Just a question? But if the fuel stoich is say 13.8, and the car strives for 14.7 wouldn't it take more fuel to reach the 14.7, thus effecting trims? Hope this makes sense.

 

14.7 is leaner than 13.8, so less fuel is needed

Scorke

 

^From what I understand the richer stoich takes a ratio of 13.8 to =14.7, meaning it takes more fuel per air then the our normally 14.7 unleaded gas.

 

Yes, you need more fuel.
Car is originally tuned for work with "normal" gasoline with stoich AFR = 14.7. If you use a special gasoline with a lower stoich AFR (say 13.8), the ECU at the beginning continues to inject thinking you are using the normal gasoline, so the mixture becomes lean and at the end fuel trims move to the positive side in order to correct this.
The bigger problem is on WOT, where the engine control is in open loop so it cannot compensate the "leaner" gasoline, so in WOT you go lean. For this reason, if you want to use a gaosline with a stoich AFR very different from 14.7, a tune is needed.
Just to finish, the advantage in using a gasoline with a lower stoich AFR is that, with the same intaked air, you can burn more fuel... so at the end you can get more power (admitting that the heating value is not lower than the original gasoline, but usually these special gasoline have also a little higher heating value).
Bye.

 

gas stoich = 14.7 = 1 lambda for gas

your gas stoich is 13.8 = 1 lambda for your gas

yes same 1 lambda!

the 02 sensor doesn't work on AFR, it works on lambda.

so the ECU will strive for 1 lambda for whatever fuel.

so if you use 13.8AFR stoich fuel then yes the car will be injecting MORE fuel than a 14.7AFR stoich fuel. (to maintain 1 lambda)

 

NJ - what memory addresses are you monitoring for the fuel trims?

on mine my trims never move off I=-10.94 C=-3.32..

so I wasn't sure if I had the correct addreses - even thou I pulled them from the MUT_TABLE!

 

I'm using 804573 for idle and 804575 for cruise and they seem to be pretty much inline with a generic ODB2 logger. I always tune maf scaling and injector latencies so they always change

 

I am using mrfred's xml file for mode23. He posted it in the stickied logging thred. I compared the logged trims with it to the logged trims in PCMScan and they are the same.

 

It is air to fuel ratio, not fuel to air ratio. 14.7 parts of air per part of fuel is US pump stoich. Lower numbers are richer, higher numbers are leaner.

Tephra is correct, 1 lambda is 1 lambda is 1 lambda. AFR is internally calculated by a wideband sensor by multiplying lambda read by a number to reach the AFR.

 

Yes, we are saying the same thing...
But if you use a fuel that has a stoichiometric AFR lower than 14.7, it means that you need more fuel to get lambda = 1. But, since our car is originally tuned to work with a fuel with stoich AFR = 1, then it will be lean and so fuel trims will go on the positive side to correct the lean mixture and get lambda = 1.

 

I might have to check for boost leaks as my LTFT's have drifted to +6% cruise again even with the richer injector latency settings. The only other change was to wrap the first half of the Upper IC pipe and Lower IC pipe with DEI Heat wrap which potentially could keep the intake charge a little denser and cooler. I've noticed my intake manifold temps are now within 10-15F of the intake temps which seems pretty good.

The other change tuning wise has been to increase timing by 4* during cruise load cells in the 2500-4000 range as a test to see if I get more MPG. So far that seems to be working well and quite a bit easier than trying to set lean cruise by changing the open loop to closed loop crossover to a lower load percent. If I reset my trip computer at a constant 70 mph on flat ground it reports back 30-32 MPG where as before it was 28-30 MPG. My car also likes to average ~14.9-15.0 AFR in closed loop already so it's already running a little leaner than 14.7 AFR.

 

28-30mpg!! Drafting what, an oversized mac truck? That's insane (at least to me haha)

 

Thats interesting.... i'll have to try that!

 

To take the cold start mostly out of the equasion I reset the MPG computer after it was about 3 minutes into the drive and I managed 28.6 mpg with normal driving according to the screen. It was a 10 minute trip with rolling hills and speeds between 65-75 mph with cruise control on. I'm prety sure I can hyper mile the entire trip around 70 mph and do even better than cruise control since it is just shooting for a set speed and will climb into low boost to maintain it.

I was planning on testing the advanced timing and lean burn cruise but HB Speed said most gains could be had from timing alone. I have no idea how much is good (or safe) but decided an extra 4* should be a good start as a test. I torqued down a few IC pipe connections a few more cranks and reseated my Airflow sensor connector "just in case" and now my LTFT idle and cruise are both around 1.3-1.5 after a drive which seems fine. I'll have to see if it drifts again like it did before since when it does it drops my mid 11's AFR's at WOT down to low 11's.

 

cold start is a **** for fuel consumption.. really need to see what I can do about that