joecar

Yeah, I get confused each time I reread it.

LETZRIDE

iTrader: (6)

alright I thought I had this all figured out and Ive run into some new issues here.

Good news- it works...

Next questions... when tuning this in, should I be leaving LC on when both MAF and VE tuning? because here is what I have found. Yesterday I tuned my VE table with the MAF disabled- I was within 2-3% in all cells. I re-enabled the MAF and tuned that yesterday and a little bit today- go all my part throttle cells there within 2-3%

Ok- now I enabled LC, and it is commanding the correct AFR based on Cylinder airmass inputs, however, the calibration is off. I'm looking at my error table for the MAF and I am anywhere between 6-8% off - I was 2-3% before enabling this?

Now, I don't know how accurate the maf AFR error table is right now, because this is the tune fully re-enabled (i.e, LTFT turned back on, DFCO re-enabled, CL tuned back in)

What I do know though is I am commanding 15.6 and I am seeing 14.32 lol

Now here is the question- do I need to re-tune the MAF and VE with LC enabled at all times? or is it expected that the LT fuel trims will bring this where it needs to be over time (which seems like a bad idea, since I think that would skew my LT fuel trims and lean me out at WOT)

joecar

When tuning the MAF did you inhibit the VE...?

Did you filter out throttle transient conditions...?

Are the injector tables correct...?

LETZRIDE

iTrader: (6)

How do you inhibit the VE?

The injector table should be correct- they are stock injectors. I only have a lid, LT headers, 3600 stall and 3.73s

If the throttle transient conditions are the OL EQ ratio- then all of those are set to "1" to not add any extra fueling yes

joecar

Inhibit VE by setting dynamic airflow threshold to 400 rpm (i.e. so uses MAF-only above this rpm).

Is there a way of discarding data frames for which throttle has changed more than (say) 5% from previous data frame (I don't use HPT other than for viewing peoples tune files)...?

LETZRIDE

iTrader: (6)

I'll inhibit the VE and retune the maf with LC disabled and see how that works.

As for your second question, I am honestly not sure, I am sure you could with the filter strings in the scanner, but I am not that talented yet.

I copied over the base spark tables (not the high/low octane ones)...I was monitoring my Aeroforce today on the way to Buffalo to grab some things and it looks like my mileage has gone down as opposed to before lean cruise?

I.e, cruising at 80 I was seeing anywhere from 22-27mpg on the gauge before...today I was 16-20 at best...but I was watching my commanded AFR on there as well and I was commanding 15.80-16.80 and my AFR gauge was reading 15.2-16.3 throughout the cruise trip on the highway...but the mpg was way down on the gauge...my thinking is maybe this is spark related?

But I copied all spark tables minus the low/high octane...thoughts?

joecar

When correcting MAF and/or VE you want to run the HO spark table... the amount of spark advance does have some effect on wideband lambda/AFR measurement;

correcting the MAF is fairly straight-forward (disable VE)(and CL/trims);

but take note when correcting VE, you need the MAF to fail (i.e. you have to make a MAF DTC show up immediately on engine start), but in the presence of a MAF DTC the PCM will read timing from the LO table, so you first have to copy the HO table over to the LO table (only for the purpose of correcting VE).

LETZRIDE

iTrader: (6)

Yep I had failed the MAF

the timing portion I know to copy the HO to the LO table...but if I am taking the LC tables from a holden Monaro...should I copy every single spark table over from that car? HO/LO included...along with base corrections?

joecar

No, just try the LC tables.

But I would disable LC during VE/MAF tuning, enable it when done.

Mike454SS

iTrader: (4)

You need to also copy over the AFR spark adder table. In HPTuners, go to Engine - Spark - Advance - Spark Correction - AFR Correction...in there you'll find a base and multiplier table.

In that table in a stock 2002 Holden file, you'll see that when the EQ ratio (inverse of Lambda) drops below 1.0 (so Lambda is higher than 1.0, and you're lean) between 1200 and 3200 RPM, they add a LOT of timing...as much as 12 degrees of advance. The multiplier is set to 1.0 everywhere.

If you pull fuel without adding timing, you will not gain MPG, you'll probably lose MPG, which I think is what's happening to you.

When an engine is lean with very low airflow (cruising), it will tolerate a lot of timing without issue, and will become more efficient.

LETZRIDE

iTrader: (6)

I'll look back into it. But would you put in the Holden low and high octane spark tables as well? since their modifiers are meant for those tables right?

I am still confused how pulling fuel without adding timing loses MPG, I would think anything that leans out your fuel should theoretically save fuel as you are using less...not saying you're wrong I just can't grasp why this is

What is the maximum amount of timing you would want to safely run while cruising? is there a ceiling limit assuming no KR is present?

Mike454SS

iTrader: (4)

More timing with the same fuel means more torque (as long as you're below MBT). The same timing with less fuel means less torque...so to get the same torque with less fuel, you need more timing.

I don't see any reason not to push it to MBT at low airflow if it will tolerate it. At the airflow where you'd use lean cruise, you really can't elevate chamber temps enough for timing to be an issue.

LETZRIDE

iTrader: (6)

ok what is MBT?

Mike454SS

iTrader: (4)

Mean Best Timing...the number where the engine produces the most torque for the given conditions. At higher airflow/load, you'll find as you add timing, you gain power, but you'll then get to a point where you knock...you can't get to MBT. At low airflow, there's much less chance of knocking, so as you add timing, you'll eventually see diminishing returns...when it's no longer gaining torque, there's no point in adding more timing.

I guess you could log the TPS and MAP sensor under otherwise identical conditions...how much throttle does it take to go say 65 mph on the exact same stretch of road a few times that same day (keep the temp/humidity/pressure as consistent as possible) as you increase timing and what happens to the manifold pressure.

I don't know that you can get truly consistent enough data like that to be 100% optimized...but over time you could make changes and see what your overall fuel economy does. When I did this in my old car, I was driving the same exact commute every day in low traffic conditions on the cruise control...and burning a tank of fuel every 2 days...and filling at the same pump every day...it took me some time to nail things down, but the mileage was improved over stock.

Mike454SS

iTrader: (4)

I guess to further answer your question...the numbers in the Holden file (the fuel subtractor, the main spark advance, and the EQ ratio adder table) are setup by the OEM, for a 100% stock drivetrain, and their warranty needs, on normal pump gas (which back then probably wasn't E10 like it is now).

If you've modified the car at all (intake, exhaust, headers, heads, cam, gears......) then the AFR and advance it wants will probably be different...plus almost all pump gas I can buy is E10 (10% alcohol), not sure what you can buy, but to be optimized on that fuel, tuning changes (timing and AFR) are necessary...the best way to learn how to do it is expiriment.

At the light load where you want to remove fuel for lean cruise, you'll probably feel it lean misfire (and maybe even throw a misfire code) before there's mechanical danger to the engine...and you'll also probably feel it get sluggish from too much advance (past MBT) before you could cause any damage...your results may vary from mine, but I'm in the camp that isn't afraid to play with the AFR and timing numbers at very low load to find whats best...I'm cautious when I'm making power and could damage the engine (high boost, high compression NA on pump gas...)...but when the throttle is barely cracked and I'm just maintaining speed, I've never hurt one.

2xLS1

iTrader: (25)

Mike, what is your opinion on the effects of LC on Cat Converter life. Since the Holdens I've seen LC enabled on all seem to be equipped with cats, I would guess it has little effect on them since GM Holden would be the ones having to warranty them and they are enabling LC.

kingtal0n

iTrader: (1)

Hello everyone, I am very pleased to see this topic. I have been doing my own research with "lean cruise" situations and have found many details, which I will now share

Lets start with the simplest easiest route to a "lean cruise" situation. If you desire an A/F ratio leaner than your OEM Narrowband will permit, and do not wish to do any modifications to your computer, there is a simple easy way: Buy a typical AEM wideband gauge, and utilize the analog output to simulate a narrowband, using a setting such as this: (0.002v = 15.2:1 ; 0.998v = 14.8:1 ) Using a factory narrowband input this will modify your cruise situations (and all closed loop operation!) to a leaner A/F ratio and your computer will be non-the-wiser.

Now, onto the explicit details of how lean cruise can help, and how it can hurt.
First thing you should know is that fuel savings are very minimal when it comes to the difference between 14.7 and 15.2, less than 5%. There is much more "fuel saving" to be had through ignition timing setting, and the reason for this is that there is alot of "head room" In a factory cruise table (for any vehicle) for the simple reason that the vehicle may at any point in time suddenly be loaded up with passengers and weight.

As you may or may not know, increasing vehicle weight (while keeping everything else constant) requires reduced ignition timing. Since most computer controlled vehicle have no way of knowing how much the vehicle weighs, the factory uses a combination of knock(sound) related timing retard, and a built in "headroom" for timing numbers to keep the engine safe. Performance gains are often had by increasing the ignition timing (removing your headroom of course) and going too far has disastrous consequences. Keep in mind conditions change constantly (air temp, humidity, octane rating, valve temp, piston surface temp, EGT, etc...) so there always needs to be some form of headroom in your timing table for those altering situations, no engine should ever be tuned to the absolute bleeding edge (unless it is a fully sponsored, all out racing vehicle with frequent sponsored engine rebuilds).

That said, how can we adjust our cruise timing/fuel for best economy? Lets get to the method I have adopted that will work on any vehicle, using math and datalogging we can make measurable improvements.

First a few more words about fueling. Anytime the throttle moves, there is generally an enrichment to compensate for pressure drop and to richen things up just in case the pedal keeps moving. This is called acceleration enrichment, and this is your primary culprit for ruining fuel economy. Many people do not realize that the injector duty will make a leap everytime the gas pedal twitches on the highway; this is directly influencing your fuel economy. So, for the sake of all further testing and the best possible outcome, we are using cruise control to maintain, to the best of our ability, an unmoving gas pedal (unmoving tps). If you do not have cruise control, you may simply detach your tps sensor (or turn off AE "accel enrichment" in the computer temporarily). These tests are done at steady speeds so there is no need for AE.

YOU WILL NEED:
A way to log fuel injector duty cycle, engine vacuum, and road speed.
A way to modify fuel and timing while driving.

The test:
Take the car to a highway and drive 60mph and set the cruise control. Log the injector duty, engine vacuum, and road speed for a few minutes.
Now, add a significant amount of timing, perhaps 3-5* btdc, depending on your engine. Did your engine vacuum increase? Did injector duty decrease? If so, you just improved your fuel economy. Keep adding increments of timing until diminishing returns occurs, or you have around 45* btdc (too much for most engines) and the engine knock sensor may start to complain, depends on compression/octane (high compression engines need less timing) so this is tuning theory in essence and you need all your senses for best results.

Once I found my best timing number for the lowest injector duty, I always leave some headroom, so pull out some of that newly added timing before going on. If the number is reasonable (usually 33-37* btdc I find for most engines, ranging from 4-cylinders to I-6's to V8s, typically the larger engines need more timing) then you can proceed to adjusting the fuel.

Fuel adjustments are slight, and minimal. You do not save alot of fuel by going much leaner (perhaps due to the nature of power extraction from fuel is relatively consistent per unit of fuel mass, the mpg gains are more likely due to the increase in temperature, as opposed to the reduction in fueling itself). I would start no leaner than 15.2:1; my testing (mostly EGT) has revealed that "lean cruise" situations rarely add any measurable increase to exhaust gas temperature on most engines during a highway cruise. I find the WOT EGT to be much higher and more obvious. That said, there is a phenomenon that seems to creep up on you if you attempt to keep an engine too lean, for too long, and I will do my best to describe it now,

If you cruise at 15.5:1 for about 30 minutes, constant OPEN LOOP (no computer adjustments), you may notice that the wideband will slowly creep to 15.6, and then 15.7, or leaner, all by itself. As a wideband sensor becomes hotter, it may begin to read richer, so this is not a situation where the sensor is heating up, but rather an actual condition the engine is exhibiting. I find that if I now increase fueling, it will take more fuel injector duty to bring it back to 14.7:1, than it would have if I was already at 14.7:1. Indeed, once you move the engine back to 14.7:1 and lock it down, and drive for a while, it will slowly creep back to 14.5:1 (for example). My experience and chemistry background tells me that there is a "wall wetting" effect, where fuel molecules are available on the surfaces of cylinder walls/ports that affects your final A/F number, and by running the engine leaner, over time (it often takes 20-30 minutes) reduces this quantity, either by law of mass action or an unmeasurable temperature increase, leading to a change in final A/F ratio. Whether this condition is detrimental to the engine is unknown to me; suffice to say, I tend to avoid it, and therefore, I avoid CONSTANT A/F ratios of 15.3:1 and leaner.

That said, I have developed a new hypothesis based on this observations. In order to prevent what I have come to call "hot lean creeping" of the air fuel ratio during a long highway cruise (and therefore potential engine disaster due to "fried" piston rings, rings which are undoubtedly sensitive to heat transfer and cylinder wall conditions) I have been running an OPEN loop fuel map consisting of "checker boarded" lean values. In other words, most of the cruise spots in my fuel map will give the engine 14.7 through 15.2:1, however, a few of them (interlaced) will hold 15.6:1. This way, while cruising, I am often between one or the other, and the A/F will fluctuate between them over time (I will see a 14.7, then a 15.6, then 15.2, etc...) similar to what you would expect from a well-programmed closed loop situation.

You may repeat this procedure for all road speeds; eventually you will find the optimum speed, because this will be the highest road speed, that when divided into your injector duty (calculated with engine pressure to determine fuel pressure at the time), aka the best fuel economy. In other words, road speed vs injector duty taking into account fuel pressure, so you can see miles per gallon, If you need an example I can provide one.


You can take this one step further and stop to adjust tire pressure, ride height, A/C, air panel/ducting, add weight, and more. Always remember that less weight and less rolling resistance means better economy; especially rotating weight. I always use the lightest wheels, the lightest driveshaft, and if the car is automatic, the lightest transmission internals and the lightest engine internals/flywheel. If the car is manual then there is much to say for the mass of a healthy flywheel and rotating assembly to store energy while the engine is in neutral (it makes the vehicle easier to drive as well). Furthermore, you might not know this but the addition of a turbocharger can also improve engine economy, provided the engine has the camshaft profile to take advantage.

And finally a word about RPM that you conduct these tests at. It is impossible to say for all engine types what is an appropriate cruise rpm and when full timing advance can be used safely. It is a well known idea that lower rpms require less timing advance for many engines. With that in mind, I would add that any timing values written here are assumed to be a final, full cruise timing number, and that certainly at lower rpm there is much less timing for sake of safety and variability in load conditions, as it is much easier to load an engine quickly at lower rpm with much smaller throttle openings (some engines take a full "wide open throttle load" with as little as 20% throttle position at 1200rpm for example). At this sort of puzzle piece you must consider the technology capability, are we talking 2016 electronics or 90's computer components, as there will be many different capabilities and options for fine tuning and adjustment when using the more advanced computer systems, and thus these fuel and ignition profiles can be more custom tailed to sensor feedback.

LETZRIDE

iTrader: (6)

Mike I swapped in all of the spark tables and modifiers from the Monaro now. I went back, pulled the plug for the maf, failed it and verified my VE table was under a 2% error all around...took it on a long drive to- about 1.5 hours. Then on the way back, I plugged the MAF back in, and set the MAF to be the sole reader from 1000rpm up....dialed the MAF in to under 2% error across all cruise tables.

Went back- re-enabled LC and when I command 15.5afr my wideband is 16.5-17.0 which is stumping me....

how can I get these numbers to dial in? do I need to enable LC and then retune the VE and MAF with it enabled? but then wouldn't my light throttle always be lean like that?

mrvedit

Wow, that is a very interesting and informative post!
So, you have been a member for 4 years and only 17 posts - I think you have been holding back with your wisdom and excellent writing abilities.
Please keep contributing, maybe on a more regular basis.

Not quite on the topic of lean cruise, has anyone created a customer PID on HPT that estimates MPG? (Honestly, I have searched.)

LSX Power Tuning

iTrader: (4)

I have one for efi live, I'll look and see what it takes to make it hpt. I used it when playing with lean cruise. I would drive the same 60 miles on the interstate with my roadrunning pcm installed and made several custom maps logging a/f, timing, mpg, and speed. I would change the a/f .1 at at time and timing 1 degree at a time and compare the data. It took alot of drivng but I was to build a timing map and fuel map for lean cruise. In the end it wasnt the time and effort for the gains. There was more to than just what I posted but that should give you and idea.