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Test #2
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Counter Pro
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| Ford trigger mechanisms |
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Looking at the Ford section of your ignition catalog (figure 6), you can see that Ford calls the rotating part of the trigger an armature and the pick-up component mounted on the distributor plate a stator.
Figure 6
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Taking a look at the parts in the buyer's guide (figure 7), there is nothing unusual to
see. The armature is a simple, 8-armed device (at least, it is for an 8-cylinder engine)
which is held in place with a pin similar to the Chrysler unit s.
The stator looks like an ordinary distributor plate unit. However, stators for the alter model 4- and 6-cylinder engines look more like GM pick-up units. |
Figure 7
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ME13 Pick-up Assy.(stator) (AM 8128445) (Fd D5TZ-12A112A, DU5) American Motors 1978-85 Ford 4- & 6-Cyl 1975-83 Ford Lt. Truck 6-Cyl 1975-83 Jeep 1977-83 Mercury 4- & 6-Cyl 1975-83 RE7 Armature (Fd D3AZ-12A099A, DT-1) Ford Lt. Truck 1974-85 Ford Products 8-Cyl 1974-85 Jeep 1977-85 Lincoln 8-Cyl 1974-85 Mercury Prod 8-Cyl 1974-85 |
| GM trigger mechanisms |
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The timer core is the rotating part of the GM trigger system, and can't be separated
from the distributor shaft. If you look at the catalog section for GM (figure 8), you
will see no timer cores lists for replacement. |
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Figure 8
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However, the GM pick-up unit, called a pole piece, is available for replacement. the
unit shown in figure 9; is representative of this type and can be found in the buyer's
guide.
These units look pretty uncomplicated. They have a series of V-shaped projections around the rim of the plate unit. When the Vs line up with projections on the timer core, a weal electrical pulse is produced which triggers the control module transistor. |
Figure 9 |
ME10 (Blue Tie) Pole Piece Assy. 8-Cyl. (GM D-1908, 1876210) Buick 1974-82 Cadillac1976-77 Oldsmobile 1973-82 Pontiac 1975-82 |
Just as a 6-cylinder Chrysler will run with an 8-cylinder reluctor, GM pole pieces can be used interchangeably. And, as you'd guess, they'll also cause the same problems. When in doubt, count the number of projections on the pole piece.
In addition, these pole piece units are very sensitive to electromagnetic pulses which are transmitted by the starter motor when cranking the engine. In order to get the right signals sent to the control module, these pole pieces are coded for polarity.
A cable wrap or cable tie is on the wires of the unit. Yellow, blue and white cable ties have been used to match specific pole piece units which specific engines. It pays to ask if there is a coded tie on the removed pole piece before selling a replacement.
Note: A very popular item in the parts line for electronic ignitions is a radio-interference capacitor which is used to eliminate radio interference. It requires replacement more often than other components in electronic ignitions, and can be suggested as a replacement part at a normal tune-up interval Figure 10 shows a listing for this component in your catalog.
Figure 10
| AMC trigger mechanisms |
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AMC tends to purchase much of its componentry from other manufacturers today,
but at one time they did make their own trigger mechanisms. To see some different
configurations for these items, check out figure 11 which shows pictures of these parts
from the buyer's guide.
The sensor or pick-up assembly looks ordinary, but the trigger wheel is fairly distinctive looking: a starlike object with a slotted tip design which straddles the pick-up sensor as it rotates.
| Figure 11 | ||
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| ME4 Sensor Assembly (8125444, 8127317) American Motors 1975-77 Jeep 1975-77 |
RE4 Trigger Wheel (AM 8125439) American Motors 8-Cyl 1975-77 Jeep 8-Cyl 1975-77 |
RE3 Trigger Wheel (AM8125440) American Motors 1975-77 Jeep 1975-77 |
| Failure modes |
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The rotating parts of the trigger mechanisms are substantial chunks of metal and look like they might last forever. Therefore, most failures, unfortunately, come from slipped screwdrivers or other mechanical failures caused by people working on the car. When component must be replaced; repair is not possible.
The majority of failures, however, are not on the rotating members, but on the pick-up units. As explained earlier, these devices carry very small trigger currents, and any visible breaks in the wires, internal shorts, breaks caused by heat or vibration, or breakdowns of the insulation on the wires will modify or cancel the signal to the control module.
This can cause no-start, hard start, port idle, poor acceleration, and more. Unfortunately, many of these problems will be intermittent in nature. The mechanic and DIY will need to learn to use hand-held testers, and to wiggle the wires gently to search out mysterious faults in the trigger mechanism.
An additional fault seen in Chrysler products is cracking of the magnet in the pick-up head, itself.
If the manuals tell him so, the mechanic must also use a heat lamp or gun to heat up the units to verify that all connections are free from any sort of corrosion.
Remember, the tendency on the part of mechanics is to think in terms of moving things. Because they can't see anything moving improperly, they often believe that these units are no fail. That's why you need to remind the mechanic to use a digital voltmeter and regular diagnostic routines on these parts when a fault condition indicates the need for testing.
Ford armature failure |
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When the engine is stopped, what does the armature do? It slides back down the shaft into its correct position. When the mechanic pulls the distributor cap, he sees nothing wrong.
Therefore, it's important to warn your customers about Ford's mysterious stoppage. Tell them to check the fit of the armature on the distributor shaft and to tug on it with their fingers. If in slips, it is too loose. Also mention that the armature tightness should always be checked at a tune-up interval.
Recap |
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Ignition points and all of their problems are gone. Replacing these mechanical items re electronic devices called trigger mechanisms by us and a variety of other names by the car makers. They are always two-component systems for which the following names are used:
GM: pole piece for the stationary component and timer core for the rotating piece.
Ford: stator for the stationary component and armature for the rotating piece.
Chrysler: magnetic pickup for the stationary component and reluctor for the rotating piece.
AMC: sensor assembly for the stationary component and trigger wheel for the rotating piece.
Heat, vibration, chemical attack from the underhood environment, and mishandling by the installer can affect all of these items to some extent. But the primary cause of failure of the pick-up assemblies is (wire breakage or shorts) (loss of magnetic strength) due to vibration.
