New possible Ethanol conversion solution

[jn2630]

I've been pondering the possiblity of having my 4.6 stroker cherokee run on ethonal. We all know the main problem with that is overcoming the air fuel ratio problem that the computer has set. Ethonal runs at a higher fuel ratio than regular gas. I had a few ideas to trick the computer into changing the ratio:

The first thing to do is put more fuel into the cylinders. This can be done by adding a voltage regulator to the MAP sensor. They can be made for around $15 and are adjustable. This tricks the computer into reading a lean mixture and keeps the injectors open longer, making it a richer mixture.

Another is to add bigger fuel injectors, thus putting more fuel in. This can be done in combination with the voltage regulator.

There is a drawback, when not in open loop mode, the computer reads the o2 sensors and detects a rich mixture, and try to lean it back out. The engine only goes to open loop mode when at Wide open throttle, and when the engine is cold.

Here comes the inovative part: it could be possible to trick the computer to run at open loop all the time, therefor making the fuel mixture rich enough for ethanol at both wide open throttle, idol, and everywhere in between.

Could this type of computer modification be possible? What do you guys think?

[gradon]

You disconnect the coolant temperature sensor at the t-stat housing and the pcm will keep it in open loop as a safe mode(better to be too rich than too lean). Buy Bratcop's PSC1 here in the for sale section, a wideband o2 sensor w/ gauge, the proper size injectors, and you can dial in whatever ratio you want. Make sure your fuel system can handle the ethanol.

[lafrad]

If you know you are going to have a constant supply of E85 (as in, never need to switch), the BEST way to do this, without rewriting the original tune, Is to upsize your fuel injectors. finding injectors that are 20-30% larger than what you are using for the engine *as is* (so if you have 20% increase for stroker already, add another 20% on to those for E85). This works VERY well for getting all the part throttle/closed loop, AND WOT/open loop areas to be the proper fuel ratios. This also keeps your MAP sensor IN range, preventing CEL's and/or messing up the spark timing map too much.

[jn2630]

This could be a good option, but I won't have a steady supply of ethanol, and wouldn't the O2 sensor realize that it's too rich and lean it out even with the bigger injectors?

If I disconnect the Temperature gauge wire, the check engine light comes on. Is there a way to trick it into sensing some signal? Maybe a big resistor between the leads?

[lafrad]

the O2 sensors work against "Lambda", and have no idea about "AFR" when you change the carbon density in the fuel being injected, you change what the proper "AFR" is.

In this case, on a STOCK vehicle, in CLOSED LOOP, filling up with e85 is going to run 20-30% lean... the oxygen sensors will sense the lean condition and encourage an enrichment process from the ECM. inspecting the fuel trims, you will see that. Unfortunately, the O2 sensors are "ignored" in open loop, so the computer will never really sense the lean condition, and will NOT add fuel to the mix.


If you give the computer a "head start" by installing 20% larger injectors, it will automatically run very close to stoichometric in closed loop, and your fuel trims will be close to "0". At WOT, since the bigger injectors deliver the extra fuel anyway, it will be running close to "proper" without any need to fudge sensors or anything.



Just a word of advice, you do NOT want to be running the engine outside of closed loop without some form of tuning available.

[gradon]

Stoich for e85 is 9.76:1, so either you keep the stock pcm in open loop somehow or buy a standalone unit. It doesn't matter how big the injectors you throw in there, the pcm will pull the fuel out to achieve 14.7:1(until it hits ~-30% and then I guess it reverts to open loop).

[lafrad]

Stoich for e85 is 9.76:1, so either you keep the stock pcm in open loop somehow or buy a standalone unit. It doesn't matter how big the injectors you throw in there, the pcm will pull the fuel out to achieve 14.7:1(until it hits ~-30% and then I guess it reverts to open loop).

This is NOT correct.

The computer will trying to maintain the proper LAMBDA reading. The Narrow band Oxygen sensors detect free OXYGEN in the exhaust, NOT free fuel. they have no idea what fuel is being used... only how much oxygen is left over.
At idle and cruise that is a lambda reading of 1.0 (perfect stoichiometry). This is regardless of what type of fuel is used.

With Pure Octane/pure Gasoline, the AFR for 1.0 Lambda is about 14.7:1 AFR
With high Quality E85, that lambda is about what you said, between 9.0:1 and 9.8:1

If you have a "Wideband Gauge", it reads the values in "lambda", then you must tell it to convert that lambda value to the fuel afr that you are running. Most people buy wideband gauges that come Preset for gasoline, which will ALWAYS read 14.7:1 at closed loop, stoichiometric operation... if you fill the tank with E85, and allow the computer to react to it, it will start LEANER than 14.7 and then dial back in on it, eventually showing the exact same numbers as gasoline! At that point, it is YOUR responsibility to re-program the gauge for the new fuel's Lambda conversion.


This isn't just hearsay... I have run thousands of miles of E85 through my 2006 Hemi, and have several tunes dialed in for E85 on the street & strip. Its an awesome fuel for racing, and its decent on the street, if you can deliver enough of it to the engine. Everything I have said above is directly verified with experience... O2 sensors, EGT sensors, reading spark plugs,fuel economy tests... Timeslips...

If you run your jeep in open loop, it will NEVER figure out that the engine is running lean. it will run your e85 at the only fuel ratio it is programmed for: 14.7:1 for the assumed incoming air charge. if you are a running a fuel where a "measured" 14.7:1 is REALLY LEAN (like e85), you will burn valves, crack spark plugs, and melt pistons. DO NOT do that.

[gradon]

Makes sense. I'd still go with the psc to dial-in your open loop afrs.