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Thread: An Idiot Learns to Tune, Part 2

  1. #1
    Fuel Injected! spfautsch's Avatar
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    An Idiot Learns to Tune, Part 2

    I've been working on the tune for my car for quite some time. A slipped optispark hub, an unfinished ignition controller project, and life in general has slowed the progress immensely, but I've arrived at a point where I feel like it's 95% perfect and I finally have all the pieces to the puzzle together (development halt on the ignition controller and working + accurate wideband). Last fall I decided when I got to this point I wanted to run a tank of ethanol free gas through it to see what happened to trims and PE AFR. Here in the Midwest it's difficult to buy gasoline that doesn't contain "up to 10%" corn liquor. Since I did most of my tuning on a steady diet of 93 octane E10, I wasn't sure what to expect, but the shift was quite distinct so I thought I'd share it with anyone interested. Here's a quick comparison running the same tune for all the log data.

    Here are the logs if anyone's interested. [link] Weather conditions were fairly consistent - hot and humid. The ones with "E0" in the filename were captured running on 10 gallons of roughly 90 octane pure dino juice. This is a MAF tune - since I didn't have a really accurate injector constant for the modified LS2 injectors I have, I made the assumption the factory MAF calibration is accurate and tried to determine the flow constant with trims and / or wideband data.

    E10


    E0


    It's difficult to see from the graphs, but the PE lambda is fluctuating between 0.86-0.88 on the E10, and 0.83-0.85 on E0 (BLM locker patch in use).

    Essentially this is a very verbose and graphic presentation of the simple idea that E10 is stoich at about a 3% richer mixture than pure gasoline. What I learned from this is that when tuning with E10 it's best to try and have your trims adding around 2%, whereas I was targeting trims that were removing about 2%. This doesn't seem like a lot, but with the E0 my cam surge is far more pronounced, so I think I'm going to scale my injector constant up a bit and see how it reacts.

    The cam surge is about the only aspect of the tune I'm not really happy with. Once I have the injector constant so E10 produces BLMs in the neighborhood of 130-132, I'm then going to go back to fine tuning individual cylinder trims to see if there's any improvements to be made. I finally broke down and bought a high quality IR heat gun and after taking measurements on a couple different days I'm seeing #2 seems to be running hotter than the other 7 holes. I'm not sure if this means it's rich or lean, but at least I have an idea which cylinder might be the culprit in causing a slightly lean condition on the right bank.

  2. #2
    Fuel Injected! spfautsch's Avatar
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    I wanted to add that if anyone looks at the logs you'll need this line in ee_definition.csv to see my wideband in 'user parameters'.

    Code:
    54,D27_LAMBDA,Pin D27 Lambda, λ,EXTENDED,8,2,0.001533,0.75,0x00,0xFF,,,,,

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    Fuel Injected! A95Y's Avatar
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    Changing the *Stoich AFR target* to 14.1 doesn't compensate for ethanol?

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    Fuel Injected! spfautsch's Avatar
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    You can put any AFR you want in those cells. I'm sure it impacts some fueling equation somewhere, but once you go closed loop the trims will correct you to stoich for whatever the oxygen sensors tell the ECU is stoich. With methanol that's around 6.5:1 and with bituminous coal it's more like 18.0:1. The oxygen sensors don't care what fuel you're burning - they just give 0.455 volts at precisely 0.0% oxygen concentration.

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    Fuel Injected! steveo's Avatar
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    I'm sure it impacts some fueling equation somewhere, but once you go closed loop the trims will correct you to stoich for whatever the oxygen sensors tell the ECU is stoich.
    based on that logic there's no point tuning fueling at all in closed loop range

    changing that stoich AFR target will land you closer to what is stoich so closed loop doesn't have to correct as much, which is a good thing

  6. #6
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by steveo View Post
    based on that logic there's no point tuning fueling at all in closed loop range
    I'm not tuning closed loop fueling, I'm trying to extrapolate my injector flow constant based on trims and PE lambda so I have the most accurate representation of this for whatever type of fuel it will run. From this flow constant I will be scaling my startup prime pulsewidth table and the proportional table of the closed loop PID controller. I don't want to bake a 3% error into these if I can help it.

    Quote Originally Posted by steveo View Post
    changing that stoich AFR target will land you closer to what is stoich so closed loop doesn't have to correct as much, which is a good thing
    I think you're missing the point of the exercise. There are millions of cars driving around today burning E10 with 14.7 as their stoich afr target, and they're all running just fine. The ECUs running these cars lack the capability to change this dynamically based on actual fuel composition. Does that mean their fueling is wrong? No, the O2s correct the trims to whatever stoich is for the fuel they're burning. Even if someone accidentally fills the tank with E85.

    I'm not terribly concerned with the AFR target - it does serve a purpose but only until BLM learning is enabled. Edit: Without the BLM locker patch this will make PE fueling adjust for fuel compensation and bank to bank imbalance as intended, and that's what I plan to do.

    Outside of that, what's wrong with trying to build a baseline tune that's as close to what GM would have done with these cars back in the 90s before the country became infatuated with burning corn liquor? I'm not going to live forever and my kids aren't gearheads, so this car will probably end up belonging to someone else down the line. That person may live next to a large body of water where ethanol free fuel is widely available.

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    Fuel Injected! spfautsch's Avatar
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    I just ran the last few drops of E0 out of the car and refilled with fresh 93 octane E10. The engine almost died 5 miles before I got to the gas station when I finished making a left hand turn and maybe got too wild with the go pedal. Trims were going > 128 on E0 so I'm pretty sure the fuel pump was sucking some air for the last 10 miles give or take. It fell on it's face as I Iet off the accelerator pedal pulling into to the gas pump slot.

    Edit: Yesterday afternoon I gradually increased the injector flow constant from 41.494 lbs/HR to 42.966 lbs/HR which explains the trims shift mentioned below.

    Immediately afterwards trims were largely > 128, but more importantly the bucking from cam surge immediately went from about 8 to 4 on a 1-10 scale. I'm planning to commute in it tomorrow and will report back.

    I'm not trying to refute your knowledge steveo. Exactly the opposite is true. But if we get to a point where our egos tell us we have nothing left to learn on a given subject, difficulties like this will arise. I'm just trying to take the immense effort you've put into eehack to the next level. If you don't appreciate my efforts, I have nothing more to offer you than "I'm sorry you feel that way".

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    Cam surge calmed with shit fuel is interesting. Could be the e0 also not pure e0 but some mix of additives with little pure gasoline.

    I found 2 things that calms cam surge. Running pig rich or fine tune individual cyl trims with proper spark advance.

    I almost have a running car again. Things that left are oil change and some leaking o-rings and will be doing some tunning also. I found that evap valve can stuck open and cause all kind of weird situation. After fixing that the trims were much more stable and constant.

    The next level of tuning guide will be power tunning and spark advance tweaks. More of an advance science experiments.
    Interesting to see how that IR measurements will give some good data.

    How about adding some termocouples on each tube and measure precisely all 8 of them with some modified controller code. Can that atmega take 8 channels of data.
    Getting EGT in the equation of tunning will bring us closer to lean cruise patch and the benefit of it.

    I am really interested to see trims with stock ignition vs 8 coils.
    How about perfectly stock healthy engine running e10 with stock tune for 94` gas quality. Will the trims goes higher since you will be adding fuel to compensate for lower power output.

    Since it is really hard to find anything other than e10 can we benefit of it and take advantage in the tune like adding more spark advance.

  9. #9
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by kur4o View Post
    Cam surge calmed with shit fuel is interesting. Could be the e0 also not pure e0 but some mix of additives with little pure gasoline.
    I'm about toast for today, but will revisit this tomorrow when the ice+bourbon cocktails have worn off. But what I feel compelled to point out is that with X amount of integrator shift, there will come a proportionately larger combustion change with fuel that burns at a higher AFR like E0. With E10 a larger amount of fuel must be added / removed to achieve a similar amount of change in combustion increase / decrease. This ties directly to the O2 prop table change I mentioned.

  10. #10
    Fuel Injected! spfautsch's Avatar
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    Quote Originally Posted by kur4o View Post
    Since it is really hard to find anything other than e10 can we benefit of it and take advantage in the tune like adding more spark advance.
    All the sources I've found say that E10 doesn't offer enough evaporative cooling to allow pushing higher with spark advance. And I'm not certain ethanol blends are that widely available outside of North America. Back in the energy crunch of the 80's we started diluting gas with corn ethanol. Then in the late 90's / early 2000's when the tree-huggers decided the world was going to end if we didn't come up with a lower carbon footprint fuel source, the government started subsidizing corn production for the purpose of ethanol. Trust me, nothing makes economies shift rapidly like offering to give farmers "free government money".

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    I just figure that my current tune is POS. I guess tuning with stuck open evap valve is a real bad idea. Never tune an unhealthy engine.

    I am sure the cyl trims are way off too. The ve tables are really lean on idle, 160+blms. Interesting now the closed loop idle with vette settings is really good and stable, You can`t tell a difference in running closed or open loop. They were good before but never stable enough.

    I am sure EOIT target will also like some tweeking. I am starting all over again with the tune, so some fresh ideas will be posted.

    It will be some e9 gas used, so I hope to take some advantage of it.

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    Quote Originally Posted by kur4o View Post
    The ve tables are really lean on idle, 160+blms. Interesting now the closed loop idle with vette settings is really good and stable, You can`t tell a difference in running closed or open loop. They were good before but never stable enough.
    Wow, there's something really wrong there (160 blms). No amount of tuning is going to solve that unless your cylinder volume constant or VE table was accidentally scaled by -20% instead of -2%.

    I've had some success tweaking the prop step size (0x270C) and found increasing the higher airflow cells improved things somewhat. Going from 24 to 28 generated more cross counts because the integrator resembles more of a square wave instead of requiring two or more integrator changes before the O2 voltage swings past the 0x26F1 threshold. And I've observed that too many integrator changes tends to overshoot the threshold - especially when coupled with too much (or too little) integrator delay. This is why I mentioned that we need to invest some thought on how to tune a PID controller because that's what this is.

    I haven't experimented extensively with changing the lowest airflow cell for idle. The integrator "waveform" here still resembles a sawtooth.

    Quote Originally Posted by kur4o View Post
    It will be some e9 gas used, so I hope to take some advantage of it.
    Don't look for some miracle by running ethanol blends. My observation about surge going from 7 to 4 was premature. The only real difference is that a 10% ethanol blend will cause your trims to add 2-5% compared to pure dino juice.

    I'm starting to think I might have a plug boot with a hole burned through. I drove it late the other night when the humidity was ridiculous and the temps had fallen down near the dew point. Then again the next morning in similar conditions and both times I was feeling an intermittent miss well before it would have switched to closed loop (I wasn't logging but the engine was cold and less than 30 seconds of runtime). I was assuming this was cam surge, but I'm not sure the actual surge is anywhere near as bad as I initially thought it was.

    I'll have a play with some water in a spray bottle after dark as soon as time permits. But this week is essentially shot since my daughter decided (unbeknownst to me) to open a not-for-profit border collie rescue in my home two nights ago. Today, some rocket scientist of a veterinary doctor thought it would be a good idea to neuter the dog before we've had a chance to build trust and wash the cow manure out of his fur.

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    That evap valve was leaking unknown amount of fuel vapors mixed with air. It totally screw all the closed loop and idle tuning.

    I did some cyl trim fix today. Somehow my last maf tune is almost perfectly dialled for the idle with fixed evap.

    I put the engine in CL and there were some splits about 4-5 points. Rigth side running alitlle richer. I did some lowering on all of right side cylinders and the trims got stuck at 128 at some point. At least now bank to bank fueling is equal, not sure about the in bank trims.
    I also confirmed that fuel robbing thing we suspect long time ago. Some lowering of the rigth side made slighly lean the left side. With perfectly dial blms you can monitor 1-2 point blm increase and int movement also and how they react to cyl trims.
    I plan to run the cyl cut thing and see how much air each cylinder is drawing.

    Map is still jumping around and I suspect some mechanical shit happens, since it is not consistent sometimes at idle it goes to 42-43, sometiomes jump to 46-47 with no apperant reason.

    I also played with some of the closed loop controls and some setting make the up-down 02 swing much slower. I didn`t record the setting but also have no idea what we are looking there.

  14. #14
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    Quote Originally Posted by kur4o View Post
    I put the engine in CL and there were some splits about 4-5 points. Rigth side running alitlle richer.
    Several weeks ago I dug through all my logging and found an hour long log from before I touched anything on the engine or exhaust (attached). There wasn't a bunch of idling to look at, but using an analysis script I wrote to look at the .csv data, the bigger picture showed that there were max BLM splits of as much as 10 in certain cells, and average BLM splits that are both fairly consistent with my current tune. I wouldn't call my current tune as good as it can get, but I think it's probably 95% there.

    Another thing I've noticed about idle and low airflow BLMs is that they seem to vary wildly with load and weather conditions. Having just spent some time rehabbing my A/C system and tuning for it, I've noticed that simply turning the A/C on (increasing load) at idle causes my BLMs to jump several points positive and become much more balanced (remember this is at closed throttle). Looking for this pattern within normal driving I'm seeing the cells with the worst BLM splits are the very low load cells - bordering on decel.

    Another thing I've finally been able to tweak is the idle air bypass size. With the 6.4L displacement I'm seeing that 7/32" is about the best. 15/64" may be better but it also may be too big for very low temps / high air density. This helped immensely with getting it to idle decently with the A/C at max load. It's still a little lumpy at idle with full A/C load, but I can live with it. The vibration of the lumpy idle doesn't bother me as much as the gear clatter from running a single mass flywheel.

    Quote Originally Posted by kur4o View Post
    With perfectly dial blms you can monitor 1-2 point blm increase and int movement also and how they react to cyl trims.
    I mentioned that I was trying to see the integrator (when graphed w/ eehack against O2 voltages) switching like a square wave. I only tried this because I noticed this pattern looking at the bone-stock log I mentioned above. I'll try to dig that log back up and post. When I compared to my running tune at the time, the integrator switched at least twice in most cells before crossing the rich/lean threshold.

    Quote Originally Posted by kur4o View Post
    I also played with some of the closed loop controls and some setting make the up-down 02 swing much slower. I didn`t record the setting but also have no idea what we are looking there.
    I'm beginning to think that tuning this integrator behavior at idle may be worth spending some time perfecting. It may be that it simply requires scaling to match injector constant. But I haven't gotten that far.

    I'm playing grandpa to a pup until tommorow night but hope to get around to checking for a spark leak this weekend.
    Attached Files Attached Files

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    I just tested some tweaked cyl trims. Took the base from the last blm stable ones at idle and adjust the off idle based on them. The engine started to run much better.
    I think that if the trims are not optimal in the long run of engine running, some cylinders will get heated more some less and the total balance will be screwed. Also at off idle and take off conditions the engine will be heat soaked differently and it will also affect that and the engine will run like crap all the time even though only idle trims are off.

    After good warming I checked the blm at CL on idle and they were almost even. Than decided to give some play with EOIT target.
    Tried all kind of it from 40 to 70 in hex. |First I thought stock was $50. It turned out it was $60, Than start increment by 1 and at $63 what a difference. I looked at the afr, map and feel for reference, if AFR goes lower the fuel is evaporated much better and the engine have excess fuel leading to richer mixture.

    I got lucky from the first try to get the sweet spot on the first try.

    The fuel evaporation test with EOIT must be done at fully heat soaked engine and increment it by 1 and wait at least 30-60 seconds to feel the change.
    I guess the optimal settings is cam, temp, head, valve dependent, and the the time needed for best fuel evaporation must be found by feel and experiment.

    Than I give it a short drive.

    Now what a difference from small eoit move $60 to $63 and part dialing the cyl trims. The engine got quieter by a lot[I could hear the stereo again]. It felt some much better[from crap running to almost stock like running].
    The interesting part is that you can not see any significant change in the logs. It is all by feel. It started to shift much better also and the overall throttle response increased.

    And that is with guess dialed off idle trims. I still haven`t figure out reliable method to get this dialed unless there is a driver with and a tuner in car. Getting some steady conditions and monitor the blm closely for splits.

    The blms are great for
    dialing bank to bank difference[split blms are almost definitely from bad ind trims.]

    I also noticed that in closed loop only couple of cells are used most of time. I am sure this is not optimal and I am looking for some tweaks there.
    Anyone got any experience with it.

    Now the wideband at closed loop goes from 14.6-15.1 all the time at stoich. At idle that changes to 15.4-16.??. I guess this could be from low airflow or it could be from not optimal CL settings.

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