Liberty KJ 3.7l P0442 causing misfire?

[jamesbeat]

I'm not having much luck lately

Last weekend, my 2003 Liberty 3.7l started shuddering at idle and the check engine light came on.

Went straight to Autozone for a scan, and the code was for a misfire (I don't remember exactly what code it was).
Their computer recommended either spark plugs or coils.
Having changed the plugs a few days earlier, I bought a six-pack of coils and fitted them.
I also disconnected the battery to reset the CEL and everything seemed to be ok.

Today, it suddenly started shuddering at idle again, and the CEL came back on.
I pulled over and shut the engine off for a few minutes. When I restarted it, it seemed to be back to normal.

I went back to Autozone, and this time the code is P0442 - small evap leak.

What's going on? Can a small evap leak cause the engine to run rough at idle?

 

[J33Pfan]

Im not the expert here, if you do a search on P0442 youll see that it might be a broken or cracked vapor hose or vapor part.

Is the Gas Cap working correctly? Is it tightly closed?

Go over the fuel vapor system for a worn or damaged part until the expert shows up.

also, do you have a pic of the old plugs?

what plugs did you put in?

 

[tjkj2002]

No a misfire can not cause a P0442 code and the P0442 code can not cause a misfire or rough idle.

 

[jamesbeat]

The old plugs looked ok but were mismatched and incorrectly gapped.
I used one of those spark plug charts and I think they were fine - I just did it as a routine maintenance thing.
I also replaced the pcv valve at the same time and changed the oil.

I can't remember what plugs I put in, but I think they were platinum something?
I'm afraid I threw away the box so I can't check.

I just discovered that I can check codes with the key in the ignition, so I double checked in case AutoZone made a mistake, but it's definitely a small evap leak.

It seems weird that a small evap leak gave me a CEL at exactly the same time that the engine started running rough.
Is there something about the evap system that can cause a rough idle?

Edit:
The thing that is really confusing me is that the symptoms were the same both times - engine started running really rough, then CEL comes on.
The first time I got a code for a misfire, and the second time, the code is for an evap leak.
Even if the evap leak is causing a misfire somehow, why didn't I also get a misfire code?

 

[LibertyTC]

Start with a new Mopar gas cap.
Then if it continues acting bad, you will have to do a full line inspection, especially around gas tank & under hood.
If nothing found...A shop w/ a smoke machine can hopefully find it then.

 

[jamesbeat]

No a misfire can not cause a P0442 code and the P0442 code can not cause a misfire or rough idle.

Any idea why it would suddenly throw a CEL for an evap leak at exactly the same time as it started running rough?
It seems like too much of a coincidence.
Is it possible that it is giving the wrong code for some reason?

 

[tjkj2002]

The old plugs looked ok but were mismatched and incorrectly gapped.
I used one of those spark plug charts and I think they were fine - I just did it as a routine maintenance thing.
I also replaced the pcv valve at the same time and changed the oil.

I can't remember what plugs I put in, but I think they were platinum something?
I'm afraid I threw away the box so I can't check.

I just discovered that I can check codes with the key in the ignition, so I double checked in case AutoZone made a mistake, but it's definitely a small evap leak.

It seems weird that a small evap leak gave me a CEL at exactly the same time that the engine started running rough.
Is there something about the evap system that can cause a rough idle?

Edit:
The thing that is really confusing me is that the symptoms were the same both times - engine started running really rough, then CEL comes on.
The first time I got a code for a misfire, and the second time, the code is for an evap leak.
Even if the evap leak is causing a misfire somehow, why didn't I also get a misfire code?

In bold is most likely your issue for rough idle.

P0442 takes 2 failed trips to turn the MIL on,a misfire takes 1 so no the PCM is not going to make that mistake.

 

[Logan Savage]

Should be a decal on the radiator top support bar that tell you the correct spark plug type & gap .

 

[J33Pfan]

spend a few bucks and get a code reader. I didnt have much luck with the bluetooth units. you shouldnt disconnect the battery to clear a code.

you need to fix one code at a time. see which cyl has a misfire code, then work on that.

for a evap leak you have to check the lines front to back. could just be a small crack in an old rubber hose. could be a bad or loose gas cap. check the hoses & inlet pipe near the gas tank too.

new coils dont mean good working coils. thats why you need a code tester.

plug charts can be harmful when you buy plugs for a jeep especially when your troubleshooting a problem.
new spark plugs can cause problems it they arent the right plugs. they could also be too loose or cracked from install. wrong gap. (its easy to do harm on a jeep)

 

[J33Pfan]

"Having changed the plugs a few days earlier," sounds like you used the wrong plugs or damaged them. Reads like you did something then had major problems afterwards. so back track and fix what went wrong.

 

[Royy]

I had three or four evap codes, that somehow were caused by the catalytic converter. I have no idea how that's even possible, it doesn't make any sense to me. I checked everywhere else for leaks, couldn't find anything.

As soon as I replaced the bad cat, all the evap codes mysteriously disappeared.

Start with the gas cap and all gas lines and hoses. If there are no leaks there, have a look at your cat. Again, it shouldn't cause any evap codes, but...

 

[jamesbeat]

Sorry, I don't think I was clear in my post above - I replaced the spark plugs because it was idling a little rough. Changing the plugs didn't make any difference, but it wasn't really all that bad at the time.

Looking at the Autozone website, I used either Autolite Platinums or Double Platinums (I think it was the Double Platinums, but not 100% sure).

I am 100% sure I gapped them correctly, and I was very careful when installing them.

What I'm concerned with right now is having to take a two-hour bus ride in the freezing cold twice a day.
My inspection is not due for six months, so as long as it is definitely not connected to the rough idle, the evap code can wait.

What is important right now is to figure out why it started running rough and simultaneously threw a P0442 code.
It just doesn't make any sense.

 

[Royy]

Only use NGK V-Power or Champion copper spark plugs. This engine really doesn't get along with all the fancy plugs. Never mind what the people at Autozone and similar places will try to tell you.

If putting in the proper plugs doesn't solve the issue, check all your hoses. Vacuum lines, PCV system, etc. Even a tiny tear can cause a lot of issues at idle.

 

[TypeRx]

I bet it is just bad luck/coincidence. You need to check the vacuum lines near the fuel tank first (after verifying the cap is good). A very small split near the charcoal canister will cause this problem. Another problem area are vacuum lines near the battery and immediately under the driver's side. Look for any small or large tear and replace, then reset the code and see what happens.


Sent from my iPhone using Tapatalk

 

[J33Pfan]

Only use NGK V-Power or Champion copper spark plugs. This engine really doesn't get along with all the fancy plugs. Never mind what the people at Autozone and similar places will try to tell you.

If putting in the proper plugs doesn't solve the issue, check all your hoses. Vacuum lines, PCV system, etc. Even a tiny tear can cause a lot of issues at idle.

for an idle issue, this post may help you. http://www.jeepkj.com/forum/f196/2003-jeep-liberty-sporty-idle-problem-48728/

If the evap problem also causes a vacuum leak, you may have a rough idle problem too.

finding a problem with vacuum lines & the evap system may solve all your problems.

I spray starting fluid on hoses & parts to see if there is a vacuum leak. if there is, the idle changes up or down. youll know if you hit the spot. just dont start a fire under there! its alot of work, you may need a mechanic to find the problem.

 

[tjkj2002]

for an idle issue, this post may help you. http://www.jeepkj.com/forum/f196/2003-jeep-liberty-sporty-idle-problem-48728/

If the evap problem also causes a vacuum leak, you may have a rough idle problem too.

finding a problem with vacuum lines & the evap system may solve all your problems.

I spray starting fluid on hoses & parts to see if there is a vacuum leak. if there is, the idle changes up or down. youll know if you hit the spot. just dont start a fire under there! its alot of work, you may need a mechanic to find the problem.

Never use any type of starting fluid anywhere near a gas engine.

Your just asking to get hurt badly and damage the vehicle.


For the OP the most common leak points on a KJ for EVAP leaks is the gas cap,leak detection pump,and the hoses on the charcoal canister.Only get replacement parts from the dealership for EVAP parts(most important is only ever use a OEM gas cap,there is a huge difference),trust me it will help chasing bad "new" parts from failzone which occure 90% of the time.