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Mystery Smell

ZAL81

Well-known member
Joined
Feb 27, 2001
Messages
122
Location
Washington, MO.
Corvette
81 Charcoal Metallic 4-spd & 94 Red 6 spd vert
O.K. Lets see who can figure this one out. About a year ago I replaced my exhaust from the headers back - y pipes/converter/Dynomax mufflers- and since that time I'm getting a strange odor at certain time. When and only when I start my car after its completely cooled off , I get a "rotten egg" type odor. This only occurs if the car is stone cold at start-up and the choke is on fast idle. At the same time my check engine light will come on. Once the car drops off fast idle, the light goes out and the odor goes away? This has only started since I replaced my exhaust and only at cold start-up. I had my mechanic doubled check the settings on my carb and he found everything to be ok. He scanned the ECM and the only code that is in the ECM is for a Vehicle Speed Sensor Fault, which I don't think would relate to my problem since the car is at a stop. I'm at a loss on this one, any ideas out there on the CAC.

Thanks ZAL81
 

Ken

Gone but not forgotten
Joined
Jan 30, 2001
Messages
8,237
Location
Hermosa Beach, CA
Corvette
1987 Z51 Silver Coupe
It's nothing to worry about; it's a temporary over-rich condition that's usually the culprit.
 
Joined
Nov 4, 2000
Messages
947
Location
Scottsville, Kentucky
Corvette
08 Jetstream Blue Z51 coupe
ZAL,
you might try resetting your electric choke a notch or two leaner. This will let the choke open faster. If your engine stalls or stumbles set it back to where you started from. 2-3 notches lean is a usual setting.:s
 

Yoda

Well-known member
Administrator
Joined
Oct 12, 2000
Messages
4,885
Location
Amarillo, TX
Corvette
1981 UL5
Interesting

ZAL81,

Did you have the headers on before you did the exhaust change? Is there a return air tube from the cat? I would be curious to see what a smog check found? That might give you clue as to where to start looking... Hydrocharbons ~Carbon Monoxide~traces of Nigtrogen or other gases.. each one is a symptom caused by anything from Idle Mixture Adjustment, to EGR valve.

Hopefully someone else has had this problem and can give you a more direct answer.

BudD
:w
 

ZAL81

Well-known member
Joined
Feb 27, 2001
Messages
122
Location
Washington, MO.
Corvette
81 Charcoal Metallic 4-spd & 94 Red 6 spd vert
BudD, I'm running the factory headers and all emission hoses and lines are connected. It passed state emissions with flying colors last year which was about 4 months after I replaced the exhaust!?

1987 Z51 , This temporary over-rich condition has gone on for a year now, how long is "temporary"?? I'm not long on patience!

ZAL81
 

Ken

Gone but not forgotten
Joined
Jan 30, 2001
Messages
8,237
Location
Hermosa Beach, CA
Corvette
1987 Z51 Silver Coupe
ZAL81 said:
1987 Z51 , This temporary over-rich condition has gone on for a year now, how long is "temporary"?? I'm not long on patience!

By "temporary", I meant "intermittent" of course. ;) As Bud said:
Hydrocharbons ~Carbon Monoxide~traces of Nigtrogen or other gases.. each one is a symptom caused by anything from Idle Mixture Adjustment, to EGR valve.

Good luck, Ken
 
C

ccflorida

Guest
Zal81,
Sounds to me like gas is in the catalytic converter and giving you back pressure to cause that engine check light to come on..Just my .02..:cool
 

Yoda

Well-known member
Administrator
Joined
Oct 12, 2000
Messages
4,885
Location
Amarillo, TX
Corvette
1981 UL5
CC you have my vote too

ccflorida said:
Zal81,
Sounds to me like gas is in the catalytic converter and giving you back pressure to cause that engine check light to come on..Just my .02..:cool

If it is stock one you can take the bottom off and clean out the guts.... according to the "Shop Manual" section 6F... I put a new cat on last summer.

BudD
:w
 

ZAL81

Well-known member
Joined
Feb 27, 2001
Messages
122
Location
Washington, MO.
Corvette
81 Charcoal Metallic 4-spd & 94 Red 6 spd vert
Put a brand new converter on when I replaced the exhaust system, which is when this whole stink started:confused
 

fastglass95

Well-known member
Joined
Jan 27, 2001
Messages
208
Location
St. Peters, MO.
Corvette
1996 LT4 coupe + 2004 Z06 Z16
Test Pipe!

Try a "Test Pipe" in place of the cat. That's what those test pipes are suppossed to be for ;) right.

You can always put the cat back on for emissions testing after you complete your "Off-Road Use" of your Vette :D

Check E-bay, a guy on there was selling new ones for many differnt vehicles. Or find a quiet shop out in the country that don't mind doing "Custom" exhaust work for off-road vehicles ;)

I have one that was rescued from a junkyard off another Vette. Fits perfectly. My kind of "recycling"
 

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