It doesn't use the AFR MAP values as its target trim points though. You can set your cruise AFR's to 7.9:1 and your trims won't change. There has to be a closed loop table somewhere for the ECU to base its +/- trims off of, cuz its definitely not trimming from the AFRMAP values.

 

The ECU does use AFRMAP in closed loop, but AFRMAP is not always derived from the fuel table(s).

 

Thanks...

It's still muddy, but less muddy.

I've turned off closed loop and I'm running full open loop at 16.8. I'm expecting some MPG improvements. Will report at next fill up.

 

Elaborate if you can.

 

man...my fuel economy tune went to SH|T with my cam install lol

 

Whassup?

My first tank of fuel (E85) with open loop idle and cruz at 16.8 and my mileage DROPPED from 14 to 12mpg. All of my driving is in town - no highway or freeway driving at all. Does this mean that for me open loop is a bad idea? I don't see how I could be doing this wrong? Ideas?

 

Did you monitor AFR while driving to see that its holding at 16:1 or better during typical daily driving? How much more throttle do you need to accelerate and hold steady cruise with 16.8:1 AFR?

 

E85 will automatically reduce mileage by about 30%. You have to realize that you are using gasoline scaling for a fuel with a much lower stoich value. That 16.8 on E85 is probably more like 11:1 with the correct scaling.

 

Touring, wouldn't that depend on the WB you are using? The LC-1 measures in lambda and converts to gasoline or whatever scaling you want.

 

yea but what your reading is AFR, hes saying that a 16.8:1 may be lean for gas but not for E85, hes saying in E85 its more like an 11:1, MrFred would probly be able to give you some tips, im just gunna mention to you that you have 272/272 cams...your fuel mileage is going to be crappy either way, i was getting 25+mpg city before i switched to my cams, im in the process of getting it back onto full open loop since the loads all changed with the cams i have to redo it

 

Yes, it would depend on the settings you're using with the WB. Most people keep the gasoline scaling on the LC-1 because it's familiar. A lean cruise on gasoline is ~16:1 which would be ~11:1 if the WB were scaled for E85.

16:1 would be ~1.64 lambda on E85 so if Jim did rescale the WB for this data his engine would likely melt.

 

No, I'm saying that 16.8:1 on E85 using a gasoline calibrated WB is actually ~11:1. this would be reflected if the WB were scaled for E85. Either way it's lean ... about 1.14 lambda in either case.

Back to the original post I quoted ... I may have misunderstood. When you say your first tank, do you mean your first tank of E85 or your first tank of E85 with the lean AFR? The variance you're seeing could easily be your driving habits ... especially with city driving. Accelerating from a stop puts you in to boost and out of that lean zone you've defined, which of course burns more fuel.

Honestly, the only was to see the difference would be to take it on the highway for about 80+ miles and then compare. Your speed and throttle will be much more constant and take most of the variables out of the equation.

 

AFR is just a scaling factor applied to lambda. Lambda = 1 is stoich for any fuel, and any scaling can be used as long as we know what scaled value represents stoich. Hence, most people are using gasoline AFR for E85 because its convenient. 16.8:1 gasoline AFR read from a gasoline scaled wideband will always be leaner than stoich no matter what fuel is being run.

 

So far on the hwy I am almost getting close to the same mileage I did on 100 octane.

Around town I am currently only getting 3mpg or so less.

This is on E85

Running closed loop idle/cruise.

 

I confused the matter. This is not my first tank of E85. Been on it for a couple months.

This is my first tank of E85 using open loop idle and cruz. My mileage did the usual drop from 17/18 to 14/15 when I went from gasoline to E85. Now it dropped to 12 with open loop idle and cruz.

I don't have a wideband. Yes, I know. I do have my CEL flash-on-knock set to 2/4 so I can closely monitor knock.

I don't think I'm using any more throttle. In fact the extra timing makes it feel snappy-er.