Bloody Megane problems again - more loss of power.

Hello again Tim! The 'blockage' seems to clear itself suddenly the other while driving after a few miles. The power all came back and it sounded more normal again, if a little bit more throaty than before. I had a little poke around the engine bay in the evening and discovered a crack in the exhaust manifold which explains the extra bit of exhaust noice but wouldn't explain the loss of power (though it might slightly knock it off tune). I had a quick scan over the hoses and nothing seemed awry. I might take some of the inlet system off to have a closer look. I'll also whip the exhaust off while I sort out the manifold to see if there any blockages in it still. The noises sounded more inlet type sounds.

The exhaust system is all new (not the manifold) so I would expect even a failed HT coil wouldn't be enough to destroy a new cat that quickly after a mile or so or driving. I've also fitted a new fuel filter, unless something had got into the fuel system before I changed it.

From your post saying about weird throaty noises, and unusualy engine tones, it seems as if something is sucking closed or obstructing the inlet. I have seen cases where the under bonnet sound proofing is sagging and will effectively seal over the air inlet pipe on cars where it is located by the radiator grill etc.

A crack in the manifold may be injesting extra air and messing with the fuelling slightly (commanded by the o2 sensor) so ought to be fixed.

A mile at slow ish speeds and load even with a failed coil pack wouldnt melt the cat, however about 3 miles at motorway speeds will!

I expect you will find a simple explanation evetually!!

Tim..

There didn't seem to be anything obstruting the air upto the throttle body, I removed all the tubing up to that point and it looked fine. The thick breather was OK too. I didn't take the inlet manifold off as the engine was too hot to start fiddling around the back of it!

I don't think my crack repair (with a manifold repair kit) has quite held up, so I'll need to replace the manifold (which I was going to do anyway). Any ideas who might sell one at a non-dealer price (£150)?

Can't go at motorway speeds with a failed coil pack ;)

I hope so, they usually end up as something simple.

Was the Cat and the rest of the exhaust replaced at the same time? As Tim said it sounds like a blocked exhaust so if the rest of the system was "older" than the cat (but still fairly new), then the failed cat could have sent broken bits backwards and created a blockage in the rear sections.

Regards, Graham L

The whole system (cat, mid and back section) were all new and replaced at the same time. I decided to get under the car on Friday and remove the cat to have a look. Sure enough took the thing off and the insides were rattling around, so its certainly the cause of the problem. I assume some of the cat's honeycomb has clogged the other boxes to some extent, but they were too awkward to remove. Looks like I'll have to go back to the garage and have a quiet word about the condition of the new exhaust system they fitted!