Date: Tue, 25 Sep 2007 22:27:27 -0700
Reply-To: Michael Elliott <camping.elliott@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Michael Elliott <camping.elliott@GMAIL.COM>
Subject: Re: The two throttle valve switches, redux
In-Reply-To: <109442.20940.qm@web82715.mail.mud.yahoo.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
On 9/25/2007 9:44 PM David Kao wrote:
> --- Michael Elliott <camping.elliott@GMAIL.COM> wrote:
>
>> Wait. I got this wrong. Lemme try again.
>>
>> On the earlier 1.9L's there are two switches on the throttle valve. One
>> closes when the foot is off the gas pedal, and the other closes when the
>> pedal is floored. They are wired in parallel and both connected through
>> one single wire to Pin 4 of the ECU per Bentley's 97.55. Both switches
>> ground Pin 4, the ECU doesn't have any way to know which switch did it.
>>
>> Now if the engine is at 1500 rpm or faster and you take your foot off the
>> gas, the idle switch closes, grounding ECU Pin 4. Bentley's says that
>> under these conditions, the ECU shuts off fuel to the injectors (24.33).
>>
>> But if you /floor/ the pedal, the full throttle enrichment switch closes,
>> which ALSO grounds ECU Pin 4. Bentley's tells us that when this happens
>> the ECU will enrich the mixture (24.34).
>>
>> So taking your foot off the gas or flooring the pedal both ground Pin 4
>> ... so, uh, how does the ECU know whether to shut off the fuel or to
>> enrich the mixture?
>>
>> --
>> Mike "Rocket J Squirrel" Elliott
>> 71 Type 2: the Wonderbus
>> 84 Westfalia: Mellow Yellow ("The Electrical Banana")
>> 74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
>> KG6RCR
>>
>
> My guess is the ECU reads the signal from AFM. The signal from the AFM is probably
> different enough between floored and foot off.
>
(To better follow this exciting thread, bottom posting makes more sense.)
Maybe so.
Say you're cruising along with the engine at 3,000 rpm. You stomp on the
gas. This pulls Pin 4 of the ECU down and the AFM says "throttle is open."
Based on this, the ECU enriches the mixture.
Or say you're cruising along with the engine at 3,000 rpm. You take your
foot off the gas. This also pulls Pin 4 of the ECU down, but the AFM says
"throttle is closed." Based on this, the ECU turns off the fuel supply.
There's nothing in the Bentley's or the Fuel Injection Manual about the
ECU using Pin 4 + AFM to decide which action to take. I wonder how we
could test this hypothesis?
If it turns out to be correct, then it doesn't explain why the O2 monitor
in my van indicated an over-the-top rich mixture last week when I was
going down long grades with foot off the pedal (Pin 4 of ECU pulled down
by idle switch and throttle presumably closed). Those two conditions
should have caused the ECU to cut the fuel.
--
Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
KG6RCR
|