Great Lakes 4x4. The largest offroad forum in the Midwest banner
1 - 20 of 24 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter · #1 ·
Hey guys, I have a very quirky problem with my Jeep that I need some insight on from all you Jeep guys out there.

I have a 2002 Wrangler 4.0 and I am having a problem with multiple misfires. I am mechanically inclined but not a mechanic by any stretch of the imagination; with that being said, I have asked for some help from a friend of mine to diagnose the issue. We (he) has ran a number of tests to determine what the cause may be so I wanted to include his results so far to help you eliminate possible problems that we may have already ruled out. Please see his notes below and reply to this post with any help that you are willing to provide. Thanks in advance for your help.

We scanned your PCM with the DRB and found multiple misfire faults stored, also found faults for cyl.3&4 misfire intermittent. The engine does appear to have a rough idle (light misfire) and low engine rpm when idling. Performed some basic checks Verified batt condition and proper engine ground, inspected the spark plugs and checked the compression found the plugs new (oe champs) which you must have installed, although 1&3 look really white the rest looked ok, the compressionn was appr. 125psi on every cyl. Vacuum was steady about 16in.hg checked for leaks at the intake with carb spray but had no indication of a idle change looked ok. Ran the balance test on the DRB and came up with cyl#1&3 also 4&6 showing low perfomed the balance test quite a few times trying to identify 1 of the cyl's to be problem child but with inconsistent results we found 1&3, 4&6 to be the cyl's that were low.(this test determine each cyl's effect on the total performance of the engine, having a low percentage means to have litle or no effect on the overall engine speed, hence i misfiring cyl.). Due to the inconsistence of the misfire we installed another used coil and ran the balance test multiple times with the same overall results. Based on the plugs and balance testing we removed the fuel rail had the injectors serviced and flow tested at a local shop(all tested ok) with seemly no change, this is hair lose time. Had found a tsb describing a multiple misfire condition during highway driving this detailed the removal of the valve cover and the removing of the valve spring retainers which we in order to turn the valves in the guides 90degrees(appearance there is a problem with them sticking) following reinstall of the valve cover a treatment of seafoam was run though the intake which had no effect on the running condition. I performed some electrical testing at the PCM & verified the correct power supply and good grounds at the module all checks were done with the back side of the ecm connectors removed and the vehicle running. Used a small hand held scope to checked the injector on time to compare with the live data from the DRB also checked the ignition primary signal bothed looked fine. I attached a pic of the cam and crank sensor signals sorry about the poor pic but its just a hand held and has no output port, the scale is 5v >>1 is the crank sensor and >>2 is the cam sensor the crank sensor voltage is batt. and the cam sensor is 5v I'm not real sure of the wave form i don't have a good running vehicle to get an image but maybe someone that knows could tell something from this pic. As a "last ditch effort" we replaced the idle control valve hoping to raise the idle but had no effect. That brings us to this point not sure where to move forward maybe you can dig up some more info? Let me know what you find.
 

·
In too deep
Joined
·
2,385 Posts
There are many things that can set a multiple misfire, electrical or machanical issues.
You seem to have done alot of tests to rule out some issues.
I would need to know when you experience the issue, ie... hot, cold, highway, morning, a/c on, constant or for the first 5 minutes after starting, mileage,
These are all clues to the problem. Also, everything that was done prior to the issue.
It sounds like a mechanical issue that is being found by the PCM and all it can do is point you in the right direction. or sometimes down a wrong path since it is confused.
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #3 ·
JeepInABox Questions

JeepInABox-

This misfire and rough idle is constant through hot and cold, morning or night. The jeep has 70K miles on it and the only things that were done before this issue (rough idle/misfire) occurred were done long before any misfire issues started - they include: new rear end, cold air intake install, plugs (champion), and O2 sensor. Your thoughts?
 

·
Registered
Joined
·
635 Posts
did you happen to check plug wires and the cap and rotor? seems like a pretty basic step he missed unless he just didnt write it down
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #6 ·
I only bought Champion because they are the recommended plug for that vehicle, supposedly Champions are what was put in on the assembly line. I tried new plugs when this issue started, and the plugs I pulled out were Bosch Platinum which of course where showing the same results/issues as the Champions.
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #7 ·
This Jeep has a coil rail rather than a cap and rotor. I put another coil rail on and the same issues continued on the same cylinders.
 

·
Registered
Joined
·
1,111 Posts
There has been a long running thread on Jeepforum.com regarding the cam position module, sensor located on the right side of the block. Concerns abnormal wear of the teeth . Might just involve later tj's though. Have to get mine in and checked before the 70k warranty runs out. TSBE05 bulletin
 

·
Happy 2b Jeepin!
Joined
·
362 Posts
i believe its the crank position sensor also, this according to what i have read, can cause these symptoms. there is a check that uses an ohm meter if it is near or below the correct number, they say to replace it, also the articles i have read note that as it starts to go bad your gas mileage will also fluctuate (sp?). their quick/trail fix for this problem is to move it closer to the flywheel, some older versions have short slots for that reason. also if you pull it out since it is a magnetized piece it will probably be covered with rust/dirt pieces. i would be inclined to replace it but also TRY to clean the sensing ring on the flywheel, mine had surface rust build-up that COULD cause issues. it seems like it would do it for all cylinders if this were the problem but who knows. one of the articles i read stated that the owner kept a spare just in case it he had trail problems. iguess water and mud getting in there can cause a issue with the sensing ring.

regardless good luck.
 

·
In too deep
Joined
·
2,385 Posts
I was thinking the signal from the crank was intermittant/incorrect and giving you this fault.
I have seen cracked flywheels/trigger wheels that tell the crank sensor incorrect postion (although slight) the pcm is looking for a specific speed increase at the crank sensor when a cylinder fires. if there is a crack it is seeing a delay.

First thing is make sure the sensor you have is clean. if not clean it and reinstall it.
To rule out dieing sensor get a new sensor to see if it is your problem. (if not you have a trail spare)
Then inspect the flywheel/ trigger wheel for damage/cracks.
 

·
Premium Member
Joined
·
631 Posts
We had a XJ a work do that and it ended up being the downstream o2. Even though there was no code it was shorted. Did you check your voltages and watch the o2's cycle to verify they are normal.
 

·
Registered
Joined
·
7 Posts
Discussion Starter · #18 ·
We had a XJ a work do that and it ended up being the downstream o2. Even though there was no code it was shorted. Did you check your voltages and watch the o2's cycle to verify they are normal.
I will have to check with my buddy who has been running tests on it. I believe that he has been using a Tech II to run a number of the tests so he should be able to read the voltages on the o2 sensors. I will respond to your question and others regarding the o2 sensors tonight when I can either get the info from him or run the test. - Thanks
 

·
Registered
Joined
·
3,625 Posts
Here is a small write up I did on my missfire codes. Not sure if it will help you at all but that coil rail is a bit touchy.

JF code P 304

Also, keep the champion plugs, they are the best as long as they are the right tip, dont mess with the gimmiky stuff. The 03 and up TJ's really like the OE stuff.
 

·
Premium Member
Joined
·
1,148 Posts
I was having the same issue with my 01 tj. where did you get the coil pack from that you put on it? may want to look into a new coil pack. I had 2 bad oem ones and was able to fix it after putting in an aftermarket coil pack.
 
1 - 20 of 24 Posts
Top