Arrrrgghhhhh - Power Loss at High RPM!!!!

[Captain_Beaky]

Hi all - The merriment of the festive season has been soured for me a little as i'm experiencing a frustrating power loss at high RPM.

The symptoms are as follows: 1)Different 'quiet muffled' exhaust note at low RPM - 2) Brash Gargling type noise at high RPM - 3) Slight loss of power over 4000RPM

I've also noticed a new metallic rattle from the exhaust system and wonder if this could be CAT problems. Any input most welcome!!!

[S1 Hunter]

Rover engine?

[Captain_Beaky]

Yes - sorry, should've said - 1998 S1 with 74k on the clock.

[JonRB]

HT leads?

I had a lumpy crackling misfire about 5k revs in the Chimaera that turned out to be heat-damaged HT leads.
Replaced the leads and it revs all the way to the rev limiter now.

Obviously different engines, but could be worth a go.

[Captain_Beaky]

mmmm possible - but there is no misfire or crackle, just a noticable lack in power - it just seems to struggle past 4000 rpm??? Will try though as it is a relativley cheap option!!!

Anyone had experience of CAT failure??? Is this even possibly the problem???

[uldis]

That's a possibility.

Also other possibilities are: collapsed air filter. clogged fuel filter, collapsed CAT, collapsed silencer, bad sparkplug leads, bad sparkplug(s), cracked exhaust manifold.

Check and report

[Captain_Beaky]

That's a pretty long list!!!!!

Would the CAT make a metallic rattle if it was on the way out??? It's definitely making a new noise, which is not the normal 'tizz' - it's more a metallic sound rather than metal on fibreglass.

In addition to this I noticed that when completely cold it was fine but on the 3rd or 4th trip up to the red line, the power loss became noticable again??? Does this narrow it down at all???

[uldis]

Hmmm, rich engines perform better cold. They start misbehaving when warm.

Maybe you should start looking at the air filter, if anything is clogging it (big leaves, small animal inside, mud)

I don't think a CAT would rattle, they're nomally ceramic, so they melt inside after prolongued high-rpm use.
The backbox is more likely to rattle (baffles).
Check this after the filter.

[Captain_Beaky]

Thanks for the tip off - I really hope it's something as easy as a few leaves in the cold air box!!! Oh well fingers crossed and happy christmas to all!!!

[Arno]

Captain_Beaky said:

Would the CAT make a metallic rattle if it was on the way out??? It's definitely making a new noise, which is not the normal 'tizz' - it's more a metallic sound rather than metal on fibreglass.

Yes.. When the ceramic element in the cat breaks up (happens sometimes) it gets loose and make a 'rattling metal can' noise.

A chunk of material can get disloded and wedged into the exit pipe of the cat and (partially) block the exhaust flow, restricting it.

You may want to remove the cat for inspection as the ceramic fragments and dust (if the core is indeed breaking up) will now end up in your silencer and thi can get clogged up too, unless you have a straight-through design sport exhaust (eg. eliseparts one)

Bye, Arno.

[fergusd]

Arno said:

Yes.. When the ceramic element in the cat breaks up (happens sometimes) it gets loose and make a 'rattling metal can' noise.

Yes indeed, see this a couple of times . . .

Fd

[awtong]

I had a cat break up but not on the elise. Symptoms on that were a metallic rattling and a loss of power. Seemed noticably worse as the engine got warmer. IIRC it also gave a slight knocking noise as the gases tried to escape

HTH

Andy

[Captain_Beaky]

Looks like that is indeed the favourite option then as the airbox was clear. Oh well - Am thinking get a 2nd hand CAT from EBay or some such similar and use it exclusively for MOT time to preserve its life. Of course this would mean the purchase of a CRP for the interim periods (and a few bonus BHP's if i'm lucky!!!)

[uldis]

Hold on before buying, are you not going to check it first?

Besides, if you really need to buy one, check here first:
www.cats-direct-shop.co.uk/