Jeep Grand Cherokee '02 - recurring (approx once a month) misfires

mratko

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#1
(Ladies &) Gentlemen of the Board,

Earlier this year I asked about a MIL code resulting from misfires on cyl 1, 2, 3 ,4, 5, and 6 of my 4.0L Jeep that now has 157,000 km. About four or five times since then (just before New Years), I have gotten the "jitters". I am beginning to recognize the feeling and stop the vehicle, shut the engine off, then restart it. When I restart it, it runs fine for a while longer.

The misfires always seem to occur when I am running at a steady clip. I am often on the highway when this happens but it has occurred two times in the city; once when I started the car. Recently I was cruising (on cruise) at 72 mph when the misfires started again. I pulled over as fast as i could (in moderate highway traffic), shut the vehicle off then restarted it. No problems. I read the codes and here is what they were:
P0300
P0303
P0306

P0300 FF Data:
Calculated Load: 50.5%
Engine Coolant: 199°F
STFT Bank 1: 0.0%
LIFT Bank 1: -2.3%
STFT Bank 2: 0.0%
LIFT Bank 2: -3.1%
Intake Manifold Pressure: 7.9" Hg
Engine RPM: 2240

I have read where PCV valves, fuel injectors, and valves can be implicated. Are there any other ideas on this one. I need to drive from UT to Michigan to get my boat and pull it back. I would like to resolve this before I leave for that trip.

Thank you for your help....

Mike
 
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#2
Here is part of a tsb that might apply to your vehicle...it has to do with the valves....Jim.....SYMPTOM/CONDITION:

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 0C (32F).

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.

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.
 

mratko

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#3
Thanks Jim.

It is difficult to constantly run above 3200 rpm with overdrive on - but I will do it for a while to get the revs up and try to get the valves to rotate. I have been using the "new premium" gas at 88 octane and will supplement that with some gas treatment too to try to clean up the injectors. A new PCV valve will not hurt either. After that, is there a way to help clean any deposits off of the valves; without a major engine overhaul?

Mike
 
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#4
You might try running some Seafoam through it...I got this info from one of their sites...Start by measuring out 6oz or 3/4 cup of Seafoam into a small jar. Now, with the car heated up and running locate a vacuum line that can be disconnected at idle, or source one from the vacuum tree under the throttle body cover or off the wastegate. Place your finger over the line to confirm it is indeed a source for vacuum. Leave your finger over the hose until you are ready to begin.

Slowly submerge the vacuum line in the Seafoam until the engine starts to stall. This step is a balancing act of keeping the engine idling while tying to induce the cleaning solution as quickly as possible. If you are having a problem with the engine stalling out, try dabbing the vacuum line in and out of the solution.

Once you have introduced the 6oz of seam foam shut then engine off and wait ~10 minutes.

Once ten minutes have elapsed and you have reconnected the vacuum line restart the engine. At this point the exhaust will smoke and you may experience some back firing. This step is the Seafoam burning off. Wait until the smoke has slowed and then take the car on a 3-4 mile drive. During acceleration expect some light to heavy smoke which will subside after a few miles......Jim


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mratko

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#5
Thanks Jim. I will give it a try. I know just the vacuum hose to use. I will track the next time (if) I have the mysterious misfires and hope that this does the trick.

Mike
 

mratko

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#6
Well it happened again - and after the Seafoam treatment. It was exactly one week after the last time. Here is the data:

June 22, 2009
*************
P0305
P0305 FF Data:
Fuel System 1: Closed loop
Fuel System 2: Closed loop
Calculated LOAD: 70.1%
Engine Coolant Temp: 206°F
STFT Bank 1: -2.3%
LIFT Bank 1: -1.5%
STFT Bank 2: 1.5%
LIFT Bank 2: -3.9%
Intake Manifold Pressure: 13.5" Hg
Engine RPM: 3072 (O/D off)

Note that I had the overdrive off. I was trying to get to that RPM where the valves will rotate. So I may have caused this if the reason is carbon build up. Is it safe to do another Seafoam treatment so soon after the last? (esp. after I burn off each treatment).

Thank you for your help.

Mike