Fuel injection question.1995 E200 M111.942

[The Pilgrim]

Hello gentlemen,

Being in the process to lower my fuel consumption, I found out the description below. Assuming the info is real (I do not have access to any other description or technical info about this engine), it appears obvious that this particular engine fuel management wastes half of the fuel straight in the exhaust system (cat).

In this situation it seems to me that the only way to correct the situation would be to use one injector from each pair and fit them near the butterfly (and take out the other 2 from the system), in order to resemble a monopoint injection style and avoid the waste spray of fuel. Of course the application of this ideea must be thought well.

So, please correct me if I'm wrong and tell me that this engine has a normal sequential injection.

Looking forward for your knowledgeable kind answers.

Yours
Stefan
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M111.940

The M111.940 is a 2.0 L (1998 cc) 16-valve engine with bore and stroke of 89.9 x 78.7 mm and compression ratio of 9.6:1. It produces 100kW (136hp) of power and 190 N-m of torque.

Applications:

* 1992-1995 E200

Unlike the 102, 103, and early 104 series engines, the engine did not use mechanical injection but the Siemens PEC/PMS (Pressure Engine Control) management system, which integrates fuel and spark management.

It is a speed-density type of system, as mixture formation is dependent on RPM, TPS angle, and manifold pressure (MAP).

Injectors work in pairs (idle, part load), or altogether (full-load).

It uses 2 ignition coils and no ignition distributor. Cylinders are fired in pairs (dual fire) - 1 and 4 together, and 2 and 3 together. The crankshaft position sensor is sensing the movement of two radially opposed position plates on the flywheel, one of which is magnetized, and the other is not. Thus, the engine management has precise information which group of cylinders to fire, and which group of injectors to spray.

M111.942

Similar to the M111.940 engine, used in the years following. It produces 100kW (134hp, 136PS) of power and 190 N·m (140 lb·ft) of torque.

Applications:

* 1995-2000 E200

 

[Dieselman]

So, please correct me if I'm wrong and tell me that this engine has a normal sequential injection.

You're wrong, don't worry about it.

 

[grober]

You are correct in so far as the injectors are paired just like the ignition coils, but remember that the camshafts are operating the valves also, so that fuel- air charge in each branch of the inlet manifold is not being drawn into the cylinder each time-- only when the inlet valve is open. Its there waiting for the next induction stroke keeping the surfaces wetted so the next squirt of fuel is free to mix properly with the air being drawn in. Its an improvement on the old CIS [continuous injection system] where all the injectors sprayed together but the inlet manifold and injection calibration took account of this. Fuel injection gets its efficiency more from accurate air/fuel ratio metering rather than distribution so while in theory having 4 individually fired injectors would help slightly getting rid of 2 injectors would completely fubar the carefully calibrated system. Here's a diagram of the electronics

 

[Ian Donkin]

To add to the above, 'normal sequential injection' is anything but - most electronic fuel injection systems run in 'batch mode' whereby a number of injectors fire simultaneously at the back of the inlet valve but only on the cylinder for which the valve(s) are open will any fuel enter the combustion chamber.

Dual fire ignition is also quite common where cylinders are paired on a coil and this is sometimes referred to as 'wasted spark' however once again only in the cylinder charged with fuel and air will there be any effective spark as in this cylinder there is least resistance to the conduction process.

If you'd like to read and understand more, there are some great '101 basics' articles (and much, much more) on how fuel and ignition works on the various megasquirt forums out there.

Or as Dieselman says, don't worry about it.

 

[The Pilgrim]

Thank you all for your time. You kinda made me a bit relaxed - that 'waste' spray may not be completely wasted.. Still, I do not feel comfy with this sollution.

Grober, that image would be perfectly understandable if a bit bigger, so if you can repost it would be very nice. And pls tell me where I can find specific info for this car model (1995 E200, W210, automatic). At least for the power train. I'm trying hard to improve my mileage and I need info which I do not find available. Any help would be greatly appreciated.

Ian, about the waste spark I have no worry, the energy wasted is of no concern for me.

And last but not least, Dieselman, if it wasn't a concern for me, there was no such a post. If you were me, would you be satisfied with such an answer like yours? I'm here to learn, not to grow my forum activity. But thank you for your time.

Yours,
Stefan

 

[kth286]

if you are saying that two injectors are pulsing at the same time, I would doubt that.

each injector will pulse in isolation when it is it's time to pulse surely.

That's the point of full electronic control.

I accept that two plugs are fired simultaneously - one of the sparks being wasted.

on my similar 6 cylinder engine (1995), if a spark is not generated for a particular cylinder, then the injector will not pulse fuel.

 

[grober]

Bigger!

Here's a bigger diagram as you can see both ignition coils and injectors are " paired" the logic is the INJECTORS are all supplied from a 12V rail and are "fired" by being momentarily earthed thro the ECU Injectors 1 AND 4 thro ECU connection B4 and Injectors 2 and 3 thro ECU connection B13
PS Regret to say the W210 4 cylinder cars are poorly documented in the public domain the 6 and 8 cylinders are better due to bootlegged workshop manuals from the states [ but of course no 4cylinder petrols were sold there! ] The M111 engines and transmissions are covered to an extent in the Haynes contemporary manuals on the C class but that's about it.
oops--- there is this also but deals mainly with engines Mercedes-Benz E-Class - Petrol W124 & W210 Workshop Manual 1993-2000: Easy-to-follow Instructions Covering Service and Repair of 111 and 104 Petrol Engine: Amazon.co.uk: Clarke R M: Books

 

[Dieselman]

Thank you all for your time. You kinda made me a bit relaxed - that 'waste' spray may not be completely wasted.. Still, I do not feel comfy with this sollution.

The spray isn't wasted at all as the valve is closed, the volume of fuel is worked out to account for the redundant spray.

The valve adequately controls the fuel ingested, which is why CIS or carburettored systems work.

 

[Ian Donkin]

if you are saying that two injectors are pulsing at the same time, I would doubt that.

each injector will pulse in isolation when it is it's time to pulse surely.

That's the point of full electronic control.

Your doubts would be ill-placed...

Taken from the excellent Megasquirt resources on the Internet that also explain the basics of mass market installations (and much more)...

There are two common sorts of injection:

Throttle body injection - usually one or two injecotrs for the whole engine
Port injection (aka. Multi-Port) - one injector per cylinder

Then there are three common modes of injection timing:

batch - all injectors fire at once, but not timed to any specific cylinder,
bank - ½ the injectors fire at once, but not timed to any specific cylinder,
sequential - each injector fires at a specific point in the 4-stroke cyle for each cylinder (i.e., 8 independent timing events)

Throttle body injected cars are usually batch or bank fire, simply because of the geometry. Most port injection set-ups before the mid-1990s were bank fire as well.

Sequential injection requires:

as many injectors as you have cylinder, with one dedicated to each cylinder (i.e., not a 4 injector TBI on a 4 cylinder).

as many injector drivers as you have cylinders,

and also requires a camshaft position sensor (a crank sensor is not adequate for a 4-stroke cycle engine).

The benefits of sequential injection are that:

you may get slightly better mileage and lower emissions at low engine speeds,
you can tune each cylinder's fuel amount independently (if you know how).

The effect on maximum horsepower is general negligible.

However, sequential injection does not necessarily mean you are injecting into an open intake valve all the time. The intake valve is only open less than 30% of the time in a typical 4 stroke engine. Once you are trying to produce more than about 25% of maximum HP your injectors are firing for longer than the intake valves are open. If your maximum HP is correctly calibrated to a safe 80% duty cycle, your injectors are injecting well over 50% of the time on closed valves.

In any case, when fuel is injected while the valve is closed, it will simply stay in the port until the valve opens. In some cases, this period of time may allow enough heating of the mixture to better vaporize the liquid fuel, improving efficiency and emissions.

So the effect of sequential timing is relatively minor, and applies mostly at low rpms. The OEM manufacturers use it mostly for emissions reasons (most of the OEM fuel injection systems up to the mid-90s were bank fire). However there is a real benefit in sequential systems in that you can do individual cylinder tuning (if you have the time, skill, and equipment).

 

[The Pilgrim]

Thank you Grober for the bigger image.
Thank you Dieselman for taking time for the not so updated citizens.
Thank you Ian for your time. I did relax my mind now, and will concentrate further in improving the mileage (HCS is the experiment now taking place, but this will be another post soon).
So, the injection department of my engine will remain as it was made

Again thank you for the time & info. Perhaps you will like to comment on my quest for the 10 litre/100km barier (city drive).

Have a perfect day.

Yours,
Stefan