2002 Liberty 3.7 misfire code issues - Jeep Garage - Jeep Forum

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Old 09-14-2015, 09:36 PM
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2002 Liberty 3.7 misfire code issues

I have read through a number of threads regarding misfires and P030x codes and haven't seen or come up with a solution that will help resolve our issues and am seeking advice on next steps.

We don't have a long history with the car, some some things are unknown. What we do know is:

130K miles. Car has difficulty starting - usually cranks 7-10 seconds before it catches and usually needs a little gas to get it to catch. This will result in a plume of blue-gray smoke and a rather prominent gas smell.

Once running you can see and feel engine vibration. Not horrific, but also not the way Jeep designed it to run. It was also giving misfire codes.

The car was taken to a shop and they recommended replacing plugs. we replaced all 6 as well as the ignition coils, as they were very old and had minimal life on them. None of the plugs were not gassy, oily, or otherwise fouled - just worn. The car continues to have difficulty starting and continued to give misfire codes of 301, 303 & 305. Compression gauge were put on cyl 1, 3 & 5 (drivers side bank) and all 3 had good compression above 120-130. We also sprayed around the engine and manifold looking for vacuum leaks and none were present. We ran a can of seafoam through the tank and have just added a can of 44K.

Since the Seafoam, Its still hard to start, however, if the car is cold, it will run with no CEL locally, highway etc...Once hot and re-start it will throw a misfire code - sometimes only 301 & 305, sometimes 301, 303 & 305. It runs fine at rpm, but as soon as i come to a stop light and sit, the CEL will start blinking and the shudder is a lot more prevalent.

There are no other error codes I'm getting, so I have been hesitant to start replacing IAC, O2 sensors etc... but am running out of options. I also have not disassembled the fuel rail or started to replace or move around injectors. I find it hard to believe that 3 injectors are bad, and hoping the 44K will clean / clear out any gunk in the rail or injectors.

Car runs great at 2500rpm and 70mph. but as soon as I come to a light - its not a happy camper.

Thanks in advance for suggestions or comments.
dean

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  #2  
Old 09-15-2015, 07:57 AM
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Re: 2002 Liberty 3.7 misfire code issues



---------- Post added at 08:57 AM ---------- Previous post was at 08:49 AM ----------

Welcome to the garage.
Since the misfires are on the same bank, there must be something common for only that bank. Also since the misfires occur on a warmed up engine only, i would suspect the 1-1 O2 sensor. On a cold engine the O2 sensor output is not used for the fuel trimming, but as soon as a certain temperature is reached, the O2 sensor output is used. A bad O2 sensor can cause the mixture to be too lean to burn well and cause misfires. Do you have a scanner with live data? If so, than check the O2 sensor voltage first. It should jump up and down from 0.2-0.8V. Than also check the fuel trim for the 1-1 sensor. Normally its +- 5, but with a faulty sensor it can become -30.
Regarding the hard start, try to prime the fuel system first. Switch ignition to run two times and than start. If it than starts without problems, then the problem is that the fuel drains from the fuel rail. This could be a problem with the fuel pressure regulator.
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Old 09-15-2015, 10:54 PM
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Re: 2002 Liberty 3.7 misfire code issues

Thank you for your response. I assume you are speaking of the upper O2 sensor, closest to the block- drivers side

Will also see if Torque will show o2 voltages.

My next step is mopar combustion chamber cleaner thru the throttle body

Dn
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Old 09-16-2015, 06:30 AM
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Re: 2002 Liberty 3.7 misfire code issues

Yes, the 1-1 sensor is the one on bank 1 (drivers side), closest to the engine. This is the sensor used for the fuel trimming.Torque does show the o2 voltages and also the fuel trims.
I won´t expect cleaning the throttle body doing any good, since the problem only concerns bank 1.
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Old 09-18-2015, 09:50 AM
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Re: 2002 Liberty 3.7 misfire code issues

The o2 1-1 seems like its doing well - ranging from 0-0.8 and the fuel trim, while I did see it get down to about -10 at idle, also seems to be OK. It was pretty consistently at 0 the whole time I drove.

Of course the day I want to run it and check, I get no CEL or misfire codes, and I easily put 30 miles on it this morning driving around town. I'm sure I'll see something come up later today when I go out for lunch or leave work, and will report if the o2 or fuel trim offers any other indications.

Switch ignition to run two times and than start

I'll try the starting guidance at lunch as well. I assume when switching from off to run, leave it there for a second or two - or longer?

Thanks
dean
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Old 09-18-2015, 12:12 PM
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Re: 2002 Liberty 3.7 misfire code issues

Drove with CEL misfire fault - monitoring o2 1-1 and comparing o2 2-1

2-1 seemed to stay very low - near 0 for the duration of the trip and spiking during accelerations

1-1 stayed at upper end of the voltage spectrum, dancing all over the place, but mainly going high when at idle.

I'll capture/post a log file file for additional reference
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Old 09-18-2015, 01:12 PM
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Re: 2002 Liberty 3.7 misfire code issues

within the attached log file, the areas where I start hitting -30 on fuel trim, is about when the CEL started blinking. Codes read 301, 303, 305 - no other codes present

Thanks
dean
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Old 09-19-2015, 05:26 PM
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Re: 2002 Liberty 3.7 misfire code issues

The -30 means that maximum fuel trimming is used by the PCM, Reducing the normal fuel injection pulse to the minimum. Fuel mixture becomes too lean and misfires occur. The high voltage on the O2 sensor is seen by the PCM as a low O2 content (rich mixture) and the fuel injector pulse will be down trimmed. Most probably the problem is the O2 sensor itself.
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Old 09-21-2015, 08:22 AM
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Re: 2002 Liberty 3.7 misfire code issues



Pulled out the O2 1-1 and here is what it looks like. Ordering a new one today.

Also ordering a IAC as it doesnt look good either. Does anyone know if its good to go out of the box or is there any calibration that needs to be done to it. If so any steps are appreciated.

Dean
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Old 09-21-2015, 09:31 PM
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Re: 2002 Liberty 3.7 misfire code issues

What is wrong with the IAC stepper motor? It is normal (but not good) that the plunjer is dirty and the air canal as well. The IAC stepper motor plunjer needs to be cleaned once in a while, otherwise the idle control gets disturbed.
After the battery is disconnected for a while, the PCM looses the IAC stepper motor settings and the next battery connection, the stepper motor will be opened and closed completely, while the PCM counts the steps. It can take a few starts for the PCM to learn the idle again.
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Old 09-22-2015, 09:33 AM
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Re: 2002 Liberty 3.7 misfire code issues

The failure was human error - I did pull it out and cleaned it, but also pushed the plunger inwards. I could not pull it out to its original length. When I placed it back in the car and started the engine the car RPM stayed at a constant 1500 and raced above 3K when touching the gas pedal. When I pulled the IAC, the plunger was still pushed in.
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Old 09-29-2015, 07:52 PM
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Re: 2002 Liberty 3.7 misfire code issues

For follow-up..... After replacing Bank 1-1 O2 and the IAC, I'm still getting misfire codes. I'm still showing readings in the .8 on the new O2 sensor and fuel trim in the -30 range. I have a feeling that one or more of the injectors are leaking which is why I'm seeing a plume of blue smoke rich with gas smells upon cold start up and not getting any other codes besides 301, 303, 305 (and at times I only get 301). I tried the trick of turning the key to the on position, then starting, but it still takes many cranks to fire (cold) and longer than expected starting when hot. I'm using Torque and I dont think it supports Long term fuel trim, just instantaneous short term.

I will put a fuel pressure gauge on the rail and turn the ignition to on - I think I will expect to see the fuel pressure bleed off if there is a leaky injector. If it looks like I'm dropping pressure, next step will be to pull the rail and look to see if any of the injectors or leaking on some newspaper.

It was also suggested to look at the compression of both sides of the engine and if one side has lower pressure than the other, it may be a sign of a slip in the timing. I recorded timing advances through ODB but not sure how to read them.

Any other thoughts??

Dean
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