AirCare and ignition timing

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   I had to take my �86 GT through AirCare earlier this week. It's always a cause for concern, as most of you with older cars can understand. 
I have a 195� thermostat installed and the EGR is functional, but I have no cat on the car. There was already a small amount of acetone mixed with the gas, as I've reported on Here. I decided to also add a liter of methyl hydrate to the half tank of gas, as this appears to help emissions in some situations.
I drove the GT up to Grouse Mountain to get the engine good and hot, and then went to the AirCare testing facility just off of Boundary Road in Vancouver.
It failed. 
The Idle HC readings were well above the maximum (380 ppm) allowed measurement. 
Then I remembered that I had timed the engine by "ear" a year or so ago. The timing ended up being around 14� BTDC. So I backed it off to about 8� BTDC after failing the test. Would this be enough to make a difference? 
I took the GT through the same AirCare station (the same lane, the same guy) about an hour after I had gone through the first time. I did nothing else except back off the ignition timing. Here's the results (pay particular attention to the top two sets of readings)...

I had no idea that a slight change in engine timing would make such a difference across the board. Frankly, I'm shocked (but pleased). 
Note: That bottom set of readings was when my cat was plugged.

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Patrick Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 19 April 2008 Location: Vancouver Status: Offline Points: 5	Post Options Post Reply Quote Patrick Report Post Quote Reply Topic: AirCare and ignition timing Posted: 13 February 2010 at 12:29pm
	I had to take my �86 GT through AirCare earlier this week. It's always a cause for concern, as most of you with older cars can understand. I have a 195� thermostat installed and the EGR is functional, but I have no cat on the car. There was already a small amount of acetone mixed with the gas, as I've reported on Here. I decided to also add a liter of methyl hydrate to the half tank of gas, as this appears to help emissions in some situations. I drove the GT up to Grouse Mountain to get the engine good and hot, and then went to the AirCare testing facility just off of Boundary Road in Vancouver. It failed. The Idle HC readings were well above the maximum (380 ppm) allowed measurement. Then I remembered that I had timed the engine by "ear" a year or so ago. The timing ended up being around 14� BTDC. So I backed it off to about 8� BTDC after failing the test. Would this be enough to make a difference? I took the GT through the same AirCare station (the same lane, the same guy) about an hour after I had gone through the first time. I did nothing else except back off the ignition timing. Here's the results (pay particular attention to the top two sets of readings)... I had no idea that a slight change in engine timing would make such a difference across the board. Frankly, I'm shocked (but pleased). Note: That bottom set of readings was when my cat was plugged.

Dr.Fiero Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Post God Joined: 12 February 2007 Location: Canada Status: Offline Points: 1726	Post Options Post Reply Quote Dr.Fiero Report Post Quote Reply Posted: 13 February 2010 at 12:49pm
	Facts are, it passed... but... I'd like to see the car hooked up to a 5 gas, then do nothing but twiddle the timing. THAT would tell you for sure, since it minimizes all the variables like how hard and fast the guy stepped on the peddle that particular time, etc etc.

Patrick Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 19 April 2008 Location: Vancouver Status: Offline Points: 5	Post Options Post Reply Quote Patrick Report Post Quote Reply Posted: 13 February 2010 at 3:29pm
	You've got to admit it though... an hour later at the same facility with the same guy in the same lane on the same dyno. Can't get much closer than that normally to see just what made the difference.

Dr.Fiero Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Post God Joined: 12 February 2007 Location: Canada Status: Offline Points: 1726	Post Options Post Reply Quote Dr.Fiero Report Post Quote Reply Posted: 13 February 2010 at 4:52pm
	Yup, for sure... I mean, the proof is right there! But - a couple degrees timing, while it should make a difference - shouldn't make THAT much difference! That's over a 100% shift in the one reading.... I'd just like to see it changed with no variability in anything (it's that operator 'error' thats the huge one IMHO).

Patrick Members Profile Send Private Message Find Members Posts Add to Buddy List Newbie Joined: 19 April 2008 Location: Vancouver Status: Offline Points: 5	Post Options Post Reply Quote Patrick Report Post Quote Reply Posted: 13 February 2010 at 5:23pm
	If "operator error" can influence the results THAT much, then AirCare testing is a complete sham. And it very well may be!