P0303 on Jeep Liberty

I have a 2005 Jeep Liberty with the 3.7L and 40,000mi. We have owned it for 4 months now and will on occassion give me a cylinder #3 misfire. Just the other day though it gave me a P0300 code which is new. I will sometimes notice it running rough at an idle, but most times it seems to run fine. Things I have done so far are:

[*] New Plugs
[*] New coil on cylinder #3
[*] Two treatments of seafoam
[*] Reset code several times and will return after a couple of days
[*] Compression check on that cylinder will sometimes be about 40PSI lower than the other cylinders.

From reading on other forums appears Jeep changed the design of the valves in 05 and are susceptible to carbon buil-up????

Thanx:)

You said you have 40 psi lower than the other cylinders what was the readings .
40 psi is a lot for a gasoline engine, there should not be more than 5% difference between the cylinders, or you will start to get misfires
Take all your plugs out and do a complete compression test take the readings,
then do a wet compression test, to check if you have bad valves or rings.

And don't forget to keep the throttle valve fully open when you perform the compression tests.

Any noise from the valves under the valve cover, the followers have been known to slip off the valves and the springs have been known to break. Valves are a common issue on that engine. I Have one in the shop right now.

2005 model with 40,000 miles? Shouldn't this still be under warranty, especially since it is powertrain?

I will try and redo the compresion check this weekend. As far as valve noise, there is definetely a noise when the car is cold for about 3-4 min., certainly not a normal noise. It is under warranty, but I'm hesitant to bring it in as I have a feeling they are going to charge me for other things until it's properly diagnosed.

Charge you for other things? [u]The vehicle is under warranty. You pay for absolutely nothing to diagnose or repair the problem.[u] This is the basic premise of any consumer product warranty.

I only have the powertrain warranty, bumper to bumper I do not have. Things like fuel injectors,plugs,and coils I'm assuming will not be covered??? I would like to think that it would be diagnosed correctly first, but have my doubts?

I've never heard of a powertrain warranty that won't cover the engine management system. Your compression test indicates you may have a weak cylinder. I love the fact that you are committed to learning how to fix your vehicle, but you paid for the warranty when you bought the vehicle. Get some use out of it!!

The only way to verify if it is covered or not is see the dealer! But I work at a dodge dealer and most sensors, coils etc are not covered past the basic 3 yr 60 000km warranty. The engine, pcm, driveline, cats would probably still be covered but it may require a deductible as some do and the diagnosis to determine if they are or aren't at fault is sometimes at the customers expense. At this point you're going to have to bite the bullet and either get dirty and do some of your own diagnosis to see if their is an issue with the valve train that's causing the noise or pay a competent tech to diagnose it. Where you find that tech is your own perogative! The valve cover is not difficult to remove, if you remove it and find a damaged spring or slipped rocker on that cylinder then you can get it to the dealer for the warranty repair. If you see nothing then it's one more thing ruled out!

Thats the difference, Jeff. All my answers are based on my experience as a Toyota tech.

UPDATE

Well since my last post I swapped injectors with cyliner 1 and the code still stayed with cylinder 3, also pulled the valve cover and found nothing abnormal.

So off to the dealer it went yesterday. They could not find a problem with cylinder three compression nor get it to duplicate. He noticed that I had autolite plugs installed and stated that they have had numerous problems with them. The only issue I have with that is I pulled the original plugs because of the misfire and they were NGK's. Calls me back in the afternoon and states that he let it idle for a long time and he was getting multiple cylinder misfires, not enough in a row to set a code though.

They are recommending to do the fuel system flush and plug change for the tune of $250.

In my mind I know this code is going to come back, but feel that I have to take this first step and when it re-occurs it doesn't come back until it's fixed.

Thoughts?????

Ferguson, can you please get me the part # for the 1999 Lexus LX 470
B2S1, O2 sensor that be the right bank first sensor as you know just mentioned it for the other readers.
Thanks Greg.

There are tsbs for valve sealing issues on that engine causing misfire codes at idle when it has idled for more then a few mins, most require new cylinder heads and valves to correct the seat issues! They're either really behind on there training or they need to eliminate the wrong plugs as the cause of the misfire and yes they're right NGK's are factory installed for that engine and autolites are junk. My advice to you is to have them install the correct plugs and see if the misfires clean up. I've fixed so many of those that didn't even show up on compression tests either. They should be able to find the tsb for it.

I got it back the other day and they only charged me for an hour labor $85. They could not duplicate the problem and found a TSB for updating the firmware on the PCM. I just checked last night and the code is already back. The light does not come on often, but the next time it does, it will go back immediately. I will also replace the plugs in the meantime to NGK's. I found TSB 09-007-06 and it's exactly what my car is doing. I'm convinced this is my problem now and I just need to convince the dealer.

http://home.comcast.net/~merchjo/jee...tsb-page-1.jpg

http://home.comcast.net/~merchjo/jee...tsb-page-2.jpg