Understanding the operation of the Motronics 2.4 ECU

[Jammess]

Have done some more reading on the operation of the o2 sensor and I don't think the ECU is going to like a constant voltage at the oxygen sensor input. If the ECU does not see a varying voltage then it may simply stay in an open loop condition and thus ignore the oxygen sensor simulated signal and operate using all other sensor inputs but omit the o2 sensor. The ECU may assume that the o2 sensor has failed. This would no doubt result in an over rich running condition. Google searches on this subject produce much information from some very good sources like Volvo and even BMW. I may have to do some more thinking.

James

[AirForceDirt]

I like the idea of a wide-band O2 sensor. Not really sure why BMW went with a narrow band for a bike with this much versatility.

I'm thinking I'm gonna work on getting the A/F ratio down to 14:1, see if thats too rich, then work from there. The bike needs a new air filter, but I don't want to add MORE air until I know I can get the extra fuel too. I want to make sure I don't end up going too far towards rich (bad fuel economy) or lean (running too hot and frying things inside).

Hesitant, however, to take the bike apart as far as it would require to get to the fuel pressure regulator, and without changing injectors, I worry that it would put pressure on said injectors (more fuel trying to go through the same hole in the same amount of time). I still wanna be able to ride this thing for another decade or so (at least).

[boxermania]

AirForceDirt

Interesting approach, haven't given much thought as to how to go about it.

As an option, it has been demostrated that doubling the pressure on an injector increases the flow ~ 41% (remeber the oricife(s) are fixed so the flow increase is not linear and will eventually max out). That being the case, replacing the stock 3.0 Bar FPR (fuel pressure regulator) with the 3.5 Bar from the prior gen K bike will increase the flow ~ 3.2 %. The cost is minimal although the replacement is a bit tedious. It worked very nicely for me, but I had various other mods. If you check the GS forums and Adv Rider you'll find a few owners have gone that route.

The other easy option is to parrallel a resistor across the ambient air sensor......I will look for the Resistance vs temperature Graph I generated and posted for reference. It will enrichen the mixture, unfortunately, I don't know by how much.

[AirForceDirt]

What would adding said resistor do? In terms of how the motronic operates..

[boxermania]

The resistor will fake the outside temperature to the ECU allowing a preset "shift" to a slightly richer A/F mixture. I found my graph, but can't post from work. I'll do so when I get home.

In the meantime, I do have the data points to share

38.5 F = 5200 Ohms
68.7 F = 2365 Ohms
99.7 F = 1265 Ohms

You could try a 2500 Ohm first and a 5000 Ohm later and see how the engine performs. For the test, just unplug the connector at the top of the filter cover and place the resistor across the two contacts in the plug.

[MattPie]

I am still sceptical towards this diagram, it seems the injector always spray fuel to a shut intake valve. Like you said, it is best to hook up a scope to verify the injector firing timing in relation to the crank angle

Yeah, it doesn't seem right that the injector fires at BDC, I'd think it would open near TDC and close near BDC, so the fuel is sprayed as the air gets sucked into the cylinder.

But I'm not expert in FI, that's for sure.

[Sunbeemer]

I verified that the Hall effect sensors trigger at TDC and BDC using a test rig and cranking the engine over by hand. Whether this simultaneously fires the injectors and the sparks plugs, I don't know.

[Phang]

This is getting interesting

If the HESs are triggered at 0° and 180° respectively, does the Motronic starts counting when the 180° HES is triggered at BDC all the way to the required spark advance angle which is between 0° and 43° BTDC? (ignition timing = 0° to 43°BTDC, according to R1150R manaul)

Counting 137 out of 180 to get 43 is quite agricultural in my opinion but it is perfectly inline with boxermania’s comment and keeping the system simple.

I think is proper to acknowledge that the Motronics system is not current state of the art engine control, but it served the intended purpose at the time.

[Sunbeemer]

The advance is adjustable by sliding/rotating the HES plate, but I think the range is only +-5 degrees from TDC & BDC. Mine was advanced ~ 2 degrees (and I can run regular gas in the winter without pinging).

[Phang]

IMHO, the adjustment at the HES plate is only adjusting the reference triggering point for Motronic. The actual ignition advance timings are stored in the Motronic memory (aka ignition map) which varies according to engine rpm, load and fuel quality (not applicable to our roadster).

Adjusting the HES plate for 2 degree advance will add 2 degree to all the timings that fired away by the Motronic

[boxermania]

I have to give some thought as to the sequence of firing for the plugs and the injectors. There is no question that, the injectors fire at unison and so do the plugs. The question is what is the offset between the two events. I can attest to the fact that the plugs fire every time that the TDC HE's is excited. Need to look at how the BDC HES fits into this scheme.

The retard function of the HES plate is limited to 3 degrees by the amount it can be rotated. This advance is referred as initial advance or when the spark will occur in relation to TDC. Generally speaking and depending on combustion chamber design initial advance can be anywhere from 4 to 16 degrees, as speed increases the events occur faster, as such the spark has to occur earlier, this is referred as the "mechanical" advance, either built in on the distributor or dialed in by the ECU based on rpm.

The term spark advance tends confuse a few people as they would take the meaning of the word literally. In the case of IC engines it refers to the time the plug fires in relation to TDC. So, 5 degrees advance means the plug will fire 5 degrees before TDC. Ideally, you want to have the plug fire at exactly TDC hoping that combustion will be instantaneous and complete (this is an impossibility due to the combustion characteristics of gasoline) that's why the spark is generated just ahead of TDC, so as to get a running start. Too much advance will ignite the A/F mixture well before TDC and will create a force opposing the upward piston motion.....usually referred as knock and resulting in power loss and in the worst case damaged parts.

As engine speed increases the spark has to happen much earlier with the same results as above if too much "total" advance (initial + mechanical) is dialed in. Phang is correct on his interpretation.

[Phang]

When I look at the diagram in Page 1 again, I realized there isn’t any ignition advance control at all if the 0°/360° HES is triggering the ignition coil directly.

While taking an afternoon nap under the coconut tree, I have this revised diagram on my mind. In short, the injectors are triggered by the Top HES and the ignition coil is triggered by the Bottom HES.

[shake1150]

ok... so let me get this straight...

1. without the Cat Code Plug (or CCP) the O2 sensor is basically not in circuit. only WITH a CCP plug, this O2 sensor plays a role in the air/fuel mixture? is that correct?

2. also, when my catalytic convert (or CAT) gets hot when riding and I can feel the heat on my feet...
is that because the air/fuel mixture is too lean or too rich? I always thought that when it got really hot was because it was running too lean... but I'm reading here thats its the unburned fuel thats getting "used up" in the CAT thats causing the heat which means air/fuel mixture too rich?

someone please straighten me out here...

I should also mention that I have a Rhinewest chip installed in mine (with stock CAT and Zach exhaust)... the CAT still gets hot sometimes, but not as often as it did with the stock setup.

[boxermania]

shake1150

1) Correct......but only during the "closed loop" operation, which would be at constant throttle (teady state). Once the throttle is opened the O2 sensor is out of the circuit.

2) "catalyst - a medium that fosters a chemical reaction"Uunburned hydrcarbons react with the catalyst to combust such and increase the shell temp. While iddling there is no air flow to remove the hat hence the possibility of getting red hot if the bike idles too long.

The Rhinewest chip acts, among other things, as a fuel nanny by slightly increasing the A/F ratio during high engine load periods (open throttle operation)

[Arbreacames]

1. without the Cat Code Plug (or CCP) the O2 sensor is basically not in circuit.

I have not seen any reason to believe that the CCP is required for closed-loop operation. Does anybody have information one way or another?

I have toyed with a variable resistance in series with the temperature probe and the results were undetectable except, perhaps, under re-acceleration. Re-acceleration felt slightly more progressive and controllable with a resistor, with a slightly sweeter engine sound. In the end, however, the effect was so mild that any benefits were negated by the fear of the god of Teutonic engineers. These observations are consistent with the fact that at less than WOT my R operates in closed-loop, even without a CCP. I welcome other observations.

[boxermania]

Carlos....nice to hear from you...its been awhile since you have graced this forum.

Carlos
I have not seen any reason to believe that the CCP is required for closed-loop operation.

Point well taken and I agree with you. The O2 sensor operation is independent of the CCP or lack thereoff. This is the way I understand it:

There are 5 or 6 fuel maps inbeded in the ECU and they are accesible by the absence of the CCP plug or via five other diferent colored plugs (Yellow, light bown, dark brown, pink....that I'm aware of). The O2 sensor is of the narrow band, this means that outside the 14.7 A/F ratio the output changes very little with large changes in A/F ratio, that's wy these narrow band sensors have to be averaged (typically) over a 1 second period.

Closed loop operation, where the O2 sensor output is used to adjust the A/F ratio to benefit from increased economy, can only take place during steady state operation......once the engine load invreases the O2 sensor is out of the picture and the ECU operates under the particular map that has been selected.

Regardig the resistor in parallel with the ambient air sensor, you are right again, there is a sligfht increase in A/F
ratio (richer mixture) which is hard to quantfy. In some cases, it is suficient to mask the "surging" that some owners complain about.

[2CV Joolz]

Hi, I hope you don't mind me dragging up an old thread but i thought it best to keep all related discussion in one place.

I'm trying to understand the roles of the 2 crank sensors, and while I don't have a huge amount of experience with such things, a single sensor with a multi toothed wheel seem much more common in other vehicles.

I read the suggestions earlier in the thread with interest, and did some tests to see if it would confirm them. By individually removing the pins from the multiplug, I disconnected the signal wires from first one sensor, and then the other, and attempted to start the engine each time. To confirm what was happening I connected a strobe light to an HT lead, and removed an injector from the throttle body allowing it to squirt into a plastic bottle instead.

Without stripping the insulation I can't be sure which wire is the top sensor and which is the lower, but one has an orange wire and one is black. The results were;
Black wire disconnected - the engine will run briefly, for maybe 5 secs, but will die if the throttle is opened.
Orange wire disconnected - will not run, it sparks and squirts, but appears to do so at about half the speed that it should.

To my mind this doesn't make things much clearer, except perhaps disproving the idea that one sensor does the ignition, and the other the injection. If nothing else perhaps it will help people trying to diagnose a faulty hall sensor.

The reason I'm doing this, I would like to fit a piggyback ECU and need to find which sensor controls the ignition timing.