Finally, I have success running E85 AND Gasoline as well as any mixture in between on the 7730. It was not hard to do an runs beautifully. With the 7730 all the enrichments are based off of lambda or the stoichiometric air/fuel ratio. The 02 sensor will always cycle lean/rich at whatever air/fuel ratio you are running. Here is how I got everything the way I wanted. First I did a little research to find out what the stoichiometric air fuel ratio was for E85. I found the theoretical number to be 9.77:1. I know gasoline is 14.7:1. Typically this means that the computer needs to target one or the other for the fuel delivery. I wanted to be able to run either fuel from whatever pump without any extra sensors. My theory was to split the difference and allow the long term fuel trims BLMs to make the broad adjustment. I first ran the engine on E10 gasoline with the stoichiometric air fuel ratio commanded to 14.1:1. I tuned the VE tables in open loop to deliver 1.00 lambda under normal conditions and .85 lambda under WOT. Next I ran the tank down nearly empty and filled it with E85. I commanded the air/fuel ratio to 9.77:1. To my surprise I was still running right at 1.00 lambda at part throttle and .85 lambda at WOT across the board. I then enabled closed loop and tweaked the 02 sensor target voltages to give me right at 1.00 lambda in closed loop. I found on E85 that the AE/DE were slightly lean, so I increased the AE by 1/2 the % difference in the gasoline vs. E85 stoichiometric air/fuel ratio. That is an increase of approximately 25% across the board. Knowing the VE table stayed right about the same was HUGE. This allowed me to command an air fuel ratio of 12.23 which is right between E85 and Pure gasoline. I then went in and changed the allowable BLM values for both running and stay-alive to allow for a range of 85 to 192. This covers the required fuel for any mixture of E85 to Gasoline. The end result is I have run atleast a dozen tanks mixed anywhere from E10 to E85 with NO driveability issues at all.

I did a little research and found that the timing requirements between gasoline and E85 are very much the same at idle, near idle, and under moderate load. At WOT the E85 likes about 6* more timing. I added 6* to the gasoline timing table across the board at 100 KPA. I tapered it off 1* per 5 KPA MAP decrease down to 70 KPA where it is identical to the gas table. I then changed up the low-octane retard calibration so that it could pull 12* instead of 6* and pull 6* base. In this heat, running on gasoline the ECM due to high knock sensor activity, reverts to low octane mode which retards the timing 6* over 70 KPA MAP. From there the knock sensor activity dies off. The ECM resets the low-octane retard logic every startup and remains in low octane mode until it is shut-down and restarted.

I get 17 MPG on E85 ($3.20/gallon) and 19 mpg on 93 octane E10 (3.95/gallon). The difference is negligable at best. The E85 gives more power so to me it is worth the fuel economy loss.

I ran my last dyno emissions test this year on E85 and quite literally blew less than 10 ppm in EVERY category, CO, HC, NOx, thats just about as clean as it gets folks.

 

Interesting!

Good writeup.

/N.

 

really wish i had E85 here.


just spend a week up in CO and found it for 2.99 and just happened to rent a flexfuel minivan. was nice and i didn't notice as much worse mpg as i've read either.


good write up.

 

Thanks, when the time comes I will
try it

 

Nice work. It is amazing how much an ECM will automatically adjust.

RBob.

 

Now if you had a wot spark advance vs afr table like $3A has you'd really have the whole field covered. Good work, man!

 

IMHO if you built an engine with the higher compression that is possible with E85 and tuned properly you should be able to get better mileage than pump gasoline, more power and lower operating costs.
I dont have a practical source here for E85 here, but I'd do it in a minute if it were available in this area (Vancouver Washington/Portland Oregon).

I was reading someplace recently that E85 is a lot more tolerant of leaner mixtures (way beyond stoich) than gasoline is. And thus some people are running E85 at E10 ratios for part throttle and cruise conditions. This gives me some interesting ideas for engine combo's.

Have you observed the same tolerance of mixture ratios that I have read about?

 

I have been a firm believer in closed loop for years even when others would say "go open loop" when one couldn't get an engine tuned right in closed loop. I think closed loop is the only way to go............except for at idle and WOT for a limited few engines.

The way you tuned for E10 and E85 is OK by using half-and-half tables. I think you would get "near perfect" MPG and HP if you installed a WBO2 as the closed loop O2 sensor and installed a switch on the dash to toggle between E10 and E85. Could even use two switches (E00, E10, E85, E10/E85 mix).

The 730 ECM you are using has many unused switch (logic) inputs. In the code, switch tables when the switch is on. The 730 memory has lots of space for code and tables.

 

Nah, a BTU is a BTU. Gas has more energy and therefore better MPG.

Everyone tries to beat the theoretically possible MPG. That fact is that weight, wind resistance, and BSFC determine MPG. When people post MPG for a vehicle I don't pay much attention most of the time because no one posts the weight, the plug color, the oil temp., etc.

You can run an engine lean and deal with it surging for so long with high oil temps.......and then it breaks, but it will give great MPG. Now a days it is almost worth it to hole pistons and hammer oil/bearings than pay for fuel.

 

Did you do any mods to the fuel system components?

 

Ethanol seems to be more tolerant of running lean, so this is why people are getting better highway MPG with it. Stoich-for-stoich, yes, gasoline will win, but ethanol seems to allow ultra-leanness without internal meltdown.