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Troubleshooting no spark

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Hello guys, I've done as much testing and reading as I can before posting here but have now got to a point where I don't know what to do next. My car is a 1973 2002 that's been sat up for 9 years.

 

There seems to be a problem with the ground on the coil. I can get 12v from the coil HT lead but only if I use a piece of wire to connect the ground on the coil to the rocker cover. But even with this in place and a healthy +12v right through to the centre pin in the dizzy I then don't get any spark at the plugs. 


I have tried opening the points while the ignition is on and don't get a spark there either. 

 

Does anybody know if I should be able to get a spark with this temporary earth wire in place?

 

And I guess I should try to solve why the earth to the coil is bad first so can anyone help me with why this isn't working? 

 

many thanks, 

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Get a good ground on the coil, then start suspecting the distributor cap and rotor. 

 

After a 9 year slumber, I suspect the brass contacts on the rotor, the inside of the cap and where the plug wires fasten to the cap are all green with corrosion.  Get 'em good and shiny, then start troubleshooting--looking for a spark beginning with the coil, then to the cap, then points, then plug wires and finally to the spark plugs.  If you're getting +12v at the low voltage terminals at the coil, it's gotta be someplace between the coil and the spark plugs.

 

mike 

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Make sure that the grounds are good by the battery, to the body, starter and also to the alternator.

Is the dizzy turning when you turn it over?

Does it turn over?


Sent from my iPhone using Tapatalk

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4 hours ago, adhards said:

There seems to be a problem with the ground on the coil. I can get 12v from the coil HT lead but only if I use a piece of wire to connect the ground on the coil to the rocker cover. But even with this in place and a healthy +12v right through to the centre pin in the dizzy I then don't get any spark at the plugs. 

 

Not sure I understand this statement. Why are you looking for 12v on the secondary side of your coil?

 

The voltages seen on the secondary side are many thousands of volts. No need to measure voltage from the centre high voltage terminal. 

 

Check for battery voltage at your primary + terminal when the ignition is turned on (it may not be ~12v if you use a ballast resistance). Connect a test light from the coil primary negative terminal to a known good ground on the block. When you crank the engine the test light should flash. If it is on permanently, or off permanently, you need to check your wiring including inside the distributor. Are you using points? If so, check the points are screwed tight to the distributor plate and that the condenser is properly connected with no shorts to ground. Disconnect the black wires at the distributor and coil and check for continuity. 

 

It’s pretty bulletproof, if you have voltage at the positive and continuity to ground while the points are closed on the negative (conversely open circuit when the points are open) it should work. After that I would suspect the coil though they are usually unfairly blamed and pretty reliable. 

 

 

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Thanks for this Mike and Dudeland. Although the car is not in great shape, it was in dry storage for those 9 years and the contacts in the distributor and the end of the rotor are fine, as is the rotor. I did give them all a clean anyway but I think the problem is before the rotor end and plug leads.

 

I do kinda understand the order of which to troubleshoot this but not the results I should see at each step. 

 

There is 12v at the end of the HT lead with the other end plugged into the coil but if I hold the end of that cable to the rocker with ignition on I don't get a spark. Should I? Do I have to turn the engine over?


So with 12v coming from coil HT lead, I should check the points? How is that done, I've tried touching the coil HT lead on the top of the rotor then opening the points but I dont see a spark between the points. I also tried this with the rotor arm removed and touching it on spindle that the rotor arm attaches to.

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Ah Simeon, this is what I'm not clear on. I don't know exactly what results I should be expecting. As you can see from my last post, I wasn't sure what I should see coming from the centre terminal on the coil.  

 

I am using points, its a very standard setup and I can't find a ballast resistor. 

 

If I have everything connected up, as I think it should be, I don't see 12v when touching the + and - on the coil but I do if I use a jumper wire to connect the - terminal to the rocker. From what you said about the test light, it sounds like this is normal?


 

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What you are saying is a wee bit confusing, but you should have +12V on the + terminal on the coil and ground at the negative terminal on the coil, when your ignition key is in the run position. It is pointless to try and measure output of the coil HT lead. For the avoidance of doubt, does you starter turn the motor over when you move the key to the start position? 

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6 hours ago, adhards said:

I am using points, its a very standard setup and I can't find a ballast resistor. 

 

Is the coil in your car the original black Bosch coil?  If so it's supposed to have a ceramic ballast resistor mounted atop the fender just above the coil.  If the coil has been replaced with a blue or red Bosch coil, the ballast resistor isn't necessary.  If it's not a Bosch coil, you're on your own.

 

Just a couple more things to check.  You say you have +12 volts at the positive lead on the coil (the small wire, not the big one in the center of the coil).  If that's the case, have someone turn the engine over with the key while you're (safely) holding the distributor end of the coil high tension wire near the valve cover.  You should be rewarded with a nice big fat blue spark as the distributor turns and the points open and close.  No spark?  Then start looking at the points (are they opening, are they burned or corroded or dirty)  If the condenser went bad, that could cause the points to burn/pit to the point where they're not working.  

 

If you do get a zap-zap-zap from the coil wire as above when you crank the engine, that means the spark is getting as far as the distributor cap, and the points are functioning properly.  That narrows it down to the cap, rotor, plug wires or the plugs themselves.  

 

And just for the heck of it (this is thinking zebras vs horses when you see hoofprints), make sure the battery ground cables (big one to the block, small one to the body) are both in good shape and are allowing a proper ground.  If, after prolonged cranking (more than 10 sec or so) the carb linkage is strangely warm, you have a bad battery ground to the block.  The accelerator linkage is serving as the engine's ground, a role it's very uncomfortable with.  It'll quickly get red hot. 

 

Check it all out and report back to us...

 

mike

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4 hours ago, Chris_B said:

What you are saying is a wee bit confusing, but you should have +12V on the + terminal on the coil and ground at the negative terminal on the coil, when your ignition key is in the run position. It is pointless to try and measure output of the coil HT lead. For the avoidance of doubt, does you starter turn the motor over when you move the key to the start position? 

Hi Chris, sorry, electrics are the dark arts to me but it's becoming more clear in this post! The car does turn over no problem there.

 

1 hour ago, mike said:

 

Is the coil in your car the original black Bosch coil?  If so it's supposed to have a ceramic ballast resistor mounted atop the fender just above the coil.  If the coil has been replaced with a blue or red Bosch coil, the ballast resistor isn't necessary.  If it's not a Bosch coil, you're on your own.

 

Just a couple more things to check.  You say you have +12 volts at the positive lead on the coil (the small wire, not the big one in the center of the coil).  If that's the case, have someone turn the engine over with the key while you're (safely) holding the distributor end of the coil high tension wire near the valve cover.  You should be rewarded with a nice big fat blue spark as the distributor turns and the points open and close.  No spark?  Then start looking at the points (are they opening, are they burned or corroded or dirty)  If the condenser went bad, that could cause the points to burn/pit to the point where they're not working.  

 

If you do get a zap-zap-zap from the coil wire as above when you crank the engine, that means the spark is getting as far as the distributor cap, and the points are functioning properly.  That narrows it down to the cap, rotor, plug wires or the plugs themselves.  

 

And just for the heck of it (this is thinking zebras vs horses when you see hoofprints), make sure the battery ground cables (big one to the block, small one to the body) are both in good shape and are allowing a proper ground.  If, after prolonged cranking (more than 10 sec or so) the carb linkage is strangely warm, you have a bad battery ground to the block.  The accelerator linkage is serving as the engine's ground, a role it's very uncomfortable with.  It'll quickly get red hot. 

 

Check it all out and report back to us...

 

mike

The coil is not a Bosch but the car has run for a few mins a couple of times and I've not done much to the car since then. I currently just have the air filter housing removed.

 

Coil is a Lucas BFU 21949600

 

I do get 12v at the positive on the coil but only when I touch the negative metre wire on the rocker cover. Should I always see 12v at the coil or only when I crank the engine? If I should always see 12v then I definitely have a bad ground to the coil.

 

Thanks for the detailed explanation of testing from the coil HT lead, I'll carry that part out this evening (7:15am here in the UK) and report back for sure.

 

Before that though, I will go and remove, clean and replace the grounds on the block and body.

 

Cheers

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45 minutes ago, adhards said:

do get 12v at the positive on the coil but only when I touch the negative metre wire on the rocker cover. Should I always see 12v at the coil or only when I crank the engine? If I should always see 12v then I definitely have a bad ground to the coil.

 

That’s normal. If you mean you are putting the meter leads across the + and -ve terminals on the coil. You do indeed have a ‘bad ground’ to the coil as the coil negative passes through the points to ground. It just means that your points are open. If you get 12 V from the coil positive to the engine block then you definitely have 12V at the coil. 

 

This was was why I asked you if you could put a test light from the coil -ve to ground. When the points are closed they short circuit the test lamp and thebulb goes out since the majority of current flows via the points as they are lower resistance than the bulb.  When the points open, the current then flows via the test lamp and so the bulb glows. Watched when the engine is cranking it should flash. 

 

Teasing a spark out of the coil as Mike describes is a better approach since this test both the points and the coil at the same time. I am just frightened of getting an electric shock and I have found the points and ‘low tension’ wiring to be the usual problem.!

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10 hours ago, mike said:

 

If the coil has been replaced with a blue or red Bosch coil, the ballast resistor isn't necessary.

 

Beg to differ Mike.  I think you may have mis-typed.  The above may be generally true for most (but not all) Bosch blue coils.  Bosch red coils, and OEM black coils employed external ballast resistors.

 

 

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Roland, thanks for the update/correction.  I installed a Bosch blue coil on my '73 many years ago and never deleted the ballast resistor, not realizing I "should" have.  I've had no problem with it.  WRT the Bosch red (now apparently silver) you're correct.  Not having ever used one I had forgotten they do need the ballast resistor.  

 

And ...

10 hours ago, Simeon said:

Teasing a spark out of the coil as Mike describes is a better approach since this test both the points and the coil at the same time. I am just frightened of getting an electric shock and I have found the points and ‘low tension’ wiring to be the usual problem.!

 When I do that either with the coil wire or a spark plug wire, I wear leather work gloves and hold the high tension wire with insulated pliers.  I've been tingled a few times and learned from my mistake!

 

mike

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I've just confirmed that I have 12v coming into and out of the coil but when I put the HT lead from the coil onto the same spot I was just using for a ground on the multimeter I don't see a spark when the engine is turned over. :(

 

I also removed the points and cleaned them up some more with some super fine sandpaper but still no joy. 

 

At this point I think I should go for trying a new condenser

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6 minutes ago, Chris_B said:

How are you adjusting the points?

I haven't adjusted them. The first time I removed moving side was just now when I cleaned them

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