E85 Tuning- Base AFR vs. ECT question

[garyd02gtp]

I am going to switch my 2002 gtp to E85. I have read all the posts about using E85, and one thing is still not clear to me- maybe you guys can clear it up....

I am putting in 60# injectors- Flow Rate vs. kpa will be adjusted to them
I will change my Stoich AFR setting to 9.85

Question is- do I need to change the PE Base AFR vs. ECT table to reflect the best AFR for the e85 (6.9 to 7.2) or do I leave it at best gas settings (11.0 to 11.5)???

The scanner, I assume, will read as if it were still gas and tune from there, correct???

And please no arguments as to skewing IFR vs. changing stoich- THANKS

[sikhabib]

you might have to adjust pe slightly to fine tune but you pretty much just leave it as is.
instead of thinking afr think lambda, When the pe table is set to 1.13 its not really commanding an afr of 13 its commanding 1/1.13 = 0.88 lambda which for normal ulp is 13afr. when you running e85 it is still commanding 0.88 lambda but afr will be 8.7

[garyd02gtp]

Thanks

[passingpower]

For your initial setup, leave your PEvsRPMvs TIME table as it is or use CCB's Vrooom table. Your open loop Base AFRvsECT should be set to E85 best torque particularly at your thermostat temp.

[garyd02gtp]

these are 2 different answers....

I did not know what sikhabib meant by leaving it at 1.13 (think that is V8 stuff) In my PE Base AFR vs. ECT it is shown as AFR (11.0, 11.2, etc.)

passingpower- you are saying that I SHOULD change my Base PE AFR vs. ECT to 7.x or whatever, not leave it at 11.2 like it is for gas


Correct- Screenshot???

[passingpower]

That’s right.
We’re discussing three tables here; you were asking about the Base AFR vs. ECT table. That’s a two dimensional table which establishes the base ratio that is used as soon as the PE Enable TPS condition is met. In (many) V8s it is an equivalence ratio meaning, its value is derived from the Stoich AFR value. On our V6s, it is a true air fuel ratio and commands the ratio you specify at each coolant temp. listed.
Sikhabib answered your question by telling you how V8 tunes establish PE AFR using the EQ Ratio vs. RPM table.
We also have a three dimensional PE Fuel Adder vs. RPM vs. Time table. That table describes how the abovementioned Base AFR should be modified even further under SUSTAINED open loop conditions. For the V6, this table ADDS a negative number (subtracts) from the Base AFR. It does not divide anything as in the V8 world. In several Stock V6 applications that table is sufficient for basic tuning. However, some of them (I’ll say it again here) are so fugly that only the EPA could love them. If you want a table that you can predict its performance, use ColoradoCoolBreezes’ VROOOM table. Google ‘Open Tuner Notebook’ for the description. BTW, view ALL write-ups with a skeptical eye. Read several of them and find a consensus. Then, ask yourself, how does that apply to MY engine? Use the search function here as often as you can (I can’t stress this enough). Finally, post questions here for the latest tuning techniques.

[Chuckg]

Hope no one minds me digging up an old post.

I'm preparing to tune for E85, and this post has some interesting info. I've already got a fuel-pump rewire, and 60lb injectors. Even have a fuel pressure gauge so I can keep an eye on the fuel pressure.

It looks like the most common approach to E85 tuning on GTPs is to just screw with the IFR table, but I'd really like to do it the "right" way as long as I know others have gotten it to work. Seems like I should be able to get to all the AFR tables that are needed (but I am using the "other" tuner, along with Eddie's sweet Tiny Tuner that has opened up a ton of tables).

[02bluegt]

Some people say to change the Base AFR, but that isn't a good way to do it, this is why:

an 02 sensor is a stoic sensor, 500 mv is stoic for most fuels that can be burning in the IC engine, so the 500 mv on gas is 14.7, but the 500mv in E85 is the 9.xx.... the best way I've seen is to lower the injector table by 30%, so you're dumping 30% extra fuel, this will correct the fueling throughout the entire range

[Chuckg]

I really don't see the logic in that argument...

The 14.7 Stoich value for gas, or the 9.86 Stoich value for e85 really have no connection to the O2 sensor readings... The O2 sensor tells us how well all the fuel has combined with all the O2. So regardless of how I have the AFR set in the bin file, the O2 sensor reads the O2 level the exact same. If it sees too much O2, then it knows we are lean. If it sees too little O2, then it knows we are rich. The O2 sensor will read 500mv when at the ideal stoich mixture, whether the car is burning pure gasoline, E10 like most gas these days, or e85. Each fuel has it's own chemically determined Stoich value.

The 14.7 value doesn't effect any part of the O2 sensor calculations, it's only a number that drives the cars calculations when it tries to calculate how much fuel to inject for the amount of air that is coming in while in closed loop.

[Chuckg]

As I mentioned, I really believe the old way of tuning for E85 by adjusting the IFR by 30% was because we could not get access to a bunch of the other tables with the older tuners. But with some of the newer tools exposing more and more of the fuel tables, I think we should be able to tune it right.

The first tables I found and adjusted:
Base Fueling, Closed Loop Desired A/F : set to the 9.86
Base Fueling, Open Loop Base AF By coolant temp : set around 8.5 or so, this table normally has values around 13 or so for gas, so the car expects to be a little richer than normal.
PE, Base PE A/F: starting with this around 8 to get the a/f down into the max power values.
PE RPM vs Time A/F : the values for gas drop a bunch over time to keep things cool under sustained PE mode. Less drop should be needed for E85, but tuning will show how much.
Base Timing AFR Spark table : normally this adds timing as the AFR drops lower and lower... but it's bottom end is 9.7, which we're just about under already with closed loop E85. I ran this table zero'd out completely anyway even with a gas tune.

Those changes were my first E85 adjustments. Then before I restarted it, I could see that the commanded startup AFR was 5.8. Thats when I found the "Startup A/F Adjustment". This table drops the AFR some amount based on temp... For gas, this was dropping the AFR by 2.x at operating temps. That was dropping the gas open loop AFR of 13.x down to around 11.x, still in the normal good range of AFR for gas. But for E85, it dropped my 8.0 down to 5.8, way under the E85 max rich of 7.34.

So add the "Startup A/F adjustment" to the list of tables that need tuning. I set mine to drop the startup AFR by .5 around normal operating temps. I'll make it get a little richer to deal with the colder morning starts that can sometimes cause trouble with e85.

I'm using "that other tuner" along with the Tiny Tuner app. Without the Tiny Tuner app, I couldn't get to most of the tables I'm adjusting. So I can see why the "30% injector" adjustment was the way to go.

[GTPpower]

X2^^

With HPT, you pretty much have to add 30% to the IRF table. If you try to change stoich to 9.8, the open loop startup is still commanding leaner, and it starts/runs bad for awhile.

If you have a PT, you can fix that problem though.