how to tell if exhaust manifold is cracked?

[EmMR2]

Hi all, possibly a random question but my car is having some strange issues with losing power and becoming sluggish then back to normal, then sluggish again. I suspect its the exhaust or something in the exhaust system and wondering if anyone here has had similar problems

[shinny]

You would hear if the exhaust manifold was cracked. I had a crack appear on a custom pipe coming off my manifold and the blowing sounded like a plastic sensor plug dragging on a belt at idle and when gently revved. It took me a day or so to diagnose the sound to this crack:



I often find my ears are a very good tool for detecting issues on the car, so have a good listen and see if anything sounds unusual

[EmMR2]

there does seem to be a bit of blowing (yes i realise that sounds dirty ) but would that account for the lack and restoration of power?

[shinny]

there does seem to be a bit of blowing (yes i realise that sounds dirty ) but would that account for the lack and restoration of power?

I haven't experienced a blow from any part of the exhaust affect power too badly, although I wasn't driving the car hard as soon as I spotted the above crack. however a blow that's sucking air into the exhaust before the lambda sensor will affect power off boost and lower down the rev range as the car would be fuelling rich. Intermittent blows are more likely to be gaskets, because thermal expansion can seal them as the car warms up. So I'd start by seeing is there are any nuts that need nipping up.

However, I would more likely expect a loss of power will be some other fault. In what way does the car feel sluggish? And what makes you suspect the exhaust? Is boost building ok?

[EmMR2]

Its an NA so no boost building, i've had a few problems with the exhaust and with it blowing i am assuming thats the main culprit. The sluggish feel i get when driving is tricky to describe, but when i pull away it doesn't deliver the acceleration it used to, when changing gear the car feels like it wants to stop dead in the road

Edit: Talking out loud about this, i actually think im looking in the wrong direction and its something as simple as air filter needs changing, fingers crossed

[CalMac]

I found that what I suspected was cracked mani resulted in metallic rattling sound at idle, which would stop as I dipped the clutch. Put a new exhaust system on and the sound went

[shinny]

You had a cracked manifold, so replacing the rest of the exhaust fixed it??

Or do you mean you replaced the entire exhaust including the manifold?

[CalMac]

I had a rattling sound, wasn't sure of the culprit but was told by a mechanic that it was probably cracked mani. Fitted new exhaust (including manifold) and the rattling stopped - therefore leading me to believe that this was the cause, as there were no loose bolts or heatshields which may have caused it.

[synXero]

Where'd you get the manifold?

[CalMac]

me? it was the original mate! changed to a Japspeed 4-1 now , would prefer a 421 but no point really as I'm going turbo as soon as I can afford it