so my jeep was throwing a check engine light so i ran the codes and its a cyl6 mf. i changed the plugs but its still doing it. my next thing i was gonna do is buy a new coil rail. anybody have any information on this? :bang:
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so my jeep was throwing a check engine light so i ran the codes and its a cyl6 mf. i changed the plugs but its still doing it. my next thing i was gonna do is buy a new coil rail. anybody have any information on this? :bang:
We don't have a lot if info on them. The either work or they don't.
Generally the 1999-2001 4.0 liters are known for the Cylinder 3 misfire, infact there is a TSB for it..Though you may be able to install a heat shield over the intake, if the shield is not too expensive then it might not hurt to try it.
There is also a multiple cylinder misfire TSB.
SUBJECT:
4.0L Rough Engine Idle After Restart Following A Hot Soak
OVERVIEW:
This bulletin involves the installation of a fuel injector insulator sleeve.
MODELS:
2000-2004 (TJ) Wrangler (Domestic and International Markets)
1999-2004 (WJ) Grand Cherokee (Domestic and International Markets)
2001-2004 (WG) Grand Cherokee (International Market)
2000-2001 (XJ) Jeep Cherokee (Domestic and International Markets)
NOTE: This bulletin applies to vehicles equipped with a 4.0L engine (sales code = ERH)
SYMPTOM/CONDITION:
Customers may describe a 20 to 30 second rough idle following the restart of a heat soaked
engine. This condition may be most noticeable when the engine is restarted following a
prior 10 to 20 minute heat soak in hot ambient conditions of approximately 32 C (90ºF)
or higher. This condition may be consistent with short city stop-and-go driving trips and
can be aggravated by the use of fuel with a high ethanol content. Depending upon
various conditions a MIL may occur due to DTC P0303 – Cylinder #3 Misfire.
This condition may be caused by heat from the exhaust manifold that following engine
shut down migrates to the area around injector #3 and causes fuel vapor to form
within the injector. This in turn may cause a momentary misfire of cylinder #3 until
the fuel vapor is cleared of injector #3. The insulator sleeve lowers the injector #3
temperature to a point below which the fuel will not normally vaporize.
DIAGNOSIS:
1. If vehicle exhibits a rough idle, and if a misfire of cylinder #3 is observed following
a 10 to 20 minute hot soak, perform the Repair Procedure.
18-031-03 -2-
PARTS REQUIRED:
Qty. Part No. Description
1 56028371AA Ignition Wire Shield
REPAIR PROCEDURE:
1. Cut insulator sleeve, p/n 56028371AA, to make two (2) insulator sleeves
about 25-30 mm (1 in.) in length.
2. Install one sleeve around injector #3, with the slit on the upward facing side of the
injector. Install the other sleeve with the slit on the downward facing side of the injector.
3. Confirm sleeve is flush to intake manifold surface around injector.
4. Check injector #3 wire and ensure that the injector is rotated to a 2 o’clock
position (from driver’s side of vehicle).
Also:
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(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