AFR with WUE engaged

[Martijnus]

MSII V3 2.886 code.

I was thinking about the exhaust gasses when the engine is warming up.
Since I can see what the AFR is and what it should be, I could use this feedback to tune my WUE.

Why do you need enrichment when the engine is cold? The fuel condenses in the intake system, making the mixture leaner as soon as it reaches the combustion chamber.

When you enrich the mixture, you compensate for this condensation, so you would like to have the same mixture in the combustion chamber, as with a warm engine.
Let's say that 25% of the fuel condensates in the intake system, you want 125% to compensate...

That means that the AFR from the WBo2 would be exactly the same as with a warm engine, in an ideal situation.

Is the above correct? I guess my AFR would probably has to be a little bit richer for optimalisation, but the issue is if I can look at my AFR during warmup to see if it's too rich/too lean.

Reason for all this is that my engine started quite good, but now when it's colder (about 10 degrees colder, at -1deg. C) it cranks, sometimes tries to run, gets a really low rpm (500rpm, while idle is above 900) and dies after a second.
If it was the cranking pulse it wouldn't get out of 'cranking' mode I guess, so I suspect the WUE.

[landybehr]

"That means that the AFR from the WBo2 would be exactly the same as with a warm engine, in an ideal situation."

That´s a question I long to see answered too ;)

We had some low temps these days,-10°C (bloody sensor read -17°C. Anyway - good chance to tune cold start). Ok, with the 10deg below freezing point and I had to give almost 45% of ASE to prevent it from dying after cranking (the less ASE, the sooner after cranking it died). I have raised the stepper position to aid the situation - don´t know whether that´s a good idea in this condition (but before playing with ASE I´ve kept the engine alive with opening the throttle a little). Now that it more or less will run after cranking I have noticed I had some 11.0:1 (petrol) at warmup. Therefore I started to reduce the WUE until figures in 13.0 region came in.

Isn´t it a good idea to have as less enrichment as possible without the engine dying - in order to save the cylinder walls from being de-oiled ? Anything I miss ?

[vinister]

i really don't think the actual AFR at idle means much of anything. Several reasons:

- When cold starting, your O2 sensor is cold, and isn't as accurate as it could be
- When cold starting, the oil is cold and heavy, and the motor parts are cold and expanded thus making everything much tighter
- Tighter engine parts = harder to run = needs more fuel to help it out
- Fuel economy and Emissions don't matter during warmup, only thing that matters, is to get the engine warmed up running smoothly

Therefore I think you should make it as rich as it needs to be in order to idle smoothly, while not too rich as this will slow the warming process.

[Martijnus]

i really don't think the actual AFR at idle means much of anything. Several reasons:

- When cold starting, your O2 sensor is cold, and isn't as accurate as it could be
- When cold starting, the oil is cold and heavy, and the motor parts are cold and expanded thus making everything much tighter
- Tighter engine parts = harder to run = needs more fuel to help it out
- Fuel economy and Emissions don't matter during warmup, only thing that matters, is to get the engine warmed up running smoothly

Therefore I think you should make it as rich as it needs to be in order to idle smoothly, while not too rich as this will slow the warming process.

that's about the same as saying, "you just have to tune the engine in a way that it's not too rich, but not too lean".
You need feedback, and you can't just rely on how smooth the engine is running, because I've had it to 20AFR during warmup and at 12AFR during warmup, and to notice the 'smoothness' of the engine in between those you'd have to be an expert.

the o2 sensor warms itself up, it could be that it's 0.1 less accurate, but I don't believe it's off by 5 afr....
Thicker oil could mean more load and more fuel, but there's a difference between 10afr and 15afr.
At maximum power and maximum torque the engine needs between 12.4-13.2 according to the manual, let's say the engine gets a load that's reasonably big, due to the thicker oil. The afr should be between the above values in that case... so that's not really an argument not to use the wbO2.

[vinister]

So... if its running smooth, and you are happy with the AFRs, then what is the problem we are trying to solve here?

[landybehr]

... then what is the problem we are trying to solve here?

not to fight each other for having the last word ;) Not happening here. After all it´s very remarkable what high level of kindness there´s present in the MSefi - forum.

Back to your question:
.. If it is only for reassuring a greenhorn like me that I´m not making a mistake or am not overlooking anything.
That could be a good reason.

[Martijnus]

So... if its running smooth, and you are happy with the AFRs, then what is the problem we are trying to solve here?

I'm not happy with the AFR's... it can run smooth, but running too rich at idle can screw up my spark plugs and oil... running too lean gives its own problems. If I start the car everyday, and it runs too rich for 5 minutes my oil get's contaminated every day... I don't want that.

Then, aside from those problems I want some fuel economy during warmup ;) no need to throw my expensive fuel away.

Like I said, it can run smooth, but if that's enough, nobody should need a WBo2 sensor "because it runs smooth enough this way".

So instead of just accepting this problem, I try to discuss the theory of AFR during warmup and every input about that can be helpful.

[vinister]

I really believe that anything between 13 and 15 and your engine will be just fine. The problem is, if your sensor is reporting 13:1, 10-20 seconds after starting, what is the actual real AFR? I'm not sure if its my engine or the LC1, but when I cold start, the AFR's show dead rich, and slowly move to stoich over about 20 seconds. The PW doesn't change all that much during this time. Once the AFR reaches stoich, I can re-start, and the LC-1 appears to show accurate AFR's, going to 13 during the ASE portion, then moving closer to stoich.

I happen to have an engine that runs smoothest at 14.7 while it warms up. Of course I need richer than that during ASE period, but this is a relatively short 200 cycles. (not sure how long that is in seconds)

However, I can hear and feel the difference between 12, 15, and 17. I can also smell and see the difference at the tailpipe. Too rich, exhaust looks 'moist', and leaves some moisture on your hand when you hold it over the tailpipe. Too lean, there is no visible exhaust and it almost smells burnt. Stoich, it just looks like normal exhaust but doesn't leave any moisture on your hand, and doesn't smell like fuel or really anything at all. I really feel that during a cold-start, for the first few seconds, these senses are more reliable than the O2 sensor feedback.

I used to have a lumpy cam that demanded 13.5:1 to idle properly. Any leaner, and it would simply start to stumble and miss, any richer and my lungs would stumble and miss.

Maybe, after a cold-start, shut off your engine after 30 seconds and check your plugs. This will put your mind at ease about possible damage or fouling, and give you a better idea of your mix.

Another trick is to turn on the ignition, and leave it on for about a minute without starting the motor. The O2 sensor should heat up and give you a more accurate reading upon fire-up. The problem with this approach is that if you are in fact too rich, you will be splashing cold unburned fuel onto a hot O2 sensor head, which is not good for the sensor.

I think you answered your own question with this statement "Isn´t it a good idea to have as less enrichment as possible without the engine dying - in order to save the cylinder walls from being de-oiled ? Anything I miss ?"

Remember that many OEM cars, upon cold-start, will be rich enough that you can smell unburned fuel at the tailpipe, and even get some on your hand when you put it over the tailpipe. Its only like that for a few seconds (the ASE). This supports my statement that during a very cold ASE period, your AFR's will have to be very rich to keep the engine running smoothly. You will not damage your engine like that in only a few seconds per day. As soon as the engine gets its footing, the fueling curves to normal, and the extra fuel that may have gathered on the plugs/walls is burned up very quickly. If you refuse to accept that approach, you may have to live with double-starting on really cold mornings, or just use a block heater.

If you really do have many starts per year at -10C, I would highly recommend a block heater, as it will save you much more damage than a little extra fuel. Put some oil in the freezer overnight then check its consistency in the morning, it almost turns to jello.

Anyways sorry if you don't like my feedback... this is a forum after all.

[landybehr]

(The AFR gauge reads 7:1 or similar for the first seconds but I think that is the LC-1 controller which isn´t supplying a signal in the heating phase?)

(some thought: a) if I can trust the AFR gauge after, say, half a minute and b) the engine looses fuel by condensation which is why you have to add some and c) the fuel that does not condensate burns like if the engine was warm THEN would an AFR of 13.0-15.0 indicate that the enrichments are fine as this AFR is the same as on a warm well tuned engine (condensation losses will not affect the lambda sond) ???

[Martijnus]

Vinister, I don't have that much cold starts (below zero)... so it all won't be that much of a problem...

The only question I'd like to see answered is how far you can rely on the AFR during warmup... if you'd set the enrichments in a way that you keep your goal afr, wouldn't that be the optimal settings?
Keeping aside that the WBo2 could be less accurate...

If you're engine's cold, and you get the same afr by enrichment of x%, you'd think your combustion would be the same as with a warm engine without the enrichments...

[devastator]

I'd be careful with the AFR values at idle anyway, as they are not usually very accurate.

[66fb]

I'd be careful with the AFR values at idle anyway, as they are not usually very accurate.

Why not? What do you base your statement on? My LC-1 seems to be doing alright as soon as it come "on line". Do you have another (parallel) method of determining O2 error?

[vinister]

There are lots of reasons why O2 is less accurate at idle

- exhaust gases are much colder, the built-in heater might not be enough, this could alter the output significantly
- incomplete burn may lead to error
- lower velocity of the exhaust gas makes it more 'pulsy' than it is at higher rpms, the LC-1 is trying to average the results for you but may introduce some error

These are all reasons why most users set their EGO control to an rpm value above idle.

It may seem to be accurate, mine seems that way too, but how do we know for sure? Like I mentioned above it may be better to pull your plugs after a coldstart and look for yourself.