AirCare and ignition timing
Printed From: West Coast Fieros
Category: Technical Topics Forum
Forum Name: Technical Questions and Discussions
Forum Description: Got a technical question about your fiero? ask it here.
URL: http://www.westcoastfieros.com/forum/forum_posts.asp?TID=1727
Printed Date: 23 November 2024 at 8:01pm
Software Version: Web Wiz Forums 12.01 - http://www.webwizforums.com
Topic: AirCare and ignition timing
Posted By: Patrick
Subject: AirCare and ignition timing
Date Posted: 13 February 2010 at 12:29pm
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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 195º 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 http://www.westcoastfieros.com/forum/forum_posts.asp?TID=1624&PN=1 - 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 14º BTDC. So I backed it off to about 8º 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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Replies:
Posted By: Dr.Fiero
Date Posted: 13 February 2010 at 12:49pm
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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. |
Posted By: Patrick
Date Posted: 13 February 2010 at 3:29pm
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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.
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Posted By: Dr.Fiero
Date Posted: 13 February 2010 at 4:52pm
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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). |
Posted By: Patrick
Date Posted: 13 February 2010 at 5:23pm
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If "operator error" can influence the results THAT much, then AirCare testing is a complete sham. And it very well may be!
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