Date: Mon, 17 Aug 2009 23:20:57 -0700
Reply-To: Rocket J Squirrel <camping.elliott@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Rocket J Squirrel <camping.elliott@GMAIL.COM>
Subject: Re: Not quite a backfire . .Over running the engine
In-Reply-To: <BAY132-DS77DCA266A0AA4B0E22495A0FF0@phx.gbl>
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Thanks, Dennis. Is the "When the engine temps goes below ~120f the ECU
will go back to open loop and the fuel cut off is no longer active" thing
mentioned in Bentley's? Is it pretty much the normal deciding point used
to determine when the ECU closes the loop?
I've gone done some pretty long grades with temps in the 20's (F) and
don't recall seeing the O2 meter do anything more interesting than sit in
the far left super-lean position. When the ECU is open-loop (after
starting, for example) the meter sits midway between the extremes.
> One problem of operating the engine for a long period this way is that
> after some time oil will get sucked into the intake valves through the
> guides.
Which could temporarily foul a plug or two, causing an engine miss until
they are washed clean by an opened throttle and a cool, clean rinse of
sweet, sweet gasoline.
--
Mike "Rocket J Squirrel" Elliott
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
Bend, OR
KG6RCR
On 8/17/2009 7:44 PM Dennis Haynes wrote:
> Having the vehicle turn the engine without power is often known as over
> running.
>
> The engine basically an air pump and even with the throttle closed some air
> will always get pulled through. When things are working properly, the
> Vanagon ECU will cut off the injectors when the throttle is closed and the
> engine is over run above ~1,350 rpm for the 1.9 and 1,450 for the 2.1. With
> no fuel and a lot of air, the engine will cool down. When the engine temps
> goes below ~120f the ECU will go back to open loop and the fuel cut off is
> no longer active.
> Also, when the engine returns to normal idle or the throttle is opened the
> O2 sensor is ignored for a short while. Folks with the 1.9 know this effect
> when they get that idle surge. The 2.1 addresses this with the raised cut
> off speed.
>
> One problem of operating the engine for a long period this way is that after
> some time oil will get sucked into the intake valves through the guides.
>
> Sometimes during this scenario you will get some unburned fuel and oil into
> the exhaust and you may get some small backfires. This is an unusual
> operating condition.
>
> Dennis
>