Monday, September 22, 2008

What's different about the Ecotec FFVs?

Found this:

Hardware changes for flex-fuel operation are limited to the injectors. Because ethanol has fewer BTUs (less energy) than the same volume of gasoline, more fuel is required to produce the same horsepower at wide-open throttle. Flex fuel engines use unique stainless injectors with a greater cone angle and higher maximum fuel-flow rate. The fuel rail matches the injectors, but it’s manufactured of the same stainless steel used for all 2.2L I-4 fuel rails.

The flex-fuel 2.2L doesn’t require a special fuel sensor. The first flex-fuel engines used a light-reactive sensor to measure fuel composition from 100 percent gasoline to 85 percent ethanol. The 2.2L has a virtual sensor—software programmed in the E37 ECM with no separate physical sensor whatsoever. Based on readings from the oxygen (O2) sensors, fuel level sensor and vehicle speed sensors, the ECM adjusts the length of time the fuel injectors open for the type of fuel used. Within a few miles after filling up, the E37 controller determines what fuel is powering the 2.2L I-4 and manages the engine accordingly.

I'm really beginning to thing that flex fuel vehicles are just regular cars with higher flow rate injectors!


Anonymous said...

I think the other side to the FFV that is toughest for a street tuner to deal with is the ECU. The injector side is easy on many vehicles with good access but the FFV ECU seems to actually use a higher fueling rate map on cold start, warmup enrichment, and open loop WOT. Since in each of those the 02 sensor is not in loop then the base open loop map can be a concern on cool mornings (or at WOT if injectors are not scaled up 30%). Guys who have upsized injectors sometimes still have some cold morning longer crank times.

A guy I have met proposes to optimize a car for E85 with higher compression and a higher power ECU which would no longer need any fuel maps- sometimes just more operating sensors- this could be the long term answer to this current ECU problem.


buzzcut said...

My suspicion is that there is a relation between open loop fueling and LTFT. The map is scaled up. That's why I'm not having any problem starting on E40+.

Now, really cold days will require more cranking, no doubt. I've seen this once myself, when it was 41 degrees outside. It would be nice to have something like hptuners, to be able to add more fuel on startup.

Sadly, hptuners is not compatible with the 2.0T. They do cover the Aero V6, strangely. And the GDI 2.0T in the Solstace.

Anonymous said...

I think you are right on open loop relating to LTFT on many vehicles. Some of these vehicles seem to have a learn feature in applied in open loop and it is likely this is a LT trim application.

The guys that report long crank times on cool/cold mornings are running straight E85- it does not take much gas to eliminate this cold start issue. Most say 1-2 gallons of added gas in a tankful of E85 eliminates it altogether.


buzzcut said...

Phil, on the way to work this morning, I set the scangauge up to show open/ closed loop and LTFT.

Then I nailed it.

It went into open loop, and it was still showing LTFT numbers. They went from 19 and 20 in closed loop to 10 and 11 in open loop.

I'm pretty sure that LTFT influences open loop operation. The only question is if it is enough to start the car on E85 on a very cold day.

My car is garaged, but it still gets below freezing out there on some winter days.