Learned Relative Octane Adjustment, 3.0T

[02LincLS]

For anyone that has Forscan or uses another data logger app such as Torque, I'm curious to know what your OCTAD_R_LRND value is.

Other helpful info is mentioning what octane of gasoline you run, and if you always run it or switch around at fill-up.

 

The reason I ask is I'm looking to eventually put a 93 tune on the car but I have some reservations since my ratio won't quite go all the way to -1.00. I have run at least 5 tanks of Mobil 93 and then switched to Shell 93 but the ratio still hovers around -.85 to -.91. While not awful, I'd like to know if this particular engine (3.0T) is very critical of fuel quality compared to say the older 2.0 ecoboost. My 2014 2.0 EB (Fusion) would always show the ratio maxed out using just 91 octane, and would do it within half a tank of gas. But perhaps I'm wrong to expect the 3.0 to be the same.

 

I tried resetting the Keep Alive Memory and it re-started at 0.00 and very slowly over 5 tanks went to -.91. Then it dropped back to -.85 and is staying there. I am data logging looking for knock or any other event that would make it adjust down, and there are none. The car pulls smooth and very hard no matter how fast the throttle is applied, at any engine speed, gear, or length of time you get on the throttle.

 

Is this normal? What are your values, what octane are you running, and are you stock PCM calibration (tuned/ not tuned)?

Edited April 29, 2022 by 02LincLS

[TomV]

This doesn't answer your question, but here are some details I found online about the topic.

 

Octane Adjustment Ratio.

For anyone’s reference, now & moving forward.

 

All Ford Ecoboosts use a dynamic multiplier known as Octane Adjust Ratio. This parameter can be monitored with our tuning devices and is helpful in ensuring the fuel in your tank is adequate. It is especially important on an Ecoboost vehicle when peak power is expected (dyno tuning, racing) to make sure the parameter is at the optimal -1.0 value.

 

STRATEGY BACKGROUND

This vehicle is equipped with several dynamic load, airflow, and torque targeting and limiting strategies. These strategies allow the vehicle to achieve consistent performance with varying atmospheric conditions and fuel quality. There are no set “boost targets” with these strategies, and as such boost pressure can vary depending on driving conditions.

 

HOW IT ALL WORKS

From the factory, Ford typically designs the base calibration to allow use of 87+ octane fuel and recommends using 91+ octane fuel for optimal power. They can do this by means of a dynamic multiplier that allows for adjustment of each of these targeting and limiting strategies which we call the “OAR” (Octane Adjust Ratio). The OAR starts life at a value of 0.0 and is allowed to learn in two directions. When fuel quality and knock sensor feedback are optimal, the OAR will adjust towards -1.0. When these are sub-optimal, the OAR will adjust towards +1.0. I bet you’re wondering why -1.0 is better?

Well for one, since this value is a multiplier and not an offset the ECU code can be optimized to use a single table comprised of negative values to handle the spectrum of operating conditions. Take ignition timing corrections for example; with an OAR at -1.0, multiplying against a negative becomes positive which is then added as positive correction to ignition timing. However, when conditions are sub-par a +1.0 OAR will result in negative correction to ignition timing.

 

HOW DOES IT EFFECT POWER?

Additionally, the OAR is used in other strategies such as LSPI (Low Speed Preignition), and part-throttle combustion stability. These are functions designed to dynamically limit load production in the event that fuel quality is not optimal. We want the ECU to limit load as it will remove stress and prevent damage automatically. The part-throttle limiter allows for casual driving at moderate loads while maintaining stoichiometric operation. This allows for increases in fuel mileage but at the expense of heat. Heat is generated much more quickly with lower octane fuels and can cause detonation. This is why it is necessary for the OAR to step in and allow for adjustment. In the case of LSPI, the OAR is used to create a blending ratio between three separate load limits to mitigate the possibility of preignition.

[02LincLS]

Hey TomV, Thanks for the reply. I did see that on my travels. It seems the data logging on the tuned vehicles using an SCT XCal or the like, can look at the individual cylinder spark timing and correction factor. I can't see that on Android Forscan using a bluetooth adapter. I do have the high speed USB cable used for module programming so maybe I should explore via PC version next.

 

I could also try using my XCal and their software to see if those parameters becomes visible.

 

If its the gas quality, then its the gas and I'll have to be careful. But if its an indication that something needs attention, I'd obviously like to resolve it before custom tuning. Things that come to mind are spark plugs, plug gaps, plug boots, intake valve cleanliness, and some other things with low degree of likelihood.

 

Car currently has 58K on it, I've had it a bit over a year and put about 20K on it. I'll have to do plugs with a tune, so I might just do these now (my tuned 2.0 Fusion would eat plugs every 30K). I just replaced the air filter, and I ordered a evap hose assembly since I had the idle stumble after fuel fillup. I also got a PCV valve since it was cheap. I am trying to find a catch can kit that fits this car.

[02LincLS]

I've been doing extensive data logging and monitoring of this Learned Relative Octane Ratio "OAR" and a few other pids. I replaced my spark plugs with identical NGK laser iridium and gapped to 0.028". My learned octane continued to drop despite only fueling with 93. I was highly hesitant to put an octane booster in the tank but ultimately needed answers on if I was seeing false knock. Well, the OAR responded immediately and went from -.031 to -.084 which is desirable.

 

I have always filled up at this same Mobil station and had no issues in the past. A Shell station nearby yielded the same results. With 3/4 tank of this supposed Mobil still in the tank, I added a 15 oz bottle of Lucas octane booster, and topped off at another Shell location where the pump was specifically marked "Top Tier". OAR jumped from -0.32 to -0.84 but more drive time is needed to see if will eventually max out.

 

A couple side notes: the octane booster was diluted a bit since I filled up 16 gallons. I would have needed only 11.7 gallons of fuel to raise 30 or so octane points (for example 93 octane +3 = 96). Since the tank was filled, it probably only raised octane about 20. Since the OAR is not pegged at -1.00, I'm thinking that the car thinks this fuel is still not quite 93 octane. I am hoping that refueling at the top tier shell station after this tank is done will leave the OAR unchanged or improved. I'll reply back here with the results in a few weeks.

 

If I ever had to run 87 octane in my turbo cars, I'd NEVER go wide open throttle. The OAR is a complex and marvelous safety system that looks at many interacting variables and always tries to make your engine run as safely and efficient as possible. It detects tiny issues way before your ears ever could, and fixes/ prevents bad situations with lightning response times. Fueling with 87 significantly limits the protective overhead, loses up to 10% hp (40+ hp in my case) and considerable gas mileage. Those that have "never had an issue" can thank the PCM, but they likely have no idea what hell it is preventing from unleashing upon their engine and wallets. and with the fuel price debacle what it is, I'm sure there are stations doing all kinds of crazy stuff. You're playing with fire using 87 because even the data from using 93 at a reputable brand is showing that the PCM is making protective corrections. At the very least, grab a cheap bluetooth adapter and monitor your OAR, especially if modified. The sale of higher octanes in this elevated gas price period is likely way down, making things worse. The Mobil referenced above is $5.50/gal and the top tier Shell is $6.00.

[TomV]

Very interesting information! Thanks for sharing!

 

Perhaps the ratio you see is due to atmospheric conditions? Where are you located? Close to sea level or a higher elevation? I'm wondering if another variable is causing the OAR to be a little less than optimal. 

[02LincLS]

I am close to sea level. While there has been a seasonal change going into summer, the behavior of the OAR is not changing. The large garret core intercooler does an incredible job keeping intake air temps reasonable, even when its 90°F outside with oppressive humidity. I am now tuned which exacerbates the issue a bit so I'm actively working with a tuner to try to figure it out. The local gas might be adding 15% ethanol now that they're allowed to which would typically raise octane, but unless the car knows to pump more fuel to compensate, it might be leaning the mix in certain situations. 93 octane might be a slow seller too so it sits in tanks and its octane drops. I wish I knew. There aren't any ethanol stations near me either so this is the best I can do for octane short of using boosters, which I don't want to do all the time.

 

My 3.5 EB Flex is happy as a clam with the same 93 octane gas (its fully stock with 130K on the clock). Its OAR is pegged at -1.00 and only if you extensively beat on the car will it drop, but it then re-corrects back pretty quick. That car that likely has carbon buildup on the intake valves as well where my MKZ doesn't, at least not at this point anyway. The flex might max its oar with 91 octane though, where the MKZ needs 93 to max it.

 

It is not false knock either since the OAR responded to the octane booster. The coolant temps are good. We're currently looking at fueling. We know we can get rid of WOT knock if we pull a little timing, but I was noticing the knock begins when the car shifts into 3rd, so it might have something to do with the load increase. I noticed some possibly slightly higher than normal fuel corrections during the knock events and I have an updated tune file to try at this point.

 

Finally, just to put it in reference, the amount of knock retard we're talking about is small; 2-3° of pull. However its best to eliminate it so the car has more correction room available if truly bad gas ever makes its way into the tank. Lately I've been watching the knock value closer as it seems to be the main driver of OAR value itself. 2 degrees of knock advance (good) or retard (bad) seems to be the threshold. If you spend 5-10 seconds with the value beyond that 2° either way, the OAR will jump up or down. I am guessing the intensity of the knock in combination with the quantity of events is what drives the number of degrees of timing adjustment. Since the PCM drops the boost to also help fix the issue, you end up leaving somewhat significant power on the table. I'm limited to a solid 17 psi right now, meaning it can hold it there (peak is about 19.5). I think it should be able to hold a steady 20 psi once its dialed in properly.

 

I have not heard a single audible knock through all of this which obviously is a very good thing. I did a 0-100 mph log (on a track, but not drag strip) and while the car pulled 2° in 3rd gear and 3° in 4th, it did the deed in 11.07 seconds. It broke the tires loose late into first gear which slowed the time down a bit. Comparing to Car & Driver's 0-100 in 12.0 seconds, I'm already pretty happy. With more practice handling the power jump, I'm sure I could improve it further. My guess is its a 12.7 second car with probably a smidge under 450hp, 500ft-lbs maybe. Some lighter wheels and better rubber will get it at least to a 12.6 or 12.5. I might do meth injection some day which would really help the WOT knock, but probably not anytime soon.

Edited June 30, 2022 by 02LincLS

[02LincLS]

Just a small update... My learned octane adjust ratio is finally hitting -1.00 on pump gas alone, without octane boosters. I only buy gas at this particular Shell station now. There are still situations where it will drop for a little while but eventually it moves back. Things that cause it to drop are mainly the fuel quality itself, but also environmental; mainly intake temperatures and load on engine (high gear, lower rpm's, uphill). Its also mainly on light/part throttle which the car is always trying to find the edge for efficiency purposes, and back off when it finds it. I'm trying not to beat on it a lot, but I might do a couple more WOT data logs to make sure that end of things is dialed in safely and see what its hitting for boost. By eye, I have not noticed anything beyond a 1-2 degree pull, if any pull at all. Still contemplating water meth which would likely let me bump power up more, with bonus of keeping intake valves clean.