[Bintin]

Hoping someone might be able to help identify this whistling sound coming from under the hood. I got the car up and running after about a year of sitting, due to the cost that I was quoted to fix some misfires (That's a whole other story). For the most part things were running well, but after a few weeks of working on it, this humming noise started happening.

The noise starts after the car is warmed up, while in any gear, and only lessens above 20mph or so. At first I was thinking a bad alternator diode, but the battery is still getting fully charged around 14.2V when running. The other reason I don't suspect the alternator is because the noise doesn't stop until after the car is shut off. I just replaced the drive belt and idler pulley. All other pulleys seemed to be in adequate working condition. A stethoscope indicated somewhere near the rear of the engine, or possibly below the vehicle. It's hard to pinpoint exactly.

Live data on my OBDII reader shows that the long term fuel trim shoots up to 20% when I'm not actively pressing the accelerator, so there's very likely a vacuum leak somewhere. i figured it would also be present when the car is cold, and be more of a high frequency hiss if it were from a leak. Unfortunately I haven't been able to get ahold of a smoke machine to test for leaks.

My only thought was that it may a leak in the exhaust manifold, but my knowledge there is pretty limited. Everything I know about cars has been from the dozens of hours spent reading and researching this one. Here's a video that shows the sound. Taken from my phone, above the drive belt. It's loud enough that folks can hear it inside the house while it's running in the driveway. Any thoughts?

 

[Ignatius Reilly]

Does it ever do it key on/engine off? Our electronic throttle bodies do make some funky noises sometimes, and the way it continued after you shut the engine off made me think it could be coming from there.

However, given your fuel trim info I would definitely look for vac leaks. It sounds very odd for a vacuum leak though. Maybe something internal to the brake booster?

 

[Bintin]

I just checked it again after driving around town. It’s only with the engine on. If I turn everything off and start up again, it takes about 5 seconds before I hear it again. Just from waving a stethoscope over the top of the engine and any crevice I can reach, it really sounds like it’s coming from somewhere lower. It reminds me of air moving across the top of a bottle rather than suction, which is kind of why I was thinking exhaust.

I’ll definitely look into the brake booster more! It does seem to sound a little louder on that side.

Unfortunately the misfires were happening long before this issue, so I’m not sure if this is a side effect, or a new issue altogether. I’ve been working on a rough idle and stuttering.

 

[Ignatius Reilly]

I just checked it again after driving around town. It’s only with the engine on. If I turn everything off and start up again, it takes about 5 seconds before I hear it again. Just from waving a stethoscope over the top of the engine and any crevice I can reach, it really sounds like it’s coming from somewhere lower. It reminds me of air moving across the top of a bottle rather than suction, which is kind of why I was thinking exhaust.

I’ll definitely look into the brake booster more! It does seem to sound a little louder on that side.

Unfortunately the misfires were happening long before this issue, so I’m not sure if this is a side effect, or a new issue altogether. I’ve been working on a rough idle and stuttering.

Interesting. I'd think a "traditional" vac leak (like from a line) would be directly tied to the engine's operation, IE starting immediately and ending as soon as the engine stops turning over and sucking in air. Maybe if it is deeper in a vacuum-operated apparatus, like the booster, it might take a second to build enough vacuum to make the noise. But from the vid it does almost sound electrical in nature.

Exhaust leaks tend to be more "puff puff puff" than a solid note like your noise. Look for an old F150 around town and you are quite likely to hear it.

I might prioritize getting your misfire/idle issues sorted first as that can lead to other problems like clogged catalytic converters, which unfortunately is endemic in our cars.

 

[Bintin]

Sorry, I probably said that incorrectly. I agree, I think a traditional vacuum leak is likely the cause of the misfiring and rough idle. I’m just not sure if the sound we’re discussing here is contributing to that as well. I will also say, I know the front ocv/Vvt has a bad seal where it meets the valve cover. From what I’ve seen online, nobody has had success finding that replacement.

I appreciate your help! Something I probably shouldn’t have done that I just did - I pulled the oil dipstick while the car had been running for a minute. The sound actually disappeared, then crept back in once I replaced the dipstick.

 

[mitro6ual]

Per the good Dr., here is a replacement OCV/VVT seal, (there may be others):
Oil Control Valve Seal (variable valve timing activating solenoid), O.D. 40mm x I.D. 28mm x Depth 8mm.
Misumi USA AE1538E5
Alt.part = Napa 10930 (pitman arm shaft seal)

For your noise issue, that definitely sounds like air escaping something. Something is getting pressurized and that pressure remains after the engine shuts off, then slowly escapes until it's all out. That means some pump gets something up to pressure wherupon it starts to leak.
Does the A/C work? It could be a leak in the lines or shrader valve (mine had that issue).

 

[Ignatius Reilly]

I appreciate your help! Something I probably shouldn’t have done that I just did - I pulled the oil dipstick while the car had been running for a minute. The sound actually disappeared, then crept back in once I replaced the dipstick.

Hey that's a pretty big clue. I'd check your PCV valve - it is right in that area where you're hearing the noise (up under the intake plenum). You may be able to snake it out without pulling that plenum. When you pull it give it a good shake - you should hear something rattling around in there if it is good. I might go so far as replacing it anyway if you don't know when it was last done, as they are only a few dollars and kind of a maintenance item.

No real issue pulling the dipstick on a running engine. In fact, I make a point to do so on cars I'm looking at buying to check for excess blowby. Just don't pull the oil cap as the timing chain is right under there and will sling oil everywhere. Ask me how I learned that.

I have also used that NAPA pitman arm seal for my valve covers. It works well, but is not a 100% fit (a little loose) so you have to smear a little RTV in there to seal it up. At least that was my experience. But it's been a few years and no more leaks.

 

[Bintin]

Per the good Dr., here is a replacement OCV/VVT seal, (there may be others):
Oil Control Valve Seal (variable valve timing activating solenoid), O.D. 40mm x I.D. 28mm x Depth 8mm.
Misumi USA AE1538E5
Alt.part = Napa 10930 (pitman arm shaft seal)

For your noise issue, that definitely sounds like air escaping something. Something is getting pressurized and that pressure remains after the engine shuts off, then slowly escapes until it's all out. That means some pump gets something up to pressure wherupon it starts to leak.
Does the A/C work? It could be a leak in the lines or shrader valve (mine had that issue).

Thanks for this! I'll look more into the shrader valve. The A/C hasn't had any problems. I'm going to pick up a PCV and give that a try. From what I can see, the tube where it connects looks pretty gummed up.

 

[Bintin]

Hey that's a pretty big clue. I'd check your PCV valve - it is right in that area where you're hearing the noise (up under the intake plenum). You may be able to snake it out without pulling that plenum. When you pull it give it a good shake - you should hear something rattling around in there if it is good. I might go so far as replacing it anyway if you don't know when it was last done, as they are only a few dollars and kind of a maintenance item.

No real issue pulling the dipstick on a running engine. In fact, I make a point to do so on cars I'm looking at buying to check for excess blowby. Just don't pull the oil cap as the timing chain is right under there and will sling oil everywhere. Ask me how I learned that.

I have also used that NAPA pitman arm seal for my valve covers. It works well, but is not a 100% fit (a little loose) so you have to smear a little RTV in there to seal it up. At least that was my experience. But it's been a few years and no more leaks.

Great idea! Without getting too great of a look, the tube connected to the pcv looks gummed up on the outside. Although, it didn't sound like that's where the sound was coming from. Either way, wouldn't hurt to replace the part! I took the plenum off once to replace the gaskets in this whole process, but I might just take it off again anyways to check the fuel pressure and injectors while I'm at it. If I can get ahold of a spark tester I'll check the coils too. They showed normal resistance, but I never checked for current.

 

[DrFeelGood]

SO, there are some great ideas here. I am going to float an idea that is from my experience.

Could it be possible that the catalytic converter is clogged and causing a steady excessive back pressure? This pressure is not audible until the engine warms enough to expand and tighten up the manifold to cylinder head interface? Would this not also account for the fuel trim discrepancy?
Mine got so bad I could not climb hills in 3rd that I could in 5th.
🤷‍♂️

 

[Ignatius Reilly]

The Dr. is wise, unfortunately you can never discount cat issues with our cars. Especially on a vehicle with a history of misfires.

Great idea! Without getting too great of a look, the tube connected to the pcv looks gummed up on the outside.

Mine is a little "damp" as well, there is a seal between the connector and the rest of the hose and I think it's common for it to weep a little.

 

[Bintin]

The Dr. is wise, unfortunately you can never discount cat issues with our cars. Especially on a vehicle with a history of misfires.
Mine is a little "damp" as well, there is a seal between the connector and the rest of the hose and I think it's common for it to weep a little.

do you recall if your PCV hose has a clip connecting to the valve. The Haynes manual I have mentions that clip. The only reason I ask is because I’m wondering if this has already been replaced once. I was also thinking the original PCV was metallic, not plastic. I bought it from a single owner with 107k, and I think they may have understated the amount of work that’s been done…

 

[Bintin]

SO, there are some great ideas here. I am going to float an idea that is from my experience.

Could it be possible that the catalytic converter is clogged and causing a steady excessive back pressure? This pressure is not audible until the engine warms enough to expand and tighten up the manifold to cylinder head interface? Would this not also account for the fuel trim discrepancy?
Mine got so bad I could not climb hills in 3rd that I could in 5th.
🤷‍♂️

I'll add it too the list! I'm hoping to do some cleaning up of the smaller parts in and around the intake, but I'll definitely take a look at that as next steps. I appreciate it!

 

[Ignatius Reilly]

do you recall if your PCV hose has a Clío connecting to the valve. The Haynes manual I have mentions that clip. The only reason I ask is because I’m wondering if this has already been replaced once. I was also thinking the original PCV was metallic, not plastic. I bought it from a single owner with 107k, and I think they may have understated the amount of work that’s been done…

Mine does have one of those Ford-style green ring clips, but I think you have the old-style PCV hose, which they updated in mid 2005 or so. That older style is prone to collapse and can cause issues. This is the newer style for reference.

I've only ever seen plastic PCVs on our cars, so it is quite possible that it is all original.

 

[Ignatius Reilly]

EDIT: Ignore me fat-fingering a duplicate post