MultiAir and Throttle Plate

[HalfPint]

I know the MultiAir engine does not use the throttle plate most of the time, but it does have have one. I assume it is used at idle, but when else? Is it closed on overrun/compression braking?

It is just open or closed, or does is the position controlled between those points?

[smark]

https://en.wikipedia.org/wiki/Throttle

[HalfPint]

Are you serious? Did you even read my post?

For reference, I've been playing with carburetors and fuel systems for nearly 45 years, and I'm passing familiar with what a throttle is.

[smark]

Are you serious? Did you even read my post?

For reference, I've been playing with carburetors and fuel systems for nearly 45 years, and I'm passing familiar with what a throttle is.

That wasn’t meant to insult you. I read you post, you should know the answer, if if you been playing with carburetors, and fuel injection.

[map]

I have never seen a mention of the throttle body positioning... just how the intake valves are controlled. I'd imagine, if you have a Scangauge (or one of the multiple diagnosis tools) you could track the TBPS numbers.

[BigDaddySRT]

I have never seen a mention of the throttle body positioning... just how the intake valves are controlled. I'd imagine, if you have a Scangauge (or one of the multiple diagnosis tools) you could track the TBPS numbers.

The Throttle Plate Position is controlled by the Throttle Pedal Position Sensor. (Throttle Pedal)
Closed 0% - 80% WOT Open Max.

It is viewable within the Can Bus.

[Fiat500USA]

I was told by the engineer in charge of adapting the MultiAir Turbo to the NA 500 that it is mainly used to boost intake manifold vacuum during certain operating conditions. Exactly when, I don't know. Driving around with one of those scanners would be interesting to see when. I could imagine that adjusting the throttle angle and valve opening you could change the velocity of the air going into the engine, so that would be interesting to see how they tuned that.

The engine can also do "internal EGR" which eliminates an external EGR valve. That is one of the enhancements of "MultiAir II" but our engines may also do that to some measure. I believe I read that in some of the engineering literature I have but don't have access to it right now. This is accomplished through the intake valve* and valve opening overlap. All pretty interesting.

"The updated MultiAir 2 system is an enhanced version of the original that brings about further improvements in terms of efficiency and driving pleasure. Specifically, because MultiAir 2 can decouple and open the intake valves independently from the intake cam lobe, the intake valve opening has been optimized to precisely modulate the amount of exhaust gas recirculated in the combustion chamber via valve overlap, giving the engine internal EGR. "

http://www.fiat500usa.com/2014/03/ne...neva-show.html

[HalfPint]

I was told by the engineer in charge of adapting the MultiAir Turbo to the NA 500 that it is mainly used to boost intake manifold vacuum during certain operating conditions. Exactly when, I don't know. Driving around with one of those scanners would be interesting to see when. I could imagine that adjusting the throttle angle and valve opening you could change the velocity of the air going into the engine, so that would be interesting to see how they tuned that.

The engine can also do "internal EGR" which eliminates an external EGR valve. That is one of the enhancements of "MultiAir II" but our engines may also do that to some measure. I believe I read that in some of the engineering literature I have but don't have access to it right now. This is accomplished through the intake valve* and valve opening overlap. All pretty interesting.

"The updated MultiAir 2 system is an enhanced version of the original that brings about further improvements in terms of efficiency and driving pleasure. Specifically, because MultiAir 2 can decouple and open the intake valves independently from the intake cam lobe, the intake valve opening has been optimized to precisely modulate the amount of exhaust gas recirculated in the combustion chamber via valve overlap, giving the engine internal EGR. "

http://www.fiat500usa.com/2014/03/ne...neva-show.html

Interesting. Without a throttle plate there would be no intake manifold vacuum at all, as the intake would be at atmospheric pressure - but I'm not sure how well it would idle, as they'd have to cut back the lift & duration very far. That might be beyond the dynamic range of the MultiAir system, hence the need for at throttle.

What got me thinking about this was the oil consumption issue on the 2.4 Tigershark, which is supposedly caused by "vacuum being created in the cylinders during deceleration".

Of course that's not a turbo engine, so it would not be under positive cylinder pressure as much. Anyway, without the throttle closed the valve guides and stem seals are never under vacuum, so would never be a way to pull oil in. The vacuum would always be inside the cylinders, and would probably be strongly pulsating. Those pulsations might pull oil past the rings more easily.

[map]

The way I'm seeing it, there would be more vacuum in the cylinder with the intake valve is clamped shut. The exhaust valve opens and most of the air is expelled. Then you have 2 downward strokes where crankcase pressure would exceed pressure in the cylinders for much of the stroke. Then the exhaust opens and expels air/fumes/oil out the exhaust, that leaked past the rings and valve guides.

[HalfPint]

The way I'm seeing it, there would be more vacuum in the cylinder with the intake valve is clamped shut. The exhaust valve opens and most of the air is expelled. Then you have 2 downward strokes where crankcase pressure would exceed pressure in the cylinders for much of the stroke. Then the exhaust opens and expels air/fumes/oil out the exhaust, that leaked past the rings and valve guides.

All the intake vacuum in every engine comes from the pumping of the cylinder, that is the source. With the throttle plate closed upstream of the intake valves, a low pressure is created in the intake manifold, everywhere downstream of the throttle plate.

So thinking about it further, they must close the throttle plate on overrun or there would be no compression braking, just like on a diesel which has no throttle.

Taking that further, if you were to try to reduce oil consumption with a firmware change as they have done, the only strategy would be to change the cam timing to reduce pumping efficiency on overrun, thus reducing the intake vacuum in general. Since they only have control over the intake valves, you'd just try to keep the intake valve open longer, along with the throttle plate, while having the fuel shut off. That way there would be no vacuum in the intake, and little in the cylinder. There would also be little compression braking, but drivers with automatics are used to that.

It still doesn't tell if the oil is coming past the rings or valve guides.

[Fiat500USA]

I wouldn't be surprised if maybe 80% of folks having oil problems is due to people not checking their oil during break-in, damaging the engines, which leads to more consumption.

We've bought 3 Fiats and one Alfa within 8 years and all these cars barely used oil. My Abarth has 60K on it now and I don't think I've added a total of 2 quarts in all those miles. Our 2.4 in the 500X we had I think it was 1/2 a quart in 30K. We have 20K on the Alfa and have added less than 1/2 a quart using 9K oil changes.

[smark]

I wouldn't be surprised if maybe 80% of folks having oil problems is due to people not checking their oil during break-in, damaging the engines, which leads to more consumption.

We've bought 3 Fiats and one Alfa within 8 years and all these cars barely used oil. My Abarth has 60K on it now and I don't think I've added a total of 2 quarts in all those miles. Our 2.4 in the 500X we had I think it was 1/2 a quart in 30K. We have 20K on the Alfa and have added less than 1/2 a quart using 9K oil changes.

My 10 year old 500 has never used oil. Same with the 500L we owned. It was hard on transmission. 90% people who drive any brand car. Very seldom check their oil level, between oil changes. I’ve always been conscious in doing so. Every fill up. After working several car dealerships over the years.

Our turbo Accord touring, the Soul ,and Fit never seem to use oil either. My daughters Jeep renegade does use oil. Not in excess.

[map]

All the intake vacuum in every engine comes from the pumping of the cylinder, that is the source. With the throttle plate closed upstream of the intake valves, a low pressure is created in the intake manifold, everywhere downstream of the throttle plate.

So thinking about it further, they must close the throttle plate on overrun or there would be no compression braking, just like on a diesel which has no throttle.

Taking that further, if you were to try to reduce oil consumption with a firmware change as they have done, the only strategy would be to change the cam timing to reduce pumping efficiency on overrun, thus reducing the intake vacuum in general. Since they only have control over the intake valves, you'd just try to keep the intake valve open longer, along with the throttle plate, while having the fuel shut off. That way there would be no vacuum in the intake, and little in the cylinder. There would also be little compression braking, but drivers with automatics are used to that.

It still doesn't tell if the oil is coming past the rings or valve guides.

If the intake valve is left closed during deceleration (as the vids imply) then TB position isn't important. Part of the reason for the design is to maintain pressure in the intake manifold. (Have to hook up a meter to check the ECM, realizing the TB would lag a bit.) If they actually shut down the FI and intake valves, I'm wondering why the mod'd Abarths would crackle on deceleration. There should be very little fuel/air in the exhaust?

As for engine braking with most engines, the engine is basically turned into an air compressor, some is due to pulling air thru a "plugged" manifold, some is compressing that air. I don't know what steps Fiat took, if any, to reduce oil consumption... but simply opening the intake valves briefly during deceleration should help. Introducing a bit of air should minimize negative air pressure at the bottom of the stroke?