Okay, so I got 465 miles on my last tank (I think it was 10.9 gallons), and that was 45 miles after the light came on. I was nowhere near the 2 stations that have E85, so...

I filled up with 87 octane. Not quite as snappy as the 93. We'll see how the mileage goes. For what it's worth, the CEL (lean condition) is still on. It might take a while for that to go out.

Oh, and the last tank was pretty good as far as engine response. About like 93 octane fuel.

 

Don't clearing the code keep it from coming back on because your back to regular gas?

 

Yes, but I want to see it go away by itself. That will tell me there's nothing wrong with the injectors. After all, there is the very slight chance the E40 loosened up crud from the fuel tank and clogged the injectors.

 

I Hope it does, Its interesting that your car runs better with 93 plus. I doubt that E40 loosen up crud in your tank, but might be in the E85. Have you checked the fuel filter? I would think it would clog your filter first before your injectors. Ethanol is corrosive but seems not effect your injectors, If it did you would know already. Take a look at https://www.fitfreak.net/forums/1st-...e-stutter.html

 

Okay, the check engine light went out yesterday, when I bump started the engine. Interestingly, I got 2 exhaust backfires in very quick succession at the same time. I think they were caused by unburnt fuel charges hitting the hot converter.

This probably means the computer doesn't like having to adjust to different ethanol mixtures. As I've seen pointed out elsewhere, some ECU's are very strict about how much adjustment they'll tolerate in the fuel trim before triggering a light.

Fuel economy seems about the same so far, but I really don't like the lack of enthusiasm in the engine from the 87 octane fuel.

 

This should explain the power difference.

Honda Knock Control
Honda knock control is designed to cope with different quality fuel in a stock engine. It is important to remember these design parameters when tuning the knock control to suit your engine.

The knock control method Honda uses can seem complicated, but it helps to understand how an engine is tuned from the factory. All tuning is performed on an engine dyno using an automated process which tunes every location in each table. For VTC engines this includes each cam angle table as well.

1. Using a (very) high octane fuel, the engine is tuned to find the ignition timing which makes the most power. This is called 'mean best torque' (MBT) ignition timing.
2. Using 100 octane (RON) fuel, the engine is tuned to find the maximum spark advance before any knock is likely. This is called the 'knock ignition limit'.
3. Using 90 octane (RON) fuel, the engine is tuned to find the maximum spark advance at this octane. This gives the low octane knock limit ignition advance. The reason 90 and 100 octane is used (approx 85 and 95 octane r+m/2 method) is because this is the likely range of fuel octane the engine will used with.

An example graph showing ignition timing for a single rpm point:


The normal ignition tables contain MBT ignition advance values (black line above). An additional table contains the knock ignition limit values (blue line above). It is possible for the knock ignition limit to be lower than the MBT timing. In this case, the ECU will use the lower of the MBT timing and knock ignition limit timing so that the engine will make the most power possible, but will not knock. eg at 80 kPa manifold pressure the ignition table contains 30º, but the most timing the engine can run is 28º (from the knock ignition limit table). Thus the ECU may run less timing than the ignition tables at certain load/rpm points, even if it does not detect noise from the knock sensor. Note that this will not show as 'knock retard', as the ECU considers this to be a 'no knock' condition.

Actual ignition timing used (green line):


The ECU has the ability to retard the ignition further if it determines that knock is occurring. From the amount of knock sensor noise, and knock sensitivity, the ECU adjusts a 'knock control' ( or 'K.Control') variable. Nominally the 'knock control' contains the estimated fuel octane, as a percentage of the difference between 100 and 90 octane. eg a value of 0% means the ECU considers the fuel 100 octane or above, a value of 25% means the ECU considers the fuel to be 97.5 octane. The K.Control is dynamically adjusted at a fairly slow rate while driving.

If K.Control is greater than 0% and the maximum ignition timing is less than the MBT timing then the difference between the knock ignition limit and maximum ignition timing will show as a knock retard value.

Actual ignition timing used (green line) with a knock control of 50%:

The ignition timing calculation is:

Ignition advance = minimum(MBT Ignition, knock ignition limit - (knock retard x knock control))


Knock Tables

Knock Ignition Limit Tables

The knock ignition limit table contains the maximum ignition advance before knock is likely. Note that this value is relative to the ignition table. A positive value indicates that the knock limit is higher than the (MBT) ignition table value; a negative value indicates that the knock limit is lower than the (MBT) ignition table value, and normally the ECU will retard the timing by the negative value.

Caution should be exercised when changing the knock ignition limit table - if any negative values are increased (ie made closer to zero or made positive), then the ECU will advance the ignition by that amount.

Knock Sensitivity Tables

The knock sensitivity tables set the amount of noise from the knock sensor which the ECU will accept before it determines that the engine is knocking. A low value will increase the sensitivity to knock sensor noise/

Knock Retard Tables

The knock retard table contains the amount of knock retard, in degrees, between the high octane and low octane knock ignition limits. The actual amount of knock retard the engine applies will depend on the knock control value. eg a knock control value of 50% will give half the knock retard from the table. Note that the ECU will only retard timing if the (dynamic) knock ignition limit is less than the (MBT) ignition value.

Tuning Knock Control

Again, the Honda knock control is only designed to compensate for different quality fuel. It will not (quickly) actively retard and advance the ignition as some other make vehicles will do. If you de-sensitize the knock sensor by adjusting the knock sensitivity table because of noisy cams, don't expect the knock control to detect knock reliably.

Because we cannot tune all the ignition, knock limit and knock retard tables in an automated fashion with spec fuels, we must use some rules of thumb when tuning these tables. These are our tuning recommendations:

• Main ignition tables - decrease the ignition timing in the main (MBT) ignition tables at rpm and load points where the knock ignition limit tables are negative. This will then allow us to use the factory knock control more effectively.
• Knock ignition limit - use low values where the engine is likely to knock. For forced induction engines on pump fuel we can assume they are tuned to the edge of knock, so columns 9 to 10 and should be 5 degrees or less, and columns in boost should be zero. Note that you should always adjust the main ignition tables if increasing values in the knock ignition limit table.
• Knock sensitivity - increase the knock sensitivity (reduce the values) in columns 4 and above. For engines with noisy cams, headers etc, you may need to reduce the sensitivity (increase the values).
• Knock retard - use a smaller knock retard than stock - 4 to 10 degrees. The lower columns (6 and below) will have little effect on knock retard as the knock ignition limit should be much higher than the MBT ignition timing in these areas.

Basically the car is tuned for higher octane than we can get and retards timing. That explains why an E85 mix doesn't drop in mileage because more power is made so less fuel is used. It explain the driveabilty problems associated with changing fuels to lower octane.

 

Thanks for posting that. Where did you find it?

 

Hondata FlashPro Help in knock control. Flshpro will be for the 09-10 Fits but some of the info is for 07-08 Fits. The knock control is for every honda with knock sensor, and most likely similar for all cars. My car runs in the MBT and I use 93 octane (98ron). It seems they also equate higher octane to better quality fuels.

 

Yup every car with a knock sensor I have tuned does this. MBT stands for Max Brake Torque to most engineers, but Hondata's write up is close enough.

93 octane is more knock resistant than 91 because there is a higher proportion of octane to heptane, and it provides a more stable slower burn. So that means they can run the most timing that is beneficial to power production and can run as lean as 12.5:1AFRs for non-turbo applications, and more like 11.3-11.7:1AFRs for forced induction (lambda value of 0.87) under load, or lean burn like the old D-series motors of the early 90's which would run between 14.7-15.4:1AFRs where possible. Which was usually anywhere below 100kPa manifold pressure or ~.55 load factor (depending on table scale).

This is why us turbo guys love E70/E85/E98 so much, in spite of needing larger injectors, PTFE fuel lines, stainless steel filter media, and beefier fuel pumps to support the nearly one third extra fuel needed. Depending on how rich or lean you like to tune, of course.

Ethanol has a 114 octane equivalent and it brings its own oxygen with because it is an alcohol fuel. It also sees stoich around ~9.5:1AFR Vs 14.13:1 for 93 octane with the ~10% ethanol they mix in around here.

So that means we can run a full 21-22* spark angle advance and 40+ psi on high compression motors, like 11.0:1CR's on a fuel like E98. But because of the much "richer" (compared to gas scale stoich) requirements of E85 type fuels, we need as much as 35-40% more fuel per the same unit volume of air.

Most cars since the early 90s have come from the factory with Open and closed loop Min and Max octane tables as well as MinOct and MaxOct timing tables. Usually in the US, Canada or Europe you will not leave the MaxOctane timing and fuel tables because even our 87octane is usually better than what you would find in Ryadh, Lagos or Kamchatka.

To even do this requires a combination really high static compression ratios, high IAT's or something like donkey piss mixed in the gas, all while driving for extended periods, usually at least several minutes of abuse, before it can bump down to the lower value tables. To do this would probably require greater-than-atmospheric manifold pressures also, as that is where susceptability to pre-det/knock is greatest.

 

You are probably seeing a lean condition, because there is an actual lean condition being picked up by the factory nernst cell o2 sensor, or "narrowband" oxygen sensor when you are running E85 because you are probably running out of injector sending your duty cycles through the roof. I would not advise running E85 till you know what your IDC's are at full tilt foot to the floor on regular pump gas. If you are only in like the 60% range you will have enough head room to use ethanol blends. This does not sound like it will be possible.

Another thing to bear in mind if you insist on running E85, heavy petroleum compounds tend to fall out of solution and clog injectors. Also, some injectors are NOT compatible with ethanol/methanol/oxygenated or leaded race fuels like C14/Q16/100LL etc.

So if you are running E85 daily, once every month you would be wise to flush out the "gunk" build-up with atleast E10 pump 93 or similar.

 

Okay, update time.

I was again away from an E85 station, so I filled up with 93. I got 502 miles on my tank of 87 octane E10.

So far, the car is a little peppier with 93, just the way I like it. The fuel light came on at 463 miles, so I should be able to get 513 miles with no problem.

Incidentally, I took the car to the drag strip Friday, and I got 7 runs. Best was 16.794 seconds at 80.39 MPH with a .124 reaction time. The Blitz throttle controller was set on SP2.

 

Thats really good mpg. Was the 463 miles with 7 runs on it too?

 

Yes, with the 7 runs. Of course, that's only 1.75 miles at WOT.

 

Thats great, you are getting better mileage then I got in my Fit. I know the scan gauge works but did not have the Fit that long after I bought it. I am getting 40 plus in a civic and extremely happy because it mixed driving and has a larger motor.

 

Okay. After 491 miles, I finally got some E35 put in. I'm sure I could have gotten to 513. If so, that would have been about 45-46 MPG for the tank.

 

To me, the purpose of E85 is wonderful...And it would be a great alternative fuel...but the fact of the matter is, it costs more and probably takes more pollution to create the fuel source.

I mean, think logically...sure, it's a fuel source with lower emissions than gasoline, but...

To harvest all that corn, takes high powered farm machines. The number one most harmful vehicles from an emissions standpoint are riding lawnmowers. Wouldn't logic basically point that large combines and harvesting machines that use diesel or conventional gasoline create MORE pollutants into the air?

so, I guess my point is...the idea of E85 is wonderful, but in practice, it's probably more environmental harm indirectly than it is help.

 

The actual cost is more than gasoline but the former president in 2005 sign a energy bill that requires more E85 and E10 to be use because its a renewable resource. Now they want to raise it to E15 or higher, the problem is the auto manufactures did not set up the cars for this. It is possible to use E30 or so but dont know at what cost to engine and fuel system.

 

I don't get involved in the politics of E85. Is it the best? Probably not. Is it the worst? Probably not.

I'm just experimenting with my car, and getting hard data on how well E85 blends work in it.

Incidentally, no matter what gasoline or diesel powered car you drive (among street-legal production cars), less than 1% of the energy from that fuel actually moves you, the driver. Chew on that for a while.

 

You are proving it works and thank you for experimenting. Its 33 percent makes power 33 percent goes to cooling and 33 percent goes out the tail pipe.

 

Actually, 33% power efficiency is an optimistic figure that only applies to very efficient powertrains. I think our Fits might be around 30%. Most are around 20-25%. Almost everything else is wasted as heat; as you said, it goes out through the radiator or the tailpipe.

Of that 30%, the vast majority goes to accelerating 1 or 2 tons of cage, overcoming rolling resistance, transmission losses, moving air out of the way, operating accessories, etc. By this metric, even a Prius is a colossal energy-waster.

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