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Old 12-17-2012, 10:32 PM
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P 0303-uh oh

Hey guys,
Just got a 2002 Jeep Grand Cherokee Laredo 4*4 as a present for my 16th birthday last tuesday. Love it. I've noticed a couple problems. For one, the steering is not center, and pulls to the right. Secondly, there is a weird...almost vibration while idling. Tonight, the malfunction indicator light popped on. I did the on/off/on/off/on/off/on and received error P 0303, Cylinder # 3 Misfire. Is this common?

Thanks,
Fin
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Old 12-18-2012, 05:33 AM
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Re: P 0303-uh oh

For the first one, let a specialised shop do an ilignment check/adjustment of the front wheels.
For the P0303 code, no, this is not a comon thing to happen. Do you know the service history of the jeep? It is in fact always a good thing when buying second hand, to start with a clean sheet. That means to do all preventive maintenance, ie change engine oil, oil filter, inlet filter, plugs and also differential and T-case fluids, transmission fluid and filter(s), engine coolant and brake fluid.
All depends ofcourse on how long you want to keep the jeep, but i would at least start with the first 4 items.
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Old 12-18-2012, 12:34 PM
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Quote:
Originally Posted by Frango100 View Post
For the first one, let a specialised shop do an ilignment check/adjustment of the front wheels.
For the P0303 code, no, this is not a comon thing to happen. Do you know the service history of the jeep? It is in fact always a good thing when buying second hand, to start with a clean sheet. That means to do all preventive maintenance, ie change engine oil, oil filter, inlet filter, plugs and also differential and T-case fluids, transmission fluid and filter(s), engine coolant and brake fluid.
All depends ofcourse on how long you want to keep the jeep, but i would at least start with the first 4 items.
It's got a clean record, no accidents or serious engine malfunctions. Drove it to school today, and it felt worse. Really odd vibrations in idle and while accelerating. Bringing it in to the shop after I come home from Christmas break, but has anyone else ever experienced this?

One thing to note-last Tuesday, I was going 65-70 on the freeway, and me and my dad heard a pop-we assumed it was the sound system, but could it be the misfiring cylinder?
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Old 12-18-2012, 05:14 PM
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Re: P 0303-uh oh

The vibrations are likely from the misfire. It could be something simple like the plug, injector, or coil pack.
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Old 12-18-2012, 05:19 PM
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Originally Posted by JeepMe View Post
The vibrations are likely from the misfire. It could be something simple like the plug, injector, or coil pack.
That's great news, thanks! So...I'm new to this whole car thing, how does a misfire work? Basically one of the cylinders basically isnt responding the way it should, right?
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Old 12-18-2012, 08:47 PM
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Re: P 0303-uh oh

A misfire is that for whatever reason a normal combustion didnīt take place.
Could be due to no spark, no fuel or a wrong air to fuel ratio.
For that reason you first need to know if the basics are ok, ie good plugs, clean air filter.
By the way, which engine does the jeep have, the 4.0 inline 6 or the 4.7 V8? Did you have a look under the hood if there is nothing strange to see?
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Old 12-18-2012, 08:50 PM
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Hmm. Could the fact that there is fluid leaking from the exhaust have anything to do with this? Assuming the misfire is not being caused by an injector malfunction, I'd assume the fuel has to go somewhere right? Maybe out the exhaust?
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Old 12-18-2012, 09:01 PM
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Re: P 0303-uh oh

All depends on when you see fluid coming from the exhaust: when the engine is cold, it is normal that moisture in the combustion gases condensates on the cool exhaust system and forms water drops coming from the exhaust pipe. This happens more when the outside temperatures get lower.
If the engine is hot, there should be no fluid coming from the exhaust at all. Gasoline would have evaporated before reaching the exhaust end pipe. Next time, just get a droplet on your hand and smell to be sure.
Do you see any white smoke with the engine hot and accelerating?
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Old 12-18-2012, 10:49 PM
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Will do. I'll check that once I get home tomorrow.

That's good though, I usually only notice the liquid on a cold start. It's been in the low 40s/high 30s, so it's probably just condensation I guess.
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Old 12-26-2012, 04:57 PM
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Re: P 0303-uh oh

I have a 2002 Liberty 3.7L with a similar 'issue.' The SES comes on at about 40 mph, and flashes, and stays on. Code is P0303, and can be cleared by code reader with the engine off but the ignition switch in the ignition but not start position. With the light on, I get a rough running engine as you would expect with it banging on five cylinders. When the code is cleared, the engine runs fine.

Now here is an interesting thing: If the light comes on, and I pull off the road and turn the ignition off, and restart, the light stays on continuously rather than flashing, and the engine runs fine till I get the Heep up to about 40 again. Then the light begins flashing and I get the miss, same code. If I connect the code reader and clear it, I get a good running engine with no light ... till I hit 40 mph.

The plugs are relatively new, changed last July. I swapped #3 plug with #1 plug; the problem and symptoms remain as before. I swapped #3 coil with #1 coil; same problem.

What puzzles me is the apparent cause and effect relationship, which seems reversed. If I had bad components, why would resetting the code seem to clear the problem, and the engine then run quite well? It seems to me that the code tripping is what is causing the problem, leading me to consider the possibility that the PCM is going belly up. I'm thinking it's pulling a HAL on me.

I've had this Liberty since it was new; it has 71,000 miles on it, and has been a sweetheart until this problem arose.

Any ideas or suggestions? TIA.
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Old 12-26-2012, 05:04 PM
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Not sure what the code is but its doing its job...if it is flashing that means danger of severe damage so the computer puts the vehicle in "limp" mode allowing you to safely get off the road to a service station. By shutting it off the code is (while not cleared) on "standby" or "check" status, waiting for whatever malfunctioned to do it again.

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Old 12-26-2012, 05:35 PM
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Re: P 0303-uh oh

P0303 is misfire from #3. #3 does not misfire until the SES comes on. The usual line of thinking on this would be that something is occurring at or near 40 mph (or those RPMs) that is causing the misfire and subsequent SES illumination. It could be an injector, but they test good, and have recently been serviced (shop-cleaned). This would seem to indicate an electrical problem and not a fuel management problem. But the plug and the coil are both good; wiring is good; connections are good. I'm not sure of the purpose of the PCM throwing a code to cause the vehicle to go into 'limp' mode. I was under the impression the code was to identify a problem, or at least point to it, and would be the result of a malfunction. There could be a breakdown that doesn't manifest itself until a certain RPM level is reached ... but the way this thing is behaving, it seems the opposite. This is why I'm considering the PCM as the culprit.

Let me get a LiveData recording off the code reader, triggering on the code tripping. I'll put it up on our website and link it from here.
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