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Thread: '73 240z - No spark from coil

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    Registered User StinkyCheese's Avatar
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    Question '73 240z - No spark from coil

    I've had my '73 240z for a couple of years and its always run pretty decent, but it overheats in city driving. Last fall I was driving and hit some rush hour and it got pretty hot (about 3/4 of the gauge). After a while I got out of traffic and it started to cool down some, but about a mile from my house it started running really rough and 1/4 mile from my house it died completely. I coasted downhill to my house and pushed it into the garage.

    It wouldn't start, but I was so tired of the overheating I took the radiator out and got it rodded out. I also installed a fan shroud. After I got all that put back together, I've been trying to get it started, and it just won't start.

    I took the coil wire off of the distributor and held it next to the valve cover while my daughter cranked the starter. I expected a spark to jump across to the valve cover, but there was no spark. Doesn't that automatically mean the coil is bad. When it WAS running, it would hesitate when it hit 3500-4000 rpm. Doesn't that indicate a bad coil, too?

    I went and got a "IC70" coil from NAPA today. That's what their computer spit out as a replacement. Its a little skinnier than the old coil, but I tried it anyway. I don't get the coil-to-valve cover spark with this new coil either! What else can I try?

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    I'm assuming you have a points ignition???

    When you turn your ignition on, do you get +12V to the (+) side of the coil? (You should.)

    If you do, then what happens if you disconnect the wires from the (-) post, connect another loose wire, and then CAREFULLY tap the other end to ground? Do you get a spark then?

    There's probably a ballast resistor involved somewhere in there too, but I don't know how it's wired. Nevertheless, you can determine if your coil is good by manually tapping a ground wire to the (-) post of the coil.

    If your coil has +12 to the (+) post and tests good, then your next step is to look at your points. Are the points and condenser new/recent? Are they properly adjusted?

    That's about all there is to the ignition, at least up to the point of the coil wire.
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    As Sarah says. Points . Condenser.

    Brian.
    Last edited by olzed; 02-25-2011 at 11:10 AM.

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    Thank you SO MUCH for replying. I'm _this_ close to hauling it to a mechanic, but I'd so much rather work on it myself and learn...

    Yes, I get 12 V on the + side of the cooil when I turn the ignition on. I took off the wires from the - post and put my test wire on. I touched it to ground and nothing happened. I did this with the ignition off and on, no reaction. Should I get a spark?

    I attached a picture of my too-small-for-the-bracket coil...
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    Yes, a spark should jump between the coil wire and ground whenever you tap the wire from the (-) post to ground -- and also have +12 to the (+) post of the coil. Maybe your coil is bad out of the box.

    There are at least two other possibilities, though. First, maybe you have a bad coil wire. What happens if you put one of your plug wires on the coil and try sparking it then? If you get a spark then, you should treat your Z to a new set of wires -- NGK, spiral-wound, of course!

    The second possibility is that you have insufficient current to the (+) post of the coil. To test this, try jumping a piece of wire directly from your battery to the (+) post of your coil, and see if you can get a spark then. If so, then you'll want to trace down a corroded connection somewhere.

    And again, I don't know how your ballast resistor wires in. Perhaps the (+) feeds to the resistor and then to the coil? So maybe you have a bad connection at the resistor? Dunno... I frankly don't know how those ballast resistors are wired and don't have a schematic at hand.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
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    John,
    You have a ballast resistor in your ignition circuit. You should have 12 VDC on the positive terminal of the coil when you try to start the car and 9 VDC with the key in the RUN/ON position.

    Here is a quick rundown on how the stock circuit is wired.
    Starting: The W/R wire carries voltage from the battery into the keyswitch. When starting the car, the switch connects the G/W to the W/R wire. The G/W wire goes into the tach, and the B/W wire goes from the tach to the positive side of the coil. The black wire comes out the negative side of the coil and runs to the positive side of the points and to the condensor and on to ground. The negative side of the points also runs to ground.

    Running: The W/R wire carries voltage from the battery into the keyswitch. The switch connects the B/W to the W/R wire. The B/W wire goes into the ballast resistor, and the G/W wire comes out. The G/W wire goes into the tach, and the B/W wire goes from the tach to the positive side of the coil. The black wire comes out the negative side of the coil and runs to the positive side of the points and to the condensor and on to ground. The negative side of the points also runs to ground.

    Having said that, failure points can include the condensor, the tachometer, and the points staying closed or open. (See page EE-35 in the factory service manual.)

    Also, please let us know whether or not you have stock points or if someone installed a different ignition system (Pertronix, Crane, MSD, HEI, etc.). If you're not sure, take off the distributor cap and rotor, take a picture of the distributor, and post it.

    Also, make sure the condensor is on the negative side of the coil. It looks like it's on the positive side in your picture. By the way, the condensor and ballast resistor look VERY old. Consider replacing them.

    It would help, too, if you would tell us if the car is an automatic or manual. The automatic had a dual point distributor.
    73 240Z
    74 260Z

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    Wow, thanks for taking the time to help!

    OK, I tried hooking the + side of the coil directly to the + side of the battery. Still no spark.

    I hooked up a spark plug directly to the coil and it doesn't spark either... The spark plug wires I got from the Nissan dealer, but I don't know the brand. They're about 6 months old.

    SteveJ, you say, "You should have 12 VDC on the positive terminal of the coil when you try to start the car and 9 VDC with the key in the RUN/ON position". My car isn't running, but the key is in the RUN/ON position, and I get 12V on the + of the coil. Does it have to be running for the ballast resistor to be used?

    Thanks for the description of the circuits. I tried to draw it up, but I'm confused..

    I have a standard transmission.

    I took a picture of the dist. I made some notes on the pictures, I'd appreciate it if you could take a look.
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    Just wandering by. I notice that you've measured 12 volts on the + side of the coil, but didn't say what you measured on the - side.

  9. #9
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    I get 12V on both the + side and - side of the coil.

  10. #10
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    If you are getting 12 volts at the -side of the coil your points are closed, coil fires when current stops flowing. Take a small screwdriver and open the points, I bet you get a spark, in that case try resetting your point gap. Also the rubbing block on the point set needs to be lubed with point grease, if you don't your point dwell will continue to deteriorate till the car stops again.

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    That second condensor under the coil, is that stock? mine doesnt have that. Of course I installed the pertronics electronic ignition, but there was only the distributor condensor. Try loosing that rascle and see if she fires.

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    Well, I admit I'm not really a points-ignition kinda gal, although I've had them before. However, it seems to me the coil is bad. I'm guessing it's got an internal short, as there seems to be conductivity between the (+) and (-) (evidenced by +12 at both terminals). I mean you've isolated the thing and tried firing it manually, energized directly off the battery, and it won't fire.

    Another little test you can do is to unhook the coil, and hook the test leads of a mechanical multimeter (with a needle) to the wires that would otherwise be connected to the coil. Put the multimeter in the DC volts mode, at a scale that is appropriate to 12V. Now crank the engine. The needle should go up and down repeatedly as you crank the engine. If that happens, your points are good -- maybe not adjusted optimally, and maybe not in the best of condition, but still functioning.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    I tried removing the spare condenser, that didnt change anything.

    When i have the distributer cap off and crank the motor, shouldnt I see a spark every time the gap opens and closes? It seems to me I've seen that before... Right now it doesn't show a spark, ever..

    I don't have access to an analog meter. I don't want to declare the new coil bad, it cost me $50! Maybe I should order the "flamethrower" that everyone seems to love and take the one I got back to napa?

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    I also opened the gap manually, no spark. when i crank it the gap definately opens and closes.

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    You could also wire a 12V light in place of the coil and see if it flashes on and off when you crank the motor. That would tell you the same thing.
    My last three sports cars while I still owned all three:

    2001 BMW Z3 Roadster 3.0i soft/hard top (sold)
    1966 Ford Mustang Coupe (sold)
    1978 Datsun 280Z (enjoying very much )

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    I'm going back to the original post where Mr. Cheese described the car overheating, cooling off a bit, but then dying a quarter mile from home. He tried starting it at that time and it didn't start.

    I'm thinking the overheating has something to do with no spark, but what?
    The overheating could have taken out the coil, I guess, but that's been replaced. In fact, I think most, if not all, of the usual suspects have been rounded up to no avail.

    Could the overheating fried some insulation someplace in the ignition circuit? Or expanded metal one too many times and created a loose connection?

    Or, maybe the overheating and no starting is a coincidence. One of the bonuses of having a 30+ year car.

    Chris

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    Good news/bad news. Good news- I have a spark now! Bad news- I don't know why. There is a wire that goes from the points to the side of the distributer (positive side?). This wire looked worn so I took it out and put in a temporary wire. Couldn't get a spark then, either. So i went to put it back in and i dropped a washer down next to the distributer shaft. I had to take off the points to get to it. When I got it all put back together I had a spark.

    I'm irritated that I don't know what fixed it. I'm still confused.

    It still isn't running. I know the spark is working, but i'm not getting fuel. I knew tis was coming - every time I went I cranked it I expected to smell unburnt fuel, but I never did. I can usually see fuel percolating in the fuel filter, but the fuel filter looks dry. I cranked it floored for a full 2 minutes and no fuel in the filter... Now I get to figure that out...

    THANKS to everyone who offered suggestions. I am so grateful that there are people out the like you who care enough to answer an amatuer's distress call! You're all awesome!

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    Wow! Could be anything. Hopefully you fixed a bad connection somehow, and the problem won't leave you stranded 30 mi from home.

    I think Jetaway is right that it's a temperature-related problem. Thermal expansion and contraction will often rear their ugly heads in a coil winding. Once you do get the car running, let it idle on a very still (not windy) day until it is hot. Shut off the engine, and then try restarting it 15 min later after the engine heat has soaked the engine compartment (with the hood closed, of course). Also try starting your car when it's bone-cold.

    I think Jetaway might also be right about insulation. Carefully check the insulation around any of the wires you might have touched when you accidentally fixed the problem. You might have had a short to ground.

    My money is still on the ignition coil. If you hooked it directly to the battery and bumped the (-) to ground, you should have gotten a spark out of the coil.

    Regarding your fuel issue: Is your pump electrical or mechanical?

    "THANKS to everyone who offered suggestions. I am so grateful that there are people out the like you who care enough to answer an amatuer's distress call! You're all awesome!"

    There are a few pro mechanics on this board, but I think most of us are hobbyists/enthusiasts just like you. Two heads are better than one, and multitudes of heads, sharing ideas, experience and information, become absolutely brilliant!
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    Quote Originally Posted by StinkyCheese View Post
    Good news/bad news. Good news- I have a spark now! Bad news- I don't know why. There is a wire that goes from the points to the side of the distributer (positive side?). This wire looked worn so I took it out and put in a temporary wire. Couldn't get a spark then, either. So i went to put it back in and i dropped a washer down next to the distributer shaft. I had to take off the points to get to it. When I got it all put back together I had a spark.
    That makes it sound like collapsed points were your problem. Taking them out opened them up. Check the gap and dwell on the points.
    Quote Originally Posted by StinkyCheese View Post
    It still isn't running. I know the spark is working, but i'm not getting fuel. I knew tis was coming - every time I went I cranked it I expected to smell unburnt fuel, but I never did. I can usually see fuel percolating in the fuel filter, but the fuel filter looks dry. I cranked it floored for a full 2 minutes and no fuel in the filter... Now I get to figure that out...
    Flooring the car while starting does nothing if you have roundtop or flattop carburetors.

    Spray some starter fluid down the carbs and see if the car wants to fire then. Otherwise start going through the FSM on the fuel system to see what the factory diagnostics are for the fuel system. (I don't claim to have much knowledge on the fuel system, so if I was tackling the problem myself, that's how I would start.)
    73 240Z
    74 260Z

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    The points have to be grounded to flow current through the coil. I think that they ground through the mounting screws, or a wire off the points bracket (haven't even seen a set of points for many years). Maybe you had a poor ground for the points. Might be worth testing with an ohm-meter to make sure you're not on the edge.

    Also, as I recall, the condenser used with a points distributor does more than noise reduction. It keeps the points from arcing and pitting by absorbing the first surge of voltage when they close again.
    Last edited by Zed Head; 02-27-2011 at 10:37 AM.

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    Click image for larger version. 

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    (secondary condensor in picture) with the blue wire ,does this go on the neg or pos of coil.
    Dave
    Last edited by gibson99; 03-25-2012 at 01:17 PM.

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    Quote Originally Posted by gibson99 View Post
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    (secondary condensor in picture) with the blue wire ,does this go on the neg or pos of coil.
    Dave
    Positive.

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    Smile

    First step: Stop what you are doing!
    Second step: Install an E12-80 electronic ignition!

    I just did the swap with my '73 and it works awsomely!!!

    It is a direct bolt on and only requires a small jumper to utilize the stock wiring.
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    You can find distributors used or new at rock auto and you can select the total advance depending on what year of 280ZX you choose. I am running an '81 w/ 55 degrees advance. It is 8 more than stock but I have a big cam an fully functioning EGR.

    Instructions for a later car but has all the important info.
    http://atlanticz.ca/zclub/techtips/d...tor/index.html

    Distributor advance chart
    http://www.classiczcars.com/forums/s...urve-Reference

    My points distributor had some kind of very mysterious problem that made me nuts so I got rid of it. My suggestion is to do the same!

  24. #24
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    Also regarding the fuel problem, change the filter in the elec. fuel pump. Yours is probably plugged, as mine was.

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