Need help noise from catalyic converter

[kalaydjian]

On my 90 se I hear a rattling noise coming from the back I think it is the cat or muffer, but the muffler is 6 months old, I have chiped my car with s4s chip can it be the screens inside the catalyic converter are broken or is it something else, it make the sound when the car is cold but when it warms up the rattling sound decreases or when I shift from 3 to neutral or 2 neutral I can hear the rattling noise, can anyone help me thank you Alain.

[h2dca]

Possibly the Back Pressure Valve, this goes between the exhaust and Cat and does develop a rattle. The BPV is there to restrict the exhaust gases to warm up the Cat quicker for emission purposes. There is info on this on Esprit World website, what it does, removing it etc. All three of my Esprits developed a rattle at the BPV hence it will be going in the bin soon when my new exhaust and spacer arrives.

[stone]

It's also possible that your chip change has led to excess fuel entering the cat and the ceramic monolith has broken down due to heat.(Assuming the monolith is ceramic) Alternatively the blanket that holds the core within the cat casing can sometimes disintegrate causing the core to move within the casing.HTH

[igreenrover]

I had a problem last year that led to the Cat overheating, this broke out the rear of the two matrix cores and the symptoms were exactly as you have. I took the BPV valve out and could see the rear matrix lose in the pipe – it was also blocking the pipe on occasion and causing intermittent restriction thus intermittent lack of boost.

I broke it out with a large screwdriver and left the front core in place, its still fine now.

Gareth


>> Edited by igreenrover on Wednesday 19th May 10:32

[rlearp]

I also found my the modified chips run rich and over a few months my cat was in pieces. I didn't care as I pulled the entire exhaust anyhow and built a new one. But when I did get it off my converter internals were fractured. I don't know if the chip caused this to happen, but I have seen overly rich mixures cause problems with cats overheating before so I assume it could be the case.

Ron

[lotusguy]

Yup,

It's the Cat matrix going Bye-Bye... ask me how I know... Happy Motoring! ...Jim'85TE

[AZ88Turbo]

Yep, cat has gooooneeeeeeee.....

Gut that pussy!!!!! You'll never regret it (not that I would know of course as that is a bit naughty )

Oh, and if you insist on getting a new one; try Midas, I'm not sure what the law requires on a 90 in California but on my 88 in AZ a new cat was only like $200 fitted, if you go to Lotus you'll spend about 1k.


Mark - 88 Turbo

[rlearp]

Even better purchase the cat on Ebay - there are lots of brand name high flow cats there for $50-$75. Then cart it to the muffler shop for some welding if you can't weld - you'll get out for under $100 I bet and have a better flowing cat.

I will get to do the cat vs. hp experiment soon. I will dyno the new turbo with a new exhaust and no cat. After that, I have a high flow 3" cat that I'll put on with a bolt in flange for emissions testing so I'll run it with that on the rollers to in order to roughly see what the differences are.

[incautious]

Does indeed sound like your cat has bitten the dust. If you indeed need a new cat and must replace it because of emission laws try the maganflow cat # 54306
it's a 2 1/2" high flow unit that will fit on the esprit.

[cnh1990]

Even if the cat matrix is not the actual there is a mounting ring on the wall of the cat. It has 2-3 spot welds that hold the cat matrix in place. A lot of people ram out the matrix and a lot of times this ring is left in place. Over time the welds breaks of from heat and a loose peice of metal will vibrate inside of the cat.

The other is the EBPV that others have stated. When the car is running use a rag and swing the valve and see if the rattle changes or goes away. Also with the EBPV removed take a look with a light up into the cat to see if anything is loose in there.