Humidity: Causing AFR to go crazy??

R

Rogue

Red 5 Standing by
Contributor
:
2003 MSP
It's been humid the past 3 days. We had our first real rain back on Sunday. Since then, my AFRs have been doing odd things:
  • Will run rich (13.x) while cruising. Use to run stoich (14.7-15.0)
  • Will dump fuel if i barely touch throttle (11.0 and lower)
  • Will run lean (14.5-16.0) if I boost, but not at wide open throttle. At WOT, will go rich (10.0 and lower)
  • Will go rich (11.0 and lower) at idle, then creep back to stoich (14.7)
Could this be caused by the humidity in the air?

BTW, I'm using the MSP ECU. I'm not sure if it's a flashed version or not.
 
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I know this is a little off topic but can you explain A/F ratio to me?

the lower the # the richer your car is (for boosted applications)

the higher the # the leaner your car runs (for boosted applications)

is stoich still for boosted cars 11.9-12.1?

and for N/A it is 13.7-14.1?

I may be answering my own question here and I probably am, but I just wanted some clarification, and I appologize if I jacked your thread
 
well, when it is humid, there is more moisture in the air, so water molecules taking the space of oxygen molecules. this decrease in oxygen molecules is apparent when the same volume of air makes its way into your engine. less oxygen molecules and the same amount of fuel as before = running richer. of course, the stock ECU should be able to adjust for this. but the stock ECU is kinda crappy, so it probably doesn't do a very good job. get some EMS and tune that thing.
 
Matthew1785 said:
I know this is a little off topic but can you explain A/F ratio to me?

the lower the # the richer your car is (for boosted applications)

the higher the # the leaner your car runs (for boosted applications)

is stoich still for boosted cars 11.9-12.1?

and for N/A it is 13.7-14.1?

I may be answering my own question here and I probably am, but I just wanted some clarification, and I appologize if I jacked your thread
Click to expand...
my understanding is that stoich is stoich for both applications.
 
ChopstickHero said:
well, when it is humid, there is more moisture in the air, so water molecules taking the space of oxygen molecules. this decrease in oxygen molecules is apparent when the same volume of air makes its way into your engine. less oxygen molecules and the same amount of fuel as before = running richer. of course, the stock ECU should be able to adjust for this. but the stock ECU is kinda crappy, so it probably doesn't do a very good job. get some EMS and tune that thing.
Click to expand...
that's what I thought...but it's killing my gas mileage.
 
it's gone way down since I noticed it running rich. I usually get at least 300mi before the light comes on. This time it came on around 280.

The AFRs are going all over the place. It'll be off the scale lean when coasting (normal) then as soon as I touch the throttle it'll dump fuel to 11.x or lower. It use to just jump down to stoich (14.7-15.0). It seems like just giving it the slightest bit of throttle, and the ECU is dumping fuel, but then on some occations it'll run lean (14-16) when boosting not at WOT. On one occation, it felt like it was about to stall when it dumped fuel as I was moving forward in slow traffic.

Also, and this'll sound odd, but I'm noticing a different vibration in the gas pedal. That's what got me intrigued at first. My car has never tickled my foot until it started to get really humid.
 
Rogue said:
it's gone way down since I noticed it running rich. I usually get at least 300mi before the light comes on. This time it came on around 280.

The AFRs are going all over the place. It'll be off the scale lean when coasting (normal) then as soon as I touch the throttle it'll dump fuel to 11.x or lower. It use to just jump down to stoich (14.7-15.0). It seems like just giving it the slightest bit of throttle, and the ECU is dumping fuel, but then on some occations it'll run lean (14-16) when boosting not at WOT. On one occation, it felt like it was about to stall when it dumped fuel as I was moving forward in slow traffic.

Also, and this'll sound odd, but I'm noticing a different vibration in the gas pedal. That's what got me intrigued at first. My car has never tickled my foot until it started to get really humid.
Click to expand...

It's all the pollen in the air. It's making her sneezy...

I'm curious if it will clear up in the next few days, since the rain is allegedly moving out and we're going to get cooler temps...
 
i talked to one of the "motorheads" here at work and he suggested it may be a vacuum leak or a faulty MAF
 
humidity and barometric pressure are things that changes the tunning of cars, since like Chopstick said, water molecules will replace air molecules and our engines has no sensor to compensate for that....it will most likely run richer.

barometric pressure will most likely shift the efficiency of the turbo.

here in PR, high humidity island, all msp go lean as it enter boost, it sucks...some runs will go too rich @ wot, some will run ok.
 
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well, it's been not humid the past couple days and it's been the same. Would resetting the ECU help?
 
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