1. Way back at the beginning, connecting up the motor and ignition gave me no spark- cleaning all the contacts especially around the coil gave a nice regular spark at the king lead- but which vanished every time I reconnected the king lead!
2. I then reproducibly got a spark on starting to crank- then nothing during cranking, followed by a spark when the key was released. That's how it stayed so I started testing and substituting ignition components.
I cling to the notion that this car did not fail during an ignition fault- it must have been running or it couldn't have thrown a cam belt-but it does look like ignition might have been a bit hit or miss even then.
So what have I done?- this is described more fully in my earlier posts- "Oil pressure ignition and fuel..." and "Lucas 157SA ignition switch...." but I summarise here:
I have changed the coil for a genuine Lucas 32C5 type DLB198
I have fitted new HT leads, distributor cap and rotor arm.
Result: No change
The spark on releasing the key was traced to ignition switch failure; probably caused by contact erosion - the ignition was connected in the ign/run position, but disconnected during cranking and the 12V detected at the coil when in the "run" position fell to zero on cranking! This also cut out the fuel pump. Releasing the key restored power to the ign, but the motor was slowing down after the crank so only one spark! I fitted a new Lucas 157SA switch type 3415
Result: Spark on releasing key now vanished; I still have a good, fat spark on first crank but still saw only a weak intermittent spark (or more commonly no spark at all) during cranking. Volts are now detectable at coil, 12V ign on but dropping to 9.9V during cranking .
This could suggest a switching fault- either through pick up or igniter failure. I tested the resistance of the pickup and found it to be 3.25Kohm; higher than the 2.25Kohm value cited by Lucas ... but there is no guide in the test card as to what values are permissible- Luckily I found a later version of card 6 which states a pickup resistance range of 2-5 k ohm; so I could conclude the pickup was not at fault. I could find no trace of a break in the distributor/AB14 wire, neither before, nor after the distributor entry plug.
To diagnose any further really needed me to understand more about how this system is supposed to work- this is the result of my investigations- undoubtedly oversimplified but hopefully essentially correct!
Ignition module function
The coil +ve is connected to the battery as long as the ign is in the run or crank position - thanks to my new switch. This connection is also monitored by (but not controlled by) the ign amplifier. The coil neg (output) contact is connected to the ignition module (inside the AB14 amplifier) which then switches this wire into and out of contact with earth. Each time its earthed the 12V input to the coil can flow through the LT circuit (secondary coil) to earth through the module. When its switched out of contact with earth the current stops and the mag fields collapse, inducing the sparking voltage in the primary coil. The module makes this switch in response to a triggering voltage fed from the distributor pickup to the other two terminals of the module.
So I'm starting at the beginning and working my way through everything again. The following is a test regime I worked out from reading various different sources- it makes sense to me anyway!
Meantime here is a pic for those happy Lotus users in sunnier climes...
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| Unacceptable face of mechanics in the UK- dodging the rain and ducking under the tarp |
1. Can current switching give a spark?
Disconnect coil positive lead and use a fly lead to connect coil negative to earth.
Remove the king lead and lay it on the block where the terminal could spark - if a spark is present (or fit a spark tester).
Turn ignition on and briefly flash the coil positive lead onto the coil positive terminal- should give a spark!
This means if a switched current is present the coil will work.
... Well I got a nice fat spark- and that was good news, but to be frank its only as expected since this is a new coil!
2. Test for presence of switched output
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| Testing circuitry- note the 12v from post D is still present- I just forgot to draw it again in the lower diagram! |
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| Disconnect coil negative and attach tester earth- probe coil positive and crank. |
Switching should be evident if the coil is replaced with a 12V LED circuit tester. Disconnect coil positive input (white wire), and connect this wire instead to the positive side of a 12V LED. Disconnect the white black wire from the coil negative terminal and connect this to the earth connector of the tester. The LED will receive 12V as long as the ignition is on, but cannot illuminate unless the coil negative is earthed so that current can flow.
Crank the motor- if the amplifier works then it will switch the white/black wire to earth and back causing the LED to flash.
... I came up empty with this one and got nothing!
3. Test for switching (pickup output) voltage
Pickup output is generated by the points of the reluctor passing the sensor- this rotation towards, past and away from the pickup generates an AC voltage which should be detectable using a digital AVOmeter set on VAC. So, disconnect the sensor input wire terminal from the amplifier and probe the contacts inside that terminal coming from the distributor. It doesn't matter which way round you probe; you are looking for AC anyway. Crank the motor and observe any AC output. I think the magnitude and frequency of this output will depend on speed of cranking and and number of cylinders. I don't have a reference voltage for the Lotus but its been reported as 0.15V AC in the forum. That report considered the voltage to be on the low side. For comparison (and of unknown relevance) a V12 Jag using the same system generates between 0.3 and 1.8V AC.
... I always saw a reading here- it was a little variable between 0.13 and 0.3 VAC but there was always something and its a similar size to that seen in the forum! This must indicate that the amplifier is faulty. Currently the AB14 has the replacement ignition module inside so I will switch back to that which came with the car.
4. Test for amplifier response to pickup output
I didn't need to do this, I'm listing it as it is the next step if I hadn't been able to find a pickup signal. Its here for completeness.
If the pickup output is absent or suspect, an imitation pickup voltage signal can be generated using a 1.5v pen cell with a 3k ohm ohm resistor in series to reduce the voltage. Install the test LED as above in test (2). Connect the dummy voltage supply you have made to one terminal of the distributor lead input at the amplifier and flash the other onto the second terminal to transiently complete the circuit- If the amplifier is working this should cause it to earth the coil negative wire and so induce a switched pulse current between from the other two amplifier terminals... which will be visible as above using the LED.
The above processes indicated to me that I had a faulty amplifier module so I swapped that over for the original (the one that came with the car) and tried again- and this time- yes indeedy(!) a regular spark at the king lead. I reconnected the leads and tested again at the plugs- also observing a spark there. Finally, I reconnected the temporary fuel supply and fuel pump before trying again.
Well there was a great deal of nervousness on my part... but after three or four attempts I did generate (at last) the odd detonation or two! I fiddled with the throttle and choke and kept cranking before finally I got a series of detonations and then ...
... IT RAN!!!!!
The video doesn't do this moment of triumph justice but here it is and I share it with the world!
I turned it off smartish as I have to check for water level and fluid leaks but it started and ran quite nicely- all I need is some better weather to try and sort it out a little more....
Conclusions
Well- it seems that I had at least two separate problems (maybe 3) with my ignition system:
1. I do not know if the odd, pierced rotor arm had an effect but it could have been a contributor to my woes!
2. The ignition switch was obviously unreliable and seems to have failed completely during my many cranking attempts to start the motor.
3. The ignition module (the new one I swapped in!) had failed.
I don't think the new coil, cap or HT leads were really necessary- but Hey, they look good and can do no harm! The single fat spark seems in my case to have resulted from module failure, but whether this is diagnostic of such failure I can't tell. I think poor battery would also probably induce the same effect.
If there is a lesson here its probably not to swap too many things at once in (almost) blind panic. I inadvertently made the situation worse by swapping in a "new" Intermotor module, which in fact didn't work and so prevented me from curing the problem by replacing the ignition switch!
One problem I do note is that while running fuel can be seen dripping into the venturi... I'm not sure if this is just because I have been overplaying the throttle in an attempt to get the things started or f there is a problem with the jets sealing, but the fuel collects in the intakes.
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| Engine idling- fuel collecting at carb intakes- all 4 show this. |
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