Worrying Engine Noise

[TouringMatt]

I'm getting what sounds like a muted whistle sound coming from the top of the engine when I decelerate - usually from the 3-2k bracket, it does it if I hold the revs and lift off the pedal too

I've located it to around cylinder #5, nothings catching externally and its defiantly coming from under the rocker cover - any thoughts?

Its sounds like a very un-mechanical noise and the engine runs seemingly fine. Could it be blocked spraybar - worn parts???



Any input appreciated

Matt

[doug325i]

Have you checked the colouration of the plugs, check No5 and compare to others, Could give you an indication if anythings really up.

Otherwise an air leak can sometime make a strange whistle

Let us know how you get on - interesting one

Good luck

[TouringMatt]

Update!

I can now pretty much rule out it being mechanical, I took the rocker cover off today, all clean and normal looking under there, checked and adjusted the tappets, checked the plugs - all normal and even ( also vacuumed a load of crap out of the spark plug holes, damn useful those Dysons ) and stuck it all back together - noise is still there

But im now convinced its an air leak somewhere, only trouble is pinpointing it, its sounds like it originates from under the inlet manifold area, but if I stand one side of the engine and it sounds like its coming from the other, go to the other side and the noise then sounds like its back on the side where I was before

When driving, if I decelerate in 4th from about 2.5k the noise is there right down to 1.5k, I only have to give the throttle the lightest touch and it stops.
So here's what im thinking, with the throttle fully shut off the engine is trying to draw air still but the butterfly causes the restriction. If the air can find an easier supply - like a knackered gasket - it will suck air through it, creating the whistle-like noise?

Its a long shot I guess but its driving me crazy - guess im gonna have to bite the financial bullet and replace all the gaskets on the inlet side


Thoughts anyone?

[Martinaston]

I'll quote one of Brianmoore's ideas here.

He used a piece of hosepipe like a stethascope to locate a broken intake gasket.

Sounds like a cheap solution to an otherwise expensive problem

[TouringMatt]

Tried it!! and still cant locate it, i will have to try again as daylight had run out , as had my girlfriends patience.......



Cheers
Matt

[Dan318-is]

its an airleak

wd40 on idle, listen for the engine not to change while u r spraying it

check AFM boot

[TouringMatt]

Emptied almost a full can of it - no change

So far i have replaced the blue and brown sensors, TB to AFM boot and fixed the TPS and reset it correctly



Matt

[Dan318-is]

m20 yes?

[TouringMatt]

Yeo, M20 2.5 1989 Vintage

[Dan318-is]

have you tried spraying around the inlet manifold gasket (where it meets cylinder head)

removed one of these tuesday an the gaskets were fookin fooked,

other than that, the vacuum hoses goin to the throttle body were the ones that bugged me on my m42

cant think were else u cud b leaking air

is it a high pitched squal on the let off of the throttle? thats exactly what mine did when i had a leak from the throttle body gasket so try that too

[TouringMatt]

I love explained a noise over the inturdnet

Ok, think of the classic snore noise - not the intake of air bit, but the whistly exhaling bit, add a bit of roughness and intensity, and that's about as close an analogy is I can muster up!

Ive literally soaked the entire inlet manifold area, to the extent that ive left a pool of WD40 behind I'll try again tomorrow

I'll give the vac hose a good look over tomorrow too

Matt

[Dan318-is]

try inlet manifold and tb areas mate thats where my squeal originated

are you manifold studs loose?

[tylerma]

have you tried the tissue test mate

[Andy335Touring]

Try disconecting the IACV whilst you are squirting stuff to locate the leak as the change in tick over won't be smoothed over by the ECU/IACV so you will notice the change in rpm easier.

You can use all sorts of stuf to detect the air leak like carb/brake cleaner,easy start and even one of those paint stripping burners, unlit obviously

and in a well ventilated area !

Some wil raise the rpm like the gas burner and some will lower it.

[Dan318-is]

FUCKIN PMSL!

classic use of smilies there

legend

[TouringMatt]

Been having a think ( rare ) and I may know what the noise is at the weekend i took the dizzy cap and rotor arm off to see what condition it was in. Cleaned it all the contacts up and used some PCB cleaner on the rotor arm - the bit that sits against the dizzy cap - should this have some kinda lube on it, and could it now be running dry.

It may explain why it sounds like its coming from under the cam cover if the vibrations are traveling up the camshaft??

Matt

[Andy_magic]

It might also be the plastic moisture cover under the dizzy cap rubbing on something too, hows the car running generally, does it sound like it's missing at all.?

[TouringMatt]

Runs fine, but there is a slight miss at idle. I can feel the car kicking a bit.....
New cap and arm you reckon?


Cheers
Matt

[billgatese30]

mine sounded very similar and it WAS the inlet manifold gasket.

i tired everyhting you did and couldn't lovate it.....then a few days later a large piece blew out and it was howling like a goodun, then i found it

mine was on number six cylinder (nearset cabin).

mine sounded almost like a squeeking to begin with, i thought it was the brakes until i realised it was coming form under the bonnet