loose pre cats. Symptoms?

[pullingpower]

What sort of symptoms would loose pre-cats cause? Just failed MOT badly on emissions which will need looking into further. I also notice a regular metallic rattle that appears to come from in front of the dash or below the car, could this be due to the pre cats??????

[tahiti450]

Pre-cats have no impact on the emissions test, their only function is to clean the exhaust emmissions during start and warm-up before the main cat lights up. If the emission test has been conducted properly , i.e: with adequate time for main cat to warm-up , then if the CO is significantly too high and Hydrocarbons are also that suggests failure of the main cat. Bear in mind that removing the pre-cats completely has no effect on the emission test done as part of the MOT since this only assesses emissions with a warm engine. You should also be confident that the test has been done correctly by someone properly trained (i.e not by the tea boy / gofer).

[zippee]

My manifolds are de-catted stainless ones from ACT and it sailed thorugh the emissions test when I had it MOT'd beginning of this month. I believe its only removal of the main Cats further down the system that can affect the emissions.
May be worth getting your local dealer/indie to check the mixture and possibly the lambdas.

Edited to add;
You also mention a mettalic rattle (does this also sound like a ticking noise), is it possible you have either a leaky manifold or manifold gasket?

>> Edited by zippee on Wednesday 15th June 12:41

[pullingpower]

Thanks; it's not a tapping, it's a rattle/clanging as if the exhaust was loose but it ain't, I've checked. Worse over bumps, round bends etc.

[trinitycall]

pullingpower said:

Thanks; it's not a tapping, it's a rattle/clanging as if the exhaust was loose but it ain't, I've checked. Worse over bumps, round bends etc.

could be a noisy shock. They sound like a pea in a tincan over bumps.

edited for typo

>> Edited by trinitycall on Wednesday 15th June 12:54

[hughesie2]

pullingpower said:

Thanks; it's not a tapping, it's a rattle/clanging as if the exhaust was loose but it ain't, I've checked. Worse over bumps, round bends etc.

that sounds like em, they shrink and then rattle, its really really annoying !!

[pullingpower]

hughesie2 said:

pullingpower said: Thanks; it's not a tapping, it's a rattle/clanging as if the exhaust was loose but it ain't, I've checked. Worse over bumps, round bends etc. that sounds like em, they shrink and then rattle, its really really annoying !!

Are you referring to the pre cats or the shocks?