<VV> 140 stalling

[Larry Forman]

At 07:56 PM 8/12/2005 -0700, Karl Behrens wrote:
>Well, I finally figured out my 140 stalling issue. At first, most 
>mentioned that the car was suffering from vapor lock. Well, here is what 
>the car is doing now! I have a 1969 500 coupe 140/glide. The car can sit 
>idle in my driveway, and runs fine. After about 30 min the car dies. This 
>is not in gear, just sitting there running. Well, the coil during normal 
>running is only getting 10 volts. But, when it stalls the coil is only 
>getting 6 volts! The alternator is putting out 15 volts, the battery is 
>getting 15 volts. The voltage regulator is putting out 15 volts to the 
>battery. So..I am at a loss. I am running the Crane Fire Ball Igntion I 
>purchased through Clark's. Now, when I noticed the car stalled, I found 
>that it blew 4 fuses. When I replaced the fuses, and stepped on the brake 
>pedal, I heared a sizzle, and the fuse blew again! I have purchased an NOS 
>Column switch to replace my orginal one. I disconnected the original 
>switch to keep from blowing fuses. Would the switch ca!
>use the
>  low voltage to the coil, or what??
>Thanks,
>Karl
>69 500 #5465
>67 Monza

Hi Karl,
There are several things going on here that might be causing your 
problems.  First let's analyze the voltage issue to the coil.  Without the 
car running, the battery voltage is around 12 or 12.6 volts.  When charging 
as in idling or driving, the voltage regulator is limiting the voltage from 
the alternator to about 15 volts.  When the car stalls and the engine 
quits, the voltage to the coil CIRCUIT is now about 12 volts or so.  You 
have a ballast resistor and when you take into consideration the voltage 
drop of the ballast, 6 to 8 volts is likely about right.  It will be higher 
when the points are open, since there is no current flowing and it should 
be close to the battery voltage.  The reason it might be around 10 volts 
when running is that current is flowing when the points are closed and 
close to zero when the points are open.  Thus the voltage at the positive 
of the coil being 10 volts is likely about right because you are reading 
close to an average voltage due to the current flow.

Since the fuses blow, I suspect you have something shorting out the wiring 
and blowing fuses.  It would be difficult to figure out what is happening 
without knowing which fuses and where they are in the circuit.  You could 
have something in the wiring shorting it to ground and when you step on the 
brake pedal, the voltage is supplied to the corner lamps drawing 
current.  Any short in any of those wires will blow that circuit fuse.

So my guess is that you need to search for a short.  I have heard of people 
taking a small buzzer and placing it in place of the fuse with maybe 
another fuse in series with it to keep from completely frying things.  When 
you energize the circuit, the buzzer will buzz.  Now you take a small 
pocket AM radio and tune it to the top of the band with no signal 
present.  The buzzer is supposed to generate radio frequency energy and you 
should hear it in the radio.  Now you can go along the wiring from the 
buzzer following it toward the circuit load or lamps or whatever, until the 
radio noise stops.  This should be the approximate location of the 
short.  It makes sense to me with my radio and electronics 
background.  Note, however, I have not actually used this equipment that 
way.  I have sources of more sensitive instruments to do the same 
thing.  FWIW, the very old HP Current Tracer, whose model number I forget, 
which was designed as a digital troubleshooting piece of equipment in the 
70s, can be used to do the same thing if the circuit is not powered but 
driven with a pulse generator.

I was helping tune a club member's car and it suddenly died.  I happened to 
see a light flash in the engine wiring.  It was a screw shorting out the 
wiring if things happened to just be wrong in the wrong position.  So look 
for something pinching the wiring.

Furthermore, if you are REALLY having vapor lock, turn off the engine, 
remove the air cleaner,s and while looking down the air horn see if you get 
a strong squirt of gas from the accelerator pumps when you twist the 
throttle linkage.  A vapor locked car will be starved of fuel and there 
will be NO fuel in the float bowls to provide any accelerator pump 
squirt.  Make sure your accelerator pump cups are in good shape, or you 
might not get a squirt regardless of  float level.

Finally, if you are then convinced you have a vapor lock condition, after 
first having replaced the rubber fuel line leading into the engine 
compartment, replace the mechanical fuel pump with an electric and be done 
with vapor lock forever.  There should be safety wiring in the event of an 
accident to turn off the electric pump when the engine is off.

Regards,

Larry