12V system with 6V coil - no spark

[5030tinkerer]

I've got an IH3200B skid loader from the 70's with a Wisconsin gas 30hp VH4D engine in it. I went to start it and it just turned over, but didn't ever start.

The issue seems to be no spark. If I pull a spark plug, re-attach the wire, and crank the engine, I don't get any spark.

Thinking this sounded like a dead coil, I picked up a 12V replacement. It said it didn't need the external resister that the original 6V coil used, so I bypassed it. Still no spark. The positive side of the coil shows 13 volts with the key on, so we are good there.

Should I have purchased a 6V coil (the old coil's positive side reads 6.03V with the key on since that is what is coming out of the resister)? Is something else perhaps wrong? Am I right in thinking that I should see a spark at the plug itself when the engine turns over BOTH when it is directly fed from the coil and when it is routed through the wire meant for a given cylinder (though faster sparking from the coil feed itself)? If I attach the coil wire directly to a plug, I get a spark (blue) only when the key is first turned to the 'on' position (I tested this with the old coil, but haven't yet with the new.

I am just now thinking that maybe I picked up the wrong coil. Things replaced up to this point in an attempt to get it running again include: cap. rotor, plugs, condensor, points.

Ideas?

 

[banjodunn]

G'day if you are running 12 v direct into the coil + should not need a 6v unit grab a test light and take the distributor cap off turn the eng over til the points are closed and put a spark plug up the coil lead where you pulled it out of the cap, now use the test light to open the points with ign on and you should get spark at the plug and the light come on, if the light is on as you touch the points arm to open then you either have not got the points closing properly or the points face has got a protective coating on it, if so turn ign off and get a points file and put between faces and give a rub. If you have no light when you open the points at the arm then you have a bad connection between there and the coil -. Hope this helps



Jon

 

[5030tinkerer]

Thanks! HUGELY helpful. I'll test it out.

If my original coil was set up to receive 6V on the positive side of the coil, is the fact that my new coil is getting 12V (since it bypasses the resistor) an issue? In other words, can I use the new coil I picked up or do I need a different, perhaps 6V version?

 

[patrick_g]

A little background:

When you crank the engine the batt voltage droops so voltage to coil is lower and spark is weaker. So... a new coil is designed to give good output with 8 volts or so input and a ballast resistor is put in series to keep from burning it out with 12 volts. The ballast resistor is installed in series with the coil primary connections. When cranking the motor the resistor is bypassed putting all available voltage to the coil to get a hot spark. Releasing the key routes the current through the resistor.

You get hot spark when cranking and when running normally too.

A symptom of a bad ballast resistor is a good start but engine dies immediately when you let the key relax into the run position.

Newer approaches sometimes eliminate a visible/accessible ballast resistor, hence a direct connect 12 volt coil and "no" ballast.

If you suspect dirty points and don't have access to a burnishing tool then use the striking surface of a book of paper matches for an impromptu emery cloth substitute. The paper match book itself can be used as a gauge to gap your points in an emergency. Likewise for gapping plugs if you are desperate.

Pat

 

[5030tinkerer]

Interesting. Given that my ballast resistor is indeed wired in series to the OEM coil and that only one wire connects to the positive side of the coil (that is, the wire coming from the resistor), I don't understand how the resistor could be bypassed in the running mode.

I see 6V to the OEM coil when the key is in the ON position. I cannot yet tell you what the voltage is when its running. I'll check tonight to see what happens to the voltage during cranking.

I suspected points in the beginning, so changed them and the condensor (the original points actually looked near new, but the original condensor had some oxidation on it, not that I believe that that matters). I gapped the new points to 0.019 when the distributor is on a lobe and plan on checking for the protective coating that Jon referred to (and may well just use your matchbook idea for burnishing).

The question remains as to whether I can use the new 12V coil or if I should go back to the OEM one that uses the separate resistor.

 

[Willl]

A ballast resistor drops its output voltage as it warms up.

 

[Soundguy]

Thinking this sounded like a dead coil, I picked up a 12V replacement. It said it didn't need the external resister that the original 6V coil used, so I bypassed it. Still no spark. The positive side of the coil shows 13 volts with the key on, so we are good there.

Should I have purchased a 6V coil (the old coil's positive side reads 6.03V with the key on since that is what is coming out of the resister)? Is something else perhaps wrong? ?

Actually.. this says alot..

You are making some electronics observations with, perhaps, no background knowledge of electronics principles.

If you have a 12v supply, and have a ballast resistor and 6v coil, then you will read battery volts at the coil primary if points are open. if points are closed, you will read a lower number.. perhaps the 6.03 you read.. all depends ont he coil primary resistance and the balalst resistor resistance.

Issue here is knowing when you are makingthe measurement whether the points are open or closed.

Also.. as greg pointed out, some ignition systems incorporated a bypass style solenoid, that essentially bypasses the ballast resistor. these are used when there is a fixed value ballast resistor.

however, if your ignition coil does not have a seperate wire on it's primary from the starter solenoid's I terminal.. then it likely is not setup this way. ( extra wire could also be hooked to the output of the ballast resistor.. as it's electrically the same point as the input of the coil primary. ) Another common ignition setup used on older equipment was a ballast resistor with a temperature coeficient. When cold, the resistor was very low ohms, and as it heated up, it's resistance went up. Thus when starting, current to coil primary was higher.. as the resistor warmes up ( very short amount of time to reach nominal temp/resistance ), it's resistance goes up and primary current goes down to a safe level.. and no fancy wireing or bypass solenoids are needed.

anylize what you have and post back.

might also check other ignition components.. while nearly bullet proof, condensors do short or open.. opne condensors will cause burned points, and shorted condensors will prevent spark as the points never are able to open, electrically speaking.. etc..

soundguy

 

[CCWKen]

Ditto what Soundguy says. Check the points and replace the condensor. Might as well replace the points too. Both combined are probably around $8-$10, maybe less.

 

[5030tinkerer]

I already replaced the points (gapping them to 0.019 when open) and condensor.

There is a singular, perhaps 18AWG wire running to the positive terminal on the OEM coil. This wire is energized when the ignition is in the on position. It comes from the wiring harness to the resistor first, and then to the coil. No other wires are connected to the resistor - no bypass possible.

Another singular wire leaves the negative terminal on the coil and goes to the side of the distributor, where the condensor and points ultimately electrically connect.

The 6.03 volt reading was taken with the points closed. I'll take another reading tonight with the points open - should have thought of that.

The fact that I got a blue (strong) spark from the plug directly attached to the coil wire when the ignition is first turned on (but never again during cranking). Do I need to have a good connection from the negative terminal on the coil to the distributor for this to have been possible? Given that I have replaced everything BUT that wire, I am tempted to think that this wire might be the culprit.

 

[Soundguy]

that wire to the distrib passes thru a insulative bushing then tot he points side and condensor.. whrn the points close, that wire sees ground... if the insulator is bad, the wire could be grounding out acting like a full time closed point.

check the ignition switch as well.. they can get restive contacts..

soundguy