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Discussion and questions related to the course Ethanol & Flex Fuel Tuning
I'm working on my personal MX5 trying to get an E85 tune going; I've completed the tune for 93 as recommended throughout the courses and I've seen substantial improvement in day-to-day performance and drivability.
For those unaware this is a Direct Injection engine, I have made modifications to the following tables for E85.
- Fuel Pressure Target - Increased from 2900PSI to 3500PSI. This is something that I've seen on other E85 tunes on the platform, so i made the adjustment.
- Injector Flow Rate - I've changed this from 856cc to 611cc using a rounded 1.4x divisor. 856 / 1.4 rounded.
The tables that I have available are in LAMBDA so I left everything the same from Gasoline, besides for slightly upping the Open-Loop fuel so it wasn't overly rich.
I did not mess with the Cranking Injection Pulsewidth and it didn't seem to be necessary, the car started right up.
Upon starting the car was sputtering/missing pretty bad at 1500 RPM (Cold Start). If I gave it a little gas to bring it to 2000 RPM it was really smooth, but..
I was seeing Actual EQ/Lambda at 1.0998 while desired was at 0.997. I didn't want to hurt anything so I turned the vehicle off.
I've been looking over the tables for fueling and I'm not really sure what the issue may be or what I need to adjust. This is my first E85 attempt on any vehicle.
Here's my available tables for fueling:
- Closed Loop Low Load AFR Target
- Cranking Injection Pulsewidth
- Fuel Enrichment (Unknown)
- Fuel Pressure Limit
- Fuel Pressure Target
- High EGT Fuel Enrichment
- High Load AFR Target
- Injection Timing Related ("This table is related to Injection Timing", It's LOAD/RPM) The numbers in this table do not make sense to me, they range between 200-400.
- Injector FLow Rate
- LTFT Zone 1-3 Upper Limit
- LTFT Zone 1-3 Upper Limit Hysterisis
- Open Loop AFR Target
- Volumetric Efficiency.
I've read on the forums of this platform that one of the guys that had done E85 himself completely botched the VE table to add more fuel, but what I've learned from this forum and the courses here is that you don't want to do that as it will botch the load calculation among other things.
TL;DR - I modified my Injector Flow Rate, but my Target Lambda does not match my Actual Lambda, which is 1.1x more lean.
P.S - The tuning tables I have access to are in Lambda but mention AFR constantly, since I am unable to calibrate the O2 sensors on this vehicle, I'm not sure if by targetting 1.0 I'm targeting 14.7 or 9.8 in this case, should I be targetting much richer lambdas?
I've been investigating this some more and I can't find any tables that may cause this, the STFT are being maxed out at 28% so changing the Injector Flow Rate doesn't seem to be tricking the ECU into adding the additional fuel. I know I could skew MAF calibrations and VE tables to add the additonal fueling, but I don't think this is the correct way to proceed.
Today I experimented a bit with the VE tables, I increased the entire VE table by 25% and was able to take the vehicle on it's first drive, LTFT ended up at roughly 20% but I was nearly on-target for demanded lambda which is a good sign. I'm starting to think this "ghetto increase" may be the correct way moving forward with this ECU as nothing else has helped.
On a DI engine, rescaling flow rate and adjusting cranking fueling should have provided better results than what you are describing. At idle and partial throttle driving generally your trims would be near spot on IF they were very good prior to swapping fuels. At higher load, injection timing changes are likely required, and you may run into limitations of potential fuel delivery.
Was putting different fuel in the car all you changed, or was work performed on the vehicle since it ran properly as well?
Hey @Mike, Thanks for the response. The vehicle has actually been on E85 for awhile (using another tune). I've been doing my 93 tune between tanks. I've noticed that changing the Injector Flow Rate table which is 856cc stock in this vehicle has absolutely zero effect on anything. To test this even further I've set this to 500cc and 2000cc and observed no difference in operating conditions or visible differences in the logs. I've reached out to the company that provides the tuning software and hope to get an answer here.
I did some digging on the forums (for my car, the ND2 MX-5) and noticed that it was mentioned that people are instead scaling the VE tables to account for Ethanol (and upgraded Injectors). This seemed very wrong to me, but I started experimenting with it and it works pretty well. I've now got the vehicle around ~5% LTFT and am comfortable enough with the tune to take some drives on it, however I am still defaulting to the tune provided by another company for the time being.
One of the issues that I'm seeing while comparing my tune to the other companies is that my Injector Pulse Width is about 10% higher consistently than with their tune. The issue here is that I've only got around ~5ms of pulsewidth on this motor @6000rpm before I start spraying into the combustion stroke. (I believe is the proper term, sorry still a noob here.) With almost all conditions the same, I'm requiring more fuel.
What's even more strange is that I'm targeting a slightly more lean AFR/Lambda, so I've got more pulse width to meet a leaner target. This happens until about 6000 RPM and then the pulse-width starts to actually decrease into acceptable ranges towards 7200 RPM. I'm still baffled why they're managing 5.02ms of pulsewidth to meet a 11.8 AFR and I'm needing 5.6ms to hit 12.3 - This is consistent throughout all load/rpm ranges, my pulse-width is higher for leaner targets.
I wonder if this could be related to Injection timing at all. Is it possible that injecting fuel earlier in the cycle can change the observed mixture? I wouldn't think so, but I am a noob after-all. I was planning to do some research and testing on Injection Timing and VVT over the next week. I do know that they have modified VVT tables and I do not, so this is my next area of study. I've already purchased the course. I would also love to see more on DI vehicles in the course-work, as they're becoming the norm.
I've also made sure that we're running the same fuel pressure. I swap back and forth between my tune and the professional tune to compare and sanity check quite often.
It sounds like the injector scalar is broken in that software. Perhaps there's a newer version with it fixed?
Injection timing can impact observed lambda. One example is if SOI is early enough, you can eject fuel out the exhaust valves. VVT also impacts injection window, for example by altering the location of the end of the exhaust stroke.
Given that VE is being fudged for other reasons, I couldn't guess what your actual VE is, but perhaps it's better than other setups. That or greater air mass could account for the difference in your on time and observed lambda.
Fuel pressure is another key factor. If they're running more pressure, they'll be able to supply a given fuel mass with less on time.