Calling all Lumenition ignition experts

[NYK]

I have an Optronic ignition fitted to my Plus 2 and am conducting final tests following full engine rebuild the Optronic system came with the dismantled car when purchased so I have never used it, although did bench test it.
I do not seem to be getting a reliable spark, I have tested the module, making/breaking blue and black wires (as per Lumenition test procedures) and get a healthy spark. I also get a good spark when moving a piece of plastic card between the IR sensor in the distributor. With the IR chopper in place in the distributor and rocking one of the arms back and forward rapidly over the sensor I also get very good sparks. However when I crank the engine (plugs out) I get an initial strong spark after which I can see no sparks or very weak sparks. I’m holding the HT lead from the coil close to earth for my tests.
I have not yet tried firing up the car as I’m not convinced I have a spark. The only difference between the ‘manual’ test and the engine crank test is that the supply voltage to the coil and Lumenition will have dropped to around 11volts during engine cranking, but this sort of voltage drop must surely be normal, the battery is a new one.
Any thoughts?

[Andy8421]

Assuming you have left everything unchanged except for cranking the engine rather than manually interrupting the sensor (sensor mounted in the distributor for both tests, no change in wiring) - then the only two differences are supply voltage and frequency / duration of sensor interruption.

It is quite possible that the module (or the sensor) has become voltage sensitive with age, equally it is quite possible that the module (or sensor) works fine for a short period of time, but a sustained pulse train causes it to fail.

If you have a spare battery laying around, you could try running a temporary supply to the module to rule out supply voltage being an issue, or if you fancy taking the distributor out, you could spin it using a drill with a screwdriver bit in the screw under the rotor arm to see if it is spark frequency causing the issue.

In either case, that's not much use and I would ditch the sensor and module and start from scratch. Nothing more annoying than being stranded by the side of the road because the ignition system has packed up.

One final thought, it is possible that the vibration of cranking the engine is wobbling a dodgy connection, and I know from bitter experience that the Lumenition sensor modules become vibration sensitive as they start to fail.

Good luck.

[Billmack]

I am agreeing with Mr.Andy. I generally replace that stuff every time. The early lumenitions seemed more reliable than the latest ones.

[NYK]

I have to agree with your conclusions there are very few variables to be considered. The wiring is all sound so I don’t think that could be the cause. I guess tomorrow I need to set up a separate 12 volt supply for the module and re-run the test. I would really want to show cause of failure before buying a new one, nothing more annoying than replacing something only to find there was nothing wrong with what you’ve just bought.

[Donels]

Just a thought. You do have a good earthing strap from engine to chassis?

[mbell]

Do you have the ballast coil system on your car? if so, could the supply line for cranking not be connected to the coil? Resulting in no spark.

Or possibly if you don't have ballast setup and your getting weak spark due to low coil voltage/current. Maybe test with separate power supply to the coil too.

[NYK]

The car is nearing the end of a very long restoration I paid great attention to chassis/engine earth. The coil is a new non ballasted coil specifically for the Lumenition. The wiring loom was reworked and extensively tested before it went into the car. The coil is seeing around 11 volts when the engine is cranked which should be fine. I think on balance the finger is pointing towards the Lumenition not liking a reduced voltage, I will be testing with the ignition running on a separate battery tomorrow.

[john.p.clegg]

The only problem I had with Lumenition Optronic fitted was the three way connector , it was not making good contact , and as it swayed as the engine moved was causing intermittent failure , not easy to diagnose but easy to fix with fine instruments , prod the connector pins and make the males larger and the females smaller...

John

[NYK]

Well after extensive testing today, I’ll spare you the tedious details, I can confirm the conditions under which it will/will not produce reliable sparks when the engine is cranked.
I will quote two voltages a/b, where a = voltage measured at the coil and b = supply voltage to the Lumenition

10.6/10.6 = good sparks
10.3/10.3 = initial spark then no sparks
10.3/10.6 = good sparks

Obvious conclusion was that the Lumenition in my car requires >10.3 volts to function. I have been in contact with the technical people who make the Lumenition, they say the unit should operate down to 9 volts. On that basis it would seem that my unit has a fault somewhere and needs replacing. I must admit I’ve not come across a failure mode where electronics become voltage sensitive like this, but we live and learn.

[rgh0]

I think you need to try 10.6 at the coil and 10.3 at the lumenition to complete the set of tests and confirm your conclusion.

cheers
Rohan

[Craven]

What is your battery terminal voltage under no load and crank conditions. 10.** seems on the low side.

[NYK]

Those voltages were taken after a bit of cranking so battery voltage had dropped a little, the battery voltage was around 12.5 at that time. Before anyone asks I have a very good earth at the battery and am not losing voltage there. I am losing around 0.3 volts somewhere in the switched wiring to the coil. So my testing included taking the the coil voltage from its normal loom supply and supplying battery voltage from the battery connection at the starter solenoid direct to the Lumenition.
I suspect I’m dropping the 0.3 volts at the ignition switch but need to do a bit more testing to verify that.