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Re: [T3] Fastback Engine Trouble...ideas?


On 28 Dec 2001, at 12:30, Christopher Sheridan wrote:

> Onset Symptoms: Started and ran fine until 15 minutes or miles into
> any given trip. Then when slowing down/speeding up in traffic, the car
> would bog and sputter and not want to accelerate. If you open the
> throttle from idle you could blow through the bog and it would clear
> out and run smooth. as condition worsened it would miss at highway
> speed, again only after it was warmed up and running about 15 minutes.

Engine appears to be FI. What year?  

> Repairs Attempted:  set valves (okay), static timing with test light,
> replaced cracked fan belt & worn generator brushes, new points, rotor,
> condensor, cap, trigger contacts looked worn, replaced with best of 3
> used that I have (the ones showing the most meat), switched out the
> fuel pump for a spare which didn't work at all, so switched original
> back on, switched out pressure sensor & thermo time switch & cold
> start valve for other used units. Replaced all vacuum lines with fresh
> and new hose clamps. Charged battery, switched distributor body for
> spare, checked all spark plug connections and mpc plug connections,
> including trigger switch, FI grounds & sensor plugs.

You've attacked this energetically, but without any particluar 
reasoning. In swapping around an assortment of used parts you 
have more chance of adding in confusing problems than of fixing 
something. I call this the shotgun approach and I find that it almost 
never works and usually consumes the most time and money.  

You need to start by making some more observations: Is the fuel 
pressure okay? Is the charging system voltage okay? When you 
swapped parts did you maintain a consistent set of FI parts, or do 
you now have a mixed set of parts from different years?  

> Suspicious areas/things I haven't done but the one that stands out to
> me is using a strobe light to time the motor and then attempt an idle
> adjustment. Just wondering if the symptoms I've described above ring
> any bells with people out there....until I get this thing fixed we're
> trapped at home with a baby!!!

Static timing done carefully is not the best, but it is good enough to 
avoid problems like this. Still, checking it with a strobe is 
reassuring. If you have a FI 72, then the timing proceedure is 
complicated and you really can't do it accurately without the 
strobe.     

Figuring out the problem is a matter of looking for the right things at 
the right time. The right time is when the engine is running poorly 
or not at all. When this happens, start by verifying that you still 
have proper spark; the timing light is good for this. Then check the 
voltage on the output side of the fuel pump relay.     

See if turning the key OFF and back ON gives it a new lease on life 
when it starts to falter.     

-
Jim Adney
jadney@vwtype3.org
Madison, WI 53711-3054
USA

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