95 Camaro Z28 - power loss

1995 Chevy Camaro Z28, 350V8, Engine Code "P" (in VIN),
109k miles, no modifications (except for Flowmaster).

Driving Florida to Texas - after about 550 miles of
constant driving (75-80mph), stopping only for gas,
as I was climbing the bridge over the Mississippi
(in Baton Rouge), the car sputtered slightly, then
appeared as if she were running on four cylinders.

The oil pressure reading dropped some and the temp
gauge began to climb past the half-way mark (was
normally hovering just above the 1/4 mark). On the
descent side of the bridge, I coasted off the freeway.
I open the hood and saw nothing out of the ordinary;
I checked the oil and water levels and both are fine.

I decided to let her rest for an hour and then see
how she acted afterwards. Over an hour pass and I
crank her up and she appears to be fine. So I take
off and pass through Lafayette and just shy of Lake
Charles (another 125 miles), she starts to hesitate
again. So I decide to stay the night and try again
during the morning time.

The next morning I start her up and drive on in to
Houston (~150 miles). Just as I get into Houston, she
starts running rough again. I also notice that gas
mileage is rapidly degrading.

If I mash down on the gas, I hear a "wheezing" noise
from under the hood, but goes away when I let up on
the gas pedal and am cruising along. I only hear the
wheezing noise when accelerating. As I've also said,
when I mash on the gas, she has almost no power, with
the strange exception when she gets up around 60-65 MPH
(which I think is around 2500-3000 RPM), then she
"clears up" and runs fine.

I limp home around 3pm and let her rest until the next
day. When I started her up again she seems to be fine
idling, but [now] when I put her in Drive and drive off,
I get this "running on four cylinders" effect, plus the
wheezing noise when I accelerate.

I'm pretty good at troubleshooting pre-computerized cars,
and have done all my own work on all my vehicles, but
this is my first car that is ECU-controlled. My motocycle
(99 Hayabusa) is ECU-controlled and if I am having
problems, I can use a paper-clip to jumper the service
connector and get a numeric readout on the dash to help
diagnose the problem. AAMOF, the motorcycle exhibited very
similar traits and I put a [variable] resistor inline on
the "outside ambient" temperature sensor, to trick the
engine into thinking it was cooler outside. The engine
would run terribly and eventually shutdown, until I made
this modification.

Is there a way I can jumper the service plug on the Z to
get a readout on the dash/etc? Is there an instrument
I can get to help with this? I've done some research on
my problem, but I've read conflicting answers, from a
fautly engine-temp sensor to a faulty ECU. How about a
good shop manual for the Z? Any thoughts on the problems
she is exhibiting?

In my googling, I've also discovered that one of the first
[simple] mods people make to this car, in high-temperature
areas, is to switch to a 160* thermostat and adjust the
ECU to turn the fans on at 160* (versus the 180* factory).
Sounds reasonable to me, unless someone has other thoughts
on this.

"mst" > wrote in message
...
> 1995 Chevy Camaro Z28, 350V8, Engine Code "P" (in VIN),
> 109k miles, no modifications (except for Flowmaster).
>
> Driving Florida to Texas - after about 550 miles of
> constant driving (75-80mph), stopping only for gas,
> as I was climbing the bridge over the Mississippi
> (in Baton Rouge), the car sputtered slightly, then
> appeared as if she were running on four cylinders.
>
> The oil pressure reading dropped some and the temp
> gauge began to climb past the half-way mark (was
> normally hovering just above the 1/4 mark). On the
> descent side of the bridge, I coasted off the freeway.
> I open the hood and saw nothing out of the ordinary;
> I checked the oil and water levels and both are fine.
>
> I decided to let her rest for an hour and then see
> how she acted afterwards. Over an hour pass and I
> crank her up and she appears to be fine. So I take
> off and pass through Lafayette and just shy of Lake
> Charles (another 125 miles), she starts to hesitate
> again. So I decide to stay the night and try again
> during the morning time.
>
> The next morning I start her up and drive on in to
> Houston (~150 miles). Just as I get into Houston, she
> starts running rough again. I also notice that gas
> mileage is rapidly degrading.
>
> If I mash down on the gas, I hear a "wheezing" noise
> from under the hood, but goes away when I let up on
> the gas pedal and am cruising along. I only hear the
> wheezing noise when accelerating. As I've also said,
> when I mash on the gas, she has almost no power, with
> the strange exception when she gets up around 60-65 MPH
> (which I think is around 2500-3000 RPM), then she
> "clears up" and runs fine.
>
> I limp home around 3pm and let her rest until the next
> day. When I started her up again she seems to be fine
> idling, but [now] when I put her in Drive and drive off,
> I get this "running on four cylinders" effect, plus the
> wheezing noise when I accelerate.
>
> I'm pretty good at troubleshooting pre-computerized cars,
> and have done all my own work on all my vehicles, but
> this is my first car that is ECU-controlled. My motocycle
> (99 Hayabusa) is ECU-controlled and if I am having
> problems, I can use a paper-clip to jumper the service
> connector and get a numeric readout on the dash to help
> diagnose the problem. AAMOF, the motorcycle exhibited very
> similar traits and I put a [variable] resistor inline on
> the "outside ambient" temperature sensor, to trick the
> engine into thinking it was cooler outside. The engine
> would run terribly and eventually shutdown, until I made
> this modification.
>
> Is there a way I can jumper the service plug on the Z to
> get a readout on the dash/etc? Is there an instrument
> I can get to help with this? I've done some research on
> my problem, but I've read conflicting answers, from a
> fautly engine-temp sensor to a faulty ECU. How about a
> good shop manual for the Z? Any thoughts on the problems
> she is exhibiting?
>
> In my googling, I've also discovered that one of the first
> [simple] mods people make to this car, in high-temperature
> areas, is to switch to a 160* thermostat and adjust the
> ECU to turn the fans on at 160* (versus the 180* factory).
> Sounds reasonable to me, unless someone has other thoughts
> on this.
Google again, using your symptoms, and you'll probably find what you're
experiencing is a case of catalytic convertor problems--more precisely,
clogging & prohibiting exhaust-flow as it heats up. Solution: replace cat.
conv. HTH & good luck, s

("sdlomi2" >) scribbled:

> Google again, using your symptoms, and you'll probably find what you're
> experiencing is a case of catalytic convertor problems--more precisely,
> clogging & prohibiting exhaust-flow as it heats up. Solution: replace cat.
> conv. HTH & good luck, s

Thanks for the feedback!! That's certainly something I hadnt
thought of. And after reading a couple of sites about this,
the car does seem to exhibit the same traits as a clogged
converter would indicate.

Would it make sense to get a straight-thru pipe, temporarily
replacing the cat to validate that it's bad? Or will the ECU
"note" the missing converter and the engine still run badly?

I'm hoping to avoid replacing parts until the problem goes away

I've read one page that suggests taking vacuum readings at
idle and at 1500 RPM, but *which* vacuum source do you take
the readings from?

I also find it odd that a cat would clog so prematurely - most
of my past vehicles have had upwards of 200k miles with no issues.

ITS YOUR COILS YOU HAVE THREE OF THEM IN A PACK MY NIEGHBOR HAD THE
SAME PROBLEM AND 2 OF HIS COILS WHERE BAD PROBLEM SOLVED AFTER HE
CHANGED HIS COILS

"mst" > wrote in message
...
> ("sdlomi2" >) scribbled:
>
>> Google again, using your symptoms, and you'll probably find what
>> you're
>> experiencing is a case of catalytic convertor problems--more precisely,
>> clogging & prohibiting exhaust-flow as it heats up. Solution: replace
>> cat.
>> conv. HTH & good luck, s
>
> Thanks for the feedback!! That's certainly something I hadnt
> thought of. And after reading a couple of sites about this,
> the car does seem to exhibit the same traits as a clogged
> converter would indicate.
>
> Would it make sense to get a straight-thru pipe, temporarily
> replacing the cat to validate that it's bad? Or will the ECU
> "note" the missing converter and the engine still run badly?
>
> I'm hoping to avoid replacing parts until the problem goes away

Replace the catcon. A straight pipe would allow the engine to run, but the
problem is the catcon provides some backpressure that the straight pipe
doesn't. The engine is expecting to see that backpressure. If it's not there
it won't run right. (rough idle)

Pick one off of a lo-miles car at a junkyard.

"mst" > wrote in message
...
> ("sdlomi2" >) scribbled:
>
>> Google again, using your symptoms, and you'll probably find what
>> you're
>> experiencing is a case of catalytic convertor problems--more precisely,
>> clogging & prohibiting exhaust-flow as it heats up. Solution: replace
>> cat.
>> conv. HTH & good luck, s
>
> Thanks for the feedback!! That's certainly something I hadnt
> thought of. And after reading a couple of sites about this,
> the car does seem to exhibit the same traits as a clogged
> converter would indicate.
>
> Would it make sense to get a straight-thru pipe, temporarily
> replacing the cat to validate that it's bad? Or will the ECU
> "note" the missing converter and the engine still run badly?
>
> I'm hoping to avoid replacing parts until the problem goes away
>
> I've read one page that suggests taking vacuum readings at
> idle and at 1500 RPM, but *which* vacuum source do you take
> the readings from?
>
> I also find it odd that a cat would clog so prematurely - most
> of my past vehicles have had upwards of 200k miles with no issues.
mst, I agree with Bob M. And since you will ultimately have a muffler
shop replace the cat when (if?) found bad, get a muffler shop to verify the
condition of yours. They have the capability. Exhaust has long been a job
we diy'ers(at least, I) can't economiclly "take away" from the specialty
shops.
Good luck. s

mst wrote:
>
> 1995 Chevy Camaro Z28, 350V8, Engine Code "P" (in VIN),
> 109k miles, no modifications (except for Flowmaster).
>
> Driving Florida to Texas - after about 550 miles of
> constant driving (75-80mph), stopping only for gas,
> as I was climbing the bridge over the Mississippi
> (in Baton Rouge), the car sputtered slightly, then
> appeared as if she were running on four cylinders.

Good advice from others.
You might want find out why the cat went bad (if it did).
Dumping raw fuel into the exhaust will kill a new cat in
no time at all.
On the vac question - use manifold vac.

Before I would suspect it being the coils, I would ohm them out and
check a repair manual to see if they match up. I read in a article
about cataylic converters from an automotive repair book. It said that
converters don't commit sucicide, thier is a root cause and if you just
replace the converter (if this is your problem) the converter can
become bad again later. Does you exhust manifold get cherry red ?
Because if it does, this means there is a restriciton in your exhust.
Also what is your vacuum gauge reading? 17-22 Hg (mercury) is normal
vacuum but has to be steady. Anything less or more than there is a
problem. Anyways if it is the converter there is something else work
up stream. More testing should be done. Just for a comformation I
would do a compresion test when the engine has been warmed up real
good. But a mechanic shop should be able to find this out using an
scanner or engine analyzer.

(mst >) scribbled:

> 1995 Chevy Camaro Z28, 350V8, Engine Code "P" (in VIN),
> 109k miles, no modifications (except for Flowmaster).

I decided this morning I would yank the cat converter
and do a visual inspection to see if it is clogged up.

I crawl under the car and to my amazement, the cat is
not a single unit unto itself, but consists of the two
upstream exhaust pipes P/N '510413' in the image:
http://www.rockauto.com/ref/Walker/Detail.html?0325.gif
(the pipes are welded to the inlet on the cat).

So I guess my next step is to do a vacuum test and hope
that it confirms a [potentially] bad cat.

On another note, I wanted to check for any error codes,
so I grab a paper clip to jumper the diagnostic connector
and it turns out this 1995 has the 16-pin connecter,
versus the 12-pin, and so I can not read the codes, as
is described he http://www.roberthancock.com/efi/
(scroll to the diagram) - a scanner is required.

Is there a way to determine if this 1995 uses an OBDII
system or OBDI? Any recommendations on a scanner?

"mst" > wrote in message
...
> (mst >) scribbled:
>
>> 1995 Chevy Camaro Z28, 350V8, Engine Code "P" (in VIN),
>> 109k miles, no modifications (except for Flowmaster).
>
> I decided this morning I would yank the cat converter
> and do a visual inspection to see if it is clogged up.
>
> I crawl under the car and to my amazement, the cat is
> not a single unit unto itself, but consists of the two
> upstream exhaust pipes P/N '510413' in the image:
> http://www.rockauto.com/ref/Walker/Detail.html?0325.gif
> (the pipes are welded to the inlet on the cat).
>
> So I guess my next step is to do a vacuum test and hope
> that it confirms a [potentially] bad cat.
>
> On another note, I wanted to check for any error codes,
> so I grab a paper clip to jumper the diagnostic connector
> and it turns out this 1995 has the 16-pin connecter,
> versus the 12-pin, and so I can not read the codes, as
> is described he http://www.roberthancock.com/efi/
> (scroll to the diagram) - a scanner is required.
>
> Is there a way to determine if this 1995 uses an OBDII
> system or OBDI? Any recommendations on a scanner?
Think you'll find your car is a "strange" creature in that respect: it
has an ODII-connector but uses an OBDI-system(I've got that same
engine/computer in a 1986 S-10 Blazer.). It even takes a special connector
for scanners, different from a 1994 or a 1996. HTH, s