Question for automotive ignition savvy techs, igniter module failure modes - Page 1
Forum section: electronics / general

author: Chris Wilson
author_rank: Super Contributor
timestamp: October 07, 2015, 10:09:05 pm
content: I have some general questions on coil on plug igniter modules (some call them amplifier modules, but as they seem to be a switching device I will call them igniter modules for the purposes of this discussion).My questions are re failure modes and testing procedures. I will use for example the expensive, and now obsolete ignition igniters for the Nissan RB26-DETT twin turbo straight six Skyline engines. I and many others have experienced issues with these. Sometimes they will fail to fire on one, or sometimes more than one, coil. The coil is not triggered at all. The thing's kaput and needs changing. But I and may others have had several experiences where the module only fails to fire one or more coils when the engine is around peak torque and cylinders pressures should be around their highest. Idle, starting and off very much boost running, is unaffected. Take it up around peak torque and boost and one or more plugs are not fired, either at all, or adequately and a stutter or lost cylinder results. Leave the status quo exactly as is, and renew the igniter, and all is fine again, so presumably neither a plug nor coil issue. Often this is also temperature related and the issue only becomes apparent at all when the igniter gets hot.Now what is the failure mode of the igniter in this scenario? Are they FET's or BJT's that trigger the coils? I dissected a couple and they are gel filled with the semiconductors are embedded in / on a small heatsink with fine gold wire leads to some surface mount components Can they see different switching currents dependent on cylinder pressure? IE, does each coil on plug see different current draw depending on the voltage needed to jump the gap? What is this interim failure mode likely to be at the component level?As an aside, short wiring lengths apart, why the hell did Nissan think atop the head, in a very hot region, with a thermal path straight into the head casting, a good place to mount the damned things?-I fixed my failure issues ages ago on my MOTEC M800 ecu'd M800 RB26-DETT engine with the two 3 cylinder Bosch igniters from a Volvo V90 straight six, mounted on an alloy heat sink, well away from engine heat and vibration, but would like to get a technical handle on why these (and I mean not just Nissan ones, other makes suffer similar issues) can falter when the plug is asked to fire high cylinder pressures, yet be OK for a while when the engine is not put under appreciable loads.Has there ever been a commercial test rig for igniters that trigger them from say a signal generator, and load their outputs either electronically, or by actually firing coil packs with variable spark gaps whilst monitoring them with a `scope? Some of the things are very expensive and I don't like the "let's just replace it and hope it cured the miss" routine with expensive gizmos....Thanks for reading!

author: joeqsmith
author_rank: Super Contributor
timestamp: October 07, 2015, 10:18:54 pm
content: Quote from: Chris Wilson on October 07, 2015, 10:09:05 pmHere's mine.

author: Chris Wilson
author_rank: Super Contributor
timestamp: October 07, 2015, 10:26:56 pm
content: Wow, I wasn't sure if I would get any replies, let alone one from someone with what looks like a great test rig! How did you make the pressure vessel, and what gas do you charge it with, if you don't mind me asking? Looks wonderfully well made, and probably terrifies small children and animals!

author: tautech
author_rank: Super Contributor
timestamp: October 07, 2015, 10:44:47 pm
content: Chris, while I've not seen a failure to fire I have seen output voltage disparancies between cylinders resulting in ignition misses when the engine is highly stressed. This was in a methanol fueled drag car and confirmation of failing ignition was seen on EGT's from the logging. We also could tie the ignition failure to periods of high boost. Scope'ing the feed to coils confirmed 100V output disparities that were fixed with replacement of the ignitor.Engine heat was never an issue as the ignitor was in the cockpit, but remember there is quite a lot generated in the ignitor itself.In this case I suspect it was primarily due to degradation of the caps used to supply the energy to the coils and re-capping may have bought the unit back to spec.However replacement also meant a substantial upgrade in energy available as well as improved reliability for the ongoing development of that particular engines performance. (20B rotary) (7 sec 1/4 mile)

author: langwadt
author_rank: Super Contributor
timestamp: October 07, 2015, 11:41:44 pm
content: Quote from: Chris Wilson on October 07, 2015, 10:09:05 pmthe semiconductor is probably an IGBTI can think of one failure mode; if the pressure is so high that you don't get a spark the energy in the coil will be clamped and dissipated by the transistor instead, if that happens too often it'll eventually overheat

author: tautech
author_rank: Super Contributor
timestamp: October 07, 2015, 11:43:19 pm
content: Chris, if coils are OK then one must suspect the supply or rather lack of supply to them. Even an old Champion spark plug tester demonstrates how compression pressures will prevent plugs from firing.Spark energy is the only fix and if the voltages are low to the coils then there will be problems like you describe.As the car is not normally connected to mains one can safely scope the input to the coils providing care is taken.It is unlikely there will be more than 500V and using 10:1 probes as it is low frequency should be OK.Get 100:1 probes if you are worried.Waveform peak voltage measurements at idle should give you the answers you are looking for.You're looking for 1 or more cylinders being lower than the others.

author: tautech
author_rank: Super Contributor
timestamp: October 07, 2015, 11:53:15 pm
content: Quote from: joeqsmith on October 07, 2015, 11:38:26 pmSorry for the confusion on plugs.Yep, it's a horny bit of kit. We dyno'd it @ 1060 HP and shoved it in a container to Brisbane the next day.Standing alongside that thing doing 1000+ HP dyno runs is something I can tell you.After 3 weeks of midnights or later and 7 days a week we were glad to see it go.Further tweaks are all based on logging and can be done at the track with laptops.

author: wagon
author_rank: Frequent Contributor
timestamp: October 07, 2015, 11:54:15 pm
content: I used to work for a company that repaired automotive electronics. I have rebuilt a few of those Nissan ignition modules over the years. We had a small pcb with SMD VB921's on them, seemed to work OK.

author: tautech
author_rank: Super Contributor
timestamp: October 07, 2015, 11:59:52 pm
content: Quote from: joeqsmith on October 07, 2015, 11:03:39 pmWigglessmith.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 12, 2015, 11:59:07 pm
content: Quote from: tautech on October 07, 2015, 11:59:52 pmYea, my wife was getting a little concerned back then. Comes a point that the chassis can't handle the power.I showed my buddy with the RX7 your video. He wants to know the displacement.

author: tautech
author_rank: Super Contributor
timestamp: October 13, 2015, 12:26:11 am
content: Quote from: joeqsmith on October 12, 2015, 11:59:07 pmA 20B block is just one more housing and center plate than a 13B. 3 rotors instead of 2. And a longer eccentric shaft too of course.We could start all sorts ofdebating the displacement of rotary's but the official displacement is 2 litre.http://www.mazdarotary.net/technical.htmMy buddy's done 8.47 with a 13B powered car and held a NZ record for a while, we've played with different fuels, turbos, even superchargers, electrical systems,ignitions, multi-plate slider clutches, drag gearboxes, rear suspension setups, logging, you name it, and they all add fractions of seconds to where he is today.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 13, 2015, 01:51:23 am
content: Thanks. He wondered if it had a third rotor or was an all custom made engine. They ever let you take it for a pass?

author: tautech
author_rank: Super Contributor
timestamp: October 13, 2015, 03:47:20 am
content: Quote from: joeqsmith on October 13, 2015, 01:51:23 amGuys over here and elsewhere have built 4 rotor units using entirely custom eccentric shafts, those I have seen are all NA and man do they sound nice, V12 like.These 20B units for drag duty are all custom units, full of many jealously guarded secret squirrel tricks and parts and a complete engine is getting on for $30K or more.I'm happy to help with a build and, but as for driving it, no thanks, I'd only end up having to do my own laundry.

author: electrolust
author_rank: Unknown
timestamp: October 14, 2015, 06:22:27 am
content: I would love to see plans for that test rig, if they exist!

author: joeqsmith
author_rank: Super Contributor
timestamp: October 16, 2015, 02:56:43 am
content: One of my data acquisition systems.

author: mikerj
author_rank: Super Contributor
timestamp: October 17, 2015, 09:17:29 am
content: Quote from: Chris Wilson on October 07, 2015, 10:09:05 pmThis is very often a sign that the ignition coil itself is breaking down. Under high cylinder pressures, the voltage required to ionise the spark gap increases quite a lot, so if the coils internal insulation is starting to degrade this is exactly when it will break down.OTOH, if the igniter is not supplying sufficient energy to the coil, a similar problem could occur. There's a few ways this could occur:1) Insufficient coil voltage (e.g. the high current switch isn't being saturated and is dropping a lot of voltage, or the wiring to the ignitor is high resistance)2) The dwell period is too short to reach the required primary current. Are they "smart" ignitors that automatically control the dwell period, or does the ECU control this?3) The coil primary voltage is being clamped at too low a value (e.g. due to breakdown of the switching device, or the high voltage clamp/snubbber in the ignitor).If you have access to the coil primary connections and a suitable scope you should be able to confirm or rule these out. The coil primary could rise up to 300v or more, so ensure scope and probes are ok for high voltages.

author: tautech
author_rank: Super Contributor
timestamp: October 17, 2015, 10:20:13 am
content: Quote from: joeqsmith on October 16, 2015, 02:56:43 amNo good showing a Tappley off Joe, most wouldn't have ever seen or know what one is.

author: Chris Wilson
author_rank: Super Contributor
timestamp: October 17, 2015, 10:32:50 am
content: As far as I know, and certainly up to about 8 years ago, a UK MOT test ( road worthiness test) on a four wheel drive vehicle, with a plate type centre differential was brake tested on the road, with a Tapley meter sat on the seat or floor. A normal two wheel brake tester roller set up is not compatible with some types of four wheel drive centre diffs, same reason why the owners handbooks warn against a suspended tow.I have sat through dozens of MOT tests pre brake testing rollers where a Tapley meter was used, and the tester was far more likely to have a feel for the general braking performance from an on the road test than reading the meters on a roller brake tester.Am I showing my age....?Thanks for all the info on ignition module testing, I am hoping to build a none mechanical test jig, but I suspect many problems blamed on the module are bad grounds or bad 12V supplies unable to switch the currents involved. Just like 80% of ECU's sent in exchange to a UK repairer test good, it's possible that the physical cleaning contacts get by pulling off the multi pin plug and fitting to a new ECU or igniter fixes theings and the old one was actually OK.

author: tautech
author_rank: Super Contributor
timestamp: October 17, 2015, 10:51:06 am
content: Quote from: Chris Wilson on October 17, 2015, 10:32:50 amYes Chris we still use Tapley's here in rural areas and your 4x4 reasoning applies here too.As for the ignition modules, you need to scope the outputs, connections are not always the problem.

author: joeqsmith
author_rank: Super Contributor
timestamp: October 19, 2015, 12:46:22 am
content: Quote from: Chris Wilson on October 17, 2015, 10:32:50 amThere was another person on here updating an old Sun system with modern electronics. I'm not sure how far they got with it. For my simulator, I am just using a clock that drives a DDS that feeds a counter that increments through some memory that holds the waveforms.

author: xwarp
author_rank: Frequent Contributor
timestamp: October 23, 2015, 08:35:12 am
content: Quote from: Chris Wilson on October 07, 2015, 10:09:05 pmJust kind of throwing this out there, based on the quoted section above, but maybe monitor the current going into the igniter while using software/hardware that you can monitor the spark firing line up to and including the conditions where failure occurs?

author: HighVoltage
author_rank: Super Contributor
timestamp: October 23, 2015, 09:31:30 am
content: Quote from: xwarp on October 23, 2015, 08:35:12 amThis is very true.If you want to measure the igniter performance correctly, you need to look at the input and output of the igniterMeasure the input current in mA (usually around 10 to 50 mA) and the input voltageOn the output, hook up a primary winding of the coil only, so you would not produce the high voltage, only the the 600 V or so of the primary flyback.Monitor the output current with a current probe and the output voltage with a good 1000V scope probeLook at the falling edge of the current and at the rising edge of the output voltageAlso, look at the voltage drop across the power transistor (Vce)And look at the voltage clamping (sometimes under 400 V)Use your scope and multiply current output and voltage and compare to other modules (Good signature behavior)All of this will tell you what system you are dealing with.Oh, and the original Nissan system was developed in Oceanside CA, where Nissan had an electronics research and development center and only really good stuff came out of it. I still have one of these original Nissan igniters of those days. But even those systems failed on the Skyline under high load. But then, the Skyline had not a "normal" engine.