Could this have been the cause of my smog woes?
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Joined: Jun 2002
Posts: 144
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From: Colorado
Could this have been the cause of my smog woes?
I was just thinking about this...
Backstory:
1. Firebird won't pass smog. Blows just a bit over on HC. Get tune up, etc, barely passes. This is last fall
2. Firebird won't idle, TB is gunked up to the point that it isn't getting enough air at idle. This was this spring.
So, as a result, I cleaned the TB, and all is good now.
But... I was wondering... would the TB have been the cause of my smog woes? Here is what I was thinking:
So you're running the car. My peak HC moments (that made me blow over) were right when they got off the throttle. So... You drive along, at speed, then you get off the pedal all of a sudden to slow down. The throttle valve snaps shut, cutting off air flow. The computer notes that the TPS has gone to idle, sends the appropriate amount of gas to the engine, and then monitors it (o2) to make sure that everything is ok. Now, on my rig, the TB is partially blocked. So, instead of getting idle air, it gets too little air. But, the computer has already started delivering idle fuel amounts (there is a delay till the O2 sensor starts it modifying the amounts). This amount of fuel would be fine for normal idle, but with partial air, it is rich. So, it blows some of it out the pipe, for a brief moment, till the o2 sensor leans the mixture out.
Does this sound fesable?
Cliffs Notes:
Partially blocked TB causing issue that computer uses too much gas at initial idle (after power), causing high HC as soon as you go to idle (drops to normal right after)?
Backstory:
1. Firebird won't pass smog. Blows just a bit over on HC. Get tune up, etc, barely passes. This is last fall
2. Firebird won't idle, TB is gunked up to the point that it isn't getting enough air at idle. This was this spring.
So, as a result, I cleaned the TB, and all is good now.
But... I was wondering... would the TB have been the cause of my smog woes? Here is what I was thinking:
So you're running the car. My peak HC moments (that made me blow over) were right when they got off the throttle. So... You drive along, at speed, then you get off the pedal all of a sudden to slow down. The throttle valve snaps shut, cutting off air flow. The computer notes that the TPS has gone to idle, sends the appropriate amount of gas to the engine, and then monitors it (o2) to make sure that everything is ok. Now, on my rig, the TB is partially blocked. So, instead of getting idle air, it gets too little air. But, the computer has already started delivering idle fuel amounts (there is a delay till the O2 sensor starts it modifying the amounts). This amount of fuel would be fine for normal idle, but with partial air, it is rich. So, it blows some of it out the pipe, for a brief moment, till the o2 sensor leans the mixture out.
Does this sound fesable?
Cliffs Notes:
Partially blocked TB causing issue that computer uses too much gas at initial idle (after power), causing high HC as soon as you go to idle (drops to normal right after)?
Member
Joined: Feb 2003
Posts: 263
Likes: 1
From: White Lake, MI
Car: 89' IROCZ
Engine: 5.7 L98
Transmission: 700r4
My IROC did the same thing at emmsion testing the 1st time. The HC would spike when the throttle was closed. In my case it was the O2 sensor. My throttle body was clean. It barely passed after I replaced it, but I have 2 mods that are for off road only.
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