I can attest to a bad hall sending unit. My 83 went out intermittently,..but
> not sure temp had to do with it although it may have. Would run fine..be
> driving down the road and the tach would take a dive to zero in a split
> second,..then back up. The engine would buck like crazy.
> Allen
>
> > Hall senders do go bad. I've seen and heard of plenty of them,
> > especially intermittent failures that don't show up when doing a test
> > on the hall sender.
> >
> > > >
> > >Dave McLaren wrote:
> > >: I have a '91 Jetta 1.8L (RV) Digifant2, 305000km
>
> > >: Apologies for being so verbose, I just had some excellent coffee :) >
> > >: ANYWAYS.... now that you have some background.... has anyone heard > of a
> > >: distributor/hall sender screwing up only when the engine compartment is
> > >: warm? In winter it was not a problem.
> > >
> > >Not directly. The hall sender virtually never fails. The hall sender > has
> > >three small wires that go between the actual hall sender (in the > distributor)
> > >and the three pin connector on the outside of the distributor. This is > fine,
> > >but often the plastic connector would get damaged and would end up being
> > >supported not by the lip of the distributor but by the wires. Those > wires
> > >can't handle the forces imparted on the connected and they can break or > get
> > >damaged. I'm not sure why this would be temperature dependent. > > >
> > >I have however seen problems where electrical connections were not tight > and
> > >could be making electrical contact when the car is cool, but if it gets > hot
> > >something could loosen just enough that contact becomes intermittent. > I'd
> > >check, clean and tighten all your electrical connections, particularly > the
> > >grounds on the intake manifold.
> > >
> >
I had the same problem in my '93 Passat GLX. It would happen once the engine got warm (obviously on hot days, it was pretty quick). My tach would drop to 0 but the engine wouldn't stall. It just would take a 'time out' while driving. Anyway, the garage I go to said it would lose track of cylinder 1 and therefore the firing order. I just replace it and worked great after. The garage is pretty trustworthy so I do believe then that the part was bad.
Mike.