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Testing the Mallory Unilite and E-Spark Ignition Modules

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Thread: Testing the Mallory Unilite and E-Spark Ignition Modules

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    Post Testing the Mallory Unilite and E-Spark Ignition Modules

    An article describing the test procedure of Mallory Unilite and E-Spark ignition modules.
    Mallory Unilite and E-Spark Module Testing

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ID:	118 Although we no longer sell Mallory products, I am keeping the support articles on the website to support the hundreds of thousands of people using Mallory components on their vehicles. I do still believe in supporting our customers, past and present, even on product lines we no longer offer!

    The Mallory Unilite and E-Spark Ignition Modules are highly accurate and reliable ignition triggers and amplifiers. The self-contained module consists of an integrated photo coupler, a signal processor, and a power switch. Every time the special shutter wheel rotor stops the infrared light from reaching the photo coupler, the electronic circuitry energizes (charges) the ignition coil. When the shutter wheel allows the infrared light to reach the photo coupler, the electronic circuitry allows the stored energy in the ignition coil to discharge to the spark plugs. The Mallory photo optic modules do not require any adjustments or maintenance, unless you live in an extremely dusty/silty location that may justify the need to wipe off the optic periodically.

    One of the statements we hear from customers when they call us about testing/replacing their Mallory Unilite module is that they have read on various web forums that the Unilite is an unreliable piece of garbage, that it is too sensitive, or a variety of other derogatory comments. We can tell you that many of these people posting those comments should probably not be working on their vehicles without skilled supervision. Many of these individuals are blaming the problem on the effect (a blown or damaged module) instead of what actually caused the module to fail.

    I will often use the following analogy when speaking to our customers about module reliability, while examining and discussing the various causes of module failure:
    If you were to purchase four brand new tires and then knowingly drive through a pile of sharp steel and all the tires go flat, would you blame the tires as being junk, the tire manufacturer, or the store that sold them to you? The reply that is given 100% of the time is, "of course not!" Often, the comments include that the driver was obviously an idiot!

    Using the above comedic example we now must ask ourselves why people find it so easy to blame the ignition module itself, and not the cause? The easy answer is a lack of understanding of the product. It is easy to blame something that you know little or nothing about. The ignition modules cannot really kill themselves, so we must try to diagnose what actually caused the failure.

    I can state that I have customers that have used the same module for 20+ years and other customers who have killed three modules on a Saturday afternoon! The gentleman who had killed the three modules had recently purchased a rebuilt alternators from a typical chain store. After speaking to me he swapped out that new rebuilt alternator for another from the same store. I suggested that even those these were new rebuilt components, and the store "bench tested" them on their equipment, that there was a problem with them both. Of course, over the weekend when all this occurred, and I was trying my best to assist this customer, I endured considerable screaming, cussing, and insults. I finally convinced him to take the alternator(s) to a local rebuilder on Monday for testing.

    The basic bench testers in the average parts store cannot test for sticking diodes or a voltage dump!

    This customer found during testing that both alternators were built with cheap (for the cost savings) diodes in them. The diodes in each of these alternators were observed on an oscilloscope to be "sticking," causing a dump of high voltage to ground (the vehicle chassis/engine). A fast oscilloscope or other digital equipment is required to perform this type of test. As the technician at this local auto electric rebuilder tested these units the customer was able to see that a 140+ amp spike was being sent to ground every time he turned off the ignition key. This explained why the engine would start once with the new module, but never again. Replacing the diode in one of these so-called "new" alternators solved his module-killing problem. (He took the other unit back to the parts store, and surely gave them some of the hell he gave me over the weekend!)

    It is possible to have intermittent problems with the Mallory ignition modules. Say the module has been damaged, but not completely dead. You could be driving along and the engine dies. You check everything out, see nothing wrong, and get back in the vehicle and to your surprise it starts right up. This could happen daily or just once in a while. Test the module and it will most likely fail testing. This is almost a benefit, in that in some instances it does not just die and leave you stranded. It is giving you a warning sign that you need to act upon. REPLACE THE MODULE! I will describe this problem in more detail later in this article.

    Step by Step Module Testing - Unilite and E-Spark

    Tools Needed: Volt Meter or DMM (Digital Multimeter), and a Credit Card (or piece of thin cardboard)

    VERY IMPORTANT! If you are using a CD (capacitive discharge) or other type of amplifier box (Crane, Mallory Hyfire, MSD, Jacobs, Accel 300+, etc.) on your vehicle you must first remove (unwire) it from the system or you will not get a valid test result! You can bypass some of these with a supplied connector that came with the unit, but otherwise you MUST unwire it from the distributor and coil! After removing the amplifier you will need a ballast resistor installed in the system to prevent killing a good module (if you attempt to start the engine). Once unwired from the system, follow your distributor instructions for proper installation using ONLY the distributor, coil, and resistor.

    The CD or inductive amplifier box is an intermediary between the distributor and coil. The amplifier box picks up a triggering signal from the distributor and then tells the coil what to do. When a amplifier is in use on the vehicle it manages nearly all aspects of ignition coil function. Because the amplifier also provides a low-power supply (signal) to the distributor, and the distributor replies with a low-power (un-amplified) triggering signal, by providing this energy supply the box interferes with proper testing procedure of the Mallory ignition module.

    1. Remove the distributor cap and rotor. The Mallory distributor rotors are usually pretty tight on the rotor shaft, but it is only a press fit. You will be able to get the rotor off by firmly pulling straight up, though in all honesty it may hurt your fingers a bit the first couple times you attempt it until you get the grip correct. Try NOT to use a screwdriver or other device to pry on it. This would be a last resort, and will likely damage the rotor.
    2. Turn the ignition key ON and use your DMM (Digital Multi-Meter) to measure supply voltage. First check voltage at the POSITIVE side of the coil by connecting the black lead of your meter to a good ground (engine block), and the red cable to the coil. The meter should read close to battery voltage. Now check voltage at the NEGATIVE side of the coil by moving the red lead from your meter to the negative side of the coil. Your meter should also read close to battery voltage. If everything is good here, continue.

      NOTE: If you do not see a voltage reading that is close to battery voltage on both sides of the coil you have one of two problems:
      1. Make sure there is not a power supply problem. Take a jumper wire from the positive post on your battery to the positive side of the coil. Re-do the test. Do you now have battery voltage on BOTH sides of the coil? If so, find out why battery power is not properly reaching the coil. Remove this power jumper wire.
      2. If the reading on ONLY the NEGATIVE side of the coil is low, the module is artificially energizing the coil when it is not supposed to be. You will need to replace the module. The only time the module should be allowing the coil to charge is when the photo-optic is blocked. The rotor has been removed and there should be nothing blocking the L.E.D. optic; therefore, the module has been damaged and must be replaced.

    3. With the DMM/Voltmeter still connected to the negative side of the coil (black DMM wire to ground, red DMM wire to the negative side of the coil) you are going to watch the meter while blocking the L.E.D. optics on the module with your credit card. Placing the credit card or other device between the towers on the module will block the L.E.D. optic. When the optics are blocked the readings on your DMM/voltmeter MUST drop below 2.0 volts. It may be just for an instant, or it may hold below two volts until you unblock the module. Either is OK. But if the voltage does not drop below 2.0v the module has been damaged and must be replaced. Again, voltage MUST drop below 2.0 volts when the optic is blocked!
    4. Now, unblock the module after performing step #3 above and the voltage reading on your meter MUST return to battery voltage. If the voltage does not instantly jump back up, it stays at its "optic blocked" reading, or does not fully recover, the module must be replaced.


    Based upon the test procedure above we can come to a few conclusions:

    • If the battery voltage is not initially present you have either an electrical problem prior to the coil (ignition switch, low battery, corroded cable, etc.), or the module is charging the coil when it is not supposed to. The module has been exposed to voltage spikes or installation errors.
    • If the voltage does not drop when the optic is blocked, the module is "open" and this was likely caused by a power surge, excessively high resistance in the plugs or plug leads, or improper grounds. Replace the module!
    • When the voltage always stays below 3.0 volts it means that the module has been spiked by high voltage or amperage, lack of a ballast resistor (if not using an amplifier box), or the wiring was incorrect. Replace the module!
    • If the voltage only drops to 3-4 volts you will get a noticeably weak spark. This is also caused by poor grounds, or a power spike. Replace the module!


    • A faulty charging system (stuck or shorted regulator/alternator), or high amp single wire alternators with a cheap diode.
    • Ineffective or inadequate vehicle grounds. The module brown wire must be connected to the engine block. The vehicle grounds should consist of: Battery to Engine; Battery to Body; Engine to Frame; Engine to Body; Body to Frame
    • Trying to start the engine using a battery booster-charger. Most of these units have very dirty electrical signals which cause power surges or spikes. The proper procedure is to disconnect the battery, charge it, and then reconnecting the battery.
    • Using non-suppression plug wire leads. You must use suppression core type plug wires, no solid core wires (stainless steel or copper). Spiral core is best, but carbon or any suppression core plug wire will also work.
    • High amp stereo equipment that is not properly grounded or the vehicle grounds have not been updated to handle the added capacity. The surges created by high power media systems can play havoc with a vehicle's electrical system. Proper sized cabling, using relays, and adequate battery supply is imperative!
    • Direct shorts in the vehicle's electrical system.
    • Welding on the vehicle or working on the vehicle's electrical system while the distributor harness is connected.
    • Faulty starting system (excess starter drag, not enough voltage/amperage getting to the starter, worn brushes/armature).
    • (Not that many people are using these anymore!) CB radio spiking on mic click into electrical system (typically only on power modified CB radios).

    One more time on the testing procedure - SHORT VERSION:

    1. Remove Cap & Rotor
    2. Turn Ignition Key ON
    3. Is there Battery Voltage (+/- 14v) on the POSITIVE side of the coil? YES = GOOD!
    4. Is there Battery Voltage (+/- 14v) on the NEGATIVE side of the coil? YES = GOOD! NO or Much Less Than Positive Side of Coil = BAD!
    5. Voltage Drop Test - Voltmeter still on Negative side of coil. Voltage Drops BELOW 2.0v = GOOD! NO Drop = BAD!
    6. Voltage RECOVERS to BATTERY VOLTAGE after unblocking the optic? YES = GOOD NO = BAD

    As soon as you get to a BAD in the procedure above, there is no need to test any more ... replace the module.

    Here is a copy of Mallory's description of this testing procedure (I feel mine is more clear, but if you want it in their words, here ya go): UniliteTest.pdf

    A Few Tips and Lesser Known Facts?

    The Mallory Unilite and E-Spark modules require a drop in voltage for the trigger side (green wire) of the module, even though the power supply side (red wire) can handle 14.0+ volts. Even though the ballast resistor is wired inline on the positive side of the coil it is actually dropping the voltage to the negative side of the coil (trigger side). This means that you MUST have ONE of these installed:

    • The correct ballast resistor. The Mallory part #700 is the best, but another ballast of compatible specs is also acceptable. (usually around 0.85 Ohms) <or>
    • OEM resistance wire in the factory wiring harness <or>
    • Internally resisted ignition coil (cannot be used with external ignition amplifier units). <or>
    • An ignition amplifier like the Mallory Hyfire, Crane, Accel, MSD, or other comparable units.

    On applications that are not using an ignition amplifier you can verify that your system has the correct resistance by connecting a volt meter to the negative side of the coil with the engine running at idle. The measured voltage should be roughly 8-9 volts.

    If you are using an ignition amplifier you do not need a ballast resistor, but you should keep one handy. If you ever need to bypass or remove the amplifier you will need a ballast to prevent damage to the module.

    Anytime you do anything type of electrical work on your vehicle, no matter what, you should unplug the 3-wire connector at your distributor. This will guarantee that you do not spike the module while working on your vehicle. Remember, it is not the module killing itself that causes failures. It is some other component or human error that kills it.

    NEVER try to boost start your vehicle using a battery starter/charger. The dirty power supply and excess amperage can and will damage your ignition module. Disconnect your distributor harness, or disconnect and fully charge your battery, then reconnect everything and start the vehicle. If you own a newer computer-controlled vehicle, this is the same procedure recommended by the vehicle manufacturers to prevent damage to vehicle computer and diagnostic systems.

    If you want to add some "minor protection," but not a guarantee to prevent a voltage spike taking out your module, install the Mallory Circuit Guard, part #29371. This simple component plugs inline on your 3-wire distributor harness and provides two features. The first is a signal filter that cleans up dirty power signal that occurs from dirty connections, or electrically-charged dust in the alternator. Think of this like an ancient rabbit ear antenna on an old television set. They never gave us a clean picture, but it takes away some of the snow. On your vehicle this takes away some of the peaks in a dirty signal. The second benefit is a compact capacitor that is designed to absorb "small" power spikes, and prevent them from getting to the module. It does absorb some smaller spikes, but is not a guarantee to protect your module. A decent sized spike will still get through! This is not a replacement for laziness in finding the cause of module failures; although, this component is inexpensive insurance to help prevent module damage.

    I recommend having a spare module on hand the same way you have a spare tire or fuses. The Mallory E-Spark module is an inexpensive replacement for the Unilite (though they are virtually identical), but the E-Spark is a better module. UPDATE: For some time the Unilite and E-Spark were separate modules (the brilliance at Mallory *sarcasm* was that simply telling the customers that the Unilite was redesigned and now half the price was expected to be too confusing to the customer. Not much faith in the intelligence of their customers it seems). The E-Spark offered a better circuit board design, the assembly was automated, and was half the cost while offering the same one-year warranty. I'm not 100% certain, but I believe both modules are now identical other than name and part number. You can now purchase the #605 (Unilite) with a 2-year warranty or the #6100M (E-Spark) with a 1-year warranty. This is how I suspect they are now identical - I doubt anyone at Mallory would provide details.

    For reference, the Unilite or E-Spark modules are no more or less sensitive that a GM HEI, Ford Duraspark, or other brand ignition modules. They just never bother to tell you the causes of failures, they merely hold out their hands for you to drop some $$$ on a new module with no explanation. The main issue with the Mallory photo-optic modules is due to a patent issue that GM holds, the Mallory modules require the ground wire connection that leaves them susceptible to attack up the ground circuit from the failure or trouble of other electrical components. To alleviate this problem without crossing into the legal realm with a patent infringement, the module (as I was told) would have to be 2-3x the size and no longer fit inside the distributor. Mallory wants to keep these distributors self-contained. This is also why a ballast or other resistor is required. These units are still the most accurate ignition triggers available and offer other benefits! If your vehicle's electrical system is in proper working order, maintained, and the vehicle owner or mechanic is properly trained, there should never be module failures!

    You may or may not know this, but the Mallory Unilite and E-Spark modules are both a trigger and coil driver/amplifier. You are not required to use an external amplifier unit. But, if you are using an amplifier and it fails you can easily bypass the amplifier and still get yourself home (you would need a ballast resistor). On other brand ignitions you are stranded until you replace the external box.

    You need to using the correct coil with your Mallory Ignition. Without getting into details here, think of a coil like your shoes. You would not wear rubber sandals to climb Mt Everest, nor would you wear snow boots to cross the Mojave desert in August. You choose a coil to match how you are going to use the vehicle and the operating range of the engine, combined with any other components that may affect your choice (such as an amplifier). See my article on ignition coils in the Ignition System forum thread.

    Plug wire selection is also important and we have a tech page that explains proper selection in detail. You need a certain amount of resistance in your plug wires to prevent voltage leakage from the coil. Too low a resistance causes voltage leaks which lead to lost power, misfiring, and more. Too much resistance in the plug wire leads also causes lost power and performance. Plug wire resistance is measured in "Ohms per foot".

    In Closing:

    As I mentioned near the beginning of this article, sometimes the module will provide an intermittent problem that can be difficult to diagnose. What we might experience is intermittent stalling. We get in our vehicle and start driving, but then a few miles down the road (usually about the time the engine has fully warmed up) the engine dies/stalls. We get out, pop open the hood and start looking for the most common causes: (air/fuel/spark) no fuel, a battery or ignition cable came loose, no spark, and anything else that may stand out as we peer into the engine bay. What if we do not see anything obvious?

    We almost always have that perplexed look upon our faces and wander back into the passenger compartment and try to start the vehicle. It Starts!? Now we are really confused. Did we touch the right component and miraculously fix the problem, or is something else going on? Often the latter is the case.

    Let's backtrack a bit. The engine started, ran fine then died. We fiddled with it a bit and then it restarted. Think cool-hot-cool.

    I have a thing with comparisons, analogies to help explain things in terms that the person(s) I'm speaking with will understand. One of those comparisons can be used on those of use who are getting a bit older or less active, and our bodies don't always warn us in advance of doing something that we'll pay for later. If we go out on the weekend and are horsing around with our kids, or doing out of the ordinary yard work or home projects, helping a friend move, or playing sports, we may feel tired but still feel pretty good from working a few muscles that do not get used as often anymore. Sore muscles or a mild headache may kick in later that evening (beer and wine in the hot sun versus being a little smarter and drinking water, or just not using sunscreen or other sun protections) reminding us of the day's activities. The next day we may feel perfect, almost renewed! Then the second or third day comes along ...

    A few days later we may feel like absolute garbage. We can barely move, various muscles in our necks, backs, legs, shoulders are aching. Sleeping may be uncomfortable that second or third night. Why am I describing this painful retrospect? I'm using this example to describe what has happened to the ignition module!

    Of course the module was not out climbing mountains, shooting hoops, drinking too much beer or running bases, but at some point the module was affected by something that damaged it. The vehicle stalling that we experienced is the module's way of telling us that it has been hurt and needs to be checked and/or replaced. This can be a benefit with the Mallory module, by not leaving us stranded somewhere, offering a little advance warning. When the module got up to temperature, something in the circuitry shut off the flow of power through the module and it was now unable to do its job until it cooled slightly. This may not occur again for days or weeks, but if the stalling becomes regular it is definitely a tell-tale to take action. Most of the time, performing the module test procedure above will provide conclusive evidence that it needs to be replaced, but in rare instances the module will pass the test above and still be at least partially defective. Replacing the module would be your last resort.
    Best Regards,

    Samuel A Solace - Pres/CEO
    Century Performance Center, Inc.

    ph (775) 746-4887
    fax (775) 624-8865

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