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HOW DOES THE ECM HANDLE DIFFERENT FUELS?

my 94 nissan sentra has been running on reqular unleaded fuel for many years and now my favorite fuel station is only supplying gasohol.

first, take the extreme as an example: regular unleaded has a certain number of BTUs/gallon and supplies this finite amount of energy in a gallon of gas. then consider 100 percent ethanol, which has significantly less BTUs/gallon. at highway cruise speed, a certain amount of energy is needed to maintain a fixed cruise speed, lets say 55 mph. would the ECM detect the lower energy fuel and adjust each pulse of the fuel injectors to deliver more alcohol at a fixed cruise speed of 55 mph, than it would for regular unleaded, thereby meaning i get less MPG with ethanol than with regular unleaded fuel?

now to the real situation: if the ECM adjusts for different energy fuels, then gasohol with

90/10 regular unleaded/ethanol would have between 3 and 4 percent less energy per unit than regular unleaded and therefore get corresponding less MPG.

my calculations suggest (unless i am missing something) that i can pay (at today's price of 387.9 per gallon) about 12 cents per gallon more for regular unleaded (than for 90/10 gasohol) and get the same energy (MILES PER DOLLAR).

SO, MY QUESTION IS: HOW DOES THE ECM HANDLE DIFFERENT FUELS?

Reply to
nucleus
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Your Sentra isn't designed to run on E-85 or any other gas/ethanol mix over 10% ethanol. The seals, fuel lines and other assorted bits will break down when used with fuels containing ore than 10% ethanol. The computer isn't designed to adjust for anything but knock, which is a function of octane. Lower the octane, the spark will be retarded and the engine will survive. Increase the octane and the spark will advance to the setpoint and the engine will run fine. Use plain old regular unleaded. You won't see any increase in performance or mileage from using premium. Use E-85 at your own risk, as it WILL cause harm to your engine eventually.

Reply to
No

No wrote in news: snipped-for-privacy@news.easynews.com:

the standard ECU adjusts fuel by measuring the oxygen content of the exhaust,BASED ON GASOLINE AS THE FUEL. it will tolerate up to 10% ethanol(E-10),with a slight decrease in mileage.

The ECU/O2 sensor system is only calibrated[programmed] for gasoline. Mot for E-85(85% ethanol+15% gas)

To use E-85,besides the seals,fuel lines,mechanical bits,would need a new programming map to deal with a different fuel,and a system to measure the feul makeup to deal with a variety of fuels(flex-fuel).

I've heard that most pump gas sold in the US today is actually E-10,and there should be a label on the pump or signs posted to that effect.

Pumps for E-85 should be clearly labelled,but are not common around the US.

Reply to
Jim Yanik

Jim,

He has a '94 Sentra.

It's not OBDII.

Reply to
No

I doubt you'll find regular unleaded in the same staion as one selling oxygenated (10% ethanol) gas. It will usually be one or the other, not both.

You should see a very slight (if at all) difference in mileage between the 2 with straight gas being better than 90-10 ethanol.

Just avoid putting E-85 in it, no matter how much the price makes you want to.

Reply to
No

A remap (K adjust for fuel/injector size), high flow fuel pump and bigger injectors are required to run E85. May be issues with cold starting requiring 2-3 cranks.

An Irish owner of a 200SX turbo (240SX S14a body with a SR20DET) has run 100% E85 with a remap for a year.

Only way to accommodate a flex fuel setup on a stock ECU is to have switchable maps, the upper address lines of the ROM are switched to set map. Create maps for various %mixes and select the one nearest to what you are running. Up to 8 maps have been done on 1Mbit ROM chips. It would be lots of bother working out what mix was after adding 5gall of unleaded to a part tank (estimated volume of fuel) of E85 and even worse for adding fuel to a part tank of previously estimated E85/unleaded mix.

Only worth doing in countries with a large price differential. France

- 98 octane fuel is around 1.60?/L, and e85 is from 0.80 to 0.95?/L. Sweden also has cheap E85.

Reply to
Peter Hill

No wrote in news: snipped-for-privacy@news.easynews.com:

So what? OBD-I still uses an O2 sensor to determine fuel/air ratio. and still based/calibrated on gasoline.

OBD-II is just extra sensors,primarily to check emissions components for failure.

Reply to
Jim Yanik

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