No spark

[db7gtgrigio]

Hi there - its been a long while since I last posted and I’m hoping for some help - my 1969 UK spec FHC has no spark at the plugs and therefore won’t start and I would much appreciate some help.

For various reasons the car has been cared for by a friend living 150 miles away for the last couple of years and he reported that the car was getting hard to start. he said that it would start just as the he stopped operating the starter motor - ie would not start as the key was turned to the right to operate starter but the moment he released pressure on the key and starter disengaged it would fire. He then reported that car would not start at all.

I visited and we did some tests. No spark at plug except very occasionally a weak spark just as key turned off the starter. There is 12v at the coil with the ignition on at the feed from the 3AW (not the original - replaced 10 years ago with a modern solid state unit). Took distributor cap off and the carbon brush did not seem to be working so replaced with NOS Lucas distributer cap.

With distributor cap off the points look good - nice and clean and gap is correct. when starter is operated there is occasionally a spark across the gap as the starter is turned OFF.

There is no volts registered at the distributer connection to the coil.

I am wondering if it could be coil or condenser - note coil was a lucas branded replacement acquired from SNGB about 8 years ago - any suggestions very gratefully received

[cactusman]

I'd start by checking the coil primary for continuity...should be a couple of ohms. Check you have 12 volts at the coil supply with the ignition on. Next remove the HT lead from the coil to cap at the cap end and connect it directly to a plug. Make sure the plug is grounded and get a friend to open the points with a screwdriver. You should get a spark at the plug? If so the issue is within the plug cap, rotor arm or HT leads. If not replace the condenser and try again. If still not change the coil. Rotor arms with rivets are notoriously poor so it may just be a dud rotor arm grounding the spark....

[mgcjag]

Hi Chris. As you turn the key it supplies 12v to the coil..continue turning and the 12v to coil should stay on but you are also operating the starter....so you need to check that the coil 12v is on during cranking...it could be a faulty ignition switch....as well as all the other points mentioned above...Steve

[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.

[malcolm]

Excellent detailed advice above from Andrew!
The very last bit about changing everything a bit at a time if all else fails is key to me.
I had a problem where everything seemed to be ok, so went about changing everything one piece at a time until the problem went. Not that expensive! And when you find the dodgy bit, all the other parts you bought needlessly are spares.
In my case, a brand new coil was faulty!

[db7gtgrigio]

Update

Car is now started by attaching direct feed from battery to coil input. Once engine started and warm it will re start without the direct 12v feed but only does so as you stop cranking the starter. There is 12v measured at the coil without the additional direct feed when ignition is on. Suggests to me that operating the starter is isolating the 12v feed to coil ie 12v only going to starter solenoid.

Does this suggest that the problem is within the ignition switch? Note that when engine is running the tacho is operational so that suggests that the wiring from ignition switch via tacho to coil is operating ok.

If it is the ignition switch it looks like a pain. my car has Britax ignition switch housing which I think requires Lucas 39679 switch which apers unobtainium.

Suggestions most welcome, thanks in advance

[mgcjag]

Hi Chris...
As your aware when the key is turned to the cranking position it should still supply 12v to the coil...so sounds like a switch problem....Iv used various switches from xj6 models... they physically fit but you need to check what the internal contacts are doing and possibly do a bit of re wireing....you need the wireing diagram for the model that the switch is from....Steve

[MSM]

Chris

I agree with Steve, it sounds like a wiring error with the connections to the ignition switch. I had a similar problem on another car with it only starting when you released the ignition key, turned out the the switch was wired up incorrectly.

The direct connection to the coil is the give away.

[db7gtgrigio]

I don't think it will be incorrect wiring to the connectors as I have had the car for 17 years and it was working fine for the last 16.5 I'm assuming that there is an internal problem with the switch that is shorting out 12v feed to coil when starter operated. have ordered a switch that I am advised will fit so fingers crossed

Chris

I agree with Steve, it sounds like a wiring error with the connections to the ignition switch. I had a similar problem on another car with it only starting when you released the ignition key, turned out the the switch was wired up incorrectly.

The direct connection to the coil is the give away.