i have a 94 grand prix and just changed a timing belt on it.it's the 3.4
dohc engine.problem now is it ran fine for about 10 minutes then upon it in
idling, i gave it some gas by way of pulling on the throttle under the hood
and there appeared to be a loud hiss from the front of engine then and
engine started to idle roughly,the cat also is making a lot of noise, like
it's all broken up inside,it wasn't this bad before belt went.but i had test
run the car several times adjusting timing belt aand it ran several times
with cams out of time,if the cat was going bad to begin with,could the
engine out of time running really destroyed it????just what are the signs of
a bad cat????what was the hiss then rough idle????is the cat bolted up to
where i can replacwe myself???

Um, get underneath and see if you can get to it. Put a vacuum gage on the
engine see if it drops way off under power, indicating possible clogged cat,
or put a exh. back pressure gage in the o2 port, 1.5 to 2.0 psi max.
"robert -wanda fox" <res0ta8b@verizon.net> wrote in message
news:Am8Fg.13342$9v1.8412@trnddc07...
>i have a 94 grand prix and just changed a timing belt on it.it's the 3.4
> dohc engine.problem now is it ran fine for about 10 minutes then upon it
> in
> idling, i gave it some gas by way of pulling on the throttle under the
> hood
> and there appeared to be a loud hiss from the front of engine then and
> engine started to idle roughly,the cat also is making a lot of noise, like
> it's all broken up inside,it wasn't this bad before belt went.but i had
> test
> run the car several times adjusting timing belt aand it ran several times
> with cams out of time,if the cat was going bad to begin with,could the
> engine out of time running really destroyed it????just what are the signs
> of
> a bad cat????what was the hiss then rough idle????is the cat bolted up to
> where i can replacwe myself???
>
>



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Well, the hissing sounds like to me a vacuum leak. As for the cat, if you
hear a rattle noise from it and you checked your exhaust to make sure there
are no broken wields or broken mounts then I would have it replaced.Very
expensive. The cat is hard to replace.You will have to disassemble the
exhaust. Most cats are mounted behind the engine right under the passenger
floor board.As for the timing, if it is off too far you can damage the
cylinders and it will run very bad.I hope this helps.Good luck.

--
Todd A. Delk
"robert -wanda fox" <res0ta8b@verizon.net> wrote in message
news:Am8Fg.13342$9v1.8412@trnddc07...
>i have a 94 grand prix and just changed a timing belt on it.it's the 3.4
> dohc engine.problem now is it ran fine for about 10 minutes then upon it
> in
> idling, i gave it some gas by way of pulling on the throttle under the
> hood
> and there appeared to be a loud hiss from the front of engine then and
> engine started to idle roughly,the cat also is making a lot of noise, like
> it's all broken up inside,it wasn't this bad before belt went.but i had
> test
> run the car several times adjusting timing belt aand it ran several times
> with cams out of time,if the cat was going bad to begin with,could the
> engine out of time running really destroyed it????just what are the signs
> of
> a bad cat????what was the hiss then rough idle????is the cat bolted up to
> where i can replacwe myself???
>
>

What about removing it? Or if you have air care, put a pipe down the
middle of it....problem solved


In article <Am8Fg.13342$9v1.8412@trnddc07>, res0ta8b@verizon.net says...
> i have a 94 grand prix and just changed a timing belt on it.it's the 3.4
> dohc engine.problem now is it ran fine for about 10 minutes then upon it in
> idling, i gave it some gas by way of pulling on the throttle under the hood
> and there appeared to be a loud hiss from the front of engine then and
> engine started to idle roughly,the cat also is making a lot of noise, like
> it's all broken up inside,it wasn't this bad before belt went.but i had test
> run the car several times adjusting timing belt aand it ran several times
> with cams out of time,if the cat was going bad to begin with,could the
> engine out of time running really destroyed it????just what are the signs of
> a bad cat????what was the hiss then rough idle????is the cat bolted up to
> where i can replacwe myself???
>
>
>

A good blast down the highway should clear the cat of any fuel
residue. A new Monolith cat is fairly cheap = hundreds less than dealer
item, so to speak.

The rough running could be a vacuum leak, or similar pesty problem
Some cars use an air reaction system to keep cat hot by supplying
bonus oxygen via a belt driven pump. The hiss could be compressed air ?