Question about 2003 Jeep Grand Cherokee

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Intermitten missfire one or more cylinder of a new engine.

When I turn on the A/C unite switch, the engine light comes on and #3 cylinder missfires. When delete the malfunction with OBD1, the engine runs smooth for a awhile and then cylinder missfires again. What causes this problem?

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  • dean_clow Jun 03, 2009

    I just put in a NEW REMANUFACTURED ENGINE and have driven about 1000 miles only. Therefore, your suggestion of cylinder compression check or the decarb the cylinders seem not

    an answer to my original question of "engine misfire" I started the engine and turned on the A/C swith.



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Misfires are always due to the fact that the engine is not fine tuned .but since you have specified in your comment that you have installed a new engine, please check the airfilter that connects the engine and fuel. and if you suspect that only the ac unit causes these problems, please check the relays and sensors of the unit.also have a check on the battery voltage levels. thanks for contacting fixya! hope your problem is tackled as soon as possible.

Posted on Jun 04, 2009

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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.
09-003-03 -2-
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.
Qty. Part No. Description
1 04318001AB Mopar Combustion Chamber Cleaner
MD-998772A Valve Spring Compressor and Removal Essential Tool
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- 09-003-03
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 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.
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.

Thanks for contacting Fixya.

Posted on Jun 03, 2009


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