RE: [DML] mixture issue

["John Hervey" <john@xxxxxxxxxxxxxxxx>]

Steve, 
I would do what you did, then after you have it running as good as you can
get it. Change the plugs ( run a hotter plug ) and the 02 sensor. 
The plugs will be blackened up and the 02 most likely isn't working because
of rich contamination. Then idle it at about 950, drive it around on the
highway for about 10 miles then come back and check the mixture. You might
be able to lower it a little more. Try your dwell meter again and it should
fall in to spec. If not then do it by ear as we say in the old mechanics
realm.
John Hervey
www.specialtauto.com




-----Original Message-----
From: dmcnews@xxxxxxxxxxxxxxx [mailto:dmcnews@xxxxxxxxxxxxxxx] On Behalf Of
stephenucedu
Sent: Sunday, March 02, 2008 6:36 PM
To: dmcnews@xxxxxxxxxxxxxxx
Subject: [DML] mixture issue

Well, today I decided to tackle what I "sensed" was a rich mixture, based on
a bit too much 
black smoke coming out the exhaust. The PO said that he had adjusted the
mixture using 
an air fuel ratio meter, and that the car seemed to run best when set at an
AFR of 12.5 at 
idle. Does anyone have a feel for that value for our engines?

Well, I used the dwell meter method to measure the duty cycle, and it was
way off - at 
about a 10 on 8 cyl setting with not much fluctuation. So, I leaned it out
by turning the 
mixture screw CCW, and I had to turn it easily 1/4 th of a turn to get it
where I thought it 
should be. So, now after full warmup (fans come on and then fans go off), I
get a dwell 
that fluctuates from 28-38 (8 cyl setting) and 38-48 on 6 cyl setting. I
runs a bit better 
than before, no pinging, and I can feel the WOT enrichment that I could not
feel before. 
Also, a white piece of paper held to the tailpipe for 1 minute at idle shows
not a speck of 
black. Have not tried to start it cold, though.

So, I feel that it is now set correctly. I would like to know 1) if anyone
has any thoughts on 
the AFR for our cars and 2) is the 6 cyl or 8 cyl reading correct? An old
Santos file I found 
said to use the 4 cyl setting. That would put my car, based on the 8 cyl
setting, at a duty 
cycle that would be way too high (multiply 8 cyl setting by 2), and indicate
that it is way 
too lean. In another note from Dave, he said just aim for a 10 degree
fluctuation. But I 
would think the absolute value is also important.

Steve Liggett
5983
Baltimore







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