2011 Cold start fine, hard starting when warm - JKowners.com : Jeep Wrangler JK Forum
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post #1 of 9 Old 09-24-2017, 08:24 AM Thread Starter
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2011 Cold start fine, hard starting when warm

I've done some searching and haven't found a thread, so I'm hoping someone can provide some guidance.

I've got a 2011 Rubicon. When I first get in it in the morning, cold start, it cranks and starts immediately. However, after driving it a bit, when I go to restart it again, it cranks for approximately 3-4 seconds before finally kicking off, runs rough for a couple of seconds and then runs smooth. No codes thrown, and drives and performs fine while running.

Any thoughts?

Thanks!
TX
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post #2 of 9 Old 09-24-2017, 12:23 PM
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How many miles? Have you changed plug wires, plugs or pcv. Run a can of BG44 fuel system cleaner. This may work as a first step. Pop your hood in a very dark place and start your engine. Look for visible sparks noting location for replacement.
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post #3 of 9 Old 09-24-2017, 04:06 PM
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@RubiCajun is accurate . The symptoms can also relate to a cracked exhaust manifold where a hairline crack that exists won't be expanded until the 3.8l v-6 is warm at which time the fissure is slightly expanded and thus permitting manifold pressure variances when you go to start her backup . Listen in the exhaust mani vicinity during one of these heated restarts and having someone turn key over for you to be using a stethoscope of your choosing ( I find a 16" long ,philips head screwdriver works great but have used a wood 1/4" dowel scrap as well as an actual automotive stethoscope, they all work ) to listen for the tell-tell ," phft phft " sound emitted from the exit mani or go further and have a smoke test performed.



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post #4 of 9 Old 09-24-2017, 04:09 PM
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addendum: maybe you'll stick around to provide details on your troubleshooting and end-results so we don't feel like cheap whores of the jeep world. We have many "one & run" new members is all, not being rude.

We'd like to meet you. Drop by the Welcome Room and introduce yourself when you get a chance.


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post #5 of 9 Old 09-25-2017, 04:51 AM Thread Starter
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It's got about 66K miles on it. Ran it in complete darkness last night and didn't see any obvious sparks, arcing, etc. I plan to throw some fuel system cleaner in today.

I'll try to do the exhaust manifold test today. I can see that an expanded fissure would cause variances to manifold pressures, perhaps causing odd starting issues, but once started, would that fissure be unnoticeable for operating the vehicle?

Doing my homework, thanks!
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post #6 of 9 Old 09-25-2017, 05:25 AM
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If slight enough , you'd experience negligible performance changes ( but can get much more noticeable) plus you acvlimate to it and aside from smelling raw exhaust gases and maybe fouling the plug wires or boots on that side from the excessive heat you could miss it. I can tell by the sound they make and it gets much hotter after running .
They are very much known to crack because of Offroading shaking and jarring.
just worth checking into ...

your throttle body is all clean ,right? The butterfly valve needs annual cleaning front and back ,at least.
All just ideas on things you should check ...




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Last edited by j3ff3ry_j33p; 09-25-2017 at 05:29 AM.
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post #7 of 9 Old 09-25-2017, 11:26 AM
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I don't have any stock in BG products but I've used BG 44 before and I call it Jesus juice because it performs miracles.
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post #8 of 9 Old 10-02-2017, 02:59 PM
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Sometimes this can be a symptom of cracked or old vapor lines but that's on carbureted engines. Not sure about the fuel injected. I'd check all your lines anyways though.

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post #9 of 9 Old 10-02-2017, 03:35 PM
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I'm new to JKs; I just got my 2010 JKU. But I had this same problem with a 2006 VW TDI. The issue was the mass airflow (MAF) sensor located after the air filter. If it is dirty, it gives bad air readings at startup for warm engines. That's why it starts rough. After it starts, the other O2 sensors take over and adjust the air/fuel mix. That is why it goes away.

I was able to clean mine off with electronics cleaning spray and it fixed the problem.
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