Unidentifiable noise

[blakshukvw]

My truck just recently started making a noise under the hood. It's a 5.0 It sounds like an unhooked vacuum line. It's coming from the drivers side of the bay. Definitely not from the intake area on the passenger side. For this reason, I don't think it's the IAC. I saw one vacuum line going to the inner fender liner from a port off of the upper intake mani and checked it. No problem there. Another weird thing is that when the truck is turned off, the noise can be heard the most and it sounds just like vacuum air being eliminated from the intake. I can't seem to pinpoint where exactly this noise is coming from and it's really bothering me. Is it possible to have an intake leak but with no CEL's?

The truck runs fine other than occassionaly while driving it will buck real hard out of the blue like the ignition was turned off then it will drive just fine like nothing happened. The truck runs cool most of the time and with the current temps we are having I wonder if that isn't caused by the CTS being confused and causing the ECU to think it should be in cold start mode and when it changes fueling maps, it causes this bucking because the transition is not real smooth. Any other ideas? I may be reaching on that one.

 

[Turdle]

If you follow the vacuum lines under the battery area, they go to a purge solenoid.
Disconnect the vacuum lines and look the plastic nipples over real well on the solenoid valve-
See if there are some holes, or a hole melted thru the fitting from battery liquid dripping down on it.

Also-under the upper plennum on the driver side there is a large vacuum line going to the pcv.

 

[blakshukvw]

I disconnected completely the vacuum line that leads to all that business under the battery tray. I just unhooked it from the factory splice that runs from the engine to body area and plugged the hole in the line to the engine and the noise was still there. Your idea of the PCV hose may just be the problem though. Does that guy run over the top of the VC on that side of the engine behind the fuel line brakets made on the VC? Does it also come off the same nipple on the bottom side of the upper mani as the one that leads to under the battery?
Would that cause a CEL or any poor running conditions? I have noticed the idles been a wee bit finiky lately.

 

[OneLever]

Perhaps these pictures will help you visualize what Turdle is referring to.

Picture 1: Left fender inner liner removed.

Picture 2: Left front wheel well looking forward.

 

[blakshukvw]

Yeah I understand where that stuff is. In fact like I said, I unhooked the supply from the upper intake to that stuff and plugged the supply and the noise was still there. I'm betting it's the PCV hose under the upper mani like turdle suggested. It just needs to get above 8 degrees first before I spend any time looking into it any further.

 

[blakshukvw]

Anyone got a pic of the upper manifold removed so I can see just where the PCV hose runs?

 

[OneLever]

Here is an excellent write up by MountaineerGreen on removing the Upper intake manifold from a 5.0L V8: Link

 

[Dan Whitaker]

I can tell you right now it's easiest to just climb on top of the engine and stick your hand between the fire wall and back of the intake manifold to locate the PCV valve.

 

[OneLever]

I should clarify, the write up was meant to provide the pictures you sought of PCV hose routing. I would not remove the Upper intake manifold to track down a vacuum leak.

 

[blakshukvw]

I found it. It was the large vacuum hose going to the valve under the battery tray. It had layed against the manifold and burned through. Now to venture into the JY for a replacement one.:thumbdwn:

 

[OneLever]

Thanks for updating us!

 

[blakshukvw]

Anyone have one of these hoses I could buy from them. All of the V8 Ex's in the JY had the upper and lower intakes scavenged and the retards that removed them cut the hose I needed on all of them. Stupid mustang guys.

 

[Turdle]

can you just get a double ended barb nipple, and splice the hose using 2 clamps?
cut the melted area clean and splice it

 

[blakshukvw]

Looks like maybe we think alike. I had aready considered doing that if I couldn't find a good replacement piece. Noone has spoke up and said they have the hose I need so looks like I'll be doing this instead. Thanks Turdle.