Is the TBI PCM capable of detecting and making the correct changes to the fueling to run either type of gas? I forsee it causing big problems because a lot of stations in this area are selling E10 going by the lean condition it gives me and then sometimes I get good old unleaded and things are back on target again. There has to be a way around this other then only filling up at one station because I commute a lot and its impossible to know what they are selling when they don't mark the pumps.

 

Check this out. I hope it is helpfull. From Innovate.

Tuning Tip: Ethanol Content

We've had a few reports where users could not “nail down” their tune on the street with the LM-1. The AFR's would jump about 0.5 AFR across the WOT band even in the same weather conditions in the space of a few days. Instead of holding a tune, the engine seemed to slowly “yodel.”

Naturally the first thing to blame was the LM-1. But it turned out that the users filled up at different gas stations, sometimes filling up on gas that had 10% ethanol mixed in. As expected, when Schnapps is mixed with cars, things get a little complicated.

If ethanol (stoich AFR of 9) is mixed with gasoline (stoich AFR of 14.7) the resulting gas has a lower stoich AFR than 'pure' gasoline. As the fuel injection is tuned to mix a certain amount of fuel for a given amount of air, the resulting mixture would be leaner when using a fuel with lower stoich AFR.

This can be calculated:

sAFR = (%ofAdditive * sAFRadditive + (90-%ofAdditive) * sAFRgas) /100

where:
sAFR is resulting stoich AFR
%ofAdditive is amount in % of mass of additive (ethanol) mixed in
sAFRadditive is stoich AFR of additive (9 for ethanol)
sAFRgas is stoich AFR of base gasoline (14.7)

For a 10% mixture of ethanol to gasoline by mass the resulting stoich AFR is 14.13

So, for an engine that's tuned to certain AFR at a certain load and RPM on straight gas, the resulting (gasoline equivalent) AFR when running the mixture can be calculated as:

new AFR = tuned gas AFR * (gasoline stoich ratio) / blend stoich ratio

An engine tuned to 12.5 gas AFR will run at the equivalent of 13 gas AFR with a 10% ethanol blend. This is what these people were seeing.

Of course, when running in closed loop, the engine will run at 14.13 AFR instead of 14.7. O2 sensors (incl. widebands) don’t measure AFR, but Lambda. Lambda is defined as actual AFR/stoich AFR. It's a ratio. In closed loop part throttle the engine is just running at Lambda 1.0, regardless of fuel. The same would be true for other Lambda values when running closed loop at WOT using a wideband. The engine would run at the tuned Lambda and everything would be fine. Open loop systems would need to be retuned for alcohol blends though.

Until next time... Keep On Tuning!

Ron says: So knowing that I think it is benificial to change the commanded "stoich value" in bin to 14.13 if you are running ethanol 10%(I did). Also the switching points may need to be changed(increased?) to account for an riched A/F(I did). Possibly not neccessary but helpful.

 

That is fine and good. I understand what all that is saying and why the E10 causes a lean condition and how to correct for it. My problem is not every station sells E10 and almost none of them mark the pumps so I'll constantly be getting a mix of regular gas and E10 when I fill up. Commanding a closed loop AFR of 14.1 to me just seems like the wrong thing to do. Yes it would be correct for E10 but would make it run pretty rich on regular gas. Instead I think the better choice would be to command around 14.4 so that its neither extremely rich or lean and more within an exceptable range of say + or - 5 from 128. Understand what I'm getting at? I don't see or feel any real difference in power running at around 133-135 but once it gets leaner towards 140-150 which I was seeing under acceleration there is a very noticable lag in power.

 

Check the MAF table around that area as well. BLMs around 135 can be expected when running on E10. It sounds like it might be two slight lean issues on top of each other.

 

I thought gas pumps are required to post the formulation?

 

The one's I've seen that do use about size 1 font and put it somewhere you won't notice it on the gas pump. I noticed down in texas they actually did post on the pumps it was E10 but so far I haven't seen that in oklahoma.

 

Aaahh! So if I understand you now, you want the PCM to be able to detect the type of fuel and then adjust accordingly. Am I correct? If so, it is possible to do but it will take some serious code changes. You conld use a fuel sensor from a later flex-fuel Tahoe which measures the amount of oxygen in the fuel . Since gasoline has no oxygen content and Ethanol does, you could calculate the amount of oxygen in the fuel and therefore the amount of alchohol. You could then have a table that adjusts the stoich AFR based on the amount of alchohol in the fuel. You would then always be at the right stoich AFR setting and BLM's would stay steady. This is how the flex-fuel vehicles do it. HTH

 

Thats what I had in mind but I didn't realize it would be that complicated. For now I think I'll try targetting 14.4 stoitch and try splitting the difference so its neither way rich or way lean.

 

With Prominator one can keep 7 tunes on it. with a click of rotary switch the tune will change for the E10.bin. Or what ever other .bin one would like to run.