Ignition coil, electronic ignition module or ignition switch?
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Thread: Ignition coil, electronic ignition module or ignition switch?

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    Ignition coil, electronic ignition module or ignition switch?

    My main question is about the stock ignition coil but it could be related to the other two components to the ignition system. Recently I have been driving along everything running perfectly and then I will get an instant cut out, my tach goes to zero if I’m idling. Then the engine will start like nothing happened, when I am traveling in a faster speed the engine instantly cuts out then cuts back in, on decel one time on cut out I got a loud exhaust backfire like a gun shot, the tach jumped from top to bottom then the engine resumed normally in all instances. I checked the wiring connections at the coil and tightened everything up. Could a failing ignition coil have this symptom? Just an occasional spilt second cut out, almost too fast to notice if the dash lights cut off, I don’t think they do but not sure. The other culprit could be my Crane xr-700 ignition module. So my main question again, would be related to the coil? No starting issues with the starter indicating low battery, it has taken a couple of starts recently on a cold start up, my amp guage has been a scosh to the right more than it used to since running the small cooling fan, I figured that’s normal. I get 12.3-12.5 v on the battery when the car is off FWIW. Does anyone have any experience with this or suggestions?

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    Über Genius First opel 1981's Avatar
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    Tach going to zero and engine cutting out at the same time is a symptom and not a cause.

    It tells you there's no signal to the tach and coil combined.

    That helps you trace it to the connection somewhere between the engine ground and the tach/coil wire connection.

    There's limited places this can go wrong so it helps a LOT.

    Are you running points or a pertronix?

    If it were me, I'd look at the green wire coming from the distributor (if points) or the black wire coming from the coil (if pretronix).

    (edited to add) There's also a LOT to be said for grounding the engine with a grounding strap. Without a grounding strap you can only get a ground through passive connections. Those are limited to the exhaust and the throttle linkage. And, really, the exhaust is supposed to be isolated from ground.
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    Senior Member The Cub's Avatar
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    Quote Originally Posted by First opel 1981 View Post
    Tach going to zero and engine cutting out at the same time is a symptom and not a cause.

    It tells you there's no signal to the tach and coil combined.

    That helps you trace it to the connection somewhere between the engine ground and the tach/coil wire connection.

    There's limited places this can go wrong so it helps a LOT.

    Are you running points or a pertronix?

    If it were me, I'd look at the green wire coming from the distributor (if points) or the black wire coming from the coil (if pretronix).

    (edited to add) There's also a LOT to be said for grounding the engine with a grounding strap. Without a grounding strap you can only get a ground through passive connections. Those are limited to the exhaust and the throttle linkage. And, really, the exhaust is supposed to be isolated from ground.
    I’m running the optical triggered Crane xr-700 Ignition. I will recheck the wires on both sides of the coil and yes when I rebuilt the engine I cleaned up the original braided ground strap and wire wheeled the threads before bolting the cleansed up bolts to the strap.

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    Bikini Inspector Frozen Tundra GT's Avatar
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    see if your coil is hot
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    Über Genius First opel 1981's Avatar
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    Quote Originally Posted by Frozen Tundra GT View Post
    see if your coil is hot
    A hot coil will usually not affect the tach, unless the coil primary winding creates a dead short when it gets hot. Usually the coil has a break in the circuit that causes it to not fire.
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    Senior Member The Cub's Avatar
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    Quote Originally Posted by First opel 1981 View Post
    A hot coil will usually not affect the tach, unless the coil primary winding creates a dead short when it gets hot. Usually the coil has a break in the circuit that causes it to not fire.
    Have they been known to short and re connect after this happens? That’s the question for all the marbles

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    Über Genius First opel 1981's Avatar
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    Quote Originally Posted by The Cub View Post
    Have they been known to short and re connect after this happens? That’s the question for all the marbles
    Short out and then unshort out? Highly improbable.

    Break the circuit then reconnect? All the time.

    The point remains that the tach gets its signal from the trigger, NOT the coil.
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    Humans are not an endangered species!
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    Senior Member The Cub's Avatar
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    I found the disk on my distributor shaft was adjusted too low perhaps making contact with the optical lens, I cleaned it up and raised it a little. I also found the positive terminal on my battery loose and replaced it. So far so good. No drop outs, I would have thought everything would surge power wise if it was just a loose battery connection. Time will tell, I’ll take the good news for now and post back if it happens again. Hopefully not.

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    4,000 Post Club m610's Avatar
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    If not solved, this might help.

    I had just finished work on Catherin's car and was listening to it idle. Then the engine suddenly shut off, as if I had turned it off.

    Cranking did not get it going again. It seemed like I had no spark.

    I pulled the #1 plug wire and put a spare spark plug in it, ready to test for spark, and I noticed the high-tension wire at the coil was loose. I had stuffed it in all the way, I thought, but it seems it was in just enough to butt up against the contact in the coil. I worked it the rest of the way in and everything was good again.

    Mike
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    Senior Member The Cub's Avatar
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    I found several of my plug wires loose in the distributor prior to having this problem, my #1 wire just popped off and I lost power. I spread out the gap to make a tighter connection then I found the other 3 loose I did the same thing now all are secure. I had the car out all day today and I’m leaning towards the loose battery connection. I took a voltage reading before I found the loose connection at start up and got 8 volts the FSM says I should get 10 or more. I’ll take another voltage reading again and post it. So far no more hiccups knock on wood.
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    Reverse Coil Polarity

    If you have the coil hooked up wrong, the coil will get hot..still work but not as efficiently...the spark will jump from the spark plug ground to the center electrode of the spark plug...then up into the coil...everything in reverse....

    The coil wire for a negative ground system means that the coil's negative side will go to ground...which is the points...

    You can also use a coil wire arc and put a pencil so the spark jumps to the lead of the pencil and then to ground...it will make an arrow pointing the direction of the spark.....(the spark is broken by the pencil lead)...just don't touch the metal where the eraser end is....it hurts.)

    Using a oscilloscope the spark line will point down when the plug fires...

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    My gt with a 2.0s seems to have the same problem. Have had some carburettor related issues, rebuild the carb and adjusted it. It runs good, sometimes now. Sometime it runs really good for miles and then starts to cut out. It only cuts out shortly and mostly more times in a row but never goes out all the way. My rpm gauge also goes down. Especially after running +30 miles it gets worse and somehow it seems to be worst at arround 2-2,8k rpm.
    Did see today that a capacitor wire have come loose from the alternator, can this effect anything ??
    Else I am a bit stuck, but will start measuring and testing from this thread tomorrow.


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    Super Moderator Ooooner's Avatar
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    Is your coil 3.0 ohm or 1.5 ohm? I had a similar problem years ago and after pulling my hair out and saying a lot of cuss words, I figured it out. When I changed the coil to a "Flame Thrower" coil, I had been using the stock "clear resistance wire". (I think that's what it's called) I bypassed the clear wire, which goes to the fuse box, with a "regular" wire. I am running the Pertronix. I'm thinking the stock coil is 3.0 ohms. In any case, after changing the resistance wire, the car has run great and didn't have any more problems.

    Maybe someone could chime in and explain the Coil Ohms and resistance wire setup better than I did!
    Last edited by hrcollinsjr; 06-24-2019 at 09:19 PM.
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    The resistance wire is a form of current ballast, which is an old electronics type of crude current regulator. Ballast resistors in other system will warm up and increase resistance when running to keep the coil current lower when running for longer periods of time. I have always assumed that the resistance wire does the same, but have never stopped to check on that, like I have with measuring the hot vs cold resistance of a ballast resistor.

    Use of a ballast in any form goes with with a lower coil resistance. The lower coil resistance allows more current to charge the coil for a hotter spark right after startup when cold; then increasing resistance reduces the coil current to keep the coil from being overheated as you run longer. Going to a 3 ohm coil with a system like a Pertronix eliminates the need for the resistance wire/ballast, and the typically better spark from these systems makes the ballast idea unecessary.
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    Quote Originally Posted by The Cub View Post
    Have they been known to short and re connect after this happens? That’s the question for all the marbles
    Actually YES. There is insulation on all the wires in the coil winding, both primary and secondary (the high voltage side) and insulation breakdown is a common coil failure, which is a shorting of some coils due to internal arcing.
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    Quote Originally Posted by Jacobhojrup View Post
    My gt with a 2.0s seems to have the same problem.
    Did see today that a capacitor wire have come loose from the alternator, can this effect anything ??
    Else I am a bit stuck, but will start measuring and testing from this thread tomorrow.


    Sent from my iPhone using Tapatalk
    If you’re talking about the 1 wire little box on the back of the alternator I believe it was intended to eliminate static from the generator noise from appearing over the AM radio stations. Mine has been removed years ago with no negative consequences because I don’t have AM in my car anymore.
    Last edited by The Cub; 06-24-2019 at 10:59 PM.

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    Senior Member The Cub's Avatar
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    Quote Originally Posted by Frozen Tundra GT View Post
    see if your coil is hot
    I guess it’s still in the doghouse. I’m still getting an occasional stall. I felt the coil after my last drive and it felt EXTREMELY hot. It could have been my imagination but that side of the engine was much hotter when I raised the hood. I purchased a new coil and I’m going to replace it today. A question I have is that the if solenoid on the starter is passing intermittent higher voltage in to coil while I’m driving could that cause the overheating of the coil as well? Is that a common occurrence? We’ll see after I replace the coil if it cools down. I get about 1.5 ohms resistance across this coil and closer to 2 ohms on the resistance wire with it disconnected at both ends. When I was measuring my incoming voltage to the coil on a drive of (no stalling on that excursion) that time it was between 7.5-9.5 volts the higher voltage was at higher RPMs. I do have a 1.5 ohm ballast resistor, I could abandon the resistance wire as another option if anyone else has found the resistance wire to be problematic and eliminated it. The XR-700 requires 6-9v input so the 3 ohm coil is not an option unfortunately with this set up.

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    Your coil + voltage sounds right in the normal range. As do your resistances. Internal coil arcing may or may not change the primary and secondary resistances.

    As for the solenoid bypass activating randomly while driving, that contact inside the solenoid is made when the solenoid plunger moves and that typically would happen when the starter is engaged. So, unless there is some broken bit floating around in there, it seems unlikely. I'd be far more inclined to believe that your switched +12v or some other wiring is erratic than that.

    Coils are pretty much impossible to catch being erratic, with the ways in which we can test them, so substitution is the usual way 'in the field' to determine if they are bad. Let us know! These erratic electrical problems are quite vexing.... I've been in electroncis in one way or another for a career and erratic electrical problems are hard to solve.
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    Senior Member The Cub's Avatar
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    After replacing the ignition coil the engine hasn’t had any issues for weeks now. Well just as I was ready to pitch the old Bosch coil in the trash I got another backfire today. My intention was to neatly tidy up this thread with a happy ending, oh well at least there’s not a whole lot to go through on an Opel GT. Back to the drawing board and I’ll re post once I figure it out.
    Last edited by The Cub; 07-28-2019 at 11:16 PM.

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    An exhaust backfire is a classic symptom of an erratic ignition connection. The momentary interruption allows unburned fuel to go into the exhaust system and the resumption of the cylinder firing and hot exhaust pulses sets it off. I've set off backfires unintentionally by touching and slightly turning the ignition switch off of a moment on my '62 Dart, and on a Piper Cherokee too LOL. Any connection point in the ignition +12 path and the ignition switch are prime suspects, and any wire that could be stressed and eventually 'worry' into breaking, including the resistor wire.
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