Date: Tue, 2 Sep 1997 03:26:04 UT
Reply-To: Dennis Haynes <dhaynes57@CLASSIC.MSN.COM>
Sender: Vanagon mailing list <Vanagon@Gerry.SDSC.EDU>
From: Dennis Haynes <dhaynes57@CLASSIC.MSN.COM>
Subject: Re: Vanagon Ignition Timing
Advancing the timing this way causes two problems. You increase the
possibility of engine knock and you also increase the production of NOx. VW
sets the timing to reduce the "Peak Flame Temperature" and uses the 3-way cat
to control this most harmful emission. This is the emission that the EPA
tried to monitor with centralized emissions testing. It is only produced when
an engine is under load. Hence, the need for a chassis dyno or test equipment
that can be carried in the car. We will probably be getting this in New York.
Most other car manufacturers use an EGR valve for this purpose. VW chose to
save money as we don't need the performance,(ha). The other concern, is that
with the timing advanced, less air is needed to maintain a set idle speed.
This raises CO and HC emissions drastically. If the cat is working, you may
not see this, but measure the emissions before the cat and you'll be amazed.
Especially during warm-up. In my experience, at least 7 out of 10 Vanagons
that come to me with a marginal failure can be corrected by properly setting
the timing and idle speed. To set the timing properly on the 2.1 liter
engine, all you need to do is disconnect the temp. sensor for the computer.
This will cause the timing to default to its baseline setting. When done,
reconnect the sensor, shut- off and restart the engine and you should be set.
Hope this helps,
Dennis.
PS. I have written a coupe of articles on Emissions systems, if anyone is
interested, I can E-mail them to you.
-----Original Message-----
From: Vanagon mailing list On Behalf Of Eric Small
Sent: Monday, August 25, 1997 12:51 PM
To: Vanagon@GERRY.SDSC.EDU
Subject: Re: Vanagon Ignition Timing
Tom Brunson wrote:
>Working with my 87 & 91 Vanagons I've been surprised how sensitive they are
to
>slight changes in ignition timing. After timing a replacement engine "by the
>book" (5 deg. BTDC) one car had terrible low-end response, feeling very dead
>when starting from a stop until the engine hit over 3000 rpm. Advancing the
>timing 2-3 deg more made a huge difference in throttle response.
>
>I wonder if the specs are that far off, or if the pulley timing marks are
very
>reliable compared to the flywheel TDC sensor used by VW to do timing.
>
>Anyone else care to say what timing they find best?
>
>Tom
Tom,
I have experienced the same results when adjusting the timing on my '86. I
have
been told by a VW mechanic that it is not possible to accurately adjust the
timing without the required diagnostic equipment. I guess it is not as
straight
forward a process as one would expect -idle at 2000RPMs, acessories off,
several
engine sensors unplugged-. I ended up adjusting it by ear to where it
performed
best without knock. In fact, I believe that I have adjusted mine with
considerable ?? advance but it runs !extremely strong! without any knocking.
I
do now run premium (93) fuel in it now just to insure against knock.
Mine GL is a completely stock auto trans set up- but with it tuned like this I
have noticed a perpensity to turn the tires on damp/wet/sandy pavement.
Actually
brought the rear around once leaving a parking lot. This is with good Michlin
XGTV 215/65VR15 tires.
Could anybody out there advise me (us) what dangers might result from my state
of tune? Obviously I like the power but I dont want to hurt anything (long
term)
either.
Eric
'86 GL (toaster-oven)
'93 Audi 100
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