No spark.

[chrisdebois]

Hello. A very basic question for a very basic Morris Minor problem I hope. I am getting no spark and changed the coil to no avail.

I have just bought a multi meter to check things out. Can you please advise the correct checks I should make to trace the problem in a step by step order.

Many thanks, Chris.

[paul 300358]

Points or electronic ignition?

First, with the ignition turned on you should have 12 volts between the coil ignition switch terminal (yellow/black wire)

If electronic ignition change back to points.

[simmitc]

A few questions to assist with diagnosis:

What year is the car?
Is it positive or negative earth?
Does it have points or electronioc ignition?
How did the problem arise - was it running OK and then suddenly would not start, did it cut out whilst running, has nay work been done between it working and not working?
How have you proved that there is no spark - tested from the king lead to the block or from a plug lead to the block?

Please report back and we can offer further advice.

[chrisdebois]

Thank you for the replies.

It started to run badly going up hill last autumn so my garage said the best thing would be to fit electronic ignition. He did that but the problem remained the same. It still ran but struggled up hill.

Then it started to not start intermittently so I fitted a new coil. That didn't change anything.

I have the points for the distributor still so maybe I should put them back in?

Chris.

[chrisdebois]

Ps. At the moment it turns over fine but will not start at all.

Pps. I checked the sparking by removing one of the plugs and resting it on the block and had my neighbour turn the engine over.

So I'm sitting here thinking maybe the original bad running was the fuel pump (which did need a knock sometimes to get going) and the newly fitted electronic ignition has gone faulty?

[simmitc]

With electronikc ignition it is important to know whether the car is postiive or negative earth. This also affects which is the best way to connect low tnesion wires to the coil.

Start by removing the high tension lead from the centre of the distributor cap, but leave the other end in the coil. Hold the loose end end of the lead about 1/4 inch / 6mm away from the block and with the ignition on, turn the engine using the starter motor. Do you see sparks? If yes the the problem is with the rotar arm or distributor cap. If no spark then it's time to check other things.

Let's get it sparking and then move on to what might cause the problem going up hill, but one thing you could test now is to remove the dizzy cap and then take the vacuum tube off the side of the carb and put it in your mouth. Suck hard. You should see the insides of the dizzy move round a little, and if you block the end of the tube with your tongue, then it should hold a vacuum for s short while. If you cannot establish a vacuum then either the vacuum advnace unit has failed or the tube has a hole in it.

[chrisdebois]

Thank you. I'll do that check asap.

[chrisdebois]

Ah - ok. A very weak and very intermittent spark coming from the high tension cable from the coil.

[myoldjalopy]

"It started to run badly going up hill last autumn so my garage said the best thing would be to fit electronic ignition."
What? That garage sounds clueless. Instead of diagnosing the issue properly, they just guessed! Any mechanic worth their salt would have got the dizzy set up right (if, indeed, that was the problem). Nothing wrong with the points system, if adjusted correctly. A new set of points would have cost far less than electronic ignition........

[chrisdebois]

So a very weak spark from the coil. The wiring is a bit old and looks like this photo. I have a multimeter so would really appreciate wher to look from here.
Best, Chris

[simmitc]

As asked earlier, is the car +ve or -ve earth? This will affect what to connect where and what readings to expect - only whether there is a + or a - in front of the display, but still a good idea to be clear what we're looking at.

In terms of simplicity to test things:
Replace the HT lead from the coil and see if it now sparks properly.
Replace the coil with the original that you took off and test again.
On both coils, test the resistance between the terminals when there are no wires connected at all.
Remove the electronic unit and refit the poinst and condenser. Make sure that the gap and timing are correct.

It's not going to be anything too complicated, just a question of being methodical and not changing multiple parts willy nilly.

[chrisdebois]

Thanks. I did the test with the ht lead and there is no spark coming from the coil. I'll put the other one back now to see if the same.

Ps. it is negative earth.

[chrisdebois]

Ok. Put the old coil back and no spark still at the ht lead.

[COMMANDER]

Certainly I would replace points and a new condenser(preferably from Distributor Doctor). Make sure the coil is wired correctly , +ve input to the +ve terminal. -ve terminal to distributor, then start all the checks as previous posts. Also do check the vacuum advance. I recently had a horrible misfire caused by a leak in the vacuum tube. My thoughts here are that possibly the original problem was a failing condenser and that maybe the garage wired the electronic system incorrectly thereby buggering it up strait away. Good Luck.

[chrisdebois]

Thank you.

Well somehow I am now not getting my 12volts from the ignition now so that is my 1st problem to solve and will hopefully fix the whole problem or at least get me back on track. The fuse is ok but I'm not getting 12 volts into the fuse box( a green wire) Trying to trace it back to the ignition switch. Is it easy enough to get the barrel out to look? Very tight behind the dashboard.

Will take a break now and take the dogs for a walk.

[simmitc]

From that we have two different coils and two different HT leads, and nothing is working correctly. Is that correct?

Disconnect all wires from the coils.

Use your multimeter set to resistance (ohms) and measure the resistance between the two low tension terminals on the two coils. You should expect a reading of between 0.4 and 2.0. Anything way outside that means that the primary circuit in the coil has fialed and the coil needs to be recycled.

Now check the resistance between the positive low tension terminal and the centre high tension temrinal. Expect a reading of between 6,000 and 10,000. Again, anything way outsidew those values and the coil should be recycled.

Note: if your meter is not auto-ranging then you will need to select the correct scale to match the expected values.

Pick one good coil and one HT lead and stick with them for now.

Use the multimeter set to DC volts (correct scale if needed) and connect the black lead to an earth point on the car.
Now connect the red lead to the white lead that connects to the coil. With the ignition on, do you have approximately 12 volts showing?
If yes, connect the white lead to the +ve or IGN low ternsion on the coil.
Connect the multimeter red lead to the -ve or CB low tension terminal on the coil. Do you should still see 12 volts?

If all so far OK then I would remove the electronic ignition completely and connect the white and black lead to the coil -ve or CB terminal. The other end of the white and black lead should be near the distributor. Check that 12 volts is present on the end of the wire.

Work through the above and report back.

[simmitc]

My last post crossed with the previous two, but is still valid. However, from your last post...

The ignition circuit (white wire) is not fused, and comes direct from the ignition switch. If the switch is faulty then that will have an impact, but not cause your orignal misfire under load. Check that both battery terminals are secure, that the earth to the body is secure, and that the braided earth strap from cross member to back of gearbox is secure and in good condition.

[chrisdebois]

Many thanks. I'll get going again in the morning with all of your helpful advice.

I think we could be mobile again soon.

Here is Mabel.

[simmitc]

Your lack of power from the switch could also be a broken wire or poor connector. For testing purposes, you can bypass the feed from the ignition switch: simply remove the white wire form the IGN / +ve terminal on the coil and run a new clean piece of wire to the positive temrinal on the battery. Use a crocofile clip so that you can disconnect from the battery when not testing, but that will provide a good supply to the ignition system.

On the other side, once you have completed all steps in previous advice and have 12 volts at the dizzy end of the white and black lead, then you can (with enough hands and eyes) perform another test to prove the components up to that point. First think that points do: they open and close, breaking and making a circuit to earth. You can simulate that. Set the HT lead from the coil to the block as previously. Connect the ignition to the battery. Alternatiely touch and remove the free end of the white/black wire to a good earth point. Expect to see a spark where you do, but also there should be a spark from the HT lead. You now know that it all works to there and can fit points fully confident that it if does not then work, it has to be in the dizzy where the problem lies - and there are a few possibilities, but let's get everything good up to that poiont before worryinh about them, other than confirming that the vacuum advance is OK as that's a nice simple test.

[oliver90owner]

Do remember that voltage measurement only indicates the potential difference. It requires current to provide energy.

Think about the water system in your house as an analogy. The water pressure (voltage equivalent) can be behind the tap, but if the tap is firmly turned off there will be no water flow (current equivalent). It is not necessarily the supply that affects the flow.

The voltage drop across the coil, when passing full current, should be close to battery voltage. Any other resistances in the circuit will share a proportion of the supply voltage, depending on the ratios of those resistances. Ohm’s Law should apply with all resistive circuits - providing the temperature of all the components remain constant.