Ignition Issue - Weak Or No Spark

[bruce]

Driving normally on the highway the other day, when all of a sudden there was a loud bang (back-fire), then the engine cut out. Could not start the car.

Tried several times to start. Decided to get towed home.

I noticed that the engine could crank over more faster, like there was no spark at the plugs. I took a plug out and earth it while starting the engine; observed no spark. Made sure the spark plug leads were secure, had a look at the condition of the points, then looked for spark again. I noticed a weak spark. Not sure if it came about by checking the leads or time that elapsed.

 

I managed to start the engine. Did some readings with the multimetre on the coil:

Primary coil resistance 1.9 ohms

Secondary coil resistance 8.2 Kohms

External resistor resistance 2.2 ohms

 

positive side of coil while engine running was 8-9 volts

coil to distributor lead 1.81 kohms

battery voltage while engine running 13.5 volts

earth leads from engine to chassis and firewall seem to be OK with low resistance.

dwell angle set a 50 degrees (t engine service manual 52 degrees)

ignition timing 10 degrees

 

I decided to put in a new condenser. Check the spark and it was a bit more brighter. More yellow than a blue spark.

Though the condenser is only 6 months old (and distributor cap). A month ago I replaced the points, since they were pitted already. I was thinking the points could of been pitting out faster due to a faulty capacitor, but it's still new. The external (ballast) resistor seems to have normal values. I don't think I found the main problem so I'm not real keen on driving far.

 

Was thinking of getting a new coil, though the resistance and voltage look OK, unless they change when the car has been driven for a while. I'm using the ke30 coil with the 3tc.

Edited June 19, 2011 by bruce

[altezzaclub]

Check the earthing from points to motor- should be good but sometimes they can sit on grease or rust and struggle to carry current.

 

I haven't measured the coil resistances, so I don't know if your's are correct, but a poor condensor is a common cause of weak spark.

 

How about an electronic dizzy conversion?

 

As for the backfire... When you checked the timing was it set correctly, or did you move it to 10deg?? ie- did the dizzy rotate by itself?

[bruce]

I've put a new condenser in. Still a weak yellow spark. Very hard to start on cold mornings.

Thinking of converting the distributor to electronic or an MSD ignition later, but just looking at getting it going reliably for now with the points distributor.

I set the timing to 10 degrees with a timing light, It's fixed in place, shouldn't move. I think the backfire was when the engine cut out and the unburnt fuel was going through the system, then it managed to ignite and cause the loud bang.

 

I tried a different coil and resistor but still the same.

 

I had an RACT guy come check it out this morning and he couldn't work it out either. I reckon I'll take it to an auto-electrician.

[altezzaclub]

Tried another coil on it?? Just maybe...

[bruce]

At one stage I couldn't get any spark. There was no spark across the points contact, but I could get a spark if I put a screwdriver across them. I realised I sanded the contacts and it left a very small gap, so it wasn't sparking.

 

I put the battery on the charger for most of the day. Was starting to get drained a bit with all the testing. Then reset the points gap to 0.5mm (dwell angle 52 degrees). I could then get a brighter spark.

 

The voltage before the ballast resistor was ~13.5 volts, and after it at the positive side of the coil was ~12.5 volts. Not much of a drop, perhaps too much current going through and burning the points and stuffing up the condenser too quick. Though the resistance of the ballast resistor seem to be within the values in the service manual. I might try a new coil and resistor and see what happens.

Edited June 20, 2011 by bruce

[altezzaclub]

The voltage before the ballast resistor was ~13.5 volts, and after it at the positive side of the coil was ~12.5 volts.

 

That's tricky- depends on how you measure it as the ignition does feed 12V to the coil under cranking, so if you checked it then you would be right.

 

However if you checked with just the ignition lights on then I'd expect 13V one side of the resistor and 8 or 9volts the coil side.

 

I've got a full wiring diagram on my computer but I need to fix it before I can use it.. :(

[bruce]

Those voltage measurements was when the car was running.

Looked for a coil at autobarn and repco but they don't come with the external resistor. Looking for a nippon denso one.

[altezzaclub]

Those voltage measurements was when the car was running.

 

Then the resistor to coil voltage should have been down around 8 or 9volts I think. That coil should be a 9V coil in use, and get fed 12v when cranking.

[bruce]

I put in a new Bosch ignition coil (SU12R) and a ballast resistor.

Can get a bigger spark. It runs and accelerates more smoother. Can start the car a bit more easier on cold mornings.

Get 9V on positive side of coil, and 7V on negative side when running. Also put some Top Gun pro race ignition leads and that made a difference as well.

 

Has been running well for the last few weeks. However the engine cut out while cruising at 80Km/h this morning. Stopped at the side of the road and it started straight away. Checked battery charge while running it was 12.5V, and check the voltages at the ignition coil, seemed to be normal. I'll have to recheck the ignition/earth wires.

[altezzaclub]

Just die instantly did it? No missfires or jerks? Something killed power to the coil completely..?

 

I've had that where a wire to the coil broke, so sometimes it would open the break up and the car would die instantly, then by the time it had stopped the wire had moved a fraction and carried power again. That took a bit of finding.

 

Did the instruments die?? Charge light come on?? Because if the key socket died it would take the instruments out as well, but a coil wire breaking wouldn't.

[bruce]

Yes, engine just cut out all of a sudden, no miss-fires.

When the engine cut out I noticed the charge light on, so power is still going to the instruments.

There's probably an old loose wire somewhere.

 

I do have an issue with the low headlights flickering that has occurred lately (high beam OK). Not sure if it is related. Can't see any obvious loose connections at the head lights.

[altezzaclub]

Arrgh! Worst sort of problem you can have!

 

Just spend the hours going over all the wiring.. A test light on two clips would be good so you can put power down some wire you've pulled off an have the bulb light up, then fiddle & twist the loomb to see if it goes out. All the electrics in the steering column will need going over too, as the headlight problem might be in the earthing switch.

 

Big steamclean before you start would help too I'm sure!

[bruce]

I ended up getting an auto electrician to have a look at it. It was actually the choke cable rubbing up the side of the distributor, causing the engine to cut out. After the cable was tucked away haven't had a problem since.

The choke cable wasn't connected up to the carby since I converted the 32/36 Weber to an electric choke.

 

Still got a hard start when it's cold. Especially if the car hasn't had a run and the battery (1 1/2 years old) drains a bit. Was thinking that since earlier KE30s don't have a start wire to the positive side of the coil that bypasses the ballast resistor the ignition is not receiving 12V. OK for a little 3K engine, but with a 3TC the voltage drops more to crank the engine over.

[altezzaclub]

the choke cable rubbing up the side of the distributor,

 

lol! that's a tricky one!

 

You're probably right if its the 9V coil on a ballast. It shouldn't be too hard to rig a bypass for the cranking time, take it off the solenoid activator wire..