Modern Vespa

I have gathered from the many effendi on this forum that the GTS ECU runs on closed loop programming up to about 6000 rpm, and at higher revs it ignores the Lambda probe and just adjusts the mixture according to engine revs, temperature and such, i.e. no feedback.

This means that a Malossi lambda emulator is only effective up to 6000 rpm, and a larger injector could enrichen the mixture above that rpm.

But I have seen ads and specifications for more recent models that say "fully closed loop". Is this correct? If so, would the ECU compensate for a larger injector, and make this mod pointless? And would a lambda emulator then have benefits beyond 6000 rpm?

Yes, I know. Someone is going to tell me it is all more complicated than that. But I would like to know what is happening here, and I would also like to know what the Malossi lambda emulator is doing with that lead that goes to he injector.

Mike

Above 6K, it doesn't matter what the Malossi lambda emulator is doing, or even whether or not there is an O2 sensor.

One of the places where you run into issues with European bikes is the dead spot in the 4K rpm range, because that's where they test them for noise. That's one of the things the Lambda Emulator addresses.

Most of the top engine tuners in the world aren't tuning Vespa scooters, but if you went to one and told him or her about your engine and what you are trying to do, that person would more than likely recommend that you install a Power Commander type programmer, like the Malossi Forcemaster or the one Polini makes, and then set it up using real time information as to how your bike is performing at different RPM ranges. The problem is not that your injector can't pump enough fuel at high rpms, it's that it isn't. If a bigger injector really makes a difference, the odds are that Polini and Malossi will include one in their kits.
Another thing to consider if you dont' want to use a Force Master is changing the fuel pressure. Changing fuel pressure regulators is common among tuners.
But none of this is useful if you don't have a better way to measure results than a quick ride up and down the freeway.

Yes, that is what I have always understood. But I have recently seen GTS specs mention "fully closed loop". Unfortunately I cannot recall where.

I have a Power Commander and a Force Master lying in my shed. I did not feel any difference with them. By adjusting the Force Master I could make the performance worse, but could not make it better. I tried the Force Master on my 250, and then a new one on my 300, same negative results. I do get a definite improvement in take-off and acceleration with the Malossi lambda emulator.

My testing is not just seat-of-pants. I have a stretch of road where I check the speed reached at a certain point from a standing start, and a long hill where I test the top speed maintained.

The reason that Malossi and Polini don't include an injector in their kits is very simply. They can achieve the same result by just increasing the injector pulse duration. Swapping injectors is much easier than increasing fuel pressure, and the result is the same - more fuel (better atomised?) at the correct moment into the engine.

Mike

Unfortunately no info to the matter, but just a thought: if the latest Vespas have a different type of lambda sensor, then it's likely there are other changes too....I have no idea how the situation is, just a thought that changing the way ECU behaves could be caused by having a better measurement signal from the sensor = more accurate way to control fueling vs. burning.

Mike, I'm not sure about this but....closed loop is closed loop and like on other bikes I've tuned, should remain effective to near maximum power revs. I've not however as yet tuned a GTS300 in the way you are doing but on many other bikes that I've tuned the lambda has remained in the loop to near full power. To meet noise regs the ecu is programmed to hold mixture and ignition to s particular part of the map often giving the impression that the loop is suspended or open. That is not the case and under the euro 3/4 regs is not permitted. In fact the engine at nearly all revs and throttle settings uses a range of information to control mixture, lambda, engine temp, throttle setting, revs etc. But you know that stuff. Just remember, 6,000rpm is not very fast and most engines need to have the control of the lambda well beyond that in order to meet emmision regulations. So my money is on the lambda still being in the loop above 6k.

Once up to operating temperature, all narrow-band lambda sensors function roughly the same (0V = lean, 1V = Rich, 0.5V = ~14.7 A/F ratio). To the best of my knowledge, the new Vespas do not have a wideband sensor. Even if they did, this would only affect closed loop.

I'm not sure that there is a hard switch-over at 6000 RPM... I would expect open/closed loop to be based on load. I have also seen "6000 RPM" mentioned on forums, but have never had any actual evidence that this is actually true... Do you have any links? Everything I am finding about the GTS doesn't specifically say "closed loop all the time" or anything similar... just that closed loop is a function. If the newer bikes are full closed loop, the injector would be adjusted out by the short & long term fuel trim adjustments. However if the bike has modifications that make the airflow beyond what the fuel trim can adjust to, the larger fuel injector could help get the fuel trims back in to the correct "window" (which is typically +/- 25%). A lambda emulator that only plugs into the lamba sensor can only make the A/F ratio richer in ALL closed loop conditions.

I'm not 100% sure how the Malossi Forcemaster 2 works, but it is essentially overriding the fuel injector signal with it's own "optimized" a/f ratio. At the end of the day this is more of a bandaid, but bandaids do work sometimes...

Thanks for the info - my comment stemmed from the car side (wideband sensors nowadays), but I've not followed the lambda sensor technology used in motorcycles.

That's what the guy who's name is on the company that makes the emulator told me. He knows a lot about this stuff. It does what a Dynojet Power Commander does. There's quite a bit of information online about how they work, more like a cattle prod than a bandaid.

Its easy to become obsessive about tweaking the amount of fuel injected but lets not forget that these tweaks can really only affect driveability and they have very little effect on maximum power output unless significant engine tuning is done in other areas. The engine can produce only the amount of power dictated by how much air ( oxygen ) it sucks into the cylinder. I have used power commanders on several different bikes and they can make big improvements to mid-range driveability in terms of throttle response and smoother running, but on a twist and go scooter this is of less significance because the engine will settle at fixed rpm during acceleration and it doesn't really matter if there is a flat spot in some areas that the transmission doesn't dwell in. Although closed loop systems may deliberately weaken mixture to hit some arbitrary emissions test target at some point there is no purpose in making mixture weak in general as this would actually increase emission and worsen fuel consumption.
The above may be less true for machines that use fly-by-wire throttle control and on the one machine I have owned with this feature I did think it was detrimental in some respects because the engine occasionally failed to answer the twistgrip in a predictable way. I am quite glad that my current maxi-scooter has proper cables connected to the throttle butterflies and an engine that responds very sweetly.

We use lambda sensors to enhance power output usually at all revs by determining a more exacting fuel air ratio. By doing this the engine emissions are kept to a minimum and power is maximised. The lambda can actually run the engine at certain revs with a less than ideal A/F ratio. Usually this means running the engine with a weak mixture, just under the ideal A/F ratio. On modern engines with modern materials this does no harm at low revs. For example, when an engine is running a lower revs in town, you don't want a rich mixture poisoning everyone around you.

Under euro 4 it's imperative to maintain mixture burn control at all revs to remain in compliance. Only at full revs does the lambda lose it's full effectiveness, but does remain a major part of the arsenal of tools to keep emissions down at full throttle on most engines.

And in the US any aftermarket street legal ECU Controller can only increase fuel output at full throttle.

Thanks for all the informative discussion. I have searched all over, but cannot find where I read "fully closed loop". I am sure I didn't imagine it. Anyway, if I ever find it again I will re-open this topic.

My GTS is kitted with Malossi V4 cylinder and head, air filter mod and Akra exhaust, so there is plenty of scope for more fuel, and the lambda emulator makes a noticeable difference to take-off and acceleration.
Mike

Does a bigger cylinder, larger valves and higher compression meet that criteria?
The other change from a Force Master or Power Commander is that the rev limiter increases. But unless you are hitting the rev limiter with your present setup, and you should be with the Malossi top end and a stock ECU, you won't notice a difference here either.

A rhetorical question? I expect that you are well aware that changes like that should improve throughput of air and in rpm ranges that the original fuel mapping was not designed for, whether closed or open loop. So some form of DIY mapping becomes essential, and of course if you go far enough the injectors may not even have enough flow to cope. Personally I would be wary of overriding the rev limiter unless you also use exotic pistons and con-rods etc., but nothing ventured nothing gained!

The GTS engines are very strong in the crank, conrod dept. Plenty of built in redundancy. A Malossi head and piston is very much better quality too compared to the good Piaggio unit the bikes come with. Some use of an increased rev limit provided by the Malossi Forcemaster is fine. Again the engines are very strong. Important not to go silly though.