[Vwdiesel] Diesel talk for beginners --- ( Does a Dieselengine slow down the Car like a gasser does ? )

[William A. Thompson]

2 cents worth ...

Was a friend's car (more on that further down) ...
'83 VW 4 door Rabbit N/A diesel 5 speed. In good
shape but for front fender slightly pushed in on
the side. Drove great until a problem started.

Initial symptom was when driving ... to him no
rhyme or reason as to when it happens ... just as
though pulling foot off the accelerator and
quickly stabbing brakes REALLY HARD ... then back
on the accelerator. Only happened once in awhile
for several weeks.  Progressively got worse ... I
didn't see the car until exhibiting extreme
bucking action ... as though very quickly
switching alternately pedals to the metal ...
first fuel then brakes ... back and forth.

When I first drove it ... clutching and fueling as
usual ... it would seem to go to a "certain RPM"
and then buck violently forcing me to stop for
fear of some kind of damage from the bucking. If I
started out again but eased on the fuel while
speeding up but shifted before the "certain RPM"
.. it would go into the next gear then when the
"certain RPM" was reached ... start bucking again.

Having read how some people here believe that a
diesel has no breaking ... I almost dismissed how
it felt like a gasser when run out of fuel except
that IT FELT LIKE VERY MUCH MORE EXTREME ENGINE
BREAKING.

Over a week or so the car got to the point that it
wouldn't even start. My friend spent several weeks
trying this and trying that ... not paying
attention when I asked him to swap out the fuel
solenoid just for grins. He checked everything
from bad fuel to fuel pick up filter to inlet
banjo ... and many more of his mind's
possibilities ... all except what I suggested ...
the fuel solenoid. He complained that solenoids
fail hard ... fail closed ... and fail permanently
.. never intermittent ... and never progressively
weakening.

He ... being an engineer ... and I ... but a lowly
technician in his mind (though I hold several
degrees in several disciplines) ... it was
difficult to even get him to listen to my "field
experienced" explanation as to the progression of
symptoms and what the problem might be. His last
line of defense was the cost of the solenoid in
what he considered to be a "shotgun
troubleshooting" approach with no basis.

Damn Boeing engineers anyways.

Finally ... I pulled a solenoid from a spare
engine ... bear of a time getting it off ...
(where is a source for an "ideal tool" for the
job?) Told him to give it a shot ... nothing to
loose but for some time and he's already put weeks
into it.

Car accelerated thru gears fine after the solenoid
swap ... except I think the bucking trashed a
tranny to chassis mount. The car now swerves to
right after accelerating hard and letting off the
fuel. Anyone concur on this diagnosis?

What I think was happening was ... as the
solenoid's coil got weaker for some reason ...
increased fuel flow would pull solenoid closed at
a given "certain RPM" due to venturi action thru
solenoid ... cutting off fuel flow ... resulting
in engine braking ... pulling the car nose down
immediately and violently. With fuel now cut off
.. engine braking drastically slows car and RPMs
.. no fuel flow allows weak solenoid to open
again ... fuel flows ... ... nose of car now pops
up with acceleration ... RPMs and fuel flow
increase ... until "certain RPM" is again reached
.. increased venturi action due to higher fuel
flow pulls solenoid closed again ... here we go
again.

Until the fuel solenoid was changed.

Point being ... as the fuel was being cycled from
flowing to not flowing by the solenoid's closing
.. the engine breaking was very much more
pronounced than what happens when cutting off the
fuel on a gas engine. Once the solenoid was
changed it became apparent that a great amount of
engine braking was occurring because of and each
time the solenoid was pulled closed by fuel flow.

Before I let my friend use my solenoid ... he
jokingly "forced" me to put up his "pink slip"
against my '84 2 door Rabbit N/A diesel 5 speed as
a wager on the issue. When I won I didn't force
him to pay up on the bet ... but several weeks
later he had another problem on his '83 Rabbit and
didn't believe me when I told him the solution. He
spent several weeks on that one until I handed him
the new banjo washers I wanted him to try.

He decided to sell the Rabbits and get something
"more reliable" that doesn't need all the
attention. I tried to talk him out of it ... but I
told him if he just has to sell them I might be
interested.

Reminding him of significant favors I had done for
him ... I dickered him down to below blue book on
two Rabbits and 4 other parts cars. Gave him some
cash to buy the van he wanted. The next day as he
was signing it all over to me his wife called ...
broke down in the parking lot with the van.

But ... damn again ... I digress.

Even in normal driving conditions ... theory be
damned ... I can feel the little diesel "engine
brake" down the long hills in these Cascade
Mountains. The experience with this weakening and
finally failing solenoid decides the issue for me.

If someone were to ask me ... "Does a diesel
exhibit engine breaking?" ... I will say "You can
bet your ass on it."

Just my 2 cents worth of "field experience".

    ...Bill



----- Original Message -----
From: "Doyt W. Echelberger"
<doyt at buckeye-express.com>
To: "H . Hagar." <h_hagar at prcn.org>
Cc: <vwdiesel at audifans.com>
Sent: Sunday, June 19, 2005 4:47 PM
Subject: Re: [Vwdiesel] Diesel talk for
beginners --- ( Does a Dieselengine slow down the
Car like a gasser does ? )


> I hear you, Hagar, and agree that you have
raised an interesting question.
>
> We science types try to depend on facts for
deciding such matters, rather
> than authority.
>
> So, I propose a few tests: Let the person who
believes a diesel engine
> provides no braking (the non-believer) get
behind a diesel Rabbit with a
> cold engine, that is parked and in first gear,
with the engine off and the
> wheels locked straight ahead. The guy who
believes it DOES provide
> braking  gets in the driver seat behind the
wheel, to steer and operate the
> clutch. The driver window is down. The car is in
a big empty parking lot on
> a hard flat surface on a clear dry day about
6-7pm, no traffic, no policemen.
>
> The non-believer starts pushing the Rabbit and
the believer keeps the
> clutch pedal down and disengaged.
>
> As soon as the Rabbit is moving at a steady pace
(about 5 seconds) the
> believer lets out the clutch.
>
> After another 5 seconds of pushing, the
non-believer stops pushing and the
> believer puts on the parking brake and gets out
of the car.
>
> Then they calmly discuss the matter, based on
their findings. They define
> terms and seek to find agreement about the
braking effect of a diesel
> engine that isn't being fueled.
>
> Then they do another test, only this time they
put the same car at the top
> of a long hill, away from other traffic of
course. This time, they both get
> in the car and the non-believer drives. He
starts the diesel, puts it in
> first, and lets it idle. He lets off the brake
and lets out the clutch and
> the car moves off, coasting down the hill in
first gear with the engine
> running. They ride along for about 10 seconds,
making observations. The
> believer then pushes in the clutch and they
coast for ten more seconds,
> making observations. Then the non-believer lets
out the clutch and engages
> first gear again. They make observations.
>
> The non-believer then shifts into second and
lets the car continue to idle
> and coast down the hill for another 10  seconds.
They make observations and
> again disengage the clutch and coast for 10
seconds and make more observations.
>
> The non-believing driver then shifts to third
gear and lets out the clutch
> for 10 more seconds, then pushes in the clutch
and they coast for 10
> seconds and  make more observations.
>
> OK, you understand,,,,they try 4th gear the same
way, and then 5th gear if
> it has one and if the hill is long enough.
>
> They discontinue their testing and drive to a
cool shady bar and order some
> cold beer and maybe a pizza, and sit around for
about half an hour,
> discussing the tests and their observations.
>
> Then they have another round of cold beers and
talk some more.
>
> If either one has been converted at the end of
these tests and
> deliberations, he settles up the bar tab.
>
> That sounds like an agreeable experiment, if you
can find a long enough hill.
>
> The next day you run the same tests, using a
gasser Rabbit.
>
> On the third day, you just go to the bar and
order the beer and pizza and
> talk about what fun it was.
>
> On the fourth day, you write up a joint report
and both sign it, and tell
> us what kind of beer you liked best.
>
> This series of tests can be run with soft drinks
if required, but I can't
> guarantee the results.
>
> Doyt
>  >>>>>>>>>>>>>>>>>>>>>>
> At 02:41 PM 6/19/2005, you wrote:
> >Oh, we could get into quantatives, but I
disagree with Hagar on the
> >brakeing issue.  Essentially a VW diesel does
not brake at all.
> >Just that a high idle provides more net thrust
(torque).
> >
> >Val
> >
> >Val and ALL : -----answer : YES YES YES it
does.  -----like a gasser
> >?   ---BUT better.
> >
> >I call for Doyt Echelberger to explain whether
his student has it "RIGHT" .
> >
> >As a slow down device "Braking"
 device --Engine  can be compared to an
> >Air Compressor
> >to compress Air   takes energy ? RIGHT ?   so
that is what slows you down.
> >RIGHT ?
> >Right so far ?.
> >
> >Road retarter ? ---bet your ass.       The
higher the Compression the more
> >it retards. RIGHT ?
> >
> >A long time ago ---eons ? we had a real good
discussion about this
> >issue.   And I Hager
> >made a lot of tests on  1.6L NA and Turbo  and
1.5 L  NA  Diesel
> >Rabbits  ----and NO way
> >can my testing be ---dismissed.   ----I Hagar
has a very keen cognizant
> >mindset.
> >
> >Someone said that a gasser did more retarding
due to the "Butterfly"
> >valve   (wrong mostly).
> >
> >Now did BOSCH use a venturi and a "Butterfly"
valve on diesels at one time
> >? ---YES.
> >
> > >From a "PHYSICS"  point of view ?   the
higher the compression  ---the
> > more it will
> >be a "RETARDER" , -----period READ MY LIPS.
> >
> >SO WHAT    is the problem
? ----simple   ---the fuel must be turned
> >off------then it is
> >a matter of valving.   -----------   Jake
brakes do not work ?  ----well
> >then I shall   have them
> >stopped from use in front of my Tar Paper
hack  ----just like it is
> >closer to town.
> >
> >Yes   there is a Highway sign to that
effect ----here close to town
> >limit.-----A NOISE
> >regulation.
> >
> >A Rabbit can not change Valving  -----but she
sure can turn the Juice
> >off.     ---like
> >Bunny Bondo does  ----and she retards very much
like a gasser.
> >
> >Remember British Columbia  is blessed with
testhills.----and Bunny and
> >Hagar goes
> >there regularly.
> >
> >Finally a Diesel will slow you down ---like NO
gasser ever did  Cubic inch
> >for Cubic inch..
> >
> >
> >Hagar.
> >
> >PS :     Doyt Echelberger am I right
    ---- I do agree that the
> >butterfly vacuum does
> >take energy from the crank --and that is
helpfull in a slowdown (on
> >gassers).      and
> >Diesels by the way..
>
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