vehicle, I do not drive it very much and finally got it above 3500 rpm or so on the highway and the check engine light comes on. There was no stuttering or noticeable loss of power while I was doing close to 70 at the time. Pulling the codes returned P0304 and P0306 for cylinder misfires.

This seems too much of a coincidence to be not related to the new CPS but hoping to hear some thoughts.

At this age, could the camshaft position sensor also be going bad? Factory MOPAR replacements for these are also NOT available but I have an NTK unit on the way that I can try.

Could it be old plugs and injectors? The fact that I received 2 codes suggests that it is something else but I really do not know. Are worn timing chains a thing with the 4.0?

Or should I try switching to another sensor brand like Tammken and cross my fingers? These appear to be made in China from all indications and the NTK unit that I installed does seem to be pretty good quality with the only difference being the spacer pad installed at the end compared to the original unit it replaced.

Thanks.

 

[williambmac]

I would clear the codes and re-drive it under the same conditions to see if it re-occurs.
You said you don't drive it often, so it could potentially be a number of things.
If you had a scanner that reads live data, watch your cam and crank rpm's to see if either one drops out.
This would give you an idea if the cam or crank sensor is your problem.
I have seen both cam and crank sensors fail, I have also seen issues with the harness going to the crank sensor.

There are also numerous other potential causes. These are problem areas you may wish to inspect.
The connector at the coil. The injector harness and connectors
The harness behind the rear of the valve cover.
How old are the spark plugs
How many miles on your jeep?

 

[ItchyDong]

I've scoped brand new aftermarket crank/cam sensors. Many of them give a "dirty" 5 volt square wave. Either the signal doesn't get pulled all the way to ground, or the square looks more triangular. In most cases the engine will run, but will show misfires on random cylinders, and won't throw a code for said sensors. So long as the PCM is seeing some sort of signal from the sensor, they usually won't set a DTC.

As @williambmac says, there's many potential causes. But I would agree it's odd that this is happening right after a no start issue that was definitely related to the sensor change. Unfortunately, to truly isolate it without guessing you'd need a scope.

I was lucky enough to find a Mopar sensor on Amazon. Another route would be a junkyard in a pinch. Did you try Rock Auto?

 

[primetime4]

Thanks for your replies. My scanner does not have a live option but may take it to a shop to check. I ordered the NTK sensors off Rock Auto so did try to find MOPAR units there with no luck. Also did a car-part search with no luck but if anyone has a lead for 2001 sensors, please let me know. I do see options for later model years and it looks similar except for the plug.

I cleared the codes and will try driving again. I only remember changing out plugs once or twice the entire time I've owned the Jeep so that is probably next on the list to replace. But it idles great so not sure if that means anything.

 

[ItchyDong]

Thanks for your replies. My scanner does not have a live option but may take it to a shop to check. I ordered the NTK sensors off Rock Auto so did try to find MOPAR units there with no luck. Also did a car-part search with no luck but if anyone has a lead for 2001 sensors, please let me know. I do see options for later model years and it looks similar except for the plug.

I cleared the codes and will try driving again. I only remember changing out plugs once or twice the entire time I've owned the Jeep so that is probably next on the list to replace. But it idles great so not sure if that means anything.

Live data isn't what you need to see a 5 volt square wave. You need a scope. Yes, some diagnostic tools have scopes built into them, but the scope is needed. Just don't want you to be confused between the two.