2007 JKU 3.8L, Vacuum leak? video link attached.

Pixel

Pixel

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https://www.youtube.com/watch?v=6WF1rKX6rIU

I have not had a chance to do any DIY smoke machine testing or take it to a shop that has one but I did look for any obvious signs like a hose that popped off and poked around with propane in any areas that seemed like it would be prone to leaking.

It is very hard to miss the sound I am referring to in this video @ 0:29 this happens every time the engine is turned off. It started as a faint hiss and has gotten much more noticeable lately. I can also faintly hear it from the vehicle cabin while accelerating from a low RPM. It sounds like a release of gas when you open a propane/co2 cylinder up. I want to say it is a cracked exhaust manifold (if you look closely a bolt head popped off the heat shield so I am guessing there is an issue there to be fixed even if this isn't the root cause.

Anyone else ever experience this?
 
That is effing weird. I don't think it's exhaust. Sounds like AC system venting or maybe evap system. Any codes? Does it make a difference if AC is on or off? Next time you make it do it, put your hand on low side AC line and see if it feels like's its coming from that system. Also check evap lines for leaks (which would likely have already set a code). Maybe listen around throttle body and air inlet tube as well.
 
WJCO said:
That is effing weird. I don't think it's exhaust. Sounds like AC system venting or maybe evap system. Any codes? Does it make a difference if AC is on or off? Next time you make it do it, put your hand on low side AC line and see if it feels like's its coming from that system. Also check evap lines for leaks (which would likely have already set a code). Maybe listen around throttle body and air inlet tube as well.
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Thanks for the quick reply. There is no code thrown that points to anything like that. I have random codes every now and again that I have just chalked up to gremlins that no one can seem to diagnose that I clear and they don't come back. The noise is still the same with the AC/Heat/Vent on regardless. A few months ago I threw a code for a misfire on #4 ended up being a bad wire and no spark from that particular coil. Replaced it with a screamin demon coil, livewires, and new autolite plugs with a .65 gap. The other day a code popped on for a misfire on #2 -- checked the plugs and wires all were ok. Cleared and never came back :idontknow:

From inside the cabin it seems most audible from the drivers side. I am almost wondering if a line popped off the back of the climate control in the dash? When turning the knob from Upper vents to upper vents+floor it seems to be difficult to move.
 
This probably doesn't help at all, and I can't watch the video now because I'm at work, but when I turn my fan off in my TJ (even if the Jeep is off) it makes a noticeable sound like gas or pressure is being released. The Jeep could be off for a few days and I hop in and flip the fan switch from on to off and it'll do it. I always thought it's just how our Jeeps were designed.
 
black pearl said:
brake booster pump maybe? Releases pressure when you lose vacuum pressure like on acceleration or shut down just guessing


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That is exactly where it sounds like it is coming from but I cannot visually see anything. When I poked around with the propane I could not find anything. It is a pretty audible sound I don't think it is going to be a pinhole sized leak if that is the case no? There is definitely a lag in acceleration on this already lethargic engine. Going to hook up a vacuum pump and see if it holds. Hopefully will have a few mins later today after work.
 
Pixel said:
That is exactly where it sounds like it is coming from but I cannot visually see anything. When I poked around with the propane I could not find anything. It is a pretty audible sound I don't think it is going to be a pinhole sized leak if that is the case no? There is definitely a lag in acceleration on this already lethargic engine. Going to hook up a vacuum pump and see if it holds. Hopefully will have a few mins later today after work.
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It could be something inside the canister itself maybe .... vacuum or smoke test would be easiest way of finding for sure then


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madstiles said:
Mine has a leak in between the booster and master cylinder it was hard to locate also until I used smoke

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Same thing happened to me. There is a seal in between the master cylinder and brake booster that sounds like that when it goes. Usually the cause is a leak of brake fluid that eats the seal. Mine was randomly misfiring due to the unmetered air but didn't respond to propane. I replaced the booster and master cylinder and all was well.
Edit : to test you could vice grip the booster hose when idling and if the sound goes away then that would indicate that seal.
 
I had the o ring between the master cylinder go bad which caused a vacuum leak. But if your brake pedal isn't hard I would think that its not a vacuum leak at the master cylinder or booster. If The hose that connects to the booster is leaking it would also cause the brakes to be hard. My jeep didn't make that noise when I had the bad o ring or the hose disconnected. It was just a constant air sound when the engine was running and stoped when the engine was shut off.

Edit: sounds kind of like my k&n intake when I shut my engine off except it doesn't last that long.

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use a long screw driver or go to harbor freight and get a Mechanic's Stethoscope for $4

have someone start it and shut it off while you have the end of either a screw driver (other end at your ear) or the stethoscope on the booster.

you'll be able to hear it clearly if it's the booster or check other components until you narrow it down.
 
Last night I was able to find some time to do some testing and maintenance. Ran the BG EPR and BG 44K products through it as directed and then changed my oil and filter. I was going to do the Mopar combustion chamber cleaner as well but didn't have anyone to keep the idle up for me while I sprayed in it. Took it for a drive and it ran ok.

Today the P0302 code came back. Just out of curiosity I pulled the plug and it was oily (Changed them in January about 4,000 miles ago when I changed the coil, plug, wires, and O2 sensors) The gap also opened up slightly as well. I put a new plug in and gapped it correctly. Still running extremely rough at idle and when trying to go above 40mph this thing rattles like hell. I had a friend around today so I figured I would try the MCCC today as well. After driving the vehicle around for a bit to get it up to temp I attempted to spray the can in while maintaining 1000-1200 rpm I couldn't even get the throttle plate open at this rpm range. At 2000 rpm the plate barely opened up enough to squeeze a quarter in. Is this normal? It is the first drive-by-wire vehicle I have owned but I know not to force it open so I didn't.

Any ideas how far the OEM 3.8L throttle opens up at specific ranges?
Could I possibly not be getting enough air in?
Could this cause a misfire code?

So many questions. I have attached a few pics of the original plugs I pulled a few months ago as well as the numbers from the cylinder compression test. I did notice the #2 plug was actually pretty dirty back then too. Didn't think much of it at the time.

maintenance-2017-01-14-compression-test.jpg
maintenance-2017-01-14-sparkplugs-pside-01.jpg
maintenance-2017-01-14-sparkplugs-pside-02.jpg
 
Your fuel trims don't look too bad but they are out of spec especially your bank 2. Generally when the combined numbers of long term and short term are over 10 then you have an issue. It looks like your oxygen sensors are correcting for the most part (short term fuel trim corrects to a degree). It also seems to correct more under throttle which would indicate a vacuum leak. Not sure about the throttle plate but your fuel trims show you running lean (too much air) as opposed to rich. The relative compression test looks good. Oil on the plug could be worn valve guides or seals, but hopefully not a head gasket as your compression test looks good. Hopefully someone with more knowledge here will chime in. Hope you get it figured out.


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Judesign said:
Your fuel trims don't look too bad but they are out of spec especially your bank 2. Generally when the combined numbers of long term and short term are over 10 then you have an issue. It looks like your oxygen sensors are correcting for the most part (short term fuel trim corrects to a degree). It also seems to correct more under throttle which would indicate a vacuum leak. Not sure about the throttle plate but your fuel trims show you running lean (too much air) as opposed to rich. The relative compression test looks good. Oil on the plug could be worn valve guides or seals, but hopefully not a head gasket as your compression test looks good. Hopefully someone with more knowledge here will chime in. Hope you get it figured out.


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I have a 2007 Jeep Wrangler Rubicon we just had to have the crank sensor replaced Ours had a rough time starting sometimes and idling seems to be doing better now


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Update: Bad Coil

So it turned out to be the Screamin' Demon Coil that I replaced on 01-14-2017 @ 124,418 miles (currently at 128,737 miles) was not working properly on #2. I used the LiveWires it came bundled with and the Autolite platinum plugs gapped correctly @ .65 The plug that I pulled from the #2 cylinder opened up to about .70

Right now I have a Delphi coil installed and waiting for Performance Distributors to replace my other one under warranty. I know its just another electronic/electrical device so stuff like this is prone to happening but has anyone had a failure this quick? I will most likely just keep the Delphi coil in the car as a backup in case this happens again anyway.

Thanks to all of you who chimed in on this.
 
Glad to hear. Honestly so many times the aftermarket stuff causes these problems. When it comes to the engine I always stick with oem for this reason. So it's running good?


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