From: davol@zosmameiko.co.uk (David Wilson)
Subject: Re: An Enigma 
Followup-To: rec.autos.vw
Organization: meiko
Date: Fri, 24 Jul 1992 09:39:53 GMT

Thanks to everyone who replied to my original posting. 

What I found most interesting about our VW camper 
engine problems was the way in which I developed all 
sorts of theories and mental models about what was going 
on inside the engine - while having almost no real 
engineering knowledge on which to base my diagnoses. 

My reactions could be compared, maybe, to those of 
'primitive' peoples first coming into contact with 
mirrors (or transistor radios). When I talked to the 
various 'experts' who offered their help in the course 
of our journey I would seize upon small fragments of 
information and immediately build them into my mental 
model - though I had no way of being able to assess
the quality of those fragments apart from seeing how 
neatly they fitted into the whole picture. 

So here, briefly is an account of what I believed was 
going on inside the vehicle. If this seems bizarre and 
simply causes amusement, then accept it as thanks for 
your previous follow-up postings. If it makes some kind 
of weird sense, then let me know. 

I pictured the 'no-trouble'' additive as a form of 
heat-activated abrasive which remained dissolved, harmlessly 
in the gasoline until, on coming in contact with the hot 
engine, would come out of solution and clean up the fuel 
injectors. 

So far so good. 

Someone told me that with this sort of automatic, fuel 
injection engine, when you take your foot off the gas
a certain amount of fuel is already committed (buffered ?) 
on its way to the injectors and is suddenly no longer 
needed. So the fuel injection computer (I'm almost 
ashamed to admit to believing this) RECYCLES the unwanted 
gas BACK TO THE TANK. But in this bit of fuel the little 
abrasive balls have been activated and when they next head 
towards the engine they clog up the filter. 
Waiting for a while allows them to dissolve again. (Except 
this doesn't explain why the filter needs changing). 

Oh, what the hell. It was a long time ago. My therapist says 
I'm almost over it now. 

In Article: 2815 of rec.autos.vw, Jack Reed writes: 

> Four things come to mind as the cause of the engine's problems.

[text deleted] .....

> A fourth possibility was that the gas actually had a lower vapor pressure than
> other brands and would "vapor-lock" under high temperature, long run time
> conditions more often than other brands. But replacing the filter wouldn't 
> have any affect on the engine if that were the case. The symptoms you describe
> are typical of "vapor-locked" engines, let them cool off and drive away. I
> suppose it's possible that replacing the filter had more of a "placebo" effect
> in that you had already diluted the gasoline down to the point that the engine
> would have run fine without replacing the filter, the two events just seemed to
> coincide.

> All of the above is just theorizing, though. 

This is interesting. Maybe replacing the filter did have a placebo 
effect. I only did it about three times and so the coincidence is 
not too improbable. 

If I didn't work with computers no doubt I would have incorporated
a fuel injection daemon into my picture. 

'A little knowledge is a dangerous thing'

Dave Wilson 

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Newsgroups: rec.autos.vw