Cold start rough idle and sometimes 303 code

[Lost1wing]

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



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.

Not true! Do you remember that YT video of that launch? Was told to go 60mph over the jump or was it 45mph? And then he did a lawn dart impression.

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[ShadowsPapa]

Not true! Do you remember that YT video of that launch? Was told to go 60mph over the jump or was it 45mph? And then he did a lawn dart impression.

Forgot about that - and the Mojave going airborne and landing very nicely on the sand.

 

[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......

What ever happened to your misfire? Did it just go away?

 

[damcon2]

What ever happened to your misfire? Did it just go away?

Bump? I think I have a similar issue and am curious if it was resolved?

 

[Hoist]

No. Problem is not resolved. Replace right side plugs and it ran better for a while until it would stumble like it was its job and i replaced the left side plugs.
I should mention, short of a Chevy Monza, that is the dumbest design I've ever seen having to pull an intake (upper) with all the crap that is attached, just to change the plugs and or coils. But I digress.....
And no, it didn't fix the misfire/stumble POS. No, its no where near as bad but its there when the engine is cold. Can be there though at a lesser degree when warmer OAT sitting. Goes away once it warms up (195 or better on the coolant). I should specify it is the number 3 cylinder. Might have 1100 or 1500 misfires with start up and none once its warmed up down the road. Should have these issues with an engine with only 73,000 on the clock.
So, I need to hook up a node and check my injector wires. Ohm the injector and go from there. I am absolutely waiting till last thing before I pull the cover with all the crap you have to get off of it before it comes off.
Really, really, really not happy with this engine. Seriously looking at another engine options and all the A pain that goes with it.

 

[Hoist]

I've also wondered if there is any point at looking at a fixed non-High/Low intake follower (rocker) with older VVT computer to get away from the VVL headaches.

 

[ShadowsPapa]

I've also wondered if there is any point at looking at a fixed non-High/Low intake follower (rocker) with older VVT computer to get away from the VVL headaches.

Sure, swap engines. You can't just swap followers - there's cams, lash adjusters as well. Likely the older pre-upgrade lash adjusters won't fit in the heads, so now you have a head swap.........................

No. Problem is not resolved. Replace right side plugs and it ran better for a while until it would stumble like it was its job and i replaced the left side plugs.
I should mention, short of a Chevy Monza, that is the dumbest design I've ever seen having to pull an intake (upper) with all the crap that is attached, just to change the plugs and or coils. But I digress.....
And no, it didn't fix the misfire/stumble POS. No, its no where near as bad but its there when the engine is cold. Can be there though at a lesser degree when warmer OAT sitting. Goes away once it warms up (195 or better on the coolant). I should specify it is the number 3 cylinder. Might have 1100 or 1500 misfires with start up and none once its warmed up down the road. Should have these issues with an engine with only 73,000 on the clock.
So, I need to hook up a node and check my injector wires. Ohm the injector and go from there. I am absolutely waiting till last thing before I pull the cover with all the crap you have to get off of it before it comes off.
Really, really, really not happy with this engine. Seriously looking at another engine options and all the A pain that goes with it.

IMO - the valve covers should have come off first. It would seem to have been a much easier option than pulling the intake to change left side plugs when the misfire is on the right bank, not the left bank. I'd have saved the hassle of the intake, and knowing that the misfire is #3 and not 2, 4 or 6, I'd have not even bothered with the left/driver side plugs until the misfire was resolved.

The misfire going away only when the coolant is at 195 or better makes little sense as well.
Yes, these default to starting on high lift - but once running, they settle to low lift well before 195 degrees and some of us won't see 195 degree coolant for quite a drive in cold weather.

Ideally, it would be good if someone who knew how to scope the injectors and coil packs and so on, to connect a scope to it. That will tell a lot more than anything else.
Concentrate where the misfire is - ignore the left/driver side bank.

 

[Hoist]

My point about the temp was less about a specific engine temp but just the fact that the Jscan quit showing misfires on the number 3 once the engine was warm. I can tell you that I have the constant MIL with the misfire code. Except for maybe a days worth of city driving after I changed the driver side plugs (I had already changed the passenger plugs a month or so before hand and also did the 1/3 coil swap to see if it followed, which it didn't).

Mechanical problems aren't often intermittent and I wouldn't think if the cam/follower was bad that it would come and go. Of course, I've never dealt with VVT let alone VVL before.

I'm sure I'll end up pulling the valve cover but its easy enough to check the injector before I go there.
I've read a ton of the posts about the 3.6 issues, and the folks that say theirs are bullet proof. Seems to me there are too many issues with the PUG/VVL to make it worth throwing more money at cams or whatever without knowing the new parts are better than the ones being replaced. Shadowspapa you have posted a bunch about the engine issues and potential causes but what are the stats on the replacement part? I waited a long time to get a Gladiator and thought this was my retirement rig (even if its used). I don't like driving beyond town because I don't consider it reliable.

 

[ShadowsPapa]

I can tell you that I have the constant MIL with the misfire code.

And it will be there because it takes about 3 key starts or cycles without a misfire for it to disappear. So if it misfires, it sets the MIL (IF it's requested to be set and many times a misfire doesn't even set the MIL if it's transient)
And that MIL will stay there for something like 3 shut downs and restarts - unless that misfire that triggered it is detected, then the MIL will stay there.
Once it's triggered, you can drive all day with no misfires and the MIL will stay (unless otherwise reset by a person or start cycles)

Mechanical problems aren't often intermittent and I wouldn't think if the cam/follower was bad that it would come and go

No they aren't - but........ we've seen this before. These are really tricky as to what determines a PCM detected misfire and what isn't.
When my 2022 had the hot-restart misfire - in the majority of cases, it never set the MIL and yet - you could feel it and JSCAN showed them.

 

[Lost1wing]

What is your fuel pressure? Use the scan tool LD.

 

[ShadowsPapa]

What is your fuel pressure? Use the scan tool LD.

I wish people would stop bringing legit troubleshooting techniques and ideas onto the internet

 

[Stan H]

Sure, swap engines. You can't just swap followers - there's cams, lash adjusters as well. Likely the older pre-upgrade lash adjusters won't fit in the heads, so now you have a head swap.........................



IMO - the valve covers should have come off first. It would seem to have been a much easier option than pulling the intake to change left side plugs when the misfire is on the right bank, not the left bank. I'd have saved the hassle of the intake, and knowing that the misfire is #3 and not 2, 4 or 6, I'd have not even bothered with the left/driver side plugs until the misfire was resolved.

The misfire going away only when the coolant is at 195 or better makes little sense as well.
Yes, these default to starting on high lift - but once running, they settle to low lift well before 195 degrees and some of us won't see 195 degree coolant for quite a drive in cold weather.

Ideally, it would be good if someone who knew how to scope the injectors and coil packs and so on, to connect a scope to it. That will tell a lot more than anything else.
Concentrate where the misfire is - ignore the left/driver side bank.

The injectors on these 3.6L have a series of miniscule holes in the intake side on the fuel rail side they are just an open pipe. That injector tip may be able to be viewed after pulling the plenum and then sticking a scope down in the intake passage way for each cylinder if it protrudes enough it could be viewed.
When I removed mine a few had like a slightly dirty tip but the miniscule holes that the fuel sprays out of were all open.

The coil packs are really easy to remove from the tubes that are attached to the heads. That they fit into. 1 small 8mm bolt and an electric plug and out they go.
I was told by a mechanic that these coil packs the extension part should remain plyable if they get hardened then they must be replaced as spark can seep through the cracks in the rubber and ground against the tubes. 1 just did mine 3,000 miles ago and with 141k and they was still plyable. Gave them to my uncle for an emergency spare for his Chrysler Van that has a 3.6L.
What scared the crap out of me was reaching the inch pounds and smashing that crush washer before it got there. I hate tightening soarkplugs in aluminum heads.

 

[Hoist]

Lost Wing, as I recall the pressure was 58 but I can check it again on the way home.

When I looked at the O2 sensors, 1 and 3 were basically the same. 2 and 4 (different numbers from 1 and 3 since I understand those are down stream) but 2 was about the same as 4.

 

[Lost1wing]

Lost Wing, as I recall the pressure was 58 but I can check it again on the way home.

When I looked at the O2 sensors, 1 and 3 were basically the same. 2 and 4 (different numbers from 1 and 3 since I understand those are down stream) but 2 was about the same as 4.

58psi is great. I was thinking that if you had low fuel pressure, cold starts would be rough and even cause a no start.

If you had a vacuum leak or an issue with the O2 sensors, I would suspect a p0420 code or related by now.

 

[Hoist]

I wondered about a vacuum leak as well. Thought about giving a squirt of carb cleaner or similar around the intake to see if that changes rpm.
No additional codes, always the misfire......

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