Cold start rough idle and sometimes 303 code

[Hoist]

On your last post, the ad was 5 times larger. These ads are useless. Subliminal or not, I don't look at them. Oh wait, let me click on that! I've always want one piece pajamas. Give me a break. I never see by-pass cable ad or a obd2 scan tool ad. But god forbid if I ever have the urge to by a Toyota, at least there's an ad for it.

Ha, too funny but true.

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[Hoist]

So, cold had misfires on the left side, nothing on the right. Number never increased beyond initial misfires. Drove up a hill to put a load on, no change. Ran rpm up to 3 grand(would not go higher when parked) and no change in misfires.

 

[Hoist]

The only change has been new plugs on the right side.

 

[Hoist]

Unfortunately I have to go out of town for business so I need to leave room in the garage for the wife’s car until I get back So I don’t want to tear it apart just yet.

 

[Hoist]

I should have bought the 95 wrangler with the 4.0. Just no box!

 

[Lost1wing]

The code has not come back and you basically don't have any misfire issues. Even for a cold start those low number of misfires are not a big deal. Zero misfires warmed up is even better. Let's go with plugs took care of it. Unless it is running like crap, drive it. Keep your tool handy so you can check on the go.

 

[Hoist]

Roger that.

 

[MPMB]

So, cold had misfires on the left side, nothing on the right. Number never increased beyond initial misfires. Drove up a hill to put a load on, no change. Ran rpm up to 3 grand(would not go higher when parked) and no change in misfires.

Nanny state of engine controls. The JT won't rev above that unless in drive. So you can't throw it into N at the light and rev the engine to frighten someone or bait into a race (there are a few vehicles slower than a JT ; and /s). "Oh look on my works (3.6l powering 37s) and despair."

There will always be misfires, as it is the nature of the beast. Don't be concerned with the low numbers. If there's a miss/misfire that's a problem, it will be evident by magnitudes. 100, 200, 300 misfires or more compared to 10-15 for other cylinders.

My misfires (from the cam/rocker issue) were triggered at 5k RPM and higher or a very aggressive launch. And when I set it off, my Cyl 1 misfires would approach 1000 and beyond.

Regarding "rough" idle, does it smooth out closer to 700rpm, rather than the 600rpm? I found mine is slightly rougher when it drops to the low 600 rpms.

Also - is your AUX still disconnected? You might want to test that, since it's a common failure point. I replaced both batteries last year - Roughly 3 years of ownership. If your JT lived in NM, it's seen heat and cold cycles that would age it prematurely as well. I remember seeing the AUX battery failure trigger a bunch of random problems.

 

[Hootbro]

So, cold had misfires on the left side, nothing on the right. Number never increased beyond initial misfires. Drove up a hill to put a load on, no change. Ran rpm up to 3 grand(would not go higher when parked) and no change in misfires.

For a cold start, those numbers are pretty good. I would say most have worse numbers on cold start being normal.

 

[ShadowsPapa]

For a cold start, those numbers are pretty good. I would say most have worse numbers on cold start being normal.

I consider low single digits on a cold start to be nothing.
It's harder to get a charge lit when things are cold. It's been that way since the very first engines were ever built.

There will always be misfires, as it is the nature of the beast. Don't be concerned with the low numbers. If there's a miss/misfire that's a problem, it will be evident by magnitudes. 100, 200, 300 misfires or more compared to 10-15 for other cylinders.

Yeah, differences are important.
I've driven 15 miles with it warmed up and had no misfires (my 2022)

Drove up a hill to put a load on, no change. Ran rpm up to 3 grand(would not go higher when parked) and no change in misfires.

As far as RPM - you can load the thing and get it to kick into high lift mode even at lower RPM.
3,000 is the oil pump change RPM - the solenoid pulls it into high volume mode at about that RPM. As far as VVL status, you can force that with JSCAN or load it and make it happen.

 

[Hootbro]

I consider low single digits on a cold start to be nothing.
It's harder to get a charge lit when things are cold. It's been that way since the very first engines were ever built.

Better than what I have had before on cold start.

All four of my JT's to include current one would have have one or two cylinders showing double digit cold start misfire counts with usually one cylinder having a noticeable higher count. Pretty sure this is what drove the PCM reflash TSB back in 2021 that I believe widen the misfire count threshold before MIL would post.

I would be ecstatic to have the numbers @Hoist just posted.

 

[Hoist]

Interesting. I still need to change out plugs on left side so they are all new.

 

[Hoist]

So to sum this up of sorts:
12.4 may not be optimal on an AGM but its not a problem
Changing plugs and going back to original (factory) coil on nbr 3 seems to have eliminated the misfires on the pax side.
No idea why there was a crank no start in the mix. Actually a couple different occasions but no associated codes to point to anything.
Drive it and see what happens next. Whatever noise I think I'm hearing may be psychological. Anyone in aviation knows you can hear a noise that was there all along but when its dark and no place to land "what's that noise" can appear.
Jeeping isnt for everyone but its never boring and like aviation, can take you places other people dont see. Just hope its the Grand Canyon and not the dealership maintenance bay......

 

[ShadowsPapa]

12.4 may not be optimal on an AGM but its not a problem

Right - not great but not YOUR issue. Mess with that later unless you get other indications of voltage issues.

Changing plugs and going back to original (factory) coil on nbr 3 seems to have eliminated the misfires on the pax side.

Definitely do all plugs. These are really sensitive to spark plug issues. In fact, some had misfires due to bad NEW plugs from the factory.

With a Jeep, you are forever taxiing and never taking off.

 

[Lost1wing]

So to sum this up of sorts:
12.4 may not be optimal on an AGM but its not a problem
Changing plugs and going back to original (factory) coil on nbr 3 seems to have eliminated the misfires on the pax side.
No idea why there was a crank no start in the mix. Actually a couple different occasions but no associated codes to point to anything.
Drive it and see what happens next. Whatever noise I think I'm hearing may be psychological. Anyone in aviation knows you can hear a noise that was there all along but when its dark and no place to land "what's that noise" can appear.
Jeeping isnt for everyone but its never boring and like aviation, can take you places other people dont see. Just hope its the Grand Canyon and not the dealership maintenance bay......

I had a crew complain about his nose landing light inop and deferred. We didn't have the manpower to work deferred items but he called in that he wanted it fixed. I went out to talk to him and explained that his broke airplane was not going to be fixed on a through flight. He said what happens if he turned on his two remaining landing lights and didn’t like what he saw. I told him " turn the lights out". I had a chat with the chief pilot that evening. We both laughed about it. The chief pilot was a Navy pilot and the pilot reporting the issue was an Airforce pilot.

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