Another post from the weird zone

[SierraHawk]

2004 E350 w/5.4 engine that has been maintained regularly. 300,000 miles but, despite a slow decrease in power over the past several years, it is running well.

This is about a strange, intermittent and unnatural sound from the engine air intake. The sound is similar to that of a conch that is being blown intermittently for a minute up to 30 minutes. I can hear it while sitting in the driver's seat under various circumstances and loads.

If I am cruising at 20mph and the mystery conch sound is heard, I can accelerate a bit and it goes away but there are other times (primarily at speeds over 40 mph) when it does not stop. The sound is a bit louder than the normal sound made by the air intake under normal circumstances.

From the start it was clear that the sound was coming from the air intake. Replaced the air filter-no change but wiped some fine dirt that has collected on the inside of the housing. I can put my hand over the open end of the air intake and the engine continues to run without a decrease in idle speed.

I've removed the air intake bit by bit and gotten back to a rectangular piece just below the windshield cowling. I am guessing that the noise is coming from a crack in the air intake tubing or from a loosened part near the intake manifold.

Removed the "dog house". Even with good lighting, it is difficult to see a crack large enough to supply the engine with air. None of the bolts I can see are lose or missing. The engine will actually run without the air flow sensor. Other than the conch sound coming through the air intake ducting, I hear no unusual hissing or other sound from something like a crack.

All ideas and narratives about a similar problem are welcome.

[SierraHawk]

Admin: Please keep this post. Dealing with power failure and first post was not finished.

[dhally]

Maybe a failing iac solenoid?

[boywonder]

Originally Posted by SierraHawk

I can put my hand over the open end of the air intake and the engine continues to run without a decrease in idle speed.

All ideas and narratives about a similar problem are welcome.

Are you removing the air filter and putting your hand over the round hole in the intake?

Sounds like you have a resonance going on in the intake tract ....

...also sounds like you have a air/vacuum leak somewhere.....

Do you have an OBDII scanner? If you can look at your fuel trims and they are very positive 10%+ that will confirm an air/vacuum leak. If the leak is downstream of the MAF sensor then the ECU corrects that by keeping the injectors open longer so that the engine gets extra fuel to make up for the air leak.

[Lilnuts2]

I would check for any vacuum or vent lines for collapse or leaking.

[SierraHawk]

About an hour after dissembling the air intake it was getting dark. Using a flash light I was able to see some kind of superstructure on top of the manifold. The next thing I see is a black plastic thing that looked like a manifold. I thought the manifold would be a freshly cast, shiny silver mashup of tubes above the heads and block but someone put a plastic manifold on my 5.4.

In a state of disbelief, I talked to my neighbor. He has owned several vans that had a 5.4 under the hood. After many years of use, the manifolds will develop a leak in the manifold. If the air cleaner does not prevent the manifold will eventually develop cracks.

[JWA]

^^^ I have a 2000 E-250 5.4, 296K miles with its original plastic intake---not sure its a certainty they all will develop a leak. I do think later years might have experienced that but having also owned a 2003 5.4, well over 250K miles that was also leak free.

I think its a crap shoot whether they leak or not----its not quite an epidemic but it is problematic if it happens.

[boywonder]

I highly recommend that you check your fuel trims with a reasonably capable OBDII scanner before digging into the manifold. It's simple and takes less than a minute.

A manifold leak will suck air downstream of the MAF (mass airflow) sensor. Since this air didn't get "counted" by the sensor the Engine control module will add fuel to make up for the extra un-counted air since the oxygen sensor in the exhaust will report a lean condition. This will show up as short term and/or long term fuel trims being highly positive by perhaps 15-25% or more. Normal healthy fuel trims are typically between +/- 5%.

You can also spray some carb/brake cleaner or starter fluid around the manifold with the engine running to determine if you have a leak. Do this very carefully to avoid bursting into flames and obviously don't spray it in the intake. If the idle speed revs up after spraying you have a leak somewhere.


Also check for vacuum line issues........do the easy stuff first.....and most importantly don't guess.....diagnose.