[T3] Intermittently running on two cylinders

Jacob Adam Schroeder jacob.schroeder at gmail.com
Wed Dec 5 13:15:25 PST 2012


I'm not sure if this means anything, but it sure is some coincidence if it
does not.  I measured the resistance of my spark plug wires.  The wires for
cylinders 1 and 3 (where no misses) were about 800 ohms, whereas for
cylinders 2 and 4, the resistance was around 1200 ohms.  I don't imagine
that 400 ohms will make a difference, but I wanted to run these by you
guys.  I have yet to conduct the other tests yet.  When I get a chance,
I'll take a look at the injector connectors.  I vaguely remember having to
adjust them years ago and perhaps it is time for another adjustment.

Jacob


On Sat, Dec 1, 2012 at 1:49 PM, Jim Adney <jadney at vwtype3.org> wrote:

> 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.
>
> --
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
>
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