All right, now that I've gone over some theory on operation of Chrysler's Electronic Ignition, let's do some testing. This is going to be long-winded as I'm trying to recognize & eliminate most of my ASS-U-M-ptions. This post will cover ignition electrical- but not spark plugs or timing controls (those are complete subjects just by themselves). First I've got to go over some warnings & explanantions.

ALWAYS RESPECT ELECTRICITY, & WHAT IT CAN DO!! Most of the times, the voltages (& amperage) present in automotive ignition systems is not lethal -usually- BUT, the involuntary muscle contractions resulting from a high voltage shock can/ will cause (severe) injuries. Don't pull-touch- get too close to ignition plug wires or dist cap or coil on a running/starting engine (at least until you know that they're in GOOD condition and securely attached). Be very careful connecting any test wires or clips to the ignition coil terminals (do so when the engine is stopped & turned off)- primary voltage can hit 300V+ - that's a pretty decent "kick". It's a good idea in general not to wear rings or watch bands when working underhood- under the right conditions 12V can hurt you, or at least make you very unhappy. Do NOT connect test equipment directly to any plug wires or the coil output- most devices are not designed to handle very high voltage & at best will be damaged.

Definitions: DVOM=Digital Volt Ohm Meter- testing equipment that's much more precise (but doesn't replace) a test light; crank the engine/turn the engine over/crank the starter= electrically activate the starter motor to spin the engine(usually does NOT imply that the engine should or will begin running); start the engine/fire up the engine= engage the ignition & starter so that the engine spins & begins running; fire the coil= triggering the ignition module so that the ignition coil produces a spark; coil= ignition coil module= ignition module or "ecu"- electronic device that switches the current flow throught the ignition coil's primary circuit on & off; dist= ignition system distributor- contains the cap & rotor to "distribute" high voltage to the correct spark plug wire, pick up coil & reluctor to trigger the module, & advance control mechanisms; KV= kilo Volts- 1KV is 1,000 volts; kOhms= Kilo Ohms (unit of measuring resistance) 1KOhm= 1,000 Ohms; mV= milliVolts 1,000 mV is 1 Volt; mSec= millisecond- 1000 mSec is 1 second; primary voltage/circuit= the low voltage (12V) side of the ignition system- includes power supply to the coil, ballast resistor, part of the coil, ign module, & wiring; secondary voltage/circuit/system= all of the parts of the ignition system that carry high voltage (kilovolts)- includes coil, dist cap & rotor, coil & spark plug wires (aka high tension leads), & the spark plugs; AM= AfterMarket parts- stuff purchased from Napa/Eclin, Standard (SMP) or your favorite chain store; OE/OEM= Original Equipment Manufacturer- for us it's Chrysler or Mopar; KOEO=Key On Engine Off- ign switch turned to the "run" position; KOER= Key On Engine Running- usually at idle unless specified otherwise

A note on DVOM's: make sure that yours has a fresh battery & that you understand how to use it. Many models have very different features. Some are "manual" range- you have to turn the selector dial to change to a different measuring range( ie. if you're in the 0-2V range, you can't read a 12V battery until you switch to the 20V range, or you'll see "open circuit" reading if you try to measure a 15kilo-Ohm resistance in the 200 Ohm range)- you also might have to physically move the test leads from one jack on the meter to another when switching from V to Ohms. Read your instructions. Others are "auto-range"- just turn the dial to volts or ohms & test. Test your leads most every time you use the meter- for volts do a quick check of batt V or, for ohms touch the leads together (should read almost 0 Ohms)- It's tough to do tests when you have a bad lead or a connection.

DVOM Leads- some are short little things with pointy tips- OK for quick/momentary tests but annoying for most work as you have to hold the tips in place while you test- ie, you end up with both hands occupied. Small alligator clip ends are better since you can attach them- to SMALL things- as you test. Some leads have large alligator clips which are nice to clip to battery connectors or to bolts/studs/brackets on the engine. If possible get leads with both size clips (or 2 sets, 1 of each)- & longer is better for automotive work. (The really nice leads I have come with large clips with built in pins to pierce wire insulation- Fluke TL-26 if your meter can use them).

Diagnosis is a logical and repeatable process of performing tests, & based on the results determining the next course of action (doing a repair or another test). "Throwing parts" at a problem may sometimes work, but it ain't efficient or cheap so I don't do it. However, there are times when "diagnosis by substitution" is the best way to proceed- to that end I have spares of most ign system parts that I got on the cheap- usually from the wrecking yard when I'm pulling parts.


Now, if my engine won't start, I pump the gas pedal twice & try again. After that I hold the pedal to floor & try once more. Still no-go? Time to open the hood & test. I'll look down the carb throat & work the throttle to see if the accelerator pump shoots a stream of gas which would confirm fuel delivery. Next I check for spark at the end of a spark plug wire. I use a spark tester with an adjustable gap (such as Thexton 458 or AMPRO T71240). A spark tester lets me consistantly QUANTIFY spark output (& there's less chance to get zapped). Connect the plug wire to the tester end, attach the ground clip to the engine, & set the gap to about 3/8" (the testers have numbers that should indicate ABOUT how much kV is present- I just measure the gap with a small ruler- my coil put out about 7/16" spark). Either have someone crank the engine while you watch or "position" the tester so you can see the gap while cranking. You shouldn't use a remote starting switch from underhood because that won't turn on the ignition bypass circuit= weaker spark. It can be difficult to see spark in bright sunlight- you can try using something to shade the tester- the color of the spark doesn't matter too much. You should have 2-3 sparks in 2 seconds- they should be steady & consistant. If that's good then you could have: fouled plugs, incorrect ign timing, or some sort of engine mech fault like valve timing, low comp, restricted exhaust, etc. If not then I check spark at the coil. The coil output wire terminal doesn't fit the spark tester (it'll fall off), you can take a plug wire & use that from the coil to the tester instead. But first I do a quick resistance test of the coil & plug wires. Most generic "suppression" wires are around 5-6 KOhms per foot. I'm happy if I see 2 KOhms to 20 KOhms or so- as long as they aren't open circuit (that indicates a failed wire- replace the set).

With the spark tester hooked to the coil, crank the engine & look for spark. It should be fast & consistant, about 8 per second. If you have spark at the coil but not at the plug wire then it's gotta be something wrong with the cap (such as carbon tracks) or rotor (burned thru). If no spark (or is irregular), try adjusting the gap down to 1/8" & recheck. If you now have spark we'll chase weak coil output in a bit, if not we'll continue with no spark. Now I test voltage at the coil primary connections. Put the black meter lead on the battery (-) post for most all these tests. Put the red lead on the (+) coil connection- KOEO I had about 7V. The reading is the result of voltage dropping across the ballast resistor while current is flowing(it should be a little higher- about 8V- I apparently have some voltage drop in my ignition power circuit I should chase). At the (-) connection I had 1.0-1.2V KOEO. This is voltage drop thru the module electronics to ground.

If your voltage readings at the coil are significantly different, we can analyze them to find the problem area. If (+) & (-) are low or 0V- go look for a bad ballast resistor (spec is .5-.6 Ohm), or another problem with the ignition power circuit(check V at both sides of the ballast- should be about 12V in & 8V out). Ballast failures are common enough that I alway keep a spare in the glovebox. If (+) & (-) are high, there is high resistance on the ground side such as bad module or connection, or loose/corroded module/ body ground. If (+) is hi & (-) is 1V or less than you likely have high resistance or open circuit in the coil. If (+) is normal but (-) is near 0V then you might have a short to ground in the (-) circuit (or in the module). If you have low resistance in the coil, then (+) would be low & you'd have a larger than normal V drop across the ballast - & you'd likely have a failed module as well. You can check resistance across the coil primary winding (be sure to disconnect the ballast, module, or one of the coil primary connections before testing). Spec is 1.6-1.8 Ohms at 70-80* F. And if I'm checking primary, then I might as well check secondary resistance as well, from (-) post to the coil output terminal. Spec is 9.4-11.7 KOhms for an OE coil. (specs can vary for AM units, my coil is unknown AM with 7.5 KOhms- which could explain why max spark is 7/16", slightly less than what I'd expect).

Now, when you engage the starter, voltage at coil (+) should increase to 9-10V. If it doesn't increase you need to test the bypass circuit (usually the brown wire at the ballast) back to the ignition switch. The (-) side is a little more complicated. The module keeps the primary circuit grounded - near 1V- until the pickup triggers it, then it will turn off the primary for just over 1 millisecond. Primary voltage spikes to about 300V for 100 microseconds (a tenth of a mSec), then for another mSec it's at 30V while the spark "burns". For every second while cranking, you have about 8 sparks; so it's 990 mSec at 1V or so, & 8 very short & complex events - 10mSec total. Now you have to take THAT & average it into a go/no-go number on a DVOM. My meter showed 2.0V on coil (-) while cranking. Some DVOM's have a "duty cycle" mode- it measures the "on-time" (low V near 0) of a repeating signal. 100% is always on, 0% is always off. I got 99.5% duty cycle while cranking. I haven't seen or used an analog "dwell-meter" in over 10 years, otherwise I'd give you some dwell readings. One thing, since the primary switching is VERY brief, there is no way to see anything by hooking a test light to the coil. If you want something more precise or definitive, you have to step up to using a scope to view the primary waveform.

If coil (-) is OK KOEO but doesn't change while cranking, that would indicate that the module isn't switching. Here I would consider trying another distributor. Just plug its pickup coil to the engine harness (good time to make sure the connector fits together snugly, & isn't corroded), & test coil output KOEO while spinning the substitute distributor's shaft by hand. This is a good method to insure your ignition can fire before attempting to start a freshly rebuilt engine. If spark's OK then I look at the engine's dist.- first making sure that it turns when the engine spins. Next I check pickup coil resistance & output. The pickup is a Variable Reluctance sensor.It is a small electromagnet winding with a ceramic permanent magnet. As the points of the steel reluctor (on the dist shaft) pass close to the pickup, it disrupts the magnetic field around the winding- inducing a brief AC voltage pulse. Voltage output varies with pickup gap (closer= more V), speed (more rpm= more V) & resistance.

A note on resistance/ ohm testing. I consider it a "BAD" test- if something is out of spec, then it's likely bad, but if it's in spec, that doesn't mean it's GOOD. You need to perform some sort of functional test to prove a part works. For example the pickup coil might test in spec for resistance, but if the magnet is cracked/broken or otherwise weak then the pickup might not produce high enough V to trigger the module. Another thing is that to perform a resistance test you must disconnect the device (or wiring harness) from any "parallel" devices or voltage sources in the circuit. (example- you won't get a correct ohm value on the ballast if it's still hooked to the wiring- & if the key is on... forget-aboudit). Resistance values change (increase) with temperature- most specs include a temp value when testing. Also, if you're measuring something with a small ohmic value- such as ballast or coil primary- be sure to check the reading with your meter leads just touched together & compensate when you test. If your leads are 0.3 Ohms & you get 2.0 Ohms across the coil posts, then your true value is 1.7 Ohms. (some DVOMs have a "Delta" function that will zero the reading with the leads connected). One more thing, I only use Ohm tests on specific components or to check wiring for shorts that shouldn't be there. For ANY wiring connections I put a load on the circuit & test it dynamically using a voltage drop test.

Spec on the pickup is 350-550 Ohms at 70-80*F, with a 0.008" gap from reluctor tooth to pickup. Pickup coil circuit should have no continuity to ground. My car had 440 Ohms at 85* & gap is ???- something in my dist is bent- the reluctor wobbles some (you can see it in the yellow scope wavefrom in my "Explaining EI" thread). With the pickup unplugged I measured 400-550 mV AC while cranking. I plugged it back in then tapped both pickup wires for DVOM leads- I got 300-450 mV AC while cranking (& module firing coil).If the pickup output is good then I'll plug it back in & test at the module. I double check module ground- KOEO I want no more than 200 mV from the module case to batt negative. If you unplug the module (it don't hurt to turn key off while unplugging electronics) - KOEO you should have batt power at 3 of 5 pins (assuming a stock 5 wire harness with dual ballast). It seems that a 8-32 machine screw is a "snug" fit in the female terminals of the connector- which is useful for checking terminal fit (a "pin-drag" test), attaching meter leads for testing, & possibly "scrubbing" off light oxidation. The dark blue wire is ign power +, and should have very little voltage drop if loaded with a few amps- say from an old sealed beam headlight. The dark green wire comes from the "auxiliary" side of the dual (4-pin) ballast. I never had or did voltage tests on a 5-pin module, so I can't say what the load (& dynamic V) is on that circuit. Most replacement modules I've seen are 4-pin. Spec on the aux ballast is 4.75-5.75 Ohms at 70-80*. The black-yellow wire is the (-) from the coil, & since it's open circuit right now it should be at ign + (batt) voltage. The last two wires (gray & brown on my diagram) are the pickup coil, so Ohms should be at spec, & no continuity to ground.

At this point the next step would be one of two things. One would be to try another module & recheck. Or two, test the coil (THEN replace the module if needed). Since the coil & ballast are pretty much the same as on points system, you can manually fire the coil (with the module unplugged) & check ouput. If you have a (good) points dist laying around then connect the points wire to coil (-), ground the dist body, then spin it by hand KOEO with a spark tester attached to the coil (should have decent output- say 3/8" gap). Another possibilty is to use a points condensor (or a 220 picoFarad capacitor?? - rated at 16V or higher) & some jumper wires. Attach the condensor wire to coil (-) & the condensor shell/braket to ground. Clip one end of a jumper wire to coil (-) as well & KOEO scratch the other end across something grounded- the alternator case works OK. You should have spark at your tester. If not the coil is likely bad. Don't forget to "discharge" the condensor when done- touch the ground jumper wire to the wire for the coil.

At this point, IF the module has good power & ground, good input signal from the pickup, & the coil can fire when switched, THEN you have performed adequate "diagnosis by exclusion". Testing has shown that the module has everything it needs to function but it doesn't- replace it & you should now have spark.


If I have weak spark from the coil, all I can do (with out using a scope) is confirm "good" voltages at coil (+) & (-) while cranking (or idling- if it will run), & test coil winding resistance. If I have the tools I will test ign primary current- about 3.0 amps KOEO & KOER. Then I'll try another coil & see if output is better. Something to double check is that the polarity is correct on the coil; ign power (brown or D. blue) goes to (+) & wire from the module (black-yel) goes to (-). If it's reversed you'll have very weak spark.

Here are some results from when the engine was running. Pickup coil output was 1.4V AC at idle, increasing to 3.0V AC at 2500. Coil (+) was 8.5-9.5V idle, 11-12V at 2500. Coil (-) was 3.0V idle, up to 7.0V at 2500 (the value increases as the DVOM averages more firing events together in a shorter time period)- measured duty cycle was 95-96% at idle.


The last thing I'll cover is stress testing the coil & checking for secondary voltage leakage. When I stress test the ignition, I use the spark tester & see how large I can make the gap before the spark becomes irregular or disappears. The idea is to see if the coil can produce enough kV to fire the plugs reliably under most engine conditions. I would expect about 1/2" on this type of electronic ignition- that's about 25kV. My Valiant is a bit weak at 7/16" - but my coil isn't in spec. At 3/8" or less you'll likely have misfire or lack of power at heavy throttle or other high load conditions. You can stress the coil directly at the output terminal while cranking, or stress at the end of a plug wire while idling (don't do this very long since you'll have a misfiring cylinder). If your engine runs rough - esp. when it rains- you might have weak ignition parts that "leak" high voltage. One way to test is to attach the ground clip for a test light to the engine, then while it's running, slowly pass the probe point of the light close to all the ignition wires, coil tower, dist cap, etc. Often spark will jump from the weak spot to the test light tip (& the engine will run rough) because it is less kV demand to jump the light than fire the plug. Use the spark tester at a plug wire to force kV higher & make jumps more likely- you'll just have to see the arcs as you'll have one cylinder not firing. Put water in a spray bottle- add a 1/2 teaspoon of salt to improve conductivity if you want to REALLY test insulation integrity. With the engine idling wet down the ignition system - I've seen engines run rough at idle after doing this, I've seen engines stall & not restart until dried off, I've seen engines that would misfire only after being loaded in gear. If something fails the "wet test", it's time for new cap-rotor, & wires- then retest. I've also seen coils that had carbon tracks or burn-thru at the output tower.

minor update- I dug out my spare ignition coil - a crusty OEM unit. Ohms right on spec- 1.6 Ohms pri, 10.8kOhms sec. Tried it on my engine & it put out a nice 5/8" spark while cranking- about 25 kV. Much more than the "new" AM- out of spec unit.

Well, that does it for now. If anyone notices any oversights or errors- let me know.

Chris

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63 Valiant Wagon
225 - 4 bbl

Very well organized and clearly written. I nominate this article be added to Electrical Sticky page.

Thanks Chris

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

I'll second that nomination.

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81 LeBaron Salon,88 5th ave,79 Aspen SE wagon,79 W150
Don't worry, nothing is going to be alright.

Welcome- it took lots of back-tracking, adding paragraphs, & just plain thinking to try & explain everything that I "take for granted" since I do this kind of work every day.

Are you taking notes? There's gonna be a pop quiz next week.

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63 Valiant Wagon
225 - 4 bbl

Nope, I just auditing this not for credit course. LOL And, I know where to find it when the time comes. It's not what you know, but where to find the info when you need it. Besides I'll be dead before this is locked into my long term memory, and my short term memory is less than reliable these days thanks to my atrophied senior citizen Abby-normal brain filled scull.



Yeah it does! good job.

Bill

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

I had a teacher in high school, that gave "open book" tests. The answers to the questions were not easy to find. He always said "you will not remember everything you see and hear, but if you know how to find it, you will always have the answer to your question". 55 years ago, and never forgot that quote.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

That was the mantra in all my engineering courses. Well like you Charlie, something sunk in...

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC