Cold start rough idle and sometimes 303 code

[Hoist]

Sooo, same start technique and Jeep ran fine no codes. Drove home after work maybe 30 minutes. Shut down for maybe 20 minutes. Jump in to go to dinner and crank but no start. No codes. Try it several times and no joy. Screw it, go to dinner, after all, Modello makes everything better.
get home, first crank no luck. Second crank and finally starts. No codes, no A light. WTH.
ill-try it again in the morning. Checked the main battery, aux disconnected and volts were showing 12.65, more than usual which has been 12.3.
Not what I was expecting with only 70k on the clock.

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[Hoist]

This is the next day. Power on, press ESS disable then start……ran fine. Tried another start same way and good start again. Drove to work with no issues. Took the Jeep to grab lunch and again, no codes or roughness at start. Well that’s a real head scratcher boys.
Is it running right because I disconnected the aux negative? Or is it because I’m using key on/disable ESS then start? Doesn’t make sense, because it still was acting up throwing a code 303 after changing the plug and coil. The one thing I haven’t tried is starting it without turning off the ESS first to see what it does. This is the longest it’s gone with the Auto start stop off!
Guess I need to see if I can make it do it again.

 

[Lost1wing]

After 3 hrs, ESS disable then start no codes runs smooth. No ESS light fault either.

Ambient temp has been showing 72deg.

You need to do a misfire count. That way you could see when it is happening.

 

[Hoist]

That’s definitely the plan. Unfortunately Amazon doesn’t seem to know when my OBS MX+ is going to ship now.

 

[Coastal]

Hate to break this to you. I have the same issue. Just dropped it off at dealership. I had a regular shop look at it and they tested the coolant for exhaust gas. It was present. Therefore. There is a high likelihood of a head gasket leaking exhaust gas into the coolant.
There is a TSB for this and Jeep Cares says they will usually honor complimentary repair for under 100k.
We will see…

TSB is
TSB 09‑011‑25

It involves replacing one of the four cams and replacing the head gaskets.

$4 k if not covered (my guess)

 

[ShadowsPapa]

12.65, more than usual which has been 12.3.

12.3 is getting low - low enough they should be charged. Even 12.65 isn't fully charged but might show that when all connected due to the load of the electronics.

 

[ShadowsPapa]

Hate to break this to you. I have the same issue. Just dropped it off at dealership. I had a regular shop look at it and they tested the coolant for exhaust gas. It was present. Therefore. There is a high likelihood of a head gasket leaking exhaust gas into the coolant.
There is a TSB for this and Jeep Cares says they will usually honor complimentary repair for under 100k.
We will see…

TSB is
TSB 09‑011‑25

It involves replacing one of the four cams and replacing the head gaskets.

$4 k if not covered (my guess)

That was the cause in your case - but doesn't mean it's the cause in his case. The cylinder 3 misfire can be a dozen different things, from minor to major.

 

[Coastal]

That was the cause in your case - but doesn't mean it's the cause in his case. The cylinder 3 misfire can be a dozen different things, from minor to major.

True.

That was the cause in your case - but doesn't mean it's the cause in his case. The cylinder 3 misfire can be a dozen different things, from minor to major.

Agree. I am salty. Sorry.

 

[ShadowsPapa]

True.

Agree. I am salty. Sorry.

Ah, a former sailor?

 

[Lost1wing]

A misfire count would be useful to determine if your p0303 is only that cylinder. You could have other misfires on the other cylinders but are not being flagged. Not seeing a p0300 is good but I wouldn't rule out the other cylinders until you confirm. Also another thing to look at, is your p0303 a pending code, active code or permanent code?

 

[Hoist]

Hate to break this to you. I have the same issue. Just dropped it off at dealership. I had a regular shop look at it and they tested the coolant for exhaust gas. It was present. Therefore. There is a high likelihood of a head gasket leaking exhaust gas into the coolant.
There is a TSB for this and Jeep Cares says they will usually honor complimentary repair for under 100k.
We will see…

TSB is
TSB 09‑011‑25

It involves replacing one of the four cams and replacing the head gaskets.

$4 k if not covered (my guess)

From reading the service bulletin, that’s only related to the cam and the gasket refers to the valve cover you have to remove to replace the cam. I don’t know if there is a separate TSB for the head gasket. They may be doing the cam since they are there and there’s a TSB for that. Hopefully the mothership will cover it as no engine should have these issues with less than 100k.
Having said that, you may be right regarding my situation.

 

[Hoist]

Hate to break this to you. I have the same issue. Just dropped it off at dealership. I had a regular shop look at it and they tested the coolant for exhaust gas. It was present. Therefore. There is a high likelihood of a head gasket leaking exhaust gas into the coolant.
There is a TSB for this and Jeep Cares says they will usually honor complimentary repair for under 100k.
We will see…

TSB is
TSB 09‑011‑25

It involves replacing one of the four cams and replacing the head gaskets.

$4 k if not covered (my guess)

A misfire count would be useful to determine if your p0303 is only that cylinder. You could have other misfires on the other cylinders but are not being flagged. Not seeing a p0300 is good but I wouldn't rule out the other cylinders until you confirm. Also another thing to look at, is your p0303 a pending code, active code or permanent code?

both active and permanent though they did clear after a couple of times.
went to Lowe’s last night and did the A warning rough idle going but not coming home. Length of shut down doesn’t seem to be an issue.
I need that old plug in so I can Jscan. Does anything work right anymore…….

 

[ShadowsPapa]

From reading the service bulletin, that’s only related to the cam and the gasket refers to the valve cover you have to remove to replace the cam. I don’t know if there is a separate TSB for the head gasket. They may be doing the cam since they are there and there’s a TSB for that. Hopefully the mothership will cover it as no engine should have these issues with less than 100k.
Having said that, you may be right regarding my situation.

Pull the valve cover and you can tell if there's a cam/follower issue. It's going to LOOK bad.

 

[Hoist]

Spell check ugh, I need the OBD plug in which still hasn’t shipped.
As to valve cover, I’m about to the point of pulling it to confirm. I may bum a borescope from parts store first to check for coolant since it sat all night.

 

[Hoist]

Borrow, geez I need another coffee……

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