Driveability problems from an exhaust leak?
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Joined: Jan 2001
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From: Belleville, IL USA
You already know I would say yes.
Leaks will cause problems even with a carburetor. I would think worse if it's before an O2 sensor.
At part throttle when backpressure is low, the exhaust travelling past the leak acts like airflow in a venturi creating a low pressure at the leak and pulling in fresh air.
The fresh air burns with the fuel in the exhaust creating turbulence, backpressure, and disrupts and pulse-tuning you may have working for you in the exhaust (especially with headers).
The result of this is poor throttle response and a loss of torque down low. At full throttle the exhaust becomes evenly pressurized which pretty much negates the effects of the leaks... unless they are bad.
Leaks will cause problems even with a carburetor. I would think worse if it's before an O2 sensor.
At part throttle when backpressure is low, the exhaust travelling past the leak acts like airflow in a venturi creating a low pressure at the leak and pulling in fresh air.
The fresh air burns with the fuel in the exhaust creating turbulence, backpressure, and disrupts and pulse-tuning you may have working for you in the exhaust (especially with headers).
The result of this is poor throttle response and a loss of torque down low. At full throttle the exhaust becomes evenly pressurized which pretty much negates the effects of the leaks... unless they are bad.
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Joined: Dec 1999
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From: Reno, NV
Car: yep
Engine: uhuh
Transmission: sure does
If the ex. leaks by the manifold and it burns a wire...yes.
An ex. leak in front of the O2 sensor will cause a problem, but I don't know if this would equate to your drivability problem.
What kind of problem do you have??
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ASE Mechanic/Machinist/Smog Tech
1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R
R.I.P. #3
My favorite quote about D.E. "He can see air"
[This message has been edited by Engineboy (edited February 28, 2001).]
An ex. leak in front of the O2 sensor will cause a problem, but I don't know if this would equate to your drivability problem.
What kind of problem do you have??
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ASE Mechanic/Machinist/Smog Tech
1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R
R.I.P. #3
My favorite quote about D.E. "He can see air"
[This message has been edited by Engineboy (edited February 28, 2001).]
Thread Starter
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Joined: Oct 2000
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From: Tennessee
It idles rough and shakes once it's warmed up, and sounds raspy under the hood up to about 2200RPM. At higher RPM's (above 3000) it seems to operate fine. Sometimes it stalls when I put it in reverse.
I've done a full tune up including O2 sensor, fuel pressure test, injector resistance, stock t-stat, TPS and MAP check, rebuilt distributor, CTS, getting ready to replace IAC valve, cleaned throttle body, valve stem seals and valve springs, compression test, vacuum checks and test for vacuum leaks. No codes.
The only suspects I have left are the alternator and battery, plugged cats (which wouldn't make sense for a low RPM problem), EGR, imbalanced injectors, and that damned exhaust leak I discovered via a large rusty water puddle under the driver's side of the engine when it was cold the other day. No coolant in the water. The misery of it all is I can't get it to duplicate the puddle again since it's warm outside now.
It's a '90 IROC 350 TPI with only 39000 miles. The leak before the O2 sensor theory sounds good, if in fact this would cause my problem. I am grateful for any help you guys might give me. Another strange fact, it used to gurgle through the exhaust when I would race it up and back off the throttle quick. I've since replaced it with a Dynomax cat-back and it doesn't seems to do it anymore (haven't driven it much yet, though).
I've done a full tune up including O2 sensor, fuel pressure test, injector resistance, stock t-stat, TPS and MAP check, rebuilt distributor, CTS, getting ready to replace IAC valve, cleaned throttle body, valve stem seals and valve springs, compression test, vacuum checks and test for vacuum leaks. No codes.
The only suspects I have left are the alternator and battery, plugged cats (which wouldn't make sense for a low RPM problem), EGR, imbalanced injectors, and that damned exhaust leak I discovered via a large rusty water puddle under the driver's side of the engine when it was cold the other day. No coolant in the water. The misery of it all is I can't get it to duplicate the puddle again since it's warm outside now.
It's a '90 IROC 350 TPI with only 39000 miles. The leak before the O2 sensor theory sounds good, if in fact this would cause my problem. I am grateful for any help you guys might give me. Another strange fact, it used to gurgle through the exhaust when I would race it up and back off the throttle quick. I've since replaced it with a Dynomax cat-back and it doesn't seems to do it anymore (haven't driven it much yet, though).
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Joined: Jan 2001
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From: Belleville, IL USA
Jethro,
when you let off the gas in gear it creates the low pressure again and the popping in the exhaust is the fresh air & excess fuel igniting.
leaks do not normally kill the engine though.
I have something for you in email.
ODB
when you let off the gas in gear it creates the low pressure again and the popping in the exhaust is the fresh air & excess fuel igniting.
leaks do not normally kill the engine though.
I have something for you in email.
ODB
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From: outerspace(maybe..pluto)?
yeah it causes problems. loss of hp and idle quality, and you could burn a wire! id get this fixed and soon the worst case is that you could burn a valve!!! that would suck!!!
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89 firebird formula
356 9:1 compression
comp cams xe262 cam
performer rpm intake
#1405 edlebrock 600
882 casting 202/160 valves
msd 6al
h.e.i. proform 50,000 volt vac. advance ditributor
700r-4 with 3.08 first gear and 3.23 posi 7 5/8 rear end.
b&m trans shift kit(will kill shifts...suck dong!!)
shorty heddman hedders with custom 3" pipe y-pipe back(no damn cat!) with 40 series flowmaster!
future mods: 406 roller REALLY REALLY REALLY RADICAL!!!!!
------------------
89 firebird formula
356 9:1 compression
comp cams xe262 cam
performer rpm intake
#1405 edlebrock 600
882 casting 202/160 valves
msd 6al
h.e.i. proform 50,000 volt vac. advance ditributor
700r-4 with 3.08 first gear and 3.23 posi 7 5/8 rear end.
b&m trans shift kit(will kill shifts...suck dong!!)
shorty heddman hedders with custom 3" pipe y-pipe back(no damn cat!) with 40 series flowmaster!
future mods: 406 roller REALLY REALLY REALLY RADICAL!!!!!
Senior Member
Joined: Jun 2000
Posts: 515
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From: Webster,Texas,USA
Car: 1990 Formula
Engine: 5.7 liter
Transmission: 700R4
hey Jeth,
an exhaust leak could also be confused by the ECM as sparkknock and over advance the timing and trip a code 43. been there and done that
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an exhaust leak could also be confused by the ECM as sparkknock and over advance the timing and trip a code 43. been there and done that
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From: Tennessee
Crap. Thanks a bunch guys and I reckon I need to get out there and find that leak today. Probably where I pulled the AIR system and plugged the manifolds with brass pipe plugs. Maybe I'll JB Weld 'em in this time 
.
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