[T3] Fluttering engine performance...

[Jim Adney]

On 22 Nov 2010 at 9:49, J. Jonik wrote:

> T III   FI  Std.  1971

> Symptom: Driving along just fine, after finding and replacing one bad
> injector, after about 7 miles on the highway, then some stop and go
> street driving, suddenly engine seemed to flutter when accelerating.
> Noticeable power loss to a degree while fluttering. Then it stopped
> doing that til the next gear change, and after the next stop. That was
> just when hitting gas after stopping, and when changing gears.

Those symptoms don't remind me of anything in particular. Maybe just 
an oddly recurring misfire. Or an out of adjustment set of trigger 
points. Have I checked yours?

> Being away from home, but having some spare parts, I found that
> Throttle valve switch clicked a lot when turning the engine over with
> big screwdriver while making sure timing was right. So, when timing
> adjustment (none needed to speak of) was done, ran the car for a
> while. Then tried to drive it. It stalled.  Trying to rev it didn't get
> any response. It just slowly stalled out. So, suspecting something
> funny with TVS, I changed it for a spare.  Car started ok, and drove
> sort of ok...but still with that flutter, although less noticeable,
> when accelerating. It was ok when idling or cruising. 

I don't know why the TVS seems to get so much attention. I have NEVER 
seen one give any problems in a '71. I've seen problems with 72-3 
TVSs, but only while crusing at constant speed.

> For no reason, I switched to a spare distributor cap.  Then the
> problem disappeared. 

Like Bryan said, make sure you have the right (short) dist cap for 
your FI dist, and make sure the carbon brush is there, making contact 
with the rotor. With care, you should be able to feel the brush make 
contact just before the cap fully seats on the dist.

> So....does this make sense? Was the problem a combo of both TVS and
> Dist. cap?  What was happening to make that "flutter"?   Was it
> something causing irregular electricity, or irregular fuel delivery? 
> Or is that the same thing? 

The best way to check a TVS is to simply unplug it and see if the 
symptom goes away. There's no harm in driving without it for hours, 
days or weeks. You may notice OTHER symptoms from the lack of the 
TVS, but that's not important; the important thing to look for is 
whether the original symptoms disappear when the TVS is disconnected.

I suspect either an ignition problem or a problem with the FI trigger 
points. For the ignition problem, look for some place where the spark 
can flash over to ground if the voltage gets just a little higher 
than normal. Suspects would be cracked or tracked cap, rotor, or SP 
connector, or a defective or fouled spark plug. What plugs are you 
using?



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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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