Anyone in the northern states with a wideband just wondering if you noticed this - all winter long my AFR's under full accelleration have been about a full point leaner than in the summer time.

I attribute this to "winter gas" which I have heard has more highly volatile compounds and more oxygenates in it. I also heard that because of the extra oxygenates even though the pump may say 93 octane it might actually be higher than this.

So I guess my whole concern is, if my car was originally tuned to run in the 11's for AFR and I am now seeing 12's at all RPM's under full boost should I worry about getting on the car?

I know it's getting warm and they will probably go back to 'summer" gas soon, but I just thought about this and figured I would look for some input. Thanks!

EVOlutionary

 

does your ems have temp. compesation tables setup in it? If so, they need to be refined. however, some variation in cold/warm weather AFR's is to be expected especially with a standalone like AEM.

 

No, I don't believe it was set up. It was tuned at 80+ degrees and has not been touched since. I guess I thought that with colder temps the air would be more dense and higher pressure seen by the MAP would correct. Sounds like no. . .

EVOlutionary

 

what are you tuned with? standalone or flash

 

No...you need to either set up those compensation tables or make a second map adding fuel across the board for winter months.

 

AEM EMS and AEM WB O2 sensor/gauge.

Thanks, I'll have to work on that next winter. Hopefully the cold is gone for now.

So no one thinks the different formulation of gas has much to do with it?

EVOlutionary

 

everytime the temp changes +/- 10-15 degrees you should be looking at your maps and making adjustments. all honestly your lucky you still have your motor. there are quite a few people that have made your same mistake thinking that it was set and that was it and boom... because they never adjusted or switched maps... get a laptop if you don't already

 

You think it’s the fuel. From my understanding, I'd say it is mostly air temp. And the octane rating will have no affect on weather or not your running rich or lean. Its sole purpose is to resist pre-ignition/detonation.

When we went off road riding, I would see people filling their bikes (stock compression, stock pipe and stock jets) with high octane fuel thinking it made a difference.
They didn't undersand that we ran high octane fuel because our bikes had raised compression.

However, you stated that when its warmer, it runs leaner. Thats weird b/c warmer air is less dense. It should be the opposite.

 

I didn't know if it was the fuel or the air, that's why I'm asking.

The reference to higher octane rating was just a side-effect from running more oxygenates in the fuel. I know octane rating alone does not have anything to do with AFR. I know when high octane fuel is necessary. I ran VP Ultimate 4 in my quad after I rebuilt the engine and upped the compression and ignition timing. It was only a few octane points higher than pump gas but had ALOT of MTBE so I had to richen up the jetting alot.

In my first post I stated that it runs leaner in the winter when it is colder. I just didn't know if that was due to the more highly oxygenated "winter gas" or if it was due to the denser air. I guess the consesnsus is the air.

EVOlutionary

 

Its the air or more spedifically the density of air.

Does the AEM have mixture tables?

 

My WBO2s change a tiny bit, but primarily because weather changes effect boost more. Cold air = more boost = possibility of leaner AFR.

 

Pressure is pressure, regardless of the temperature or type of fluid you're compressing.

PV=nRT

P (pressure) stayed the same
V (volume) stayed the same
R (universal gas constant) stays the same
n (number of moles) must go up since
T (temperature) went down....

number of moles is directly related to density...

Essentially the MAP sensor has no way to tell the EMS that the air is more dense. The combination of tuning the MAP with the IAT sensor should account for this.

Which also gos back to the MAF/MAP debate, the MAF meters the MASS of the air, so it it less sensitive to temperature fluctuations.

We don't want to turn this into a MAF/MAP debate though....

 

^ Excellent explanation. So theoretically if my IAT tables/trims (not sure what to call it) was set up correctly I would not see this rise in AFR due to drop in temp.

Thanks,

EVOlutionary

 

Dude, I'm so stupid. It all just clicked - last time I logged something I noticed my IAT sensor was malfunctioning. There is something wrong with the wiring or the sensor because it fluctuates rapidly from -100 to about 77 degrees all the time without changing.

So if the EMS thinks it is 77 degrees out and in reality it is 47, the car will run lean. Wow. Thanks everyone for helping me to figure this whole thing out.

EVOlutionary

 

Good to know you got it sorted out.....