E85 fuel map.

[Mr Gadgets]

I am interested in using E85. I purchased a GM flex fuel sensor and had it in line with my return fuel and enabled the Flex Fuel option.
I found the sensor was intermittent, at times it would go from 7% to 0%. I realized I could not trust it, so I removed while testing the engine on the test stand.

The motor will be boosted and I dont feel I can trust the sensor to give me a true reading while under boost, 100% of the time.
My question is this. Can MSII be setup to sense the fuel mix and adjust the VE table and all other parameters, then be left at that setting until another sense is taken? GM has removed the sensor on the newer vehicles and I was told that when you fill the tank, the computer knows it, and senses the fuel, then locks it in. Not sure if that is true, but I would like to be able to sense what is in the tank, and then when in boost, not let a sensor make changes.

I can attempt to run on E85 all the time ( hence, one tune), but the availablity in my area is not very good. This motor will be in my boat and once on the water, it is 40 miles or so back to the pump. If I need to mix more fuel, it would make changes and then run rich.. I would like to avoid that.

Another option might be to run a gauge on the dash to sense the flex fuel and then manualy change the VE table or msq's to accomodate, but that seems like a poor solution.. It would be nice to manually sense the fuel and have the MS make changes then lock it in, until the next fuel load. My tank is 100 gallons, so it seems the mix would stay consistent until the next fill.

Any ideas on how to deal with the changing content of the fuel??

Thanks!
Dick

[devastator]

It seems you have a problem with the fuel composition sensor, (flex fuel sensor), and not the fuel mixture changing in the tank. The best solution to your problem, IMHO, is to get the sensor working properly as it will do all those things you want it to do. Have you tried putting the sensor inline with the fuel supply to the pump instead of the return line?
If you tune your engine for E85 and have to put straight gasoline in it, you could have a separate MSQ stored on your computer for this, as well as one for 50% gas and 50% E85 mixed. But, again, the flew fuel sensor should take care of this if you get it working properly.

[Mr Gadgets]

The problem I have is I don't trust the sensor. I watched it jump to zero at an interval of maybe 20 times in a minute. They say it will fail and go to 170hz. But it was jumping from 7% to 0% constantly. That would pull the timing offset in and out. That is how I found it, watching the timing jumping around.
The size of the lines wont allow me to install it in the main supply line. I need to support upwards of 1200hp and the 5/16" line on the output of the sensor is way too small for that.
My concern is, if I get a new sensor or fix this one (people have mentioned that washing it with dry gas will help when a sensor dies), what if the sensor looses power? It can't put out 170hz then! If that happens for a split second at 12psi boost.. the motor is junk.
It is installed in my return line which is just a bleed line for my dead head style of fuel psi regulator. This regulator is required for the type of pump I am using (racepump.com) and it uses an orfice (I believe .040") to regulate the amount of fuel bleeding off. I installed that orfice inline after the sensor. That would keep the sensor full all the time and it seemed at first to work fine, then the jump to zero % started to happen. At that time I did not have time to look into it. I was chasing other gremlins.
I am working on a replacement circuit that I can manually insert a square wave to the MSII, that would represent the amount of ethenal in the tank, which I will read by the sensor on a gauge. Then adjust the circuit to give me what the gauge says. That would be a constant and I would not rely on the sensor to control the fuel map.

Thanks
Dick

[devastator]

The size of the lines wont allow me to install it in the main supply line. I need to support upwards of 1200hp and the 5/16" line on the output of the sensor is way too small for that.

You could add an extra, low pressure, fuel pump, with a continuous loop back to the tank, and the sensor inline. This way you'll be sampling the fuel while the engine is running and the small line size won't affect your fuel flow.

[Mr Gadgets]

The bleed off return supplys a continious flow back to the tank. So I do have constant fuel flow. Whether or not it is enough, or my sensor was defective, is the question. I never got a chance to work on that problem. My first reaction is that the sensor is bad. It would show a constant 7% with regular gas going through it. Then just jump to zero and back to 7%. They say that when they fail they go to over 100%, or actually 170hz. But in this case I did not see that. I saw it fail in the opposite direction, which I can not tolerate at any decent boost level.

Even if the sensor was working 98% of the time, it still would not be a good fail safe situtation. I think another circuit with adjustable output would be more reliable than the sensor reading the fuel content. I will still have the sensor and read a gauge, then set the extra circuit to put that amount into the MSII to control the fuel map. It would be great to input a signal to set the fuel map and then create a map that stayed at that level and remove the flex option, running on the new map, until the next fill up where fuel content could be checked and a new map created. That would give a safety margin that would eliminate the possiblity of sensor failure all together. Not that I want to remap every fuel fill. Being a boat, it would be part of a routine. Load up the boat, to the station, fill up, check the E level and remap.
I suppose it could be done with 100 different maps and just input the correct one. But it would get to be a bit tedious..

[devastator]

Actually, you wouldn't need several different VE tables. You could just change the Req_fuel setting or increase/decrease the entire VE table at one time. MT has built in calculators that will shift the entire table by a certain number or percentage.

[Mr Gadgets]

That is true, didnt think of that. But your right, I could use the Req_fuel. I wonder if the fuel map or Req_fuel shows a change as the input from the Flex sensor changes?? That would make it easy to track and I could figure out how much change would be needed.
Thanks for the thought.. I will ponder it.

Dick