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RE: Fuel inj question



Rich Deede wrote:

> Have you considered the transfer pump, this is how mine acted before it
> went.  HTH

A good check for this is to fill the fuel tank and see if it improves.

Speaking of a mysterious stumble, I'll tell ya'll this story in  case it
ever happens to you.

My wife's 86 Jetta GLi (recently totaled by a cell-phoner, RIP) started
missing at 3800 rpm at the end of a long trip, especially under high load.
Not just a stumble, more of a gut wrenching, teeth jarring afair, in which
you're convinced your drive shafts are gonna be tweaked.  Once you got past
4000, the thing would run like gangbusters to redline.  That rules out fuel
delivery capacity.   It was reproducible at any time, and I really couldn't
understand what was going on.  Me and Mr Bentley went to the basement for an
entire Saturday, and checked everything by the book.  I even made up some
new tests, once I figured out the CIS-E.  Everything was PERFECT!  I mean,
if it said "control pressure should be in a range between 3.4 and 3.8 bar,
by George it was 3.6 bar.  If it said the cold start should run for between
4 and 6 seconds, it was 5.0.  But you'd think the engine was comin' outta
there at 3800 rpm.

I had talked to my local 3rd part VW guru, who knows VWs inside and out, and
he was buffaloed.  And although I haven't taken any of my cars to a shop in
over 25 years, I actually considered doing it, except that I was convinced
that the poor guy at the VW dealership would be baffled too.

I was at the end of my rope, and decided to wing it. I  After it was warmed
up, I disconnected the idle stabilizer (which had checked fine)and the
differential pressure regulator and went for a ride.  It was CURED!  So I
stopped and reconnected the idle stabilizer.  Stumble time again!  Now what
could the idle stabilizer possibly have to do with 3800 rpm?

Apparently (this is my theory anyway) these engines have a resonant
frequency at 3800, and gets particularly rough.  The idle stabilizer coils
were apparenty shorting out against the case under the vibration, and
depriving the rest of the system for current, which made it alter fuel flow
to the injectors enough to make it misfire.

Just a story to remind you that sometimes there are things going on with
engines that you'd never imagine.

Mark Langford, Huntsville, Alabama
87 16V Scirocco,  89 Audi 100, 74 2110cc Karmann Ghia, 72 VW Bus
mailto:langford@hiwaay.net
see KR2S N56ML at http://home.hiwaay.net/~langford


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