Misfire on startup, no codes

[Tob]

After sitting for over a day, sometimes the engine stumbles and runs roughly (and what I assume is misfiring) like it wants to stall after starting up, for maybe 10 seconds, then if given a bit of throttle, starts to run normally again. The OBD is not giving a CEL. It's an '04 4.0L with 110k miles. Where should I start looking for a diagnosis?

 

[Kid Mechanic]

Tune-up history? Maybe it’s time to go through the motions…cleaning sensors, new plugs, et al.

 

[CharlesHS]

Could be leaking fuel injectors.... or possibly a check valve that is leaking by....
You will need to do a little troubleshooting to narrow down what the problem actually is....

 

[Tob]

Tune-up history? Maybe it’s time to go through the motions…cleaning sensors, new plugs, et al.

The spark plugs don’t have many miles on them. Any sensors in particular other than IAC I should focus on?

 

[Tob]

Could be leaking fuel injectors.... or possibly a check valve that is leaking by....
You will need to do a little troubleshooting to narrow down what the problem actually is....

Is it possible to diagnose a leaking injector or check valve by watching fuel pressure? My fuel rail doesn’t have the Schrader valve on it

 

[twistedlv]

Is it kind of a clattering noise on startup? Might be a weak lifter.
Pretty common. Mine does that once in a while.

 

[CharlesHS]

Is it possible to diagnose a leaking injector or check valve by watching fuel pressure? My fuel rail doesn’t have the Schrader valve on it

The newer TJs don't have the schraeder valve so testing system pressures, leaking check valves and injectors is made more difficult.
You could remove the spark plugs to see if they look damp, but that requires the removal of the igniter rail.
One of the other members may have an easier way to diagnose this problem on the newer TJs.

 

[Kid Mechanic]

The spark plugs don’t have many miles on them. Any sensors in particular other than IAC I should focus on?

You say it might die when starting, so maybe let it and see if it throws a code.
I just like to clean the little air sensors and such once in a while to keep them happy.

 

[Tob]

The newer TJs don't have the schraeder valve so testing system pressures, leaking check valves and injectors is made more difficult.
You could remove the spark plugs to see if they look damp, but that requires the removal of the igniter rail.
One of the other members may have an easier way to diagnose this problem on the newer TJs.

I am going to be replacing my fuel rail soon. I did something stupid with the fuel damper a while back and don't trust it. Plus, I'd like to have the ability to check fuel pressure.

 

[Tob]

Is it kind of a clattering noise on startup? Might be a weak lifter.
Pretty common. Mine does that once in a while.

No clatter, more like the engine is stumbling and weak. I think if it were a lifter, wouldn't it be pretty consistent? My issue seems to be random. The only time I can 100% count on it not having this stumbling issue is when the engine has been running or is warm. Otherwise, it's a toss up whether it does this or starts up fine, after sitting for a day or so.

 

[fourpointzero]

No resolve here? Ive been dealing with a similar thing just about every time, after sitting the night, on first start of the day. My TJ is garaged, so its not weather related, unless humidity is a culprit. Did it again later this evening, after sitting for about 2.5 hours. It doesnt die on me, it just idles like its misfiring.

Im wondering if its my cam sensor (if that's what its called) as Ive changed my plugs approx 40k miles ago (5 years now) and cleaned my throttlebody, IAC and housing last year. All 02 sensors are relatively new too, NGK brand.

OP, did you figure it out? Cant be my fuel pump, because thats new as of last Aug, and it fires right up, no delay. It's just a weak, misfire for the first 3 to 4 min. I'll post a video in the AM, Thur, for reference.

 

[Tob]

No resolve here? Ive been dealing with a similar thing just about every time, after sitting the night, on first start of the day. My TJ is garaged, so its not weather related, unless humidity is a culprit. Did it again later this evening, after sitting for about 2.5 hours. It doesnt die on me, it just idles like its misfiring.

Im wondering if its my cam sensor (if that's what its called) as Ive changed my plugs approx 40k miles ago (5 years now) and cleaned my throttlebody, IAC and housing last year. All 02 sensors are relatively new too, NGK brand.

OP, did you figure it out? Cant be my fuel pump, because thats new as of last Aug, and it fires right up, no delay. It's just a weak, misfire for the first 3 to 4 min. I'll post a video in the AM, Thur, for reference.

No solution, but that sounds pretty close to my issue. I also have a new-ish fuel pump and new injectors which solved my long start issue temporarily.

 

[RMETeeJay]

Have you checked for vacuum leaks? Unmetered air can cause a lean condition when the computer calls for a rich condition (cold start, open loop).

I’ve read (but never confirmed myself) that old rubber elbows, etc on an intake system can also shrink when cold , leading to leaks. I would still test when stone cold.

 

[pagrey]

@fourpointzero you might try to cycle the key a few times on cold start to prime the fuel pump. If you aren't holding pressure it can take time to get the system up to pressure if the check valves aren't checking or the fuel pump is on the way out.

 

[fourpointzero]

@pagrey it shouldnt be my fuel pump, since its very new and fires right up without hesitation, every time. Though, who knows, maybe the pump is already crapping out. But I'll try what you suggest.

As is, It idles like its misfiring for a couple of minutes, then it adjusts and runs fine.

@RMETeeJay I'll look for leaks. Thats a very good possibility as the Jeep is closing in on 25 years of age and the weather here in NJ is everything from freezing to hot as b@llz.

 

[RMETeeJay]

Here's a cheap way to test. Head on down to Wawa and pick up a dime cigar.
https://wranglertjforum.com/threads/cheap-engine-vacuum-leak-tester.19643/

 

[pagrey]

@pagrey it shouldnt be my fuel pump, since its very new and fires right up without hesitation, every time.

Agree 100%, just an easy free test to eliminate that from the list even if it is all the way down at the bottom.

 

[fourpointzero]

FYI update: I recorded a video yesterday morning and of course the jeep starts right up with no misfire. Go figure. Same this morning. Who knows......could be anything. I mean, just about 200k and it's still doing hour long road trips. So I cant really complain.

 

[pagrey]

Hopefully the gremlin has moved on.

 

[Nickxm92]

I have the same exact issue. Getting a cylinder 6 misfire code when it happens. It will continue over a few starts and then the CEL will disappear even when the problem persists. I will be diving into it all today and keep ya posted if I get it cleared.