Whistling from under the hood, when accelerating

[jamesweed]

Hello,

1985 CJ7 , AMC 258 i6 / 4.2l , 4.0 head with MPI. about 20k miles since rebuild

During acceleration , when the engine speed hits about 1500 rpm thru about 1800, I hear a whistling sound from under the hood. It is momentary only in that RPM band. IT goes away at cruise, and at lower engine speeds.

The engine runs great, gets typical fuel consumption, about 18 -19mpg combined.

Just wondering if anyone else with MPI experiences this, or if I should be chasing down an intake leak or something.

Another note, its got the hesco supplied air filter, K/N.

Thanks,

James

 

[Torxhead]

First guess would be a vacumn leak, a place to start looking would be the throttle body base.

 

[jzjames]

Also look over your air pump (emissions) system, especially around the air pump manifold. It might have a pinhole leak.

 

[hole]

Hello,

1985 CJ7, 258, 4.0 head with MPI. about 20k miles since rebuild

During acceleration , when the engine speed hits about 1500 rpm thru about 1800, I hear a whistling sound from under the hood. It is momentary only in that RPM band. IT goes away at cruise, and at lower engine speeds.

The engine runs great, gets typical fuel consumption, about 18 -19mpg combined.

Just wondering if anyone else with MPI experiences this, or if I should be chasing down an intake leak or something.

Another note, its got the hesco supplied air filter, K/N.

Thanks,

James

Mine has the same setup and sings like a bird under acceleration. I suspect its the Hesco/filter setup because I've checked darn near everything on the intake. Down the road I plan on trying to mount a later Wrangler airbox and do away with the K&N

 

[tinman]

Mine has the same noise, and I'm also looking to do the wrangler airbox. We'll see if that fixes it.

 

[ThisGuyUKnow]

Hello,

1985 CJ7, 258, 4.0 head with MPI. about 20k miles since rebuild

During acceleration , when the engine speed hits about 1500 rpm thru about 1800, I hear a whistling sound from under the hood. It is momentary only in that RPM band. IT goes away at cruise, and at lower engine speeds.

The engine runs great, gets typical fuel consumption, about 18 -19mpg combined.

Just wondering if anyone else with MPI experiences this, or if I should be chasing down an intake leak or something.

Another note, its got the hesco supplied air filter, K/N.

Thanks,

James

Its that open style/ cold air intake that is whistling. One of many reasons I dislike after market intakes of this style.

Grab a breather from a97-98 TJ, it will be a lot quieter.

 

[jamesweed]

thanks all for the comments. I figured it was maybe something to do with the filter.

Checked for leaks this weekend couldn't find anything.

 

[rockinreel]

Use a three foot long garden house and put your ear on one end. You will definitely locate the sound. Mmmmm, I just remembered you said higher RPM's, not at idle. Might hear it at idle with a hose.

My whistle was an after market plate between the intake manifold and the (new) carberator. Old gaskets can allow air to seep throuh. In my case, the plate adapter bolts were too long causing the plate to not quite mount flush to the intake. Once the sealant on the gasket gave in to the air suction... whistling began.

 

[ThisGuyUKnow]

Use a three foot long garden house and put your ear on one end. You will definitely locate the sound. Mmmmm, I just remembered you said higher RPM's, not at idle. Might hear it at idle with a hose.

My whistle was an after market plate between the intake manifold and the (new) carberator. Old gaskets can allow air to seep throuh. In my case, the plate adapter bolts were too long causing the plate to not quite mount flush to the intake. Once the sealant on the gasket gave in to the air suction... whistling began.

The OP is running a 4.0 based MPFI set up. The whistling is a common problem with this set up when people use open style breathers like the hesco one.