Curious: How does twin spark fix surge?

I am lucky enough to have never experienced the dreaded surging. Still, I am curious as to what about the twin-spark corrects the issue.

As I understand, surging was a function of oscillation between closed-loop/open loop fuel feedback modes. What I do not get is why adding another spark addresses the root cause. Also, why not go with a multi-spark discharge (MSD) as opposed to two plugs? Is there something about the physical location of the spark that affects the surge?

i'm not sure that it does - i've read reports of twin-spark 1150RT's surging ( and in fact mine had a very mild case between 3-4k rpm)

I'm not sure either but, tuners have been dual plugging BMW's since the R100's.

I suspect it offers a different combustion pattern. Even plugs with different electrodes may have an effect.

There seems to be many things to try, dual plugging being one of them.

$.02

Paul

A wrench told me that the small plug fired milliseconds after the primary to provide for more complete combustion. Theory was that incomplete primary combustion created a slower vapor burnoff within the cylinders. The resultant effect was an afterburn thad disrupted smooth operation.

But what do I know, I build houses for a living.

Kevbo's take:

Facts:

The moronic relies on the O2 sensor to control the mixture. The O2 sensor, as you might guess senses only oxygen. It does not directly measure the mixture. If incomplete combustion occurs, then there will be unburned fuel AND oxygen in the exhaust.

Speculation:

The O2 sensor detects this oxygen and infers that the mixture is much too lean, and makes a large mixture adjustment. Now the mixture is very rich, and there is zero O2 in the exhaust, so the moronic starts leaning the mixture again. This repeating cycle constitutes the surging.

Dual plugs help assure complete combustion on every firing. With complete combustion, the exhaust O2 content more accuratly reflects the operating mixture, and the moronic is not chasing it's tail due to currupted data.

Thanks for the insights...

I did not realize that some twin sparks surged. Eeek, I thought I was immune! Still seems a MSD type system would result in a more complete burn. I sorta recall that the two plugs may be different types; if so hard to replicate with a single plug driven by MSD.

Cheers

Uh, wasn't the whole idea of the 2-spark to fix the surging and pinging with 1-spark engines? :huh

Vhat surging?

Der ees no surging!!!

I was under the impression that the twin-spark design was intended to reduce emissions. Today's twin-spark boxers comply with 2010 EU emission standards.

Whether it cures surging or not, I don't know. I would imagine that dual O2 sensors on the R12's probably do more than two sparkplugs per cylinder.

As a general rule if your engine isn't in a 'proper' state of tune it can/will surge. Twin spark or no...

JJ

When the piston is at full compression, the combustion volume is shaped like a flat dome. A *very* flat dome -- about three inches in diameter and 1/4" tall. Combustion is not instantaneous -- it takes a little while for the flame front to get to the outer edges. By igniting it at two different physical points, combustion is more complete. The more complete the combustion, the lower the noxious emissions byproducts, and the easier it is for the moronic to control the engine.

I just (about 200 miles ago) had the heads on my 02 R1150GS dual-plugged. When I pulled the heads, I had to scrape about 1/16" of carbon off the pistons and heads, so I can't say that the dual-plugging is the only improvement, but the bike runs like a different machine now. The surging is just barely perceptible (as opposed to the herky-jerky it used to do). I will be posting pictures and a full writeup when I get the chance.

I have an '04 GS dual spark with 3000 miles on her and she surges....kind of a pain, but if someone has any ideas of what can be done I'm all ears!!

Lookin' forward to that write-up.

Same for me. When I did my 02 GS (9k miles) there was a substantial amount of carbon on the pistons and heads. (reminded me of an old Chevy that was burning oil when we pulled the head. Lots of carbon! Lots of scraping)

Thats why I suggested to some of guys with pinging problems, to pull the heads and see if the carbon build-up is contributing to their problem.

Paul

Purty strange stuff, here. Some dual-plugs surge, and some single-plugs (like mine) have no surge at all. Some ping, some don't. In fact my 02 doesn't have any of the bad habits regularly decried here, except that I have inexplicably (i.e., without hitting anything) broken two rear spokes. Aren't these things supposed to be mass-produced with some level of standardization and uniformity? I thought Krauts liked regimentation. Maybe Fritz and Franz at the factory should get together over a schnapps and share notes.
I can't think of any other brand/model of motorcycle I have owned that has offered the wide variety of owner experiences described here.

Aw c'mon, fellers! Remember how it all starts in there.

For ignition to take place, there has to be combustible mixture between the electrodes of the plug when she sparks. The leaner the mixture, or the less turbulence, or the bigger the fuel droplets, the lower the chances that the spark will have something it can light up.

Double the plugs, double your chance.

Put another way, with two plugs, you can run leaner, or have a lousier intake tract, or less efficient combustion chamber shape and still make it go bang. If you're surging because the Moronic leans to the lean, two plugs will provide steadier running by lighting the mix more consistently than one.

And I guess two plugs offer some added redundancy over a MSD system. I assume that w/one plug fouled the beast will still run on the remaining plug.

Yes, the service department says that they will run fine on the second plug. Soooo, carrying a spare set of primary plugs may sound redundant, but.... How will I know when I have a single sparkplug failure??


My '04 Adv has 12,500 and doesn't surge, but it will ping when it's hot out with a hard roll on the throttle. Better gas and/or additives DEFINATELY help!

<BR>

Nicely said Stephen. It would have taken me two pages to say that.

***********

Why did the Motronic run the mixture so lean?

The design purpose of the O2 sensor is to control the oxidation (another word for combustion) in the catalyst. So really, the fuel mixture in the engine is not controlled for HC emissions say. Instead the engine's Oxygen output is controlled, for proper catalyst operation. The catalyst needs oxygen to operate, that is why there is an oxygen sensor.

The Motronic ECU creates fuel mixture swings from a just about perfect (hardly any oxygen in the exhaust), to very lean (a lot of oxygen in the exhaust). This 'swing' goes back and forth every other second or so. Lots of oxygen, little oxygen. Lots of oxygen, little oxygen.

In this way the catalyst 'breathes'. When the exhaust gas is oxygen rich, the catalyst 'inhales' a breath of oxygen and stores it chemically on the surface of the precious metals (think hemoglobin).

Then the exhaust gas is made oxygen lean. The oxygen stored on the surface of the precious metals is 'exhaled' and oxidizes (combusts) the remaining HCs and COs into CO2 and H2O.

The engine ECU is really controlling the richness and leanness of the oxygen in the exhaust.

The swings between these two conditions is usually mild enough to be imperceptible. If, for various electronic reasons within the ECU, the mixture swings too lean, then the surge cycle is punctuated by a lean misfire. This is what the rider feels as 'surge'.

The cha-cha goes like this:

• A few lean misfires cause a momentary sharp drop in horsepower.
• The horsepower 'hiccup' releases the torque on the drivetrain.
• The drop in torque 'unwinds' the rubber 'cush drive' coupling in the driveshaft.
• The next few good power pulses wind everything back up.
• The rider is in the middle of the 'bouncing ball' of kinetic events.

Myth: If the engine is run very rich the catalyst will overheat and melt. Fact: With no oxygen remaining in the exhaust gas from a rich fuel/air mixture, the catalyst is completely inert.

- Jim<BR><BR>

Since twin sparks obtain higher combustion of gasoline, one would hope that BMW would tune the Motronic differently to reduce surging. e.g. BMW would have more room for error in adjusting O2 levels yet still obtain high combustion efficiencies, thus reducing surging.

That's what I'd do, if I worked at BMW. OTOH, if BMW absolutely HAS to reduce emissions, then there's been no changes to the Motronic and we're pretty much back at square 1 with merely incremental improvements in surging.