Date:         Tue, 16 Jul 2019 03:18:09 +0000
Reply-To:     Richard Koerner <rjkinpb@SBCGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Richard Koerner <rjkinpb@SBCGLOBAL.NET>
Subject:      Re: Throttle-on running issue
In-Reply-To:  <1213332725.1738004.1563241046579@mail.yahoo.com>
Content-Type: text/plain; charset=UTF-8

 Additional thought:  your fuel tank is right behind your radiator.  Things get hot down there; fuel in gas tank gets warm, quite quickly; vapor pressure of gasoline is reduced making it even easier for bubbles to appear in fuel line to injectors.  Then...the stumbling.  I drove all day across the desert in southern California and into Nevada at Laughlin.  Everything was fine.  But then slow driving into town, across superheated roadway late afternoon.   Immediate problem with engine stumbling.  Next morning, all was just fine, even climbing a few thousand feet and miles and miles beyond.  But sure enough, in the elevations of Colorado, motor bogged down once again; tried replacing fuel pump and filter....no joy.  The problem was that the motor was starving for fuel, GOOD fuel without bubbles.  Once back home and with brand new fuel tank (with 12 mm outlet by the way), my problems were long gone.  And, have stayed that way.  It's all about fuel vapor pressure; heat and altitude are killers for this.

    On Monday, July 15, 2019, 6:37:59 PM PDT, Richard Koerner <rjkinpb@SBCGLOBAL.NET> wrote:  
 
  Sure sounds to me like a clogged fuel tank outlet.  Others have suggested using a plastic tank of gasoline into fuel pump to confirm this problem, though I'm not clear on how to rig all of this up.  Another approach (temporary) is to add a 3 foot section of fuel line, blow HARD into it to dislodge the crud at fuel tank outlet; I've never done this, nor have I ever heard of anyone doing it, but in theory it makes some sense.
Of course, a whining fuel pump will indicate that fuel pump is cavitating....causing fuel line to be full of bubbles, which is of no use to injectors.  So if your fuel pump is not silent, I think the clogged outlet is your problem.  Our vans are ancient; even if garaged 100% of the time and always kept mostly full of gasoline (like I did with mine), you won't escape this problem.  Better to do at home than 2000 miles away on a road trip (speaking from experience).
Another clue about clogged fuel tank outlet is that in morning, when gasoline in tank is nice and cool, the problem will be less than later in the day when gasoline has warmed up.  Gasoline vapor pressure issue.  Those bubbles....hence the stumbling.

Anyway, if you've never replaced your fuel tank, you will need to do it sooner or later anyway, and it might solve your current problem.

Rich
San Diego

    On Monday, July 15, 2019, 6:07:10 PM PDT, Chris S <szpejankowski@GMAIL.COM> wrote:  
 
 I searched first and could not find.

We have a 2.0 ABA with 1.8 head with Digifant II FI.

The engine will start fine from cold.  As it warms up it will stumble on throttle.  Press throttle open - Baaaaaaaaah - nothing.  Lift throttle, returns to idle, sputters a bit like it’s missing, but then continues to idle fine at normal speed.  Crack throttle open gradually and it may catch the first time, but then baaaaah, until you lift.  The hotter the engine, the worse it is.

I’ve found no vacuum leaks in intake.  Unplugging O2 sensor makes no difference ( a new sensor is on the way just in case).  Unplugging Temp sensor only raises idle slightly, but no difference.  I changed fuel pump and fuel filter with my new spares, no difference.  I swapped AFM, no difference. Spark Plugs are recent.

My son mentioned some stumbling issues when it was raining hard, and current issue appeared after he filled up with gas.  I added gas dryer, but no difference.

Ideas?

Chris in atnaltA.