Hey guys, I’ve got a little issue here that I’m hoping someone has encountered or can help brainstorm a resolution. When the cars running and I pull the oil filler cap off there’s an abnormal amount of vacuum. Enough to making a decent whooshing/suctioning noise when I pull it off. Also tied in there is a weird squeaking and vacuum leaky noise on the passenger side of the motor. Sounds like it’s around the upper/lower plenum. As soon as I take the cap off, the noise goes away. Also when shutting the car off there’s a long squeal/squeak that’s post key off, engine no longer turning over. I’ve sprayed down the engine bay with brake clean looking for vacuum leaks with no resolve. (05 revup 6mt sedan)

p.s. if this had been solved and I haven’t found the posts yet please feel free to redirect me.

 

Sorry for the late reply, there will always be intake vacuum present with the oil cap removed if you have the PCV system hooked up, it's literally sucking those crankcase vapors up through the PCV valve into the intake tract. Since you are also hearing a leak on the passenger side I would start by pulling and inspecting the PCV valve (it's on the passenger side, screws into the valve cover). Those rubber hoses degrade over time and it it's all OEM stuff you should probably just order the silicone hose replacement kit for the 3 rubber lines that make up the PCV system.

 

I checked the PCV valve, it functions properly. I think I’ll probably do all the silicon hoses when I do valve cover gaskets +catch can maybe it’ll miraculously fix itself after that 😂 thank you for the insight!

 

Odds are you have a vacuum leak in that area you are describing and when you pull of the filter cap it sucks in more air from the "larger" hole. Having a vacuum at idle is pretty normal and can even stall your car out if you wanted. Unplug the brake booster line that goes into the plenum and you'll see what I mean.

I have Z1 silicone hoses and I wouldn't recommend them for PCV hoses. Mine got all oily and gross, so I replaced them evap hose instead.

You can use spray bottle with water, unlit propane, and other things to find a vacuum leak too.

If it's small enough you can make a small smoke machine for about 20 bucks in parts. I made one to troubleshoot a vacuum leak I had.

 

evap hose? And I deff know what you mean coffeysm. I’m gunna go in and do new valve covers (only cus I’m way to lazy to do the spark plug tube gasket “mod”) I’ll just do plenum gaskets and all that junk when I’m in there

 

Yea, look for evaporative hose that won't collapse and can handle oily residue. If you don't and when you turn on the car especially with the junky hoses that come with those oil catch cans it will collapse from the vacuum.

For testing purposes only you can isolate the vacuum hoses. I'd unplug the brake booster from the plenum and cap it off, disconnect the PCV, and things like that. Then if your noise disappears it's probably one of those hoses.

The plenum gaskets are metal and should still be good, unless you bend them or something.

 

so I got a chance to try and isolate the noise, unplugged the booster vac line and the line from the plenum to PCV and played back and fourth with those I noticed that when booster line was in its spot and the pcv wasn’t active but still installed, I believe I had the vac line open, iirc, it didn’t make the noise and then would start making it again when I plugged the line back in. Made sense it could’ve been the pcv. I replaced that and honestly the noise post KOEO the noise almost sounds more aggressive. So back to square 1 🤧

 

Welp here’s the culprit! The noise started happening right after I put cheap intake on 🙄 this is the hose from the back of the valve cover yo I take on the drivers side. Who knows why I never checked that before 😂 She’s much quieter now that I replaced that junk with a decent thickness heater hose that won’t colapse. Thanks for all your input guys!

 

Yep! I like to use fuel injection hose (not just regular fuel line it's rated at a much higher psi for injection systems) because it's gas/oil resistant and won't collapse. Glad you finally found the problem.