boost leak? blocked cat? seized pulley?

[-=DV=-]

ok ladys and gents ive been having an issue with my 165 over the last couple of days and it goes as follows, as i hit the gas, she spools up as per normal, until she hits around 4 psi, then its somewhat like hitting a brick wall, and u start hearing a loud whurring type noise (not a spool type wurr, but more like the turbo pressurising and pressure pushing back through it, or something like that anyway) acceleration violently drops off, until you hit about 4 grand, where intake pressure suddenly drops off around 3-4 psi.

now theres a few things im thinking about blaming for this, but with very limited time to work on my car these days i want to pinpoint what its most likely to do so i dont waste valuable time that could otherwise be spent doing overdue assignments or studying for exams. so here goes.

im thinking ive got myself some pesky boost leaks (although it doesnt feel or seem like other leaks ive had, this is just a weird hunch)
maybe whats left of my cat has finally collapsed/melted and its almost completely blocked, making breathing extremely hard,
or the bearing in my a/c pully has been on the way out for some while now, possibly it has finally seized and its just putting THAT much load on the engine?(would really explain the wurring noise im hearing)


any ideas?
thanks in advance

[oldcorollas]

boost leak wouldn't be a solid wall...just less thru rev range.. unless it was a pipe missing kinda leak.... but then turbo would spin easier..

pulley? if a pulley has siezed and the belt is slipping on it.. you WILL smell it

from this list, i vote cat collapse.. sounds similar to one that was psted relatively recently...

can you pull off that section of exhaust and shine a torch in? or even just let it down far enough to shine in and see? (miror and handy positioning?)

if you could measure the exhaust pressure (sayy.. with a itting on the O2 sensor hole and some silicon tubing) you could tell pretty quick if it was the cat.

[-=DV=-]

thanks mate, do any other possibilities spring to mind, that my inexperience may have led me to not even consider? or does the blocked cat prettymuch hit the nail on the head for the described symptoms?, i was more leaning towards the blocked cat aswell, as i sort of do have a habit of mixing metho and various octane boosters and such in my petrol...ive heard that metho isnt ur cats best friend....

[-=DV=-]

also what am i looking for exactly when i have a look in there, ive never had the oppertunity to inspect a healthy cat so i dont really know exactly what im comparing it against?, cheers

[Andrew162]

On a healthy cat (what I've seen before), you'll see hundreds of square holes kind of like on a flyscreen grille but about double the size. Each of these holes will extend right the way from beginning of cat to end. On a not-so-healthy cat I'm guessing that you'd have a bit of a collapse somewhere in this section. If you shone a torch into a blocked or collapsed cat, you won't get much (or any) light coming out the other end.

[Hydra]

Also, make sure the header -> turbo bolts/nuts are done up still, and no leak exists there. I was getting similar problems and my front turbo was missing 2 nuts on the flange!! nfi how they worked their way off but they wont ever again... loctite!

[oldcorollas]

this is typical. (and also here http://www.catalytic-converters.com/newcat.htm)

[-=DV=-]

thanks for the help guys, +rep all around.im pretty sure it is the cat, havnt had a good chance to pull it all apart and have a look....but i thaught the easiest way of testing would be to pull the O2 sensor out (its before the cat) and go for a quick drive (now i know its sorta naughty, but it was the easiest way to check) so anyway despite running on completely effed up mixtures and throwing away all the other little goodies that having an oxy sensor helps you out with, it ran ALOT better, it didnt feel so choked as soon as it made any decent boost or at higher rpm, so i guess the cat is getting gutted tomorrow and a high flow cat put in after the flex pipe.......

~edit~just thaught id add, removing the o2 sensor left a gaping big hole before my cat, giving the exhaust somewhere to flow, incase any1 was wondering wtf my logic behind it was lol

[LeeRoy]

Cats don't normally just colapse, they slowly die - i've shat 2 of em now. Firstly it should rattle at a harmonic rpm if not rattle constantly, then after a while it will clog up and jam in the hole and stop rattling. However, in the 2 i have killed both have rattled heaps, then got quiter, and in the end just rattle at around 3k rpm.

Get under the car and hit the cat and listen for rattling by hitting it. Ps it will be hot if youve been driving so you might need some riggers gloves.

- LeeRoy

[30psi 4agte]

havent run over something or hit anything lately ?

[3sgte]

ST 165 have a rubber flange at the throttle body that is known to split and leak under boost.

That would be my first guess.

As for a bad cats, that is a possibility. The bad ones that I saw (1x 185, one MR2) were still intact, but the holes on the in side of the cat were blocked.

Seemed to go hand in hand with cooked exhaust valve seals.

[EldarO]

ok ladys and gents ive been having an issue with my 165 over the last couple of days and it goes as follows, as i hit the gas, she spools up as per normal, until she hits around 4 psi, then its somewhat like hitting a brick wall, and u start hearing a loud whurring type noise (not a spool type wurr, but more like the turbo pressurising and pressure pushing back through it, or something like that anyway) acceleration violently drops off, until you hit about 4 grand, where intake pressure suddenly drops off around 3-4 psi.

now theres a few things im thinking about blaming for this, but with very limited time to work on my car these days i want to pinpoint what its most likely to do so i dont waste valuable time that could otherwise be spent doing overdue assignments or studying for exams. so here goes.

im thinking ive got myself some pesky boost leaks (although it doesnt feel or seem like other leaks ive had, this is just a weird hunch)
maybe whats left of my cat has finally collapsed/melted and its almost completely blocked, making breathing extremely hard,
or the bearing in my a/c pully has been on the way out for some while now, possibly it has finally seized and its just putting THAT much load on the engine?(would really explain the wurring noise im hearing)


any ideas?
thanks in advance

mate had a silicon joiner pop off, colossal hole in the intake, his car wouldnt rev over 3k, just because it was overfuelling so much.

that said, yours is making boost, check your exhaust.

Eldar.O.