The pictures are of the original unit fitted to
my car, which bears the date code "2385", indicating
that it was manufactured in week 23 (early June) 1985, only a
few days before the vehicle was assembled.
The spark is timed to occur when the rotor arm is opposite the
appropriate plug lead terminal in the distributor cap. Because
the ignition timing advances and retards with varying conditions
of the engine and can also be adjusted by rotation of the distributor
body on the engine, it is necessary for this to be possible through
a small arc of rotation, as shown in the diagram. Of course the
arc needs to be small enough to prevent cross-firing with the
With increasing engine speed, the centrifugal
"bob-weights" provide dynamic advance by rotating the
upper shaft clockwise on the lower. During this process, the relationship
of the reluctor and the rotor arm remains constant, so the rotor
arm continues to align with the plug lead terminal in the distributor
cap when the spark occurs.
There is a vacuum advance module which, with
increased throttle opening, rotates the mounting of the pick-up
anti-clockwise on the base plate, generating the spark at an earlier
position of the rotor arm relative to the cap. This requires that
the point of the rotor arm be wide enough to remain in contact
with the cap terminal.
In the case of my 17D series "detoxed"
engine there is also a vacuum retard (not fitted to later engines),
which comes into play on over-run against a closed throttle. This
has the opposite effect by rotating the pick-up mounting clockwise
and generating the spark at a later position of the rotor arm
relative to the cap terminal. Again, the rotor arm tip has to
be wide enough to remain in contact with the cap terminal.
So as a guide when setting up the distributor
on the engine at cylinder 1 TDC (read the manual to
see how to do this), the rotor tip should align more or less exactly
with the cap terminal.
An ignition failure after 29 years was initially
attributed to a problem in the amplifier, but extensive testing
showed no fault. Even so, the amplifier was replaced and all seemed
A second failure occurred one year later, when
I found that the original distributor to amplifier link-lead
(part number PRC4503) had become badly burnt as a result of having
been factory-fitted under the alternator (mine is mounted on the
left side of the engine, because of the factory-fitted aircon)
and near the exhaust manifold. Apparently this is a well known
It is a twin-core screened lead with a molded-on
connector at the distributor end and non-reversible spade-connectors
at the amplifier end. It is an easy fix to replace and re-route
over the top of the alternator.
later Range Rovers the amplifier module was miniaturised and built
onto the side of the distributor body. This type of distributor
has superceded the original pattern on the spares market. The
later distributor uses a different link-lead to connect the distributor
directly to the coil (red wire to coil +ve and ignition live,
black wire to coil -ve). Remember to order the "O"
ring separately, as it doesn't come with the distributor.
early type ETC4715
late type ECT4715P
note that it is supplied without the
"O" ring seal
However when I attempted to fit the later type
distributor to my car I found that the amplifier module fouls
against the PAS pump mountings, which restrict rotation of the
distributor body and thus prevent the correct timing being set.
I have not found a fix for this yet. It is not a problem
on vehicles with the later type PAS pump, which uses different
the top alternator bracket has been removed
temporarily for access
H&H Ignition Solutions
can move the later type amplifier to fit between the vacuum module
and the 6 o'clock cap clip, but that would not help in my
case because the amplifier hangs down too far to clear the water
They can recondition the early type distributor,
including replacement of the pick-up sensor.
After having a new pick-up sensor fitted, I could
not get the engine to run properly. It was possible to correctly
set the timing statically, in which position (with the engine
stopped at TDC) the rotor arm pointed midway between plug terminals
1 and 8. Also, the distributor body was rotated clockwise (ie
retarded) from the original position.
As soon as the vacuum retard pipe was connected
the engine would barely run and then only very roughly. Attempts
to adjust the ignition timing by rotation of the distributor body
proved only to make matters worse. Connecting the vacuum advance
pipe made no difference.
Further investigation showed that the seal on
the retard side of the vacuum module had failed, so it was replaced.
There was no improvement.
Much deliberation and wide consultation failed
to come up with either a cause or solution. The link-lead was
new and both the amplifier and coil were obviously generating
the spark. All the indications were of a problem within the distributor,
but a further complete strip and rebuild showed nothing amiss.
The wiring of the new pick-up module was shown to be physically
correct when compared with the original.
After many days (and sleepless nights!) of thought,
I came up with the hypothesis that the pick-up leads might have
been wrongly connected from a functional perspective. Testing
by using break-out leads at the amplifier end of the link-lead
proved the hypothesis, meaning that the new pick-up was wired
the other way round internally.
In this situation the spark is still triggered by
the voltage drop generated by the reluctor and pick-up. However,
because the waveform is inverted this occurs prematurely, ie the
ignition becomes significantly advanced.
This can be overcome at the static timing point
by an alternative position of the distributor body (as observed).
The engine will run with the vacuum pipes disconnected because
the spark actually occurs when the rotor arm is within the functional
arc of the plug cap terminal, albeit at the most clockwise (retarded)
Once the vacuum retard pipe is connected, the
spark occurs when the rotor arm has moved further clockwise beyond
that arc and can no longer connect to the correct spark plug lead.
Adjusting the advance/retard position of the distributor body
on the engine cannot overcome this and only serves to move the
spark to a timimg point where the engine will no longer run at
Rewiring of the new pick-up sensor lead connections
has solved the problem. I hope this sad story may be helpful to
anyone else who is unfortunate enough to encounter the same difficulties.
This ignition system is similar to the Mobelec
Magnum electronic ignition system which I retrofitted
to one of my earlier cars. The basic kit retained the original
contact breaker points.
Click on the picture below if you want to read the fitting instructions.
The optional fitting kit (this one is the 144 B4,
for an anti-clockwise rotation Ducellier distributor) replaced
the contact breaker points with a magnetic pick-up, similar to
the Range Rover system.