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Miss Fire On Dyno Rb26 Any Ideas?

portaz

By portaz,
in Engines & Forced Induction

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GTScotT Grand Master

GTScotT

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What brand injectors are they?

I highly doubt the waste spark will have anything to do with it. At what cycle are the injectors pulsing? 360 or 720? Make sure its on 720 IMO.

I'm still mostly concerned about the injector seals, more than anything else.

portaz Mentor

portaz

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The adaptronic select plug in ecu and many others at the lower price point use wasted spark which in my understanding is 3 outputs, as in cyl 1 and 6 fire at same time but cyl 6 is on exh stroke so spark does nothing hense the wasted, sequential direct spark that stock ecu and more high end such as adaptronic 1280 and haltech platinum pro 2000 use have 6 outputs so only fire one cylinder at a time. I'm happy to be corrected but that's my understanding. However it's more than likely my 20 year old wiring harness that can't take the load of wasted spark as it should be able to but Andy and jez want to get to the bottom of it for future reference and to put both their minds at rest in case it happens again. But it seems the more expensive ecu's would not experience this issue. And jez and Andy have been really great.

Scott

SargeRX8 Grand Master

SargeRX8

Posted
Posted (edited)

The adaptronic select plug in ecu and many others at the lower price point use wasted spark which in my understanding is 3 outputs, as in cyl 1 and 6 fire at same time but cyl 6 is on exh stroke so spark does nothing hense the wasted, sequential direct spark that stock ecu and more high end such as adaptronic 1280 and haltech platinum pro 2000 use have 6 outputs so only fire one cylinder at a time. I'm happy to be corrected but that's my understanding. However it's more than likely my 20 year old wiring harness that can't take the load of wasted spark as it should be able to but Andy and jez want to get to the bottom of it for future reference and to put both their minds at rest in case it happens again. But it seems the more expensive ecu's would not experience this issue. And jez and Andy have been really great.

Scott

The way you've explained wasted spark is exactly right. It fires two coils with one signal/driver. The cylinders are at exact opposite position to each other. Its interesting that your spark wasn't happy. It shouldn't be the case. Technically, on paper, this system should work, the only difference is the "wasted" spark is called wasted simply because it is just that, a waste. Its an extra fire of the coil which is absolutely not necessary. So after a drive, if you've done 100000 sparks on each individual cylinder in a sequential setup, an equiv wasted spark would have done 100000 sparks with an extra 100000 wasted sparks. What would be really interesting is the cause of your problem. If you've tried another select ECU and the problem is still evident, I'd wanna figure it out just for the sake of it. Maybe, as you said, the wiring is too old and can't deliver a strong enough spark through the old wiring. Maybe the wires are corroded, maybe damaged, who knows. But a split signal or interference from an outside source could be enough to cause the signal to fire the spark plugs to be lost and a misfire occurs. All the ECU does is send a signal to two coils instead of one.

Is that signal reaching its destination? Is there enough voltage in the car to be firing two coils at the same time? There seems to be a loss in power(electric). If the signal is being received(can potentially be verified with a timing light on each coil) then something tells me the car is failing to produce enough volts; provide high enough current; transfer enough current/volts to fire off the spark. If the ECU is not at fault, the signal will be sent to fire will be sent.

I think my understanding is correct and this would be something I'd be interested in testing out and I think Jez is more than capable of cracking this one. Keep up posted and glad to hear the problem is gone.

Edit: The fact that it occurs under load leads me to believe that both sparks are receiving the correct signal but the spark it self is simply not strong enough to stay on. If you guys are bothered to tinker around, maybe hook up a second battery to up the current. Maybe, is possible, give direct power to the coils and see if it can deliver a strong spark. A timing light hooked up to the coil, load up the boost and see if the timing light is picking up the signal.

Edited by SargeRX8
portaz Mentor

portaz

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We did try another select ecu same same, timing light in each coil all good, oscilloscope to check voltage drop we think was ok no obvious loss but its really something we could only check by loading up 2 coils and measuring that way or by pass and run new wires. I wonder if it could have anything to do with porting and efficiency of combustion chambers etc. Andy & jez seem very determined to get to the bottom of it but to be honest I don't like the idea of wasted spark of which I had no idea about before and I much prefer the sequential direct fire so all good and now I can sleep without my head racing all night

And really thank you so much jez I know your time is previous as is Andy's I really appreciate your efforts pity all tuners arnt so determined

kitto Mentor

kitto

Posted
Posted

It probably isn't a wiring issue. Somewhere i read that you have a newish coil pack loom?

As you have an igniter, the wiring from the igniter to the coils is doing the work. The signal from the ECU to the igniter is just that, a signal to tell the power transistor's in the igniter to switch the high current earth for the ignition coils. There is no load on the signal wiring.

What i dare say the issue was, was the coils simply couldn't work under boost because the duty cycled asked from the coils was doubled because of the wasted spark. Even though the ignition on the exhaust stroke isn't really putting any load on the coil, it may have been enough to cause the coil packs to break down when asked to keep firing under boost. Having a high dwell combined with the doubled duty cycle may have played a part.

You have splitfires though yeah? I would have thought they would hold up ok.

DVS JEZ Grand Master

DVS JEZ

Posted
Posted

Bet it feels good to have the car back Scott :)

Even on a gate pressre and cruise tune.

We did alot of diagnosing and testing, with the direct fire ecu there is only a small intermittant pop during wot power runs.

The dwell was 3ms with the wasted spark spark setup, we tried playing with dwell with no little to no change, and as advised by splitfire we didnt want to raise above 3ms (already above their max 2.8ms)

One thing we did find tho was running the engine richer resulted in a smooth run with no missfire, (with the direct fire ecu 1280s) especially on cyl 3 which told us there was a ve imbalance as sch. A smoke test did not show up any leaks (maybe not enough pressure due to open valves etc) but spraying brake cleaner aroud cyl 3 injector and gaskets resulted in the afrs dropping from 14.2 to 12.9 at idle. I changed the injector orings, nipped up all the plenum bolts, resealed the old djetro fittings etc. which helped but still shows an afr drop with brake clean of 13.2 from 14.2. So there is still a definate leak that needs to be fixed before we can finish the full tune

Pezhead Grand Master

Pezhead

Posted
Posted

I've been chasing issues on my Autronic SMC wasted spark set up since the day I bought the car. I've added a 500R about two years ago and that didn't sort it. Mine was generally fine until the engine got hot then spark would break down.

I've finally solved (I hope) my issue by going to individual coils. My setup had bosch duel fire coils for the wasted spark set up. There were only three coils that each had two spark leads. I didn't like that at all. So I went to 6 individual Bosch HEI coils. Seems to have sorted my issue, but have to wait to finish the tune until I have a job and save some coin to do it.

I find spark related issues so tricky. People with the same set-ups get different results. Always the way with electrical components unfortunately. One weak link and the whole system suffers.

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