[T3] Intermittently running on two cylinders

[Jim Adney]

On 1 Dec 2012 at 11:46, Jacob Adam Schroeder wrote:

> My car has developed an issue lately where occasionally it will feel like
> it is running on two cylinders.  When it does this, I can pull the wires
> from the fuel injectors on cylinders 2 and 4 and notice no difference in
> the sound of the engine.  If I pull 1 or 3, I hear the RPM decrease and it
> sounds like it is running on only 1 (if that is even possible).  It is a
> 1972 Squareback with stock FI (except for Pertronix electronic ignition --
> which I plan to return to the stock set up soon).

Is this all the time, or just at idle. Sometimes we can get confused 
by something that happens only at idle. It's not uncommon to have a 
cylinder or 2 not fire normally, at idle with a cold engine. If this 
is happening while driving, you would feel like you had almost NO 
power.

It's not the Pertronix, because that would effect any or all 
cylinders. It's probably also not the same ground problem as 
Daniel's, because 68-9 injector grounds are different, and have their 
own very special problems.

Certainly you can go around randomly cleaning up every connector in 
sight, but you're actually more likely to do harm than good by this 
approach. Likewise with fuses, of which NONE serve the FI 
electronics.

Cylinders 2 & 4 don't point to any particular problem. If it's always 
those 2, then there must be a problem with those cylinders. It could 
be FI or it could be ignition, but IT MUST BE SOMETHING THAT'S NOT 
SHARED IN COMMON WITH 1 & 3.

The first thing I would check would be the resistances of the spark 
plug connectors on 2 & 4. They should measure ~1000 Ohms. If they 
measure infinity, you've found your problem. Replace the bakelite 
ends and you're back in business.

Also check the inside of your distributor cap and wipe off any 
condensation you find in there.

If that doesn't do it, the next thing to check would be the tightness 
of the female connectors onto the injector pins. To do this you have 
to take the connectors apart. This takes patience and possibly a 
special tool, for which a Bobby pin might work. You have to back the 
2 pins out of the white plastic connector body and then check each 
one to make sure it fits snugly onto the injector pins. If they are 
loose, you can squeeze them VERY gently with pliers and tighten them 
up. Be careful, don't get carried away, or you'll end up making extra 
work for yourself.

If you find any of these to be loose, you're probably better off 
working your way thru all 4 injector connectors. Yes, even the ones 
that seem to be working okay most of the time. This is a fairly 
common problem, because Bosch seems to have made replacement 
injectors with slightly thinner pins starting around ?1980? Fixing 
these connectors is quite a bit of fiddly work, but it's often very 
rewarding.

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