Re: used parts/bad mpg

[Mark Shaw <autox@inficad.com>]

I'm not sure which year you have, but sounds like an early MkII with
Bosch K-Jetronix.   This may sound weird, but a similar problem
plaqued my son's '84 Scirocco Wolfsburg.  The mechanic could find
it after we diagnosed the usual stuff.  The symptoms were an uneven
idle, mileage near 20 mpg, and an overrich smell in the exhaust...
otherwise it worked fine.

The solution was a new ground cable from the engine to the chassis!

After careful observation over a couple of weeks we noticed (we used
to carpool to work) that the problem with the idle was related to a
low voltage reading.  In the morning when it was cool the alternator
would charge fine, but in the afternoon when the A/C was on and the
engine was hot the voltage would drop to about 10 volts when the
idle became unstable.  The low voltage was due to excessive voltage
drop in the cables from the engine/alternator case to the
chassis/battery.
We were loosing about a volt, which caused the alternator to think that
it had charged the battery and to drop off current.  The extra current
for the A/C then drained the battery down.

When the system hit about 10 volts the cycling on the O2 sensor
would saturate to the rich side...voila!  the culprit.

So, morale of the story, check the voltage on your engine
control module for anything less than about 11 volts.

Mark


Ian wrote:

> >From the top;
>  my wife normally drives the car so I don't know when this started
> (unfortunately she tends not to follow the mileage)
> Symptoms: 20mpg, faint fuel smell in engine area
> Idle is good, I do hear something of a 'put put' sound when I take my
> foot
> off the gas after revving it a little. No funky colored smoke coming
> out of
> the exhaust, no other unusual noises or sounds. Fuel line connections
> to and
> from fuel filter look good
> Recently replaced: fuel, oil, air filters, plugs & wires, O2 sensor,
> and
> transmission
>
> So far from the wonderful people who have responded I need to check
> "all the fuel connections, fuel distributor, cold start valve, fuel
> filter,injectors, all those connections. make sure she is firing on
> all 4 no
> misses. platinum plugs (bosch) of course, exhaust clogged ( possibly
> cat )(
> hope not ) vac lines and all that"
> "clean ALL the FI connections with some
> contact cleaner, and don't forget the O2 sensor connection.  also,
> check
> and see if the temp sensor is sending the correct signal"
>
> I'm in for a busy weekend ;-)


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