No spark

[Heronscourt]

I’ve finally got to the position in the rebuild where I’m trying to start the car but have no spark. With ignition on I have power to the coil positive terminal, a continuity test of its primary winding is ok. I have 12 volts at the positive and negative terminals when tested to ground but with the ignition switch on and a test lamp across the coil terminals the lamp doesn’t light up nor does it blink when cranking. Removing the distributor cap and opening the points with a non metallic probe does not produce a spark at the contact breaker. The wires to the points terminal post are correct with the insulators in the correct position. Any suggestions as to where to investigate further gratefully received.

[mgcjag]

Hi Alan.....ignition off...disconnect the wire from the dizzy to the coil.....with a meter test on the end of the wire as you open/close the points.....you should see an earth on/off as points open close......im assuming you have standard dizzy and no ballast resistor.....Steve

[Heronscourt]

Thanks Steve, I’ll try that in the morning and let you know what I get.
Alan

[Heronscourt]

Couldn’t wait until tomorrow, strange result. I had the test light across the positive and negative coil terminals as before with no light so decided at the same time to bypass the wire from the coil negative pole to the distributor as you suggested while leaving the test lamp in position. My thoughts were that even though it’s a new loom there may have been a fault. I clipped the bypass wire to the coil negative pole and grounded the other end to the distributor base plate. The test lamp lit up and stayed lit even when I removed the probe from the base plate. I decided to turn the engine over and the test lamp flashed on and off. All this with the bypass wire removed so it appears that I’ll have a functioning ignition when I fit the distributor cap and put the plugs back. I’d removed them to avoid flooding the engine when turning it over with no spark. I still don’t know why it didn’t function before so I’ll go through the earths at the distributor before trying again. My thoughts were faulty capacitor but the distributor has been fully refurbished.
I’ll update you when I’m sure it’s all ok.
Thanks for the advice, it obviously produced results even though I don’t know why.
Is it possible that what I did jerked the capacitor into action?

Alan

[vee12eman]

Hi Alan,
My recent experience with new condensers (I presume that is what you mean by capacitor?) is that they are rubbish. Different car (Austin), but the brand new condenser failed within 10 miles and I changed virtually everything else before refitting the 40/50 year old original, found in the bottom of a pile of knackered spares destined for the tip. Instant transformation. When taking the car to the club and describing the issue, the engine guru who regularly attends just smiled, said that it’s always the condenser these days and handed me another, old one, as a spare. I’ve since spoken to and ordered new condenser units, rotor arms and points from the Distributor Doctor.
Experience with new points was not much better. A new set for a VW Type 2 required adjustment twice shortly after fitting, once stranding me on the freeway hard shoulder in rush out. Another guru pointed me at the points, recently fitted, and to my shock, it was the exact problem - never a problem years back when I changed points on a regular basis.

[abowie]

No spark.


Symptom: car won’t start or run at all.


NOTE: assumes NEGATIVE earth, points in distributor.


To Confirm: Put a plug tester in series with a plug. It should flash when engine is cranked. If no flash check other plug leads as well. No flash = no spark.

If you do have a flash the problem is NOT spark per se, although it MAY be plugs. See 9.
Otherwise the problem may be timing, or fuel or compression. These steps will not help those things.

Take each step one at a time, in order. At the end of each step try to start the car.

1. Battery flat.
If the car cranks over it is almost certainly OK.

2. Engine earth.
Spark requires a good earth to the negative terminal of the battery. Check that the engine is earthed with an ohmmeter or voltmeter between the battery and the block.
Visually inspect the engine earth lead (LHS behind the reaction tie plate. If in doubt run a thick cable (jumper lead) from the battery negative terminal to the engine.

3. Check power to coil.
Remove the positive connector to the coil. Put a 12v test light in series and turn on the ignition. The light should come on and be steady.
Jiggle ignition key to eliminate switch fault.
If no power, run a wire directly from the positive battery terminal to the positive coil terminal and try ignition. If it works problem is between battery and positive terminal wire. Check fuse 7 and chase wiring with multimeter. Recheck ignition switch. NB starter button will not affect spark.

4. Check points are opening and distributor is turning.
You can do this visually. Remove dizzy cap and get someone to crank the engine. You should see the points open and close. Use a torch; it’s dark down there.
Put a 12v test light between the negative coil terminal and the black/white wire to the distributor. Crank the engine. The light should flash off and on as the points open and close. This should work with electronic ignition modules as well because what you are testing is the circuit through the points (mechanical or electronic) to earth.
Note: the light may stay on or off when not cranking depending on whether the points stop closed (likely) or open (unlikely). This isn’t important.
Check the points gap (14 to 16 thou) and inspect the electrode faces for pitting. If any doubt replace points and reset gap. Even when you’re sure it’s not the points, suspect them. It’s always the points.

5. Condenser.
A dead condenser looks just like a good condenser. Just replace it. They can be tested with an ohmmeter but if you put a new one in and it doesn’t fix the problem it probably isn’t the condenser.

6. Check the coil.
If the points are working and the condenser is OK. Get a spark plug and a plug lead. Connect the plug lead into the HT coil connector. Earth the plug by resting it next to a head nut. Turn on the ignition. Use a nonconductive (plastic) tool and open and close the points manually. (Alternatively you can connect a wire to the negative LV connector and tap this on an earth.) There should be a spark on the plug each time the points open. If you have spark the coil is OK. Move on to 6.
If NO spark AND you are happy with 1-4 above, the coil may be faulty. Check the resistance of the low voltage (primary) circuit by connecting an ohmmeter to the two LV terminals. This should be between 0.5 (low resistance/sports coil) and 3.5 ohm (standard coil). Check the HT (secondary) circuit resistance by measuring between either LV terminal and the centre HT terminal. This should be in of the order of 5000 to 15000 ohm. Note that coil failure can be exacerbated by heat so even if it checks out cold it may be faulty hot.
Replace the coil anyway with a known good one. (You can just sit one next to the old one and connect the 3 wires to it).

7. Leads
Remove the coil HT lead. Inspect for cracking or corrosion. Coolant can leak from the thermostat housing down onto the top of the cap and cause corrosion, especially with “screw in” contacts.
Check resistance with ohmmeter; it should be virtually zero with copper core wires.
Check the resistance of each of the plug leads by removing the plug cap and using a multimeter between the end of the wire and the corresponding contact inside the distributor cap. With copper core wire it should be virtually zero. If not check the cap socket for corrosion.
Modern cable resistance is more complex and you would need to check the figures with the manufacturer. As a general guide though a lead should be between 2000 and 8000 ohm.

8. Plug caps
The original plug caps have a carbon resistor in them. They will have a resistance somewhere between 5000 and 15000 ohm. Modern or reproduction caps should be spot on 5000 ohm. If you suspect the caps, replace or eliminate them. You can solder a ring connector onto a fine 1” self-tapping screw. Screw this into the lead in place of the plug cap. Use the ring connector to connect directly to the threaded end on the spark plug.

9. Spark plugs.
Remove the plugs. Check for fouling and check gaps. If no success, replace with new plugs.

10. Distributor cap
Inspect for cracks or corrosion. The cap really should look brand new inside. Clean up the lead connector sockets if at all corroded. The central contact for the rotor button should have a resistance of the order of 30000 ohm. If the cap looks OK still try replacing it with another one, or a known good cap and set of leads.

11. Rotor button
Inspect and replace if it looks worn, pitted, burnt or otherwise faulty. Try another one anyway if it looks OK.

12. Distributor
Remove the distributor and carefully inspect it. Ensure that it wired correctly. Specifically check the insulators between the points and the coil and capacitor leads are in the correct place.
Check that that the coil lead is connected and conducts to the capacitor lead.
Check that the internal earth lead is connected to the distributor body and the centre plate.
Check that the distributor turns freely and is mechanically intact.
Check that there are no small screws or other foreign parts loose inside or causing a short.


13. Other things
If you have got here and not fixed the problem.
The checklist above is fairly complete. Sometimes though electrical components can look OK but be faulty. Replacing each component, one at a time, with a known good (not necessarily new) component will sometimes smoke out a mystery.

[Heronscourt]

Thanks to everyone, especially Andrews very comprehensive testing list. I thought I’d got it cracked but now haven’t got spark at the plugs. It’s a new distributor cap and leads, the screw cap type of leads, new rotor arm, condenser, new plugs with gaps checked etc so I think my next check has to be the secondary coil windings resistance and put a plug lead into the coil and check spark. If that fails I have another new cap and leads to try. I’ve got spare condensers to try as well. Strangely when the engine was rebuilt it was bench tested with these ancillaries and ran beautifully.

[rswaffie]

I recognise that comprehensive list! I seem to remember following it when I had a similar issue. It really helped in problem diagnosis. My issue turned out to be a loose earth wire in the dizzy - the small one that goes from the dizzy body to the contact breaker.

[malcolm]

Thanks to everyone, especially Andrews very comprehensive testing list. I thought I’d got it cracked but now haven’t got spark at the plugs. It’s a new distributor cap and leads, the screw cap type of leads, new rotor arm, condenser, new plugs with gaps checked etc so I think my next check has to be the secondary coil windings resistance and put a plug lead into the coil and check spark. If that fails I have another new cap and leads to try. I’ve got spare condensers to try as well. Strangely when the engine was rebuilt it was bench tested with these ancillaries and ran beautifully.

Why not buy a new coil as well? They're as cheap as chips, and everything else you have is new. I assume you have a new king lead from dizzie to coil? I've had them break down.