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No spark, what am I missing

B

Barnster

Enthusiast
Messages
21
Location
Harrogate
Hi everyone,

Looking for a bit of a sanity check.

I have an '84 F6. Got it running a couple of months ago with a couple of wires and switches to simulate the ignition switch (no keys). I have now replaced the igntion barrel but It won't start.

Standard 1108cc engine, no visible modifications. 120psi across all 4 cylinders. Ducellier R324C33 distributor. Fully charged battery. I dropped the tank to replace sender unit and fresh fuel (not spark related I know)

I am testing for spark by removing plug with HT lead attached and grounding to distributor mounting stud (which has continuity to battery -ve terminal)

So far I have:

Replaced ancient coil with new Accuspark part.
Replaced points, condenser, rotor arm, cap, spark plugs and HT leads with new items.
Bypassed the ignition circuit part of ignition switch with direct lead from battery to distributor +ve terminal to rule out short somewhere.
-ve coil terminal goes to screw terminal on distributor. Condensor also connects to this terminal and obviously is secured to distributor housing.
points gap is 0.4mm.
Points appear to be opening and closing - metered to test continuity from points "arm" and the terminal on the outside of the distributor - open until points close then circuit is closed.
I have also tried a known working, non ballast coil from one of my minis and the same situation.
The distributor body has not been moved or rotated.

No spark and the frustration is building.

Can anybody offer any more tests or perhaps highlight something I have fogotton please?

Thanks
 
To ensure the coil's producing a spark try this: Using a long H.T. lead connect one end to the coil's central (H.T.) terminal and push a spark plug into the other end. Rest the plug on the battery's -ve terminal and ask an assistant to switch on the starter. You should see regular blue sparking at the plug, assuming the plug's earthing properly on the battery earth. Alternatively, rest the plug on the engine block, but it's important to confirm the plug is earthing. Assuming it is, if there ISN'T a spark, either the coils' not doing its funky stuff or the H.T. lead is damaged. Report back after this with the results and I'll suggest the next stage. It's important to change only ONE thing at a time, or you'll become hopelessly confused, believe me!
 
@André4Renaults I have just tried this test and there is no spark. Incidently I tested the spark plug electrode to the HT lead connector on the plug for continuity I got some wild readings. Is it possible for spark plugs to be "bad"?

I have tried the coil and the HT lead in question on my mini and it runs fine.
 
I have tested the continuity on the plugs in my R5TX and they all have 100% contact from electrode tip to lead connector. Hard to believe I have a complete bad batch of new plugs...... I will report back.
 
Sounds like it should work. Is there a ground missing? Plug grounded to engine as you test and engine grounded to battery.
 
I had a similar problem years ago and it was the brand NEW rotor arm that was faulty ! Looks like you have checked everything...will have another think about it.
 
Barnster said:
@André4Renaults I have just tried this test and there is no spark. Incidently I tested the spark plug electrode to the HT lead connector on the plug for continuity I got some wild readings. Is it possible for spark plugs to be "bad"?
Click to expand...
Yes, it sounds like a duff set of leads-it does happen! using a multi-meter set on the maximum resistance setting (usually 2M Ohms) you should have very little resistance at all from the lug inside the distributor cap and the spark plug terminal. Whatever the resistance values they should be consistent across all the leads.
 
If there's no spark at the points, it might be worth double-checking the connections on the side of the distributor (insulating washer, etc.). Could there be a fault/break with/in the low-tension wire from the coil to the distributor?
20250510_191641.jpg
 
I'm going round in circles at the minute testing every connection! I have a rubber grommet/washer insulating the distributor "terminal" from the body of the distributor where it passes through the body. With no wires connected there is no short between the terminal and the body on the distributor. When the wiring is all connected up to the coil/battery there is a circuit between them at all times - I'm guessing this is wrong but not sure why or what is causing it.
 
OMG ! you have tried everything. Have you tried using your original distributor cap and rotor arm ? Some of this repro crap is rubbish these days.
 
Yes, I've gone back to the originals this morning out of frustration. Tried starting - had a little splutter but didn't fully fire and now back to nothing.
 
I have just tested everything again with the original parts and new parts. What I have discovered is that if the +ve side of the coil is connected to the battery directly or via ignition switch, when rotating the engine so the points open there is a constant closed circuit between the points. (tested with meter across distributor casing and points arm. If I disconnect the +ve side of the coil, there is an open circuit when the points are open and closed when the points are closed. Does this point to anything in particular?
 
Barnster said:
I have just tested everything again with the original parts and new parts. What I have discovered is that if the +ve side of the coil is connected to the battery directly or via ignition switch, when rotating the engine so the points open there is a constant closed circuit between the points. (tested with meter across distributor casing and points arm. If I disconnect the +ve side of the coil, there is an open circuit when the points are open and closed when the points are closed. Does this point to anything in particular?
Click to expand...
Yes, there's a dead short somewhere! I'll explain what should happen: When the ignition's turned on the current runs from the battery, through the key and to the +ve side of the coil. The current then runs from the "CB" (contact breaker) side of the coil to the distributor; when the points are closed the current runs to earth, so the coil is changed up. As the points open, the supply of current is switched off and the result is a HUGE voltage in the H.T. terminal.

Your picture of the distributor body shows the connection from the coil into the distributor and this wire is connect to the points inside the distributor, but should be insulated. This wire should be at +12 volts when the points are open and at zero when they're closed. Check that this is the case and if not, examine the points and confirm they're correctly bedded and that the insulated side isn't accidentally touching the distributor body.
 
Well, stranger than strange. Took distributor cap off to test voltage at points rather than testing continuity. 12v when open, 0v when closed. Put back together, tried and hey presto! Great that it's working, not so great that the problem hasn't been diagnosed.

Thanks you for all your help & suggestions folks.

BS
 
I'm wondering if your rubber grommet is not fully insulating- are you sure it insulates on both sides of the distributor body (inside and outside) and also insulates internally between the screw thread and the body? Could be in some positions it just touches somewhere, like if pushed down by cap or tightened/loosened.
 
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