Corolla Exhaust - light fizzy rattle

[JohnD]

this is a 2001 1.4 VVTi. There is a noise which I thought sounded like a cracked or loose heatshield on the exhaust manifold - it sounds like something light and loose vibrating. The noise is constant with engine running, and getting worse. It used to come and go with engine speed.

However an exhaust shop, and the (non-main) dealer who sold it had a look and both say it is something wrong with the manifold itself, or inside it. As far as I can see without dismantling, the manifold is just iron pipework - I can't see a small piece that could be loose or prone to crack. Is there a lambda sensor inside it? I can't see it. What else could it be?

 

[Burnerman]

Do you think your manifold will have a crack in it, and the noise you hear is it blowing? Not unknown......the lambda sensors will be just before and just after the catalytic converter...the first silencer like think after the manifold. There's nothing on a lambda sensor to rattle.
Failing this, its a loose baffle somewhere or maybe a heat shield that prevents too much heat transfering to the car floor.
John

 

[JohnD]

thanks for your interest

it doesn't sound like a blowing leak or joint. The manifold heat shield is about 250mm each way, protecting the bulkhead behind the engine (it is not under the floor and I don't believe there are any baffles near it).

The cat will be under the floor so not near the noise

I thought it would be the heat shield, but the exhaust shop had a look under the bonnet and on the ramp, and says not.

 

[JohnD]

in the pictures on fleabay, there is a thing with a cable coming out. Any idea what this is?

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=270613718273&ssPageName=STRK:MEWAX:IT

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=280525280434&ssPageName=STRK:MEWAX:IT

 

[Burnerman]

What we're looking at here are used Corolla manifolds, complete with the lambda sensor attached - obviously the cat bolts immediately onto the manifold, hence its position.
I have had these heat shields come loose (usally they rust away below the bolt heads) - if your 10mm bolts will unscrew it could be worth popping it off to see whats underneath.
John

 

[JohnD]

thanks, I will see if I can get the heatshield bolts off (probably rusted solid

but I can use copaslip on reassembly, and maybe large stainless washers.

I can't understand why the exhaust shop and the dealer say it needs a new manifold My first thought were also of heatshield, it's that sort of noise.

 

[Burnerman]

Truthfully, if the heatshield is in a bad state with the bolts sheared off, I have left it off before now......
The manifold would only need replacing if its cracked - look for soot marks with a mirror and if someone will put the palm of their hand against the open tail pipe whilst you listen the noise will be amplified.
Sometimes the lambda sensors don't want to shift. If thats the case, I buy a new one first, then cut the wires off so I can get a good hexagon socket over the sensor. The official split sockets aren't man enough and just spread.
If your bolts do come out, then coppaslip and stainless washers is the way to go.
On some cars, the manifold to cat coupling is a flexible one, using springs that again rust away. I don't suppose the noise is from there?
John

 

[JohnD]

thanks

will get the spanners out next weekend

As the garage claims it needs a new manifold I am tempted to get one first. Will it run with no lambda connected? or can I repair the cable if I cut it off?

 

[Burnerman]

The engine ECU wouldn't like the fact that the lambda was disconnected - I'm not sure what the long term effect would be but I guess the worst scenario is that the cat would suffer.
You can certainly splice the four cables....if your luck is in, the lambda may even unscrew using an open end spanner if you can get one in.
In my experience, you have to cut the wires off real close to the sensor so you can push a socket on.
Post back with the outcome?
John

 

[ray99]

Are you absolutely 100% sure it is the exhaust manifold?
When they first came out those engines had a problem with internal baffles in the INLET manifold coming loose and vibrating / buzzing. As far as I can remember noise appeared about 3000rpm.
Hold the revs so you get the noise and place the tip of a screw driver blade against the manifold and the handle against your ear and that might help determine the location of the noise.

 

[JohnD]

I don't know when the VVTi engine came out, but this is a 2001 model. Would that match the inlet manifold problem?

 

[ray99]

I don't know when the VVTi engine came out, but this is a 2001 model. Would that match the inlet manifold problem?

I was a Toyota technician at that time and we had to change quite a few for this problem under warranty. Noises are impossible to diagnose without having a look at the car but just wanted to make you aware of the possibility that it was not the exhaust. The screwdriver test should help unless you can borrow a stethoscope.

 

[JohnD]

thanks!

 

[JohnD]

I got an engineers stethoscope, and yes, it does appear to be coming from the inlet manifold at the front, not the exhaust manifold at the back.