Lambda Controller - PeachParts Mercedes-Benz Forum

duxthe1 · #1 12-01-2008, 02:12 AM

Over the past few months I've been working on designing, building, and programming a lambda adjustment module. It reads the O2 sensor voltage and gives a lambda percentage readout on 10 LEDs. It also outputs the O2 sensor voltage which is controlled by a potentiometer. In the center range of the pot it outputs an unmodified O2 signal. From center you can adjust the mixture either leaner or richer. The adjustment occurs in six steps as you turn further away from center. It has colored LED readouts for the adjustments....green for no adjustment, red for a rich adjustment, and blue for a lean adjustment.

The project is based of of a Microchip PIC18lf2525 microcontroller for which I've written a little less than 1800 lines of code for. Awaiting delivery of a few last minute parts, I'm planning to start the beta testing in my 90 300TE by next weekend.

300EVIL · #2 12-01-2008, 10:55 AM

Sounds interesting.... You'll obviously be using a wide-band O2 sensor, correct? A narrow-band won't do what you are proposing. Will your output be controlling the EHA? I'd also consider using a digital readout for better accuracy.

duxthe1 · #3 12-01-2008, 01:40 PM

No wide band, it's using the factory sensor. The range of adjustment is only 30% lambda either way. It doesn't affect the EHA directly. It only changes the O2 signal enough that the CIS-E will make the fuel adjustments automaticly. The management does have to be in closed loop before the controller can adjust it.

I didn't do a digital readout for 2 reasons. 1. The lambda signal is constantly moving so tracking it down to the milivolt would just keep a fluctuating readout. The 10 LED readout acts as a buffering interface. If the lambda is in the 50% range the 50% LED will be lit. I don't see the need read out the lambda within a closer tolerance. A 10% discrepancy in actual Lambda would just barely be within the range of being able to notice a difference from behind the wheel. 2. Keeping it simple. A digital readout would add to the complexity and after 1793 lines of code in Assembler, I'm not looking for more complicated.

Thanks for the input, though. All ideas are welcome. I hope to be able to develop it to the point of having a good product that will perform well in the field.

c280nz · #4 12-01-2008, 02:33 PM

im not sure how well this will work if at all,
the standard o2 sensors only read from about 14.2-15.2 and the whole time the standard computer bounces between these two figures in closed loop for fuel economy, i cant see any benifit from making it richer while at light load?
and wont it still just adjust within this range?

what im saying is can you explain a bit better what it will actually do? and how it will adjust to make the car richer or leaner, as the computer automatically adjusts to small differences, or is it to be basically just a guage.
possibly your car might have a different ecu with different fuel adjustments to myne and hence i shouldnt have posted anything?

duxthe1 · #5 12-01-2008, 08:26 PM

The idea behind the project is to be able to make adjsutments to the fuel mixture on the fly while in closed loop. With the lambda set to ~50% for normal unadjusted driving, the controller should be able to move the lambda up or down ~30% in 5% increments. So with a good 50% basic adjustment you could adjust the lambda to either a maximum of 80% or a minimum of 20%. I didn't see any situations where a normal engine (non forced induction)would want or be able to operate outside of those tolerances.

The controller adjusts the mixture richer by outputting an O2 sensor voltage that is leaner than it actually is, thus allowing the CIS-E to adjust it richer. The inverse is also true, if you want to adjust the mixture leaner then the controller outputs an O2 signal that is interpreted as rich allowing the CIS-E to adjust itself leaner. The CIS-E module tries to oscilate the mixture around 50%. The controller is designed to basicly allow you to select different values (other than 50%) around which it's adjustments are centered. Such that if I want to center the CIS-E around 40% then I decrease the O2 sensor's voltage by 10%. This lower O2 sensor voltage is interpreted as 10% lean, and the CIS-E will adjust it 10% richer. All the while the CIS-E thinks it's still centering around 50%

The concept behind the controller is to be able to dial in a bit more fuel at the stoplight when there is a BMW next to you, or to be able to dial the mixture leaner when you are on the highway at a nice cruise, and then be able to set it so there is no adjustment for general putzing around. All with just a turn of a knob.

300EVIL · #6 12-01-2008, 09:16 PM

Hmmm... I'm a bit skeptical about the whole idea but "maybe" it will work as long as the altered signal looks exactly like the NBO2 output and shows a slightly lean condition. It may throw a CEL though....

Here's your biggest problem.... The optimum AFR for making power is around 12.5:1 the stock NB02 sensor won't even come close to reading that.

In my opinion, the best way to do this would be to bypass the factory ECU and use a WBO2 to control the EHA directly. Optimally you'd also need load and RPM inputs but by then your basically looking at EFI. Theirs not many hidden patches to engine management other than reconfiguring everything. With what you are proposing, it sounds like a minimal power gain with the possibility of a CEL.

Take my post with a grain of salt however. I'd hate to get your hopes down and would like to see your results. I'd personally love to see you prove me wrong. Gonna need to see some dyno charts though!

Good Luck!
Adam

RBYCC · #7 12-02-2008, 03:14 PM

Quote:

Originally Posted by duxthe1

The concept behind the controller is to be able to dial in a bit more fuel at the stoplight when there is a BMW next to you, or to be able to dial the mixture leaner when you are on the highway at a nice cruise, and then be able to set it so there is no adjustment for general putzing around. All with just a turn of a knob.

Enrichment alone at idle and initial acceleration is not going to make your car any faster.

If you want to work on something for performance then why not look at a timing adjustment.
Fuel enrichment and timing on a NA engine go hand in hand...

And then there is the ECU.

Joreto · #8 12-02-2008, 03:40 PM

I don't think it'll work even for initial acceleration since opening the throttle passed a certain % the car goes into open loop and doesn't listen to the signal from the O2 sensor. The greatest benefit from this may be for fuel economy when cruising (leaning out the mixture) and maybe a bit more performance at part throttle (when enriched) but then you'll lose fuel economy.

JayRash · #9 12-02-2008, 04:00 PM

on my old NA setup i had 2 variable resistors which if i recall did alter the resistance of the temp sensor input to both ecus injection and ignition. Any way did dyno the car and ended with a 203 hp M103. Later on with a more flowing exhaust i got it up to about 210 but then i had to move the R16 euro ECE SWITCH to inside the car as that also changes timing advance / retard. Did that cause i had become so used to knowing to which position the R16 needs to be at depending on ambient temps. Winter / summer and sorts.

duxthe1 · #10 12-02-2008, 09:04 PM

The throttle switch on CIS cars doesn't activate until WOT, so the car should remain in closed loop until it is activated. Part of the beta testing will be to determine if the full load throttle switch needs to be disconnected.

I agree that timing has a good bit to do with power production but at this point I'm not too concerned with it. Open hemispherical combustion chambers (like open chambered 103s) tend to not tolerate much spark advance so I don't think there is a lot of room for improvement. For now I'm just concerned with control over fuel, given that the ignition trim resistor give a small bit of control over the spark map.

JayRash · #11 12-03-2008, 02:10 AM

Quote:

Originally Posted by duxthe1

The throttle switch on CIS cars doesn't activate until WOT, so the car should remain in closed loop until it is activated. Part of the beta testing will be to determine if the full load throttle switch needs to be disconnected.

I agree that timing has a good bit to do with power production but at this point I'm not too concerned with it. Open hemispherical combustion chambers (like open chambered 103s) tend to not tolerate much spark advance so I don't think there is a lot of room for improvement. For now I'm just concerned with control over fuel, given that the ignition trim resistor give a small bit of control over the spark map.

Take it from me, this car will love advance, enriching wont give u much pwr especially if u consider how restricted the air flow is in those cars at low engine speeds. what the M103 lacks is pull low end, and advance will improve that. IMHO. I admire your efforts and i understand the drive behind tuning this system, good luck

Joreto · #12 12-03-2008, 04:17 AM

Quote:

Originally Posted by duxthe1

Part of the beta testing will be to determine if the full load throttle switch needs to be disconnected.

I see one problem here and that is that if the WOT switch is disconnected than the ECU would think that it's at part throttle and will not enrich the mixture, you could go around this problem by enriching the mixture with the controller but that would mean that you'll be also running very rich a part throttle i.e. when cruising ... what you could do is maybe disconnect the WOT switch from the ECU and then have it activate the controller, it might work but it's not the best solution. Best way in my book is to find a way to modify the signal to the EHA, say monitor rpms, engine load (map sensor) and modify accordingly .

duxthe1 · #13 12-11-2008, 10:15 PM

I did my first testing today

I logged about 20 miles without a C/E light. Most of that driving was with the controller set for no adjustment, outputting the same O2 voltage as was input. I did most of the driving with no adjustment making sure that my circuitry would be able to mimic the O2 signal sufficiently to fool the CIS. So far, the CIS module is interpreting my output fine. I put the Lambda tester on it at the shop and it had good oscillation. After work I pulled it in and put it on the gas analyzer. Turns out it worked better than I though it would. I recorded my CO and HC values at idle and at 2000 RPM. Unadjusted my idle CO was ~.40 - .70% and at 2000 my CO was ~.55 - .85%. The Lambda controller would lean the idle to .12% and lean 2000 to .16% CO. Not bad, I must say, but it turns out it will richen much better than it leans. At full rich adjustment idle would go over 7.0% CO and 2000 would go to ~6.6% CO. I really didn't expect it to richen that well but my ASSumption is that the CIS is willing to work harder to prevent a severe lean condition than a rich one. Remember that I get an adjustment by fooling the CIS lean to get it richer and vice versa.

I did get one good stoplight to try an enriched acceleration. I'm not going to say that it was night and day but I did notice a bit better pep.

I am not confident saying that there is more peak power but it felt like the power band had gotten wider. Typically my TE doesn't get any steam behind it until the revs are up quite a bit. Enriched, it felt like it was willing to pull with gusto sooner and longer.

Having the O2 sensor voltage display is neat to watch but also distracting in traffic. I was surprised how much time is spent in a decel fuel cut. If there is one thing CIS does well, it is cut and apply fuel without hiccups. Maybe that smoothness is why Mercedes stuck with it well after most manufacturers switched to EFI.

duxthe1 · #14 12-12-2008, 07:44 PM

I did all of my driving today with various amounts of negative enrichment. At the higher settings the power loss is evident. I didn't notice any pinging but it is pretty cold here and the air is thin. Pinging isn't normally a problem for my TE, even in the summer with 85 octane, but I do see 103s that will ping on cheaper fuel once in a while.

With another 20 miles under it's belt, still no C/E light

duxthe1 · #15 12-13-2008, 10:09 PM

Today was a mix of driving with fuel being added and subtracted. No real problems to report. There is a bit of a delay from setting the controller to add fuel until the CIS actually adjusts it. Since the controller affects the CIS's feedback system, it has to see the adjusted values for a bit before the mixture actually starts to change. I noticed this on the gas analyzer and now during actual driving. The dealy seems to be around 10 to 20 secs. I think that when the O2 sensor is really good and hot the delay is less. At stoplights I adjust when the crosswalk signal changes and that seems to work well. I have gotten a couple of good enriched accelaration runs today. It definately likes the extra fuel. I have a fair hill near the house that has a 30mph limit. At 30 mph, I normaly am just on the border line of being able to climb it in high gear without a down shift. When leaned out a downshift is certain, when enriched it pulls the hill in high gear with ease. Not emperical data, I know, but proof of concept none the less.

I've been talking with my co-worker about trying it in his stroked 500SL. That puppy really likes to run rich but he keeps it tuned pretty lean most of the time.