John-
It's possible that the two items are related. I wouldn't expect a
"tired" timing belt to change the timing mark; it would simply stay lagging
the ideal location. However, I assume [yes, yes I KNOW what it means] that
you're viewing the mark with a light, and that means that you're seeing the
result of timing changes including the engine management controls
themselves. On older cars, you'd have had a vacuum canister on the
distributor, and fly-weights inside, changing advance in response to engine
vacuum and rpm. I believe yours is going to be all-electronic, but the
principle is the same, with a "map" telling the system how much to advance
or retard based on those & other inputs like engine temperature. If you
have a bad sensor, the timing can be jumping in response, and if it involves
rpm, that could cause a brief moment of bad timing at the shift point.
Something as simple as a poor connection could cause it, but I'm going to
guess that whatever sensor is used to determine engine speed is the first
place to look.
With any luck, someone with more experience on later 8-V cars can jump
in here and expand on this for you; my latest year 8-V is / was an '84 Jetta
(not on the road, but I still have it).
Ron
----- Original Message -----
From: "John Lagnese" <[email protected]>
Cc: <[email protected]>; "The List" <[email protected]>
Sent: Sunday, February 09, 2003 11:54 PM
Subject: [a2-16v-list] Shifting backfire
> Hi,
> I'm getting a curious problem in my daily driver. Its a 91 Jetta GL 8V.
Its got
> 194K. When I shift above 4k there a small pop, like a backfire? Do I have
a
> sticking valve? Its got a new mid and rear muffler, so the exhaust is
tight.
> Also same vehcile, why would the timing mark jump around? Is my timing
belt
> tired?
> Thanks,
> John
>
>
>
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