Pressing gas while braking - is that ok?
 

My car (2001 Chev Impala) makes a kind of hissing noise while accelerating
(together with loss of acceleration power and worse gas mileage). It's
getting louder and louder. Many advices from the groups suggest it must be
from Catalytic Converter. But my dealer says it's not the converter based on
their test, and it's normal!!!!!!
The cat converter seems located in the middle part of the bottom. To be sure
it's the converter, can I do this way:
- get one person press gas pedal when the other foot on brake,
- get my ears to the ground close to the converter to listen........

If it's workable, could cause any damage to the car?

Simon wrote:

> My car (2001 Chev Impala) makes a kind of hissing noise while accelerating
> (together with loss of acceleration power and worse gas mileage). It's
> getting louder and louder. Many advices from the groups suggest it must be
> from Catalytic Converter. But my dealer says it's not the converter based on
> their test, and it's normal!!!!!!
> The cat converter seems located in the middle part of the bottom. To be sure
> it's the converter, can I do this way:
> - get one person press gas pedal when the other foot on brake,
> - get my ears to the ground close to the converter to listen........
>
> If it's workable, could cause any damage to the car?

In my experience, catalytic converters don't make a hissing noise ... or
any noise at all for that matter. If you hear a hissing noise, it's
probably something else ... like a vacuum leak or something. Pressing
the gas and the brake at the same time will burn something up ...
transmission, brakes or tires... or some combination of all 3.

"Simon" > wrote in message
...
> My car (2001 Chev Impala) makes a kind of hissing noise while accelerating
> (together with loss of acceleration power and worse gas mileage). It's
> getting louder and louder. Many advices from the groups suggest it must be
> from Catalytic Converter. But my dealer says it's not the converter based
> on their test, and it's normal!!!!!!
> The cat converter seems located in the middle part of the bottom. To be
> sure it's the converter, can I do this way:
> - get one person press gas pedal when the other foot on brake,
> - get my ears to the ground close to the converter to listen........
>
> If it's workable, could cause any damage to the car?

It surely sounds like an exhaust restriction--if not the cat conv., then
perhaps a collapsed interior wall of the exhaust- or tail-pipe. Haven't
experienced but one in recent years, altho' it was somewhat common on some
70's models.
Also check to ensure there is no crushing of one of the pipes from having
hit or *bottomed out* on something. HTH, s

On Thu, 8 Sep 2005 22:00:50 -0600, Simon > wrote:


>My car (2001 Chev Impala) makes a kind of hissing noise while accelerating
>(together with loss of acceleration power and worse gas mileage). It's
>getting louder and louder. Many advices from the groups suggest it must be
>from Catalytic Converter. But my dealer says it's not the converter based on
>their test, and it's normal!!!!!!
>The cat converter seems located in the middle part of the bottom. To be sure
>it's the converter, can I do this way:
>- get one person press gas pedal when the other foot on brake,
>- get my ears to the ground close to the converter to listen........

>If it's workable, could cause any damage to the car?


It's a *terrible* idea. You'll burn out your transmission and put terrible
stresses on the entire drive train. Pay the $60 diagnostic fee and have a
mechanic fix it.

The first thing you need is some logical troubleshooting skills.
Testing/replacing parts one by one is the "shotgun" approach and you'll be lucky
if you fix it for less than 5 times what a mechanic would charge. Replace ONE
part unnecessarily and you'll have already wasted more than the mechanic's
diagnostic fee and replace TWO components unnecessarily and you'll have wasted
the labor charge too.
Get a dealer shop manual and study the troubleshooting sections. They usually
have flowcharts so that any idiot can logicaly troubleshoot a car. Keep in mind
that the dealer shop manual will set you back upwards of $120. If you're not
serious about doing all your car repairs from this date on or not intending on
keeping the car for at least another 4 years, then it probably isn't worth it.
If you're cheap, you might want to have a look at the chilten's or hayne's
manuals. Often the chilten's is available at your public library. The problem
is that they try to cover too many models and years. When you see mention of
water cooling in a 70's VW bug, you know that the section was simply
cut'n'pasted from another manual.

Simon wrote:
> My car (2001 Chev Impala) makes a kind of hissing noise while accelerating
> (together with loss of acceleration power and worse gas mileage). It's
> getting louder and louder. Many advices from the groups suggest it must be
> from Catalytic Converter. But my dealer says it's not the converter based on
> their test, and it's normal!!!!!!
> The cat converter seems located in the middle part of the bottom. To be sure
> it's the converter, can I do this way:
> - get one person press gas pedal when the other foot on brake,
> - get my ears to the ground close to the converter to listen........
>
> If it's workable, could cause any damage to the car?

Even if you replicate the sound while under the car it could be coming
from a dozen differrent sources, so you will be no more ahead. Just
take the car to a competent dealer for a diagnosis.

Is this a trick question? If you put it in neutral. then for sure have
the person hold the brake, but if it is in park, then no issues.

A hissing and loss of power and crappie mileage can easily mean a vacuum
leak. Hissing is usually caused by air leaking.....

How are the heater controls? Do any of them act strange? Does the
cruise kick off? How about the brake pedal, feel normal?

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's


Simon wrote:
>
> My car (2001 Chev Impala) makes a kind of hissing noise while accelerating
> (together with loss of acceleration power and worse gas mileage). It's
> getting louder and louder. Many advices from the groups suggest it must be
> from Catalytic Converter. But my dealer says it's not the converter based on
> their test, and it's normal!!!!!!
> The cat converter seems located in the middle part of the bottom. To be sure
> it's the converter, can I do this way:
> - get one person press gas pedal when the other foot on brake,
> - get my ears to the ground close to the converter to listen........
>
> If it's workable, could cause any damage to the car?

"AZ Nomad" > wrote in message
...

>
> It's a *terrible* idea. You'll burn out your transmission and put
terrible
> stresses on the entire drive train. Pay the $60 diagnostic fee and have a
> mechanic fix it.

Apparently he already had it at the 'dealers'. But then, you said
'mechanic' ;>)

"Mike Romain" > wrote in message
...
> Is this a trick question? If you put it in neutral. then for sure have
> the person hold the brake, but if it is in park, then no issues.

Im with you, Mike...
In Park, you can rev it up a bit with no problem. In neutral, you could
also do it, but if it somehow
slipped into gear, your head could look like a pizza.

If you can't get it to sizzle this way, you could very carefully jack up the
drive wheels, and see if
you can reproduce it with the wheels turning freely. This is a good bit
more dangerous.

Use a long piece of heater hose as a stethoscope. Don't get your head or
other body parts where
you might get yourself hurt. Use jack stands, not coke bottle cases or
cinder blocks.

Of course, if you can find a competent mechanic, that would be a safer
technique.

> writes:

>If you can't get it to sizzle this way, you could very carefully jack up the
>drive wheels, and see if
>you can reproduce it with the wheels turning freely. This is a good bit
>more dangerous.

Hmm, is this a good idea? Seems like it would be tough on the CV joints with
the wheels just hanging there. Or did you mean something like putting
jackstands under the control arms.