multiple cylinder misfire

[offroadaz]

Recently my check engine light came on saying error p0306 which is a misfire in cylinder 6. I changed my plugs and I thought that had fixed it.

The light stayed off for awhile, but it came back on about a week later. I ran some STP fuel injection cleaner through it hoping that would help and I thought it had. I cleared the codes manually and all was good for about a week. Now the light is back on.

I have done some basic troubleshooting, I can clear the codes and as long as I stay below 3,000 rpms it seems that I can avoid having the code thrown again. But as soon as Im passed that the code pops back up

On our way up north the other weekend the light came back on again and I could not go faster then 45mph up the hills. Usually I could hold steady around 60mph

I scanned the codes again and now I have errors P0300 P0301 P0303 P0304 and P0306

One other weird thing, instead of the check engine light being steady it occasionally flashes on and off. Not sure why

All of these are related to cylinder misfires

It seems weird that all of my plugs would be bad again and that the Jeep would misfire on so many cylinders.

Has anyone had this happen before? Any ideas on what else I can check



Vehicle: 01 4.0 TJ 76,000 miles

Steps taken:
Replaced spark plugs
3 month old crank position sensor (do you think its bad?)
Ran fuel injection cleaner through it
New fuel pump and filter

[KennethS]

Since it seems to be related to more than just one plug, maybe it is something in the ignition control circuit - the ignition module or coil (does that year even have those?)

And I would not use STP injector cleaner - during my college years working at the local auto parts stores I learned that it's not really effective. I like Berryman B12 Chemtool instead.

[offroadaz]

Since it seems to be related to more than just one plug, maybe it is something in the ignition control circuit - the ignition module or coil (does that year even have those?)

And I would not use STP injector cleaner - during my college years working at the local auto parts stores I learned that it's not really effective. I like Berryman B12 Chemtool instead.

Yep I was thinking that, maybe its the coil rail. But Im confused as to why the codes dont seem to come on until Im over 3,000rpms

Id rather not spend the $200 on the coil rail only to find out its something else

[BeaterXJ]

i don't know what year the vehicle is, obveously '96 or newer b/c it had obd2, but the light flashed b/c it only illuminated during missfire

[BeaterXJ]

i don't know if you know anybody @ a jeep dealer but if you did you could ask if their are any tsb's or "fix it right the first time" publications that relate to your codes

[TanTJJim]

i don't know what year the vehicle is, obveously '96 or newer b/c it had obd2, but the light flashed b/c it only illuminated during missfire

To be a little more specific, it will flash during a catalyst damaging misfire. If it's picking up a minor misfire it will just turn the check engine light on, a larger misfire or multiple misfires which can damage the cats in a short period of time will cause it to flash. Not trying to step on your toes, just adding a little more info.

BTT, what type of plugs did you put in it? I don't want to start a spark plug war, but I absolutely hate Champion spark plugs. Which I also believe is what Jeep is still putting in from the factory. If you put in Champions I would try a different plug first before changing $200 coils. I've always had great luck with NGK's in anything. Autolites also seem to work in a wide variety of vehicles without any problems.

It's been a while since I've taken a coil rail off but I believe there are some rubber boots that go between the coil rail and the spark plugs. On most coil on plug systems you can remove these and replace them separately. If that's the case I would recommend replacing those as well, if they are bad they can cause the spark to jump from the coil to the cylinder head instead of going through the spark plug causing a misfire. Hope that helps!

[ademster]

Sounds like your crank position sensor is failing..


It may not be recieving signal art that RPM..

or your Cam Sensor, ( the distributor looking thing ) is whats called a Hall Effect sensor... it may have debris, or the magnet it self has become weak!

I will do a quick search after I eat dinner.

[BeaterXJ]

To be a little more specific, it will flash during a catalyst damaging misfire. If it's picking up a minor misfire it will just turn the check engine light on, a larger misfire or multiple misfires which can damage the cats in a short period of time will cause it to flash. Not trying to step on your toes, just adding a little more info.

BTT, what type of plugs did you put in it? I don't want to start a spark plug war, but I absolutely hate Champion spark plugs. Which I also believe is what Jeep is still putting in from the factory. If you put in Champions I would try a different plug first before changing $200 coils. I've always had great luck with NGK's in anything. Autolites also seem to work in a wide variety of vehicles without any problems.

It's been a while since I've taken a coil rail off but I believe there are some rubber boots that go between the coil rail and the spark plugs. On most coil on plug systems you can remove these and replace them separately. If that's the case I would recommend replacing those as well, if they are bad they can cause the spark to jump from the coil to the cylinder head instead of going through the spark plug causing a misfire. Hope that helps!

No problem, not stepping on my toes at all. i just replaced dustins plugs and yes you can replace the plug boots. when dustin asked the parts places for ngk's they didn't list them for his but yet the plugs i pulled out were ngk's, figure that out! Saturn ion's would do the same thing (set missfire codes) and we had to replace the ign. coil module to take care of the problem but thats a totally different vehicle so not really anyhelp

[Curly]

I agree with what jim and Ademster said. The reason you can't go over 45 is the computer will limit rpm under certain code conditions. This is to protect the cat.
Next time the light flashes, I suggest you pull over as soon as it is safe, and turn the key off for 1 minute or so. Then restart, and see if the light has stopped flashing. Chances are it has. Cat's are expensive, you don't want to replace them if you don't have to.

What are using to read the codes? Can you access the freeze frame data? This is captured during a code event, may shed light on the actual failure.

[TanTJJim]

No problem, not stepping on my toes at all. i just replaced dustins plugs and yes you can replace the plug boots. when dustin asked the parts places for ngk's they didn't list them for his but yet the plugs i pulled out were ngk's, figure that out!

Thanks for the reply, I wasn't quite sure if you could do the boots or not. And that is weird with the spark plugs, kinda cool you were able to put ngk's in though. I like to use those plugs in everything if at all possible.

[FourxDad]

Try the plug wires, at night in the dark run the engine with the hood open and look at the wires if they are cross firing you will see it

[FlexyXJ]

Lets remember everyone, that Multiple Cyl misfires can also be FUEL related....not always spark. The difference in crank speed can also be contributed to a cylinder not getting FUEL as well as spark.


Joe

[offroadaz]

Sounds like your crank position sensor is failing..


It may not be recieving signal art that RPM..

or your Cam Sensor, ( the distributor looking thing ) is whats called a Hall Effect sensor... it may have debris, or the magnet it self has become weak!

I will do a quick search after I eat dinner.

I forgot to mention I replace both the CAM and Crank position sensor around the same time. Bought the parts from autozone


I looked around and did find this TSB. It sounds almost exactly like what my jeep is doing, the only difference is they say its more noticeable in cooler weather. Not too sure if I want to undertake this project to fix it though, sounds a little complicated

NUMBER: 09-003-03

GROUP: Engine

DATE: Aug. 01, 2003

SUBJECT:
4.0L Multiple Cylinder Misfire
OVERVIEW:
This bulletin involves inspection of all engine exhaust valves and a decarbonizing procedure if necessary.

MODELS:
1999 - 2004 (WJ) Grand Cherokee (All Markets)
2001 - 2004 (WG) Grand Cherokee (International Markets)
1999 - 2004 (TJ) Wrangler
1999 - 2001 (XJ) Cherokee

NOTE: THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH A
4.0L ENGINE (SALES CODE = ERH).
SYMPTOM/CONDITION:

The customer may experience an incident of engine misfire during certain vehicle operating conditons. The misfire may occur when the vehicle is operated between 80 - 112 KPH (50 - 70 MPH) and under light loading conditions, e.g. slight uphill road grades. This condition may occur at all ambient conditions, but is more noticeable when ambient conditons are less than 0 C (32 F).

If the vehicle is equipped with On-Board Diagnostic (OBD), a MIL illumination may also have occurred due to Diagnostic Trouble Code (DTC) P0300 - Mulitiple Cylinder Misfire.

Various single cylinder misfire DTC’s may also be present. If the frequency of misfire is high the Powertrain Control Module (PCM) may place the engine in “Limp-In” mode.

The misfire condition may be caused by one or more engine exhaust valves that are slow to close. Late closure of an exhaust valve may be the result of no valve rotation and associated build up of carbon on the exhaust valve stem.

DIAGNOSIS:
1. This condition may occur when the engine is not allowed to run at engine RPM’s that are greater than 3,200 RPM. At 3,200 RPM or higher the engine exhaust valves will rotate if not impeded by high carbon deposits. Low engine RPM’s and high carbon deposits are associated with short trip driving where the vehicle engine is not allowed to fully warm to normal engine operating temperatures. Cold ambient temperatures will increase engine warm-up time and add to the opportunity of carbon deposit build-up on the stem of the engine exhaust valve.

2. Verify that an engine misfire condition is present. Use of the DRBIII® during a road test, or a Co-Pilot data recording, may help to determine engine misfire and misfire counts. If carbon deposit accumulation is severe, then a cylinder leak down test may detect one or more cylinders leaking greater than 15%. Save any misfire DTC Freeze Frame Data that was stored for later misfire correction verification.

3. Verify that the engine misfire condition is not caused by faulty engine
mechanical or electrical components.

4. If the engine mechanical and electrical systems are operating properly
perform the Repair Procedure.

PARTS REQUIRED:
Qty. Part No. Description
1 04318001AB Mopar Combustion Chamber Cleaner

EQUIPMENT REQUIRED:
MD-998772A Valve Spring Compressor and Removal Essential Tool

REPAIR PROCEDURE:

INSPECTION:
1. Raise vehicle hood.

2. Remove the engine valve cover and all six exhaust valve rocker arms (the intake rocker arms are also removed during this step). Refer to the appropriate vehicle Service Manual for detailed removal instructions. The valve cover gasket is reuseable. Keep each pair of rocker arms matched to their respective valve and cylinder.

3. Inspect the end, or tip, of each exhaust valve stem where it makes
contact with the respective rocker arm.

4. Determine if each exhaust valve is rotating within its respective valve guide. An exhaust valve that is rotating will have a “bulls eye” or circular wear pattern on the face of the valve stem tip. If the exhaust valve is not rotating a straight mark-like pattern will be present across the face of the valve stem tip.

5. If there are exhaust valves which are not rotating then proceed to the VALVE ROTATION section of this Repair Procedure.

6. If all exhaust valves are rotating, then this bulletin does not apply and further diagnosis is required. Install the engine rocker arms and valve cover. Refer to the appropriate vehicle Service Manual for detailed installation instructions.

VALVE ROTATION:
1. If one or more engine exhaust valves are not rotating, perform the valve
rotation procedure to all six (6) exhaust valves.

NOTE: IT IS IMPORTANT THAT THE VALVE ROTATION SECTION OF THIS
REPAIR PROCEDURE BE PERFORMED.

2. Clean and mark the tip of each exhaust valve stem with a paint marker. The paint mark will be used later to assist with determining if the exhaust valve has been rotated

3. Bring number one (#1) cylinder piston to top dead center using the mark on the crankshaft front dampener/pulley. This step is important to prevent the possibility of the exhaust valve from falling completely into the cylinder.

4. Install the essential service tool valve spring compressor, MD-998772A,
to the #1 cylinder exhaust valve spring.

NOTE: THE FOLLOWING VALVE ROTATION PROCEDURE WAS DEVELOPED WITH
THE USE OF VALVE SPRING COMPRESSOR TOOL MD-998772A. THE MD-998772A IS AN ESSENTIAL SERVICE TOOL AND PART OF THE DEALERSHIP REQUIRED TOOLS.THE MD-998772A COMPRESSOR ENGAGES THE ENTIRE PERIMETER OF THE VALVE SPRING RETAINER, UNLIKE OTHER MAKE VALVE SPRING COMPRESSORS.

5. Compress the #1 cylinder exhaust valve spring enough to gain access so that the exhaust valve can be rotated 90 . Rotate the exhaust valve 90 . Slowly remove the compression on the exhaust valve spring. Verify that the valve keeper is properly seated to the valve stem and valve spring retainer.

6. The 4.0L firing order is 1 - 5 - 3 - 6 - 2 - 4. Without rotating the engine
crankshaft repeat steps 3 through 5 to cylinder #6.

7. Rotate the engine crankshaft 120 and repeat steps 3 through 5 to cylinders #5 and #2.

8. Rotate the engine crankshaft another 120 and repeat steps 3 through
5 to cylinders #3 and #4.

9. Install all cylinder rocker arms (intake and exhausts) and retaining bridge. Make certain that the push rods are properly seated to their respective rocker arm and lifter. Tighten the respective cylinder bridge/rocker arm cap screws to 30 Nm (21 ft. lbs.) when each cylinder piston is at top dead center (cylinder intake and exhaust valves are closed).

10. Install the engine cylinder head valve cover. Tighten the valve cover bolts to 10 Nm (85 in. lbs.). Refer to the appropriate vehicle Service Manual for detailed assembly instructions.

DECARBONING COMBUSTION CHAMBER AND VALVES:
1. Start the vehicle engine and allow the engine to reach normal operating temperature.

2. Remove the air tube from the engine throttle body.

3. With the engine at idle, spray the entire contents of Mopar Combustion Chamber Cleaner, p/n 04318001AB, directly into the throttle body. As the cleaner is being ingested, allow the vehicle to “load up” with the cleaner to the point that the engine is almost stalling out. Maintain this condition until all of the cleaner is used/ingested.

4. Stop the engine once the entire can of cleaner has been ingested.

5. Install the air tube to the throttle body.

6. With the hood closed and the vehicle parked inside the garage, allow the vehicle engine to heat soak for two to three hours. This will ensure that the engine will maintain its temperature and will allow proper solvent penetration.

7. After engine soak, start the engine and drive the vehicle until the engine is
has reached normal engine operating temperatures.

8. If the vehicle is equipped with an automatic transmission, place the gear
selector into “L” (low). If the vehicle is equipped with a manual transmission,
place the transmission into first gear.

9. In a safe vehicle operating location that will allow the vehicle to be driven safely and at the posted speed limit, accelerate the vehicle until the engine reaches 4500 RPM.

10. Hold the engine speed at this RPM for 15 seconds.
09-003-03 -4-

11. Slow down and in a safe location pull to the side of the road. Allow
the engine to idle for five seconds.

12. Repeat steps 9 through 11 five more times.

13. With the vehicle at operating temperature and using any available Freeze
Frame data recorded when the misfire DTC occurred, verify that the
misfire condition has been corrected.

14. Erase any engine DTC’s once the misfire condition has been corrected.