I guess I should have mentioned it but I forgot on my last post. The 6.5L engine is diesel
Adding a bit more to this. I ended up going 300 miles today in the van. I found a killer deal on craigslist for a 94 G20 non turbo 6.5L 2wd Diesel van with really low miles and a blown tranny for $750 cash. So I had to fill up at some random gas station. But, that last tank of E0 even with probably 100 miles of doing 70+mph I still ended up overall at 25mpg. I had to go a bit faster since I had to get there before they closed and I got there 5 min to closing.
So my conclusion is that OBD1 systems really can't adjust any better than a carb for E10 and will probably drop 15-25% in mileage and a bit in power. Some new cars don't like it and some don't care, it is hit or miss and on newer cars I think it really varies depending on driving style a lot more.
Most OBD1 systems can only adjust the fuel about 10% one way or the other. With E10 I noticed mine pretty much always stayed pegged at adding more fuel and it was more or less close with the fuel mix that way. One interesting thing I saw was lower TPS and MAP readings across the board with E10 compared to E0. Not sure what that is from other than it is probably a bit from the Oxygen contained in the fuel somehow and more gas going into each combustion event so it is making more power with less air. The disadvantage I see from that is you are increasing pumping losses.
I guess one thing to try would be to increase EGR flow by about 25% or more to compensate for it. I can't change mine since the EGR valve is bad on the van and I just disabled the EGR from the computer. If I can reach back to it with a hammer I might beat on it and see if I can get it to move again.
I figure anyone running an obd1 system with E10 isn't going to hurt anything on the engine and there isn't much advantage to just retuning the spark and VE tables. So best thing would be to just leave it as is unless maybe adding EGR flow or forcing it to lean out on lighter loads would help. I don't really want to put the wideband O2 back on it or drill and mount an EGT sensor so I probably won't do much more experimenting on mine.
And one more point to confuse everyone... My bike is a DR650 650cc air cooled low compression carbed bike that gets less power and mileage on E10. The Hyosung GV650 650cc water cooled carbed high compression bike that went with me to Cali and back gets very slightly better mileage on E10
But then again it isn't stock and is tuned rich since it is more for power than mileage.
I hope the trolling goes away in this thread. I really would like to get my mileage back to the old numbers. Either by washing gas or retuning. But the noise in this thread makes it hard to get anywhere.