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sdh796 07-13-2011 04:56 PM

Phantom Misfire Codes and Check Engine Light Nightmare
My Jeep is a 2002 Wrangler X, (4.0L 6 Cylinder) with about 76,000 miles on it. It's been throwing misfire codes (all of them, each cylinder and random misfires) since March of this year.

Replaced a Oil Pressure Sending Unit a few months ago when the oil gauge went haywire... ripped a wire, spliced and replaced it... no problems.

Few weeks later, check engine light come on, engine dies... open the hood and the Crankcase Vent tube is laying on the crankcase... replace it, and the Crank Position Sensor (as indicated by the OBD) the first one was "bad" it too was replaced... After a few dozen miles, the misfire codes came back again.

Originally, you could feel it misfiring, losing power, dying, etc..

Replaced the coil, plugs (regular Champion plugs)... It was time anyway... Check engine light still coming on after about 100 miles and if it gets over 65 mph or 3000 rpm....
The jeep would lurch and lose power at speed, definitely felt it misfiring...

Replaced the ECM, a mechanic I trust said it was bad... Engine Light still came on after about 100 miles and over 65 mph/ 3000 rpm...

Replaced the valve springs.... the engine felt and sounded great when I got it back... light just came on after, you guessed it about 100 miles and over 65 mph... Still feels and sounds great.... but the engine light reappeared again...

Replaced the Cam Position Sensor last week... More or less because it was easy and cheap it felt like I was doing something, but to no avail, after a few miles at highway speeds.. it was back...

It no longer feels like it is misfiring, as it did before the Valve Spring and ECM replacement... I am at a loss... wondering if it's a shorting wire? Can't figure out why it doesn't "feel" like it's misfiring, but still throws the codes at a predictable interval...

Also... Are there "plug wires" that can be checked on an engine that uses a coil pack?? I have gotten lots of free advice that suggested plug wires... but that seems to be the whole point of a coil pack...

What is the most likely culprit?? Wiring, exhaust plug or leak, vacuum leak, manifold crack, fuel delivery??

It ONLY happens at high RPMs/speeds... If I slow down, the flashing CE light will sometimes disappear and not come back... If I push it, it will continue to flash and eventually go solid until I clear the codes... The ONLY codes are misfire codes, usually random misfire....

Jerry Bransford 07-13-2011 07:58 PM

In response to your PM, I've given your symptoms some thought and just can't put my finger on anything I can even suggest at this time. You've replaced the items I would have replaced, you've really got a stumper of an issue going on here.

I just don't know what to suggest, sorry.

rrich 07-14-2011 12:52 AM

How 'bout a few shots in the dark?

Use a spray bottle to spray water on the plug boots under the coil pack. If you can make it burp or misfire - BINGO! Insulation problem.

Try disconnecting, then re-connecting the plug for the Crank Position Sensor. Put some dielectric grease on the terminals before reconnecting. That connector gets wet when the hood's drip rail overflows. The signal is a very weak voltage, easily affected by resistance - from slight corrosion.

Same procedure on the connector to the coil rail - pack it in dielectric grease.

Does it feel like it's losing power at speed? That's a symptom of a coil rail shorting internally. I see you've replaced it once, but sometimes a new one is as bad as the one you took off - especially the cheapies - Chinese junk (Autozone and the like.) CarQuest, NAPA, and real parts houses sell OEM rails made by Standard Ignition.
Try borrowing a "known good one" from a friend's that running right to try it.

Let us know if those things help.

sdh796 07-14-2011 07:42 AM

Thanks for the help, I will look at the coil pack again as soon as I get the chance. The first one I got was bad, I will check this one.

It doesn't seem to lose speed anymore, or feel like it's misfiring.

I was under the Jeep last night grasping at straws and noticed that fluid is leaking from somewhere, which makes even grasping at straws more difficult. Going to clean and drain the differentials, which appears to be one of the leaky sources and see if I can see anything more after that.

I appreciate both of you looking into this... At the least, I feel less crazy for not being able to pin point the problem....

BurntFrostTJ 08-08-2011 06:40 PM

Had the same problem with my 02 TJ after i replaced the crankshaft position sensor. There is a procedure that in some cases needs to be done to the computer to correct it. They have to use a scan tool to do a learn sequence. I was getting a P0300 misfire code and a blinking engine light from time to time but the engine wasn't missing. Apparently the computer can't handle the variance in the input from the new sensor until it is retrained so it assumes the engine is misfiring and throws a code.

Cbartrip6 09-14-2011 08:47 AM

I too have an 02 TJ and I got this issue this week. Crazy, the car was just shutting off around 2,500 RPM or 65-70 mph. The only difference is that my car was throwing the A0445 Code (major EVAP leak). The top hose in my evap canister had a tear in it, perhaps from dry rot. Replaced it 4 days ago and I have not had anymore surprises on the expressway. Hope this helps.

Cbartrip6 09-16-2011 01:24 AM

Correction. It was the P0455 code.

mcjeeper 02-09-2012 12:20 AM

Sounds like either a lack of fuel or too much fuel which would explain the blinking CEL. A blinking CEL means damage to the cat could occur if not repaired. You need to check your fuel pump pressure, at a higher speed it should produde more pressure. Also check your fuel pressure regulator. My Jeep had a similar problem and but did not throw a code for the problem. Jeeps have issues with the TP sensor ( Throttle position sensor) if the PCM is reading a different value than your giving it, it will give it different amounts of fuel. The only way to know is to hook up a good scan tool and read it. A p0300 is a general misfire and is not related to any one cyl. Check your fuel system and TP.

HotRock 03-31-2012 08:45 AM

EGAD! I have the same problem with my 02 4.0. It only has 48,500 miles. I think Chrysler should come with a fix for this. I've read and searched. I know there is a procedure via service bulletin but I cannot find anyone that has used the procedure with success. In fact nobody even admits to trying the procedure. One post above says he changed the valve springs but that didn't correct the problem. How can rotating the exhaust valves 90 degrees correct anything. Some autos the exhaust valve never rotates and never gives any problems. I hate this electronic stuff.

sdh796 05-14-2012 10:32 PM

Thanks for the responses... Has been a continuous nightmare, no end in sight... Checking for manifold leaks... OBD2 scanner indicates same codes, P0300 & 0306 any time I'm over 60-65 mph or over 3000 rpm... Anyone have any idea about the meaning of a manifold absolute pressure reading of 46% immediately preceding a misfire detection? One of the blessings of breaking down and buying a nice code reader is I now have lots of empirical data to describe things I still don't understand...

Riderx612 06-21-2012 07:19 PM

Any luck??
I have the same exact issues you have with the same year jeep. Have you found a solution yet??Mine has gotten worse with the engine ticking very loud at all RPMS now

jonwanner 06-21-2012 07:49 PM

A coil on plug type ignition system uses a rubber boot between the pug and coil with a spring like conducter inside rather than a plug wire. They are serviceable seprate from the coil. You say you replaced the coil, just one cylinder or all six? I presume the coil came with a new boot. Are you getting the p0300 code first and then the p0306? Usually the computer throws the 300 code when it detects missfire, once the missfire occurs enough to narrow it to specific cylinders it will throw codes for those cylinders.

jonwanner 06-21-2012 07:51 PM


Originally Posted by Riderx612
I have the same exact issues you have with the same year jeep. Have you found a solution yet??Mine has gotten worse with the engine ticking very loud at all RPMS now

The engine ticking suggests a different problem. Maybe in the valvetrain.

29ster 01-07-2013 07:39 AM

What I did on my Christmas Vacation - Phantom Misfire code over 3000 RPMs
Man Ive got a head scratcher . Ive tried most everthing: Here is the rundown:

Three weeks ago:
My daughter’s 2002 jeep wrangler, 4.0 6 cylinder, auto. Driving to work in it yesterday, bucking all over the road, trying to keep up with traffic, got to 67, 68 mile per hour, 3100 RPMs and the check engine light starts to flash. Flashes 3 or 4 times slow down and it stops, speed up, 3 or four times and slow down and it stops, again and again. Arrived at the office and threw a scanner at it and no codes. It did have a random misfire code in the history though, clear that. On the way to the airport , I again took the Jeep up to 70 trying to keep up with the traffic and the check engine light started it’s dance again, but felt fine so I continued at that speed and it started to buck a bit and the light flashed continually. I slowed a bit and realized the engine has a dead miss or multiple dead holes. Very sluggish, vibrating, etc I’m thinking… oh no…I blew the damn thing up. Note at 70 miles per hour the engine is taching at 3200 rpm or slightly better for extended period of time. I nursed it to the parking lot and jumped in the van for my trip to the airport and DC. After the meeting ended late and arriving back at the parking lot at 1pm last night, I keeping my fingers crossed that a) it will start, and b) it will get me home. Note; oil pressure and temp was normal during the drive. I jumped into the Jeep turned the key and it started right up, no miss, running smooth on all cylinders, check engine light on solid. Turned the key on and off three times and retrieve codes p0300, p0302, 303, 304, and 306. Random misfire code and 4 cylinder misfires…. Hmmm. Note, just recently (three weeks ago) and because of this same situation with my wife driving it and a p0300 code (I didn’t believe her by the way), I replaced the coil pack, the spark plugs, cleaned the battery terminals and it seemed to run fine. This summer I replaced the crank sensor because the vehicle would just cut out on my daughter and then restart. So…. I’m thinking valve springs…

Two weeks ago - I discovered the TSB on this situation and performed the TSB on the jeep over the holidays. I Pulled the valve cover off, removed the exhaust valve springs and inspected the tips of the valves. A few looked as though they were not rotating so I did what the TSB instructed and rotated all exhaust valves 90 degrees, reinstalled the springs and ran a whole container of upper engine cleaner through the throttle body. Gave it a two hour soak, and then ran the jeep at 4500 rpms for 15 seconds in low gear and back to idle 6 times as prescribed. Cleared the misfire codes and gave the vehicle back to my daughter. The jeep ran well, sounded good, and seemed to have more power afterwards. Two days later I took a ride with her and got on route 309 and she proceeded to attempt to keep up with traffic. As soon as the jeep exceeded 65 MPH, around 3000 RPM, the check engine light started to flash. She slowed under 65 and the light stopped. I instructed her to remain under 65 MPH and after another 50 miles or so the light did not return. AARGH! The Jeep ran perfectly the remainder of the day under 65. My next step… I ordered new valve springs . My best estimate is either weak valve springs or a severely fuel starved engine at sustained high RPM. I do not have scanner data since we did not have a scanner on it when we were on our trip so…

Last weeked:
Another weekend of head banging. I installed the new valve springs and also installed another new crank sensor last night. Did not help…same problem. Exactly at 3100 rpms the check engine light flashes, under 3000 goes away. Take it back over 3000 exactly, and in a few seconds will start flashing under no flash. I can duplicate it under a load in any gear, or no load in park. Pending P0300. LTFT numbers look normal. RPM on the scanner follow JEeps tach. Normal. Engine Vacuum rock steady at 17 when the CEL starts flashing, and fuel pressure rock steady at 50 psi. The jeep is back with my daughter in Phila but the problem is yet unsolved. Definitely RPM related. Cam sensor, is this a programmed event to keep the jeep under 3000 RPMs? almost seems like it it is so precise....a flash…? Oh yeah, I installed new rear brakes too and that didn’t help the problem either. ;-)
Here is an interesting tidbit, I pulled the vacuum line off from the spot on the intake for the PCV line in order to hook up the vacuum gauge; we had a small window of time where the CEL did not flash over 3000 rpm. I plugged the PCV back on and it came on again over 3000 rpm. I re-pulled the PCV valve hose back off the intake and plugged the vacuum gauge back in and it did not come on. Eureka! Bad PCV! So…on the way to the Auto Zone to pick up a new PCV with the vacuum line plugged, it came on again over 3000 RPM, Damn, too good to be true… but that wasn’t it. But it was curious that I had that short stay of CELs during that couple of runs over 3000 rpm. Co-incidental I guess but it almost made me think it was leaning out due to a bad PCV even though the LTFT didn't indicate that.

outofmoney 01-09-2013 09:29 PM

While you are throwing money at it, might as well replace throttle position sensor and see if that helps!

bdaddybbq 01-09-2013 10:44 PM

In having a similar problem with my 2001 4.0 6 cyl. At highway speed it bucks on me sometimes when I hit bumps sometimes when I go around a corner. Some days it won't start up in the morning and will be very hesitant. I will have to rev it up until it backfires then it will run most of the way to work. Sometimes it will go days with out a hiccup. I've replaced the fuel pump but really nothing else because I'm not sure where to start. I do have a high pitch squeal coming from the motor towards the back but can't get a wrench on it to tighten it. I think it is the manifold. I have no check engine light but I do lose mph and my fuel gauge drops and the light comes on. I'm just completely at a loss as to what to do.

Cbartrip6 01-10-2013 09:11 AM

I apologize for not updating this thread earlier. And there were two issues going on at once. I had a bad vacuum hose that was throwing the evap codes and when i replaced the hose and cleared the code, that issue was resolved and the light did not come on.

Just as you experienced, that did not solve the RPM issue. That ended up being a faulty crankshaft position sensor. once that was replaced, she drove like a champ again!

Hope this helps and it ends up solving your issue.

bdaddybbq 01-10-2013 11:12 AM

Thank you. I know what I'm doing this weekend.

29ster 01-11-2013 07:25 AM

I replaced my Crank Sensor again with no luck. STill have the misfire at exactly 3000+ rpm, not below. Definitely RPM related and not load related as I can get the light to flash in the driveway if I hold that rpm for a period of time. TPS is an interesting thought but I would think the TPS is in different positions when under load vs in park at that RPM and I got no indications of that either on the scanner or DVOM. Only thing left is the cam sensor but this cam sensor has never been out of the vehicle so I doubt it is a sync problem. SO here are the list of things I performed/repalced to attempt to correct the CEL flashing at 3000+ rpm without success.
  • Cam Sensor
  • Champion Plugs (gapped correctly)
  • Coil Rail
  • TSB that tells to inspect and rotate exhaust valves and decarbonization upper engine efforts
  • Replaced Valve Springs *(all 12 just in case)
  • Throttle body cleaning (again)
  • Another Cam sensor
  • Check for wire chaffing at the rear of the engine
  • Fuel pressure check (solid 50 at time of CEL activity)
  • Engine vacuum check, no fluctuation at time of CEL activity (17 inches)
  • LTFT check including at time of CEL actvity- ok
  • STFT check ok
I've been telling my daughter its supposed to do this to keep here under 70 mph and it does make me cringe to cruise the freeway at that RPM anyway... She tells me traffic is flying by like she is a grandmom going to church in the right lane. She hates that :whistling:
:banghead: Maybe I should just install taller tires :doh:

HotRock 02-15-2013 02:59 PM

29ster, your Jeep problem very closely resembles mine. I have at times had the CEL blink at close to 2000 rpm. Most of the time it's 3000 rpm range. I've changed the throttle pos sensor, plug rail, had the valves rotated. All to no avail. I'm at a loss except maybe the gas cap and replacing some vacumn lines. Will keep at it and see what happens. Good luck.

HotRock 03-10-2013 12:41 PM

I replaced the "purge valve" yesterday. Went for a drive and the light didn't flash until I got it to 4000 rpm. But after that it would flash at 3000+. Let off the accelerator and slow down and the light would quit flashing and go off. No codes thrown. ??????

HotRock 03-11-2013 09:15 AM

Has anyone tried replacing the engine control module,(computer)? How much does that thing cost?

29ster 03-12-2013 08:12 PM

I've basically given up. Anyone have a set of 2005,2006 rubicon wheels for sale? I'm just gonna put on taller tires and keep it below 3000 rpm for extended periods of time. I've replaced everything, sometimes twice and it is eerily predicitible. Just over 3000 rpm will start the CEL flash, bring it under it stops. I believe now it is a programming issue.

ajcxnejx 03-12-2013 08:25 PM

There is a procedure that in some cases needs to be done to the computer to correct it.

HotRock 03-20-2013 07:01 PM

I decided to try replacing the Crank Position Sensor. I was cautioned at the dealer to install the sensor all the way against the flywheel. There is a fiber spacer on the end of the sensor that will then get wiped off when the starter first turns the flywheel, thus leaving the correct gap. I went for a couple of test runs and have not been able to make the CEL flash or come on even up to 4500 rpm. Maybe, must maybe and hope it is fixed. One other thing I did while changing the sensor, I unplugged the ECM one plug at a time and repluged them. Don't know if that had any effect but it is something else I did.

HotRock 05-24-2013 09:12 AM

Apparently the Crank Pos. Sensor fixed my problem. CEL hasn't come on again. Yeeee haaaaa! :dance:

29ster 06-19-2013 08:37 AM

3000 RPM mystery

Originally Posted by 29ster (Post 3495432)
I've basically given up. Anyone have a set of 2005,2006 rubicon wheels for sale? I'm just gonna put on taller tires and keep it below 3000 rpm for extended periods of time. I've replaced everything, sometimes twice and it is eerily predicitible. Just over 3000 rpm will start the CEL flash, bring it under it stops. I believe now it is a programming issue.

I wonder if the flywheeel is slightly out of round and when the rpms get that high it cannot follow the crank sensor correctly. The fact that I can get it to do it in neutral at that rpm suggests it may be. Can't be valve float because I replaced the springs too.
Maybe I'll just take the 3.73's out of it and go with a different ration. I road in a 99 yesterday and at 70 mph it was tacing 2500 and was dramatically more comfortable at that RPM.:doh:

HotRock 06-21-2013 05:01 PM

Doubt the flywheel would be out of round. I don't know what you mean by following.......Who installed your Crank sensors? Was it done correctly? Exactly how was it done and did it move when tightening it down? I held mine while I tightened the bolt that holds it in place because the hole is oblong for adjustment. They must be finicky little raschals. So far mine is running great after the CPS was installed. BTW I did use a genuine sensor purchased at the Jeep dealer.

Kssig1 06-21-2013 05:56 PM

Sorry I just noticed this thread. I have tried aftermarket crank sensors before and for some reason they never worked for me for very long. I only use factory parts for the crank sensor and they seem to work much better. I tried two different brands in my 98 4.0 without luck until I bit the bullet and bought one from the stealership.

Steve00 07-28-2015 07:50 PM

I know this is an old thread but I am having same issues that sdh796 and 29ster had. Flashing CEL and P0300 and several P030x codes and only seem to happen when running highway speeds. My TJ is a 2002 4.0 auto.

Did anyone ever figure this one out??


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