Loud roaring from engine bay >2k RPM when driving

[Contax]

If that's the case , it's either muffler puncture or worse scenario , the cat has gone liao... sent it to a workshop or AD to determine the case.

[Brock]

I didn't smell any exhaust fumes coming from the engine bay.

 

That's the strange thing. At stationary, the sound is fine. It's only when the car is moving and past 2k RPM does it sound like a WRX exhaust!

[Brock]

How possible does the CAT break down? My ride is coming to 3 years only!

[Dwoon]

Can advise what is the symptoms of the CAT gone? I understand that they can sometimes melt, but that clogs up the flow instead leh....

 

I suspect mine might be gone (~ 4 years already) .... but then.... the rich petrol smell on cold starts, is gone once the car warms up... which indicates its' still working???

[Dwoon]

Think the 1st thing you should do is to isolate whether it's an engine roar or the exhaust being loud.

 

Open bonnet and listen to where the loud sound is coming from. (get someone to help slowly rev the car while you're listening at engine bay). Is it there? Or is there sound coming from the rear (muffler area)

 

If you can only get the loud roar at low rpms when moving, then perhaps you can go to a large empty carpark, lock your car into 1st gear and then ask someone to drive it around so you can hear. At 1st gear, think that at 20km/h already at 2K rpm so can hear from the ground, when car is moving slowly in carpark. (maybe can even run alongside the car to hear, at that speed )

[Contax]

One of the main culprit to cause a premature death of the cat is excessive idling during cold start in the morning.One should just move off without letting the engine idle for too long. A variety of conditions may cause the catalyst to overheat and potentially melt down. Some factors that can cause this are:

 

- some engine oil in the exhaust system which is cause by engine wear, or by damaged rings or valves)

- an engine misfire or ignition failure (causing unburnt fuel to enter the exhaust)

- a cracked exhaust valve (again, causing unburnt fuel in the exhaust)

[Brock]

Will try this but the running part a bit 'siong'. The problem seems to be evident when the car is in motion, not stationary. And it's from the front maybe underside of the car.

[Brock]

I move off almost immediately after cranking the engine, if not, it's just a max of 10 seconds.

 

I will be bringing my car to an outside mech to test drive and take a look / listen. Hopefully it's not too serious that it causes a big hole in my pocket.

[Xtremez]

do keep us updated of the outcome gd luck

[Brock]

Ok. My usual servicing mech test drove my ride. At first we suspected it was the aftermarket filter after really hard throttle (both stationary and moving). However, after removing the filter and testing it at stationary, the roaring noise seems to come from the inlet manifold, very near the air filter area. He suggested that I visit him another time for him to take out the manifold and inspect the inside of it.

 

Can anyone with more knowledge explain in greater detail what seems to be going on?

Edited September 24, 2007 by Brock

[Dwoon]

Intake manifold ah..... never come across this area "lau hong" leh .... exhaust manifold yes... that one quite common when the seals give way due to the high heat experienced at that area.

[Brock]

Borrowing this picture...

 

 

(22) is where the sound is coming from. (23) is the throttle body.

[Dwoon]

I noticed that some cars have plastic intake manifold..... wonder whether are they prone to cracking?

[Sfrtuscani]

send back to agent

[Brock]

Yep. Mine is plastic. Mech is going to disassemble it and take a look whether it's cracked or not.

[Brock]

I don't see how your reply is helpful. That was already an option that has crossed my mind. If you have read properly, I have sent it to my mech to take a look. I'm asking for more helpful information to have a better diagnosis and troubleshooting. Thanks anyway.

[Brock]

$598.

 

That was the price I paid to fix my ride. Took the mech about 3-4 days to rectify it. The problem was when I stepped on the throttle, there is a LOUD ROAR and a metal cracking noise from the engine itself.

 

The mech and his guys examined the internals of the engine. Most of the explanation is too technical for me. Basically, he narrowed the cause of the problem to be either a change in the timing belt (which did not happen...only 30k mileage) or the next nearest thing, which is the lightweight crank pulley (most likely). The piston was out of place....the gaskets and valves were not closed properly and had to be changed as well. Something about 'it' was 3 teeth off the usual. The air valve had to be changed as well (GM part...$18).

 

On the way back home, stop-go, city driving as well as a few high revving (up to 3.5k), everything seems fine. In fact, pickup seems to have improved as compared to before the problem happened.

 

I had that LWCP running on my ride for about 3-4 months before the problem surfaced. This LWCP is WITH the harmonic damper. I doubt it's the LWCP and I tend to think it's more of the installation of it that contributed to the problem. My 1st LWCP did not have a harmonic damper and it was running fine for 1 year odd.

[Dwoon]

Hmmm... strange... LWCP does not control the timing.... if I'm correct, it might affect your alternator's charging ability should it be an undersize one. I don't see how it could have changed the timing leh.....

 

I run a LWCP as well.... no problems for the past half year or so.... only those awful squeaks from its belt before warm up.