Jump to content
Sign in to follow this  
engimuneer

GM NON FFV's have FFV Fuel Map

Recommended Posts

No, it's you who doesn't get it.  The stoichiometric ratio is different for E85 than it is for gasoline.  E85 runs at stoichiometric at about 9.8:1 air to fuel.  Gasoline is 14.7:1.  When running with either of these fuels at their respective stoichiometric ratios, the lambda value given by the oxygen sensor will be 1, but the actual amount of fuel going into the engine will be much greater with E85.

 

The computer, which sets the injector pulsewidth, knows exactly how much fuel is going into the engine.  In order to achieve a lambda value of 1, the fuel trim needs to be higher for E85.  The reality of the situation is that the oxygen sensor doesn't have a clue what fuel you're running.  It just analyses the exhaust gas and reports that to the computer.

 

A wideband O2 sensor can be useful for running at ratios other than stoichiometric, but it cannot replace a fuel composition sensor.

 

The oxygen sensor doesn't read the Air:Fuel ratios, it reads everything on a scale where Stoich = 1.0 higher is lean while lower is rich. All fuels report the same value for stoich as it is independent of the true air:fuel ratio.

 

A narrow band is the same but it cannot read anything outside of stoich.

Share this post


Link to post
Share on other sites

Example.

Gasoline stoich is 14.7:1 which has a Lambda value of 1.0

 

Ethanol stoich is 9:1 which has a Lambda value of 1.0

 

Lambda 1.0 on Ethanol is not the same amount of fuel as Lambda 1.0 on Gasoline because they have vastly different stoichiometric air:fuel ratios. But the Oxygen sensor will still report a 1.0 Lambda Value for both scenarios.

Share this post


Link to post
Share on other sites

Allch Chcar - I think the boys are right on this one. When there is one map, no true decision by ECU the cause of needed adjustments for trim (was it a gas problem or E85 is present?) then the ECU simply ramps up the fuel supply happily believing it is running E85 and no light appears because the wide band (or narrow band) is showing enviromentally correct results (near stoich). As such, under certain conditions, a gas problem will never set a CEL until fuel delivery is so poor that even the fuel called for exceeds the map/trim allowances for E85 or the O2 says LEAN.

Share this post


Link to post
Share on other sites

And I was going to ask a "dumb" question a few days ago and I'm glad I waited because you guys answered it.

 

The thing I see is without the fuel sensor, how does the engine know (I mean factually know) what fuel map to run with? And how can it adjust for E85, E70 in winter, or if I choose to run E50 or E40 which gives ME the best fuel mileage with my flex fuel vehicle?

 

My experience with loop systems, no matter what the loop controls, the conditions into the system need to be monitored in real time to maximize the output conditions of whatever the loop is controlling. If you adjust solely on the garbage or exhaust side of the system, you are too late to properly adjust and could adjust for something totally wrong (like a faulty fuel regulator). All these other sensors mentioned in our vehicles were meant for other uses other than to determine what fuel it is injesting to help it optimize the fuel settings. I know GM was planning on redesigning the majority of their engines. Maybe that is step one to bringing the fuel sensor back to be better flex fuel powerplants?

 

Just an opinion here but if and when the fuel sensor gets put back in, then complete optimization of E85 fuel could be utilized to achieve greater fuel economy than today's gasoline EPA requirements. The EPA needs to set guidelines for E85 fuel to "help" the automakers put FlexFuel back on top of the list of priorities. With all of the government help with grants to support alternate fuels, one would think the government would talk to one another to get the ethanol group to talk with the EPA and get on the same page.

Share this post


Link to post
Share on other sites

Okay then. As usual I thought I knew what I was talking about while rambling on incessantly. :D

 

And like most things that get "worried about later", making these cars FFVs may just end up buried... I sure hope this is not the case.

 

The Focus went FFV after a couple months, so it could always happen later. I am still curious if the fleet sales affect how likely it is to become a FFV. :-\

Share this post


Link to post
Share on other sites

Okay then. As usual I thought I knew what I was talking about while rambling on incessantly. :D

 

Don't worry about it.  It happens to everyone now and then.  It's a sign that you care about what you're talking about.

 

Remember,

You can run flex fuel without a flex fuel map and all the info needed comes from Oxygen sensor.  ;)

 

Of course, but there you're not dealing with EPA certification.  ;)

 

I really think, as many here do, that the EPA needs to deal with flex fuel differently.  At the same time, the fuel composition sensor really does need to come back, so that things like fueling, lean burning, and spark advance can be set more accurately for the actual octane of the fuel in the tank.  Allch's suggestion of a wideband O2 sensor would be helpful for allowing monitored rich or lean burning, but wouldn't be absolutely necessary.  It would help maximize mileage though.

 

Summarized:  The automakers could certainly be doing flex fuel better, and the government isn't doing them any favors on the certification front.

Share this post


Link to post
Share on other sites

I will say that the GM S10 2.2L in 2001 programming was absolutely rock solid for cold start, hot start, fuel recognition, and operating efficiency on E85 and anything in between---NEVER an issue with any of this EVER. And customers that had them- particularly the manual trans ones loved them on E85 and found them underpowered on gas. Only 10-14% diff in fuel consumption and HAD A REAL ALCOHOL SENSOR !

Share this post


Link to post
Share on other sites

Just reread this thread and wish that anyone interested in ethanol would! Great info, summaries & perspectives.

 

I have found that the newer FFVs can run with either the real sensor or the algorithm that sniffs the exhaust.

 

Also, the new flex fuel sensor is only $66, rather than the $300+ for the old version. Cheap retrofit and I believe many wiring harnesses still have that input available at the ECM connector, but you'd have to run your own wiring from there.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Sign in to follow this  

×
×
  • Create New...