First of all, i guess the search feature is down, or else the word "humidity" has never been said on this site

anyway, Im pretty sure that im noticing lower BLMs (richer) while its more humid out. this seems logical since more humid air compaired to dry air has a higher specific heat and can cool the MAF wire more for the same amount of airflow. therefore more fuel is added as a result of more heat being drawn away from the MAF wire. is there anything done by the ECM to account for humidity changes? Can i account for humidity at all?

most likely too in depth of a question for me to ask yet, but if the answers above are "no", can some humidity sensor be added and implemented in the source code to adjust fuel and even spark if neccesary?


anyone have some input on this?

 

1). Not sure, it has been seen.

2). Errr, No, Yes.

3). - -, Yes.

4). see above.

RBob.

 

Yes, of course humidity has an effect. Usually not enough to through your tune out of "acceptable" range blm and int wise in closed loop. Open loop may cost you a small bit of power - that's why all the big race teams have all kinds of weather logging equipment and different tunes for each track. Is it enough for you to worry about? Not as long as you're not riding the ragged edge with your tune. You could use a G3 moates adapter and have one bin for low humidity and one for high if you're super worried about it.

As far as addining it in the source code, that all comes under your limits as a programmer, I can't give ya a yes or know on that one. But IMHO it would be waaaaaayyyy more work than any benefit you'd see.
John

 

ok, that all sounds good to me. my BLMs are fairly inconsistant from day to day, and even between early morning to work and late afternoon from work. identical bin ofcoarse. i dont have any humidity readings, but it was something i was thinking about.

 

Think about what you wrote for a minute. Yeah, it's raining today, so it is more humid.
Does the humidity cool the MAF and produce a false reading ? I don't know, though I doubt it, but what the humidity does do, is displace oxygen in the air.
The ECM responds by adjusting the fuel/oxygen ratio sensed by the O2 sensor to correct the mix.
It's not adding more fuel, you're getting less oxygen, resulting in a rich mix. Your BLM tracks this, and the ECM compensates, just like it's supposed to.
Make sense ?

 

Water vapor displaces oxygen and other gasses in the air, so it will cause the motor to run slightly richer. It may even have a slight effect on the rate of heat transfer, but usually this wont be more then a few percent from my experience with MAF. The same probably holds true for SD as well.

 

yea i thought about the water displacing oxygen too, but i didnt mention it cuz i didnt know if it was significant enough or not. if it is, well, cant do anything about that.. hmmmm, how about an inline intake de-humidifier???

 

BLM Variances can easily be attributed to many things. If it's the same tank of gas, the PURGE HC concentration and flow rate and temperature of the tank (which affects purge) are what I see affecting it the most.

Humidity variances in a warm climate might have some effect on MAF or MAP, but I can't say I've seen it or studied that phenomenon on our cars. I've read about it, but that's about it.

 

so, a bit off topic, red'n'gold, do you disable purge whilst you tune? my vent valve thing is gone right now so i doubt it's hurting me much but i wonder.

 

Yeah, if I'm working on the main fueling (e.g. on an engine dyno).

On MAF, purge can cause BOTH lean and rich, since it's both unmetered air and fuel.

On MAP, purge can ONLY cause richness. Because any air will be sensed in the pressure.

But, the amount of air entering through purge will only account for a small small fraction of the air. For example at idle, if you fully open it and it's flowing all air, it may cause 4 IAC counts difference. But, fuel vapor is about twice as dense, and since gasoline burns at about 14.7:1, each 1 percent of flow through purge (% of total flow), if it's all fuel vapor, will cause 30% change in fuel mixture!! The temperature of the fuel tank causes big changes in purge flow, also, if the engine is off and/or not purging for a long time with a warm tank, the purge can be extremely rich. Also, overfilling the tank is a big no-no.

This is why all systems have a "closed loop" feature to bring purge in slowly, and wait for the loop to catch up to it, then bring in more, and wait. Also, many systems will try to learn how much fuel concetration is from purge, so that the fuel trim doesn't have to "work" so hard (i.e. cause emissions), and so that long term adapts can be adapted with purge on - so cold starts have accurate trim.

 

cool, i'll adjust accordingly. sounds like our purge system could use some modding, my tank is constantly gurgling and hot so it might impact me a bit more. thanks!