4.0L Multiple Cylinder misfire


Super Moderator
Lately I have been getting a random missfire in my jeep.
(lack of offroading).
I have been using it all winter as a daily driver and with regeared axles and transmission/transfer case, my RPM's rarely got over 3000 rpm's. I have been getting the check engine light flashing at 2800+ RPM's with a slight down hill on certain sections of the freeway after I reached operating temp.
Well the other day I got more than a "check engine light", I was pushed into a 'limp home mode" coming home in a fierce head wind and freeway speeds around 75mph (3100rpm) . When I got home I pulled my OBD II reader out and got P0300 (random misfire) and P0301(misfire cylinder 1), P0302, P0303 P0305, and P0306.
I have replaced the plugs, ignition coil rail, throttle body position sensor (a slight voltage drop at the beginning) it was not related to this problem.
SO I isolated it down to a Technical Service Bulletin.


The customer may experience an incident of engine misfire during certain vehicle operating conditions. 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 conditions 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 - Multiple 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.
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(R) 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

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.

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

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 90°.
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.

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 1200 and repeat steps 3 through 5 to cylinders # 5 and # 2.
8.Rotate the engine crankshaft another 1200 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.

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.
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.

So it looks like I will be pulling the valve cover this sunday or monday over at Big O tire ( a friends shop). Will grab a few picks when I do this.
Sorry it has taken me so long to finish the story but my first attempt to fix it, didn't. So it has taken me a bit longer to find and fix this problem.

Well like I said I was going to manually turn my exhaust valves, I tore the valve cover off and removed the rocker arms, marking each one with a number 1-6 and with an I or a E for exhaust or intake.
After careful inspection I didn't see any of the valve stem tops with distinctive parallel lines, all had good circular or bulls eyes on top.
With nothing better to do I turned them anyway. afterwords I installed new plugs and heat-soaked the motor with DC's de-carbonizer in the cylinders 4+ hours.
During the drive home it shot me a P0300 code again(the choice words I invented cant be repeated on a famialy board).

Well a few days later Scotty bought snap-ons new Ethos scanner tool.
We finally located my problem, first off, this scanner tool can take direct readings live from the jeep during a drive and take a snap shot when the jeep throws a code.

Now on a drive a few days later we got it to throw a code on the freeway.
It appears that the OBD II computer can learn that a throttle position sensor has weakened and it needs a small % of manual gain to compensate its actual position and what the motor needs. My throttle position sensor has never thrown me a code or given me any reason to suspect that it has had a problem, so when the Ethos took a snap shot it tracked my position sensor dropping from a 10% gain to a -10% as we descended a slight down hill and the cam, and rest of the motor tried to catch up to the reduced torque needed to maintain my current speed.During that 20% allowed my engine to throw a mis-fire, thus my problem.

So I replaced my TPS with a genuine Chrysler TPS and (knock on wood) three days so far no codes nor profanity.


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I'm glad you have isolated the problem. Scantools are a gem when it comes to diagnostics now a days so as long as you know what your doing and what your looking at.

A swing and a miss....I pulled a code today on the way to work...random miss fires again.
Thinking O-rings on the injectors?
Dont forget to check the engine wiring harness specifically the part that routes behind the cylinder head for chaffing or a worn insulation that causes a bleed through voltage between the wires. I rarely encounter this but i would not eliminate it from the possible cause.
Has anyone resolved this problem??????????? because my 2000 TJ is doin the same thing and I have had the valve springs checked and compression checked all checked out but its still doing the same thing. I have spent plenty of money on trying to fix this issue and it has gotten me no where lol. Any help is appreciated.


I just picked up a 01 Wrangler with a multiple cylinder misfire code. The dealer changed the coil pack and TPS with no result. Finally they blamed the ground connection on the individual injectors. Two of the connectors had pins partially falling out due to someone possibly tugging on them. Thankfully this fix was on their dime as it needed to pass inspect before I bought it it was a lengthy diagnosis. I'll report back if the codes come back.
Still havnt found the cure to my misfire problem, waitting to get a couple of free days to drop my rear tank and replace the fuel strainer in the tank to see if that helps. I have a small hesitation when I step on the gas, I already replaced the throttle body sensor and the idle air sensor.
Did you really use the E3 plugs?? I had bad luck with them . I'd put origional NGK or normal Champion or Autolite plugs in before doing anythnig else. Be sure to gap them.

The E3's reduced my MPG 10%+ and I could hear puttering like misfires but didn't throw a code.

Also with the possible misfire or backfiring. Clean the TB and IAC. These likely got all sooted. Wouldn't hurt to be clean anyway. ( oops just reread the above) be sure the cabling to teh IAC and TPS is clean.
Degolyerent, the fuel pressure is fine standing still with the gage on it, but I still get a slight hesitation from idle as I flip the butterflys open. Just a slight one but I can hear it and feel it. With 11 years on the fuel strainer I think its time to throw a clean one in. Dont know if this will fix it but a day working on the ole jeep is 1/2 as good as a day wheeling her.
I got the code again tonight after picking it up, guess my problem wasn't the wiring, at least where they checked. Very discouraging the dealer is getting this back tomorrow. I signed on it two weeks ago and have driven it a total of three days!!! They are going to get a real good Pep Talk when I drop it back off, Fix it or find me a different one. (Actually since I bought it used from a Chevy dealer I will be insiting they have the Jeep dealer down the road work on it till it is fixed) Again thankful they have an agreement to fulfill, their dime. In the mean time I going to request a new loaner as I am sick of driving their junk ones. My first Jeep by the way. Please tell me these problems don't happen all the time.:???:

The dealer ordered a new ECM for my Jeep. Will report if this solves my random misfire. Makes sense to me since it would act normal for several minutes if during experiencing a misfire I would stop and re-start the engine.
Chip01TJ said:
The dealer ordered a new ECM for my Jeep. Will report if this solves my random misfire. Makes sense to me since it would act normal for several minutes if during experiencing a misfire I would stop and re-start the engine.

After going through two rebuilt computes the dealer finally gave in and put in an OEM computer and so far so good. After buying this a month ago looks like I might get to drive it a full week finally. At least the last loaner they gave me was a 08 Jeep Unlimited. Keeping my fingers crossed!

Utah_jeepster said:
Hopefully this fixes your problem, dropping the tank this weekend and replacing the fuel pump and screens.

Good luck to you I'm still running.
My light came back on after a week with a new ECM. The dealer I bought it from is still responsible to fix and they sent it to the Jeep dealer to get a valve job.
They found a cracked head upon pulling it.
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Just a progress report on this thread, the dealer found a cracked head, replaced it and so far so good with no multiple cylinder misfire codes after a good month of running.

Well here is the latest progress report, I found a listing it might be a slight vapor lock with the fuel rail, so with nothing better to do I wrapped the fuel rail with heat shield tape, a 20$ investment and several hours of tapping fun. Will drive it tomorrow and let everyone know.


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