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Closed loop triggering

NPS

NPS

Cruisin' Guzzisti
GT Contributor
Joined
Dec 11, 2008
Messages
262
Location
Churchdown, Gloucester, UK
I realise this might be a tough question and one that many don't have direct experiance of, so an apology to start with!

My B11 suffered with the usual cylinder heat temp sensor holder break about 6 months ago. I turned one out of ally and replaced. Being an electonics hobbist I added an LCD readout of the signal from the sensor and callibrated it. So I got a reading that showed that in the UK summer the temp levelled out at about 95-100C. It went up to 120 in slow stop start traffic.

I have also added a Bosch lamda sensor in the exhaust in place of the standard one and it gives two signals. One to replace the on off signal to the ECU and another variable voltage 0-5 v to indicate the air fuel ratio.

In the summer I noticed that the ECU would not go into closed loop operation, oscilating the mixture on the lambda signal until about 20 minutes into my journey. This happend to be at about 85C head temp so I initially thought the trigger for closed loop was temperature. But then I noticed that on my journey home from work, the first part of the journey was stop start in traffic and the engine warmed up to 85 in about 15 minutes instead of 20. The closed loop operation, however, would start sooner at 10 minutes at a lower temperature.

With winter comming on the temperature does not rise to 80c even after an hour and closed loop operation seldom triggers.
I'm slightly comfused. Is closed loop meant to be time/temperature triggered or time triggered or temperature triggered. Or some other input that I have not realised.

If anyone can shed any light I would be moste grateful!

Nigel
 
Nigel,

I'm not sure of the answer either, but the stock Lambda is not an on off switch to the computer. The voltage changes based on the amount of O2 to generate a current in the sensor. I've seen voltage swings from 40mv, up to 480mv volts on my B11 with VDSTS software. This occurs once the lambda is up to operating temperature. This voltage swing is supposed to signal changes in pulse width for the injector, which I also observe as the voltage changes.

That said, I'm not sure if the Bosch unit you substituted is providing the proper signal to the ECU. I'm not sure if this link will help or not. http://auto.howstuffworks.com/question257.htm
 
John
Thanks for your input. The standard lambda on a Guzzi (with one) is a narrow band lamda with output between 0.1 and 1.1 volts.
I haven't measured the output on a standard guzzi lamda sensor so I'm just going by what I have leant about zirconia sensors. Perhpas the Guzzi one is different and that is where I may have made wrong assumptions.

What you have said about seeing the injector pulse width change with the sensor output has got me thinking and I will do some measurements with VDSTS.

From my observations on the road, I see the AFR allternating when in closed loop mode around 14.7 AFR. This happens several times a second on my setup as the signal that Im feeding to the ECU is at 10hz, and it responds. In my case Im facking the signal to the ECU. I'm providing an alternating signal to the ECU at 10 hz. That is 1 to 0.1 volts. The ECU thinks its 14.7 AFR but in fact it is 14.4 AFR. The ECU responds instantly by maintaing AFR 14.7 (but really 14.4). I'm modifying it through my additional electronics to get slightly richer and smoother running.

That aside, the problem is getting into closed loop to start with as my B11 wont do it until very warm/hot. I have thought of faking the cylinder head temp to tell the ECU its running at 100C when it is at 75C.
 
Nigel, you're treading in new "end-user" territory for the 5AM ECU. Interesting to hear that it is closed loop only on occasion... I don't think that was known. Based on your data, I suspect it is strictly temp related. IMO, 14.4~14.7 is critically lean for an air-cooled engine.
Fooling the temp. sensor is a trick used on late 90s/early '00 Guzzis, and seemed to work OK on pre-02-sensored ECUs.

Keep us posted as to any new data you uncover.
 
The intersting thing is that the outcome of the ECU program does not appear to be consistant at what point it wants to go to closed loop mode.

Two weeks ago I replaced my cylinder head temp sensor with a standard sensor and holder and the temp that i see now is 5-10C lower and the ECU only goes to closed loop in the last 10 minutes of a one hour journey into work in 0-5C temperatures in the UK.
It is temp related but I thin there is a formula in the programming where the rate of warm up is important as my jouny back from work showed as it would get into closed loop sooner.

When starting from cold the ECU always works in open loop working of the injection timming map. Modified for pressure and temp it delivers a pulse to match throttle opening and rpm. Leaned that from my16m (cliff in Aus) unit that I had on my Sporti 1100.

The B11 in my case will run in open loop at 11-13 air fuel ratio until it decides to go to closed loop when hot. The the AFR goes to 14.4 which I have arranged to give economy and smooth running.

I'm thinking I will do some tests to elevate the temp signal after it gets to say 60c. Let the ECU think the engine is at 100c and see what it responds with. As I read the cylinder head temp sensor and can dynamically create a fake output to the ECU from my box of electronics riding piggy back I think I can do this.
 
Very interesting.

One thing I have found is that the engine temp sensor will usually get a false reading due to there being an air gap between the tip of the sensor and the head. I always pack the holder with some sort of 'Thermal Paste' (I usually use zinc based anti seize) and this results in a far more accurate temerature signal to the ECU, (As observed with Axone.). This may of may not be relevant, the VDST should tell you though.

Pete
 
Nigel,

It sounds like you have some good work going on. The best I've been able to observe from the stock Lambda or equivalent is a voltage change about every 3 seconds. To me that isn't frequent enough. Perhaps once you work you equipment out you would have a kit available for the rest of us?

An interesting side is the part number for the 750 Breva Lambda is the same, yet it reads higher voltage then the B11.
 
Interesting. I make no claims about knowledge here, but my Norge was on an Axone a couple of weeks ago. Doubt if it was that warm, but I was shown the ECU switching from closed to open loop according to throttle position. Also I saw the lambda reading varying constantly as it was thought that mine was faulty - it wasn't.
 
Brian thanks for the input
In my observations at tick over the ECU uses the map in openloop mode so the lambda does not come into it, But as soon as the throttle is moved slightly the lambda is used by the ECU ( after the point the engine is hot enough and the ECU has decided through some yet undocumented logic to switch to closed loop, after that point it stays in closed loop apart from tick over or sudden open throttle).

The lambda does move around constantly as this is what is providing feedback to keep the air fuel mixture at 14.7 at stoicometric. Sorry I could never spell that work it might be right but I can't tell!
The "according to throttle position" interests me. I have become a little narrow sighted thinking that the ECU works in only one way but I realise now that there is another darker side. Perhaps some intelligence in those circuits and chips. Please would you elaborate on "the ECU switching from closed to open loop according to throttle position" just in case I have missed something?
 
Sorry, there's not much else I can say. I was just watching as Baldrick fiddled, but he did show me the display with the indication of closed/open loop. I got the impression that it was closed until some specific throttle opening. This was all on the bench, so the engine was not loaded.
I'm pretty sure Pete and others will know far more.
 
From what Todd told me the other day, I'd understood that the closed loop mode is under 3000rpm, which probably makes sense. That doesn't mean it can't switch off at a lower regime if the conditions are right.

I suppose MotoScusi could contribute here, dunno if he's on the current board incarnation?
 
Just an update but not much changes.

From my observations closed loop is entered after a number of minutes (could be revs) and dependant on head temperature.
Less than 95c it stays in closed loop. Greater than this and closed loop will be entered (and it stays there except in rapid opening of the throttle or sustained large amounts of throtle) after a period of running that seems to be determined by how quickly the temperature got there in the first place.

This winter again I have rarely seen closed loop where the ECU occilates the AFR around 14.7. It is nearly always in open loop at about 11 (under acceleration) to 13 AFR when cruising at 40-70mph.

On a motorway in summer at 80mph when normally in closed loop, it will occasionally start to switch back to open loop and go rich in response to the 40%+ throttle opening.

Have been monitoring visually the AFR, throttle and characteristics since I installed the Bosch wide band lambda nearly two years ago and it it has given me a few ideas. I would like now to move to adjust the injector pulse on the fly to maintain the AFR at a slightly more leaner 13.5-14 AFR. I also understand that wide band lambda sensors measure O2 and that its output might not be entirely accurate. However, I have found that when it shows 11 and the engine misses it likely too rich so I think Im in the right ball park. I'm not aiming at doing anything commerically at them moment as its just a hobby.
 
How are you verifying closed vs open loop? Is it a channel in VDSTS?
 
Re: Re:Closed loop triggering

RJVB said:
From what Todd told me the other day, I'd understood that the closed loop mode is under 3000rpm, which probably makes sense.
Click to expand...
Actually it is dependent on both Throttle position and RPM, NPS touches on it above.
 
I have an LCD display of the AFR updated at 10hz between my handlebars.

In closed loop AFR changes constantly about twice a second around the 14.7 AFR in order to use the catalyst in the exhaust to most effect. In Open loop it mostly goes rich but is fairly steady if the throtle and rmp is steady as its working from the fuel map.
 
NPS said:
I have an LCD display of the AFR updated at 10hz between my handlebars.

In closed loop AFR changes constantly about twice a second around the 14.7 AFR in order to use the catalyst in the exhaust to most effect. In Open loop it mostly goes rich but is fairly steady if the throtle and rmp is steady as its working from the fuel map.
Click to expand...

Oh yeah, you told me that before. :)

Todd, does this explain why my pc-v map on the Griso 1100 is mostly removing fuel? Basically, I've only been riding in cold weather recently so if NPS is seeing 11-13 AFR then the PC-V would mostly end up removing fuel to get to the 13.2 I have mapped. The bike runs great and feels stronger so I thought it was weird that it was mostly removing fuel. Up until now I thought it might be because you changed the map when you flashed my ECU.

Dan
 
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