Well, it's a quiet day on the list, so I'll jump in here even though it's
not my car model of expertice.
At 09:20 AM 4/23/2000 -0400, Bill Saidel wrote:
>.... the car started before balancing the carbs but then backfired under
load.
Could be lean mixture, or erroneous spark of various sorts, of emissions
control problems on the newer cars (newer than 1967).
>.... no spark at all. .... but I noticed some things that make me think I
have multiple
problems.
>....
>1) no electronic ignition I think. But first, what means electronic
ignition (told you I'm a novice with these things...)... The distributor
has points.
Electronic ignition usually replaces the points with something else. That
could be a photo-electric switch with a slotted rotor interupting a light
beam, or a hall effect sensor triggered by a rotating lump of steel with
bumps on it, or in odd cases something triggered by a rotating magnet.
This pickup device will in turn signal an electronic circuit to switch the
current to the ignition coil on and off, thereby doing the same job as the
contact points.
The electronic part of the device can vary considerably, with some fitting
entirely inside of the distributor, and some having a substantially large
unit mounted elsewhere outside of the dizzy. Some electronic ignition
units do nothing more than switch the current to the coil the same as the
original contact points. Others may change the wave form of the input
current to give a higher voltage spike for a shorter duration. Some will
use a substantially large capacitor to store some additional electricity to
increase the duration of the spark. A few rouge models may actually
increase the voltage supplied to the coil with the intention of creating a
stronger spark, but these may actually damage the coil.
The first and most commonly understood advantage of electronic ignition is
the reduction of periodic maintainance due to elimination of the contact
points, which can burn, pit, wear, or otherwise get out of adjustment.
However, this advantage may in some cases be more than offset by the fact
that the replacement electronic unit can fail in operation and leave the
car dead on the road. Because of this quirk of the electronic parts, you
might consider carrying a complete duplicate set of the electronic parts
for emergency maintainance, or a set of the original contact points to
return the system to stock configuration to get you car going again, or
maybe carry a cell phone and auto club card in the car at all times. I
would find it easier to carry a replacement set of contact points (and
stock condenser) than to pack along the parts for en external electronic
ignition system. The electronic ignition that fits entirely within the
body of the dizzy may be reasonable to pack along if you don't mind the
cost of the spare parts.
As to any other advantages of electronic ignition boosting the strength of
the spark, I find that a 40,000 volt sport coil works just fine in concert
with the original contact points setup.
>2).... When I put the old coil back in, spark was still lost. Wires to the
negative side...
Negative earth electrical system I presume.
>one goes to the tach;
Correct.
>a 1000 ohm resistor is connected to the + which does go to the distributor.
1000 ohm resistor? What the heck is that? If it's in series on the way to
the dizzy it won't pass any significant current when the points are closed,
but can supply a voltage when the points are open. This might be used to
power an electronic device inside the dizzy, but otherwise ya got me. If
it's in series between the ignition switch and the coil the same applies,
no significant current, just a voltage reference. I don't recall a 1000
ohm resistor being used for anything in a 12 volt elctrical system except
maybe inside of some electronic unit.
>Yes, I might have mixed up the wires but I hear the starting motor turn
and turn and ... (which is a good sign?)
That doesn't mean anything. The starter motor can run with the entire
ignition system disconnected.
>3) Reading voltage across the coil, no matter how long I charge the
battery, it never goes over 10 V.
If you have a baLlast resistor on the supply side of the coil you should
see about half of system voltage at the coil, about 6-7 volts with ignition
switch on but engine not running, or 7-8 volts with the batteries on an
external charger or with the dynamo/alternator running at speed. When you
turn the ignition switch to crank the engine ir bypasses the ballast
resistor and applies full system voltage to the coil for starting, which
might be anything from 7-12 volts during cranking (depending on the
condition of the battery), but most likely in the 10-11 volt range if it's
actually cranking over normally.
>4) I don't think I'm getting spark to the distributor because the wire
from the coil to the distributor doesn't spark across the block when I
tried that.
I suspect you have the wires switched at the coil. You may have anywhere
from 2 to 4 wires there. On the supply side ("+" or "bat" or "ign"
terminal with a negative earth system) you need power from the ignition
switch. If there is a ballast resistor you will have two wires here, one
from the resistor and another direct from the start terminal on the
ignition switch. If no ballast resistor you will have just one white wire
from the ignition switch. On the "downhill" side of the primary circuit
from the coil ("-" or "cont" or "dist" terminal with a negative earth
system) you should have one wire going to the side of the dizzy so the
points can interrupt the ground side of the primary circuit. If you have
an electronic tach this same side of the coil may carry an additionsl
signal wire for the tach. In some MGs the electronic tach signal comes
from the supply wire, in which case there will be no separate tach wire on
the coil.
If you were to have electronic ignition all bets are off on the wiring.
Most electronic units require at least one additional wire to supply
voltage to the unit inside of the dizzy. With an entirely internal unit
this would run from the supply side of the coil to the dizzy. With an
external unit the additional hot wire can run from the ignition switch to
the external box, or from the supply side of the coil to the external box.
An external electronic ignition unit will generally have at least four
wires, power, ground, signal from the dizzy, and current to the coil.
Additionally it is likely to have another wire to supply power the the
smallet unit inside of the dizzy which replaces the points. If you do have
(non-factory) electronic ignition I hope you have and keep the paperwork
that came with it, because you will get no help from the factory workshop
manual.
>5) Here's an out and out question. What looks like a capacitor (a small
blue jobbie) is attached to the + end of the coil. Its ground appears to be
the chassis because it is only connected at one end. What is this?
Radio noise supression capacitor. The car will run without it, but if it
has an internal short it will kill the ignition. If you have the wiring
correct otherwise, you might try disconnecting this part to assure that it
is not shorting out the hot side of the coil. These suppression capacitors
may be found other places in the system as well, such as in or near the
fuel pump, near the wiper motor, near the heater motor, and/or near the
radio itself. These are usually connected to the power supply wires to the
associated device, and as such, a short in any of these capacitors could
ground out the supply side of the ignition.
>6) And the piece de resistance (as I mentioned to Carl), the jet does not
move when I turn the jet adjusting screw on one carb. ....
Get the ignition working first so it runs. Sweat the small stuff later.
>....
>How do I cure the back pain on Sunday from leaning into the motor
compartment on Saturday? I know...occupational hazard for us OF's but
still, ....
Drink heavily? Otherwise spend some time in a hot tub to relax the
offending muscles. Works for me.
On a side note,
At 02:19 PM 4/23/2000 EDT, REwald9535@aol.com wrote:
>.... I have a silly question, you did bolt the coil in didn't you?
(circuit is grounded through mounting bracket)
Sorry Rick, the coil bracket does not act as a coil ground (except for
noise supression). The ignition system will work with the coil body
isolated from the chassis. Two small wires and one fat one is all it takes
to make a coil work.
And a happy Easter to everyone from here as well.
Barney Gaylord
1958 MGA with an attitude
http://www.ntsource.com/~barneymg
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