OEM Priorities in tuning

[1project2many]

It helps to remember OE tuning priority. 1) Emissions, 2) Economy, 3) Warranty, and 4) Driver experience. $42 has a PE delay factor and many of the truck cals had a large delay which was only bypassed if RPM went above 4500 or so such as during a hard downshift. Fuel economy may be part of the PE delay factor but emissions compliance and catalytic converter operation are major players. When the AFR gets rich HC and CO increase, O2 decreases, and the cat tends to coold down and stop working. Lower than normal AFR plus a non reacting cat meant bad marks at the EPA emissions test center. The code and calibration are specifically written and adjusted to allow WOT operation during testing without going into open loop or cooling the cat.

Don't think GM isn't above fooling with the EPA. The reason highway lean cruise mode wasn't enabled in these pcm's is that cals were originally set up to stay out of lean cruise during EPA pollution testing but would enter lean mode during mileage testing and real world driving. Once the EPA realized what was up GM got into trouble for having an emissions defeating device installed and ended up disabling it in all subsequent cals where the code is present.

As an aside, it's worth noting that cat overemp protection code can prevent continuous operation of lean cruise mode. If the model determines cat temp exceeds safe limits it can (depending on the code) force 14.7:1 AFR and / or adjust timing to cool the converter and prevent meltdown.

Remember: Emissions, Economy, Warranty, Driver Experience.

[EagleMark]

It helps to remember OE tuning priority. 1) Emissions, 2) Economy, 3) Warranty, and 4) Driver experience. $42 has a PE delay factor and many of the truck cals had a large delay which was only bypassed if RPM went above 4500 or so such as during a hard downshift. Fuel economy may be part of the PE delay factor but emissions compliance and catalytic converter operation are major players. When the AFR gets rich HC and CO increase, O2 decreases, and the cat tends to coold down and stop working. Lower than normal AFR plus a non reacting cat meant bad marks at the EPA emissions test center. The code and calibration are specifically written and adjusted to allow WOT operation during testing without going into open loop or cooling the cat.

Don't think GM isn't above fooling with the EPA. The reason highway lean cruise mode wasn't enabled in these pcm's is that cals were originally set up to stay out of lean cruise during EPA pollution testing but would enter lean mode during mileage testing and real world driving. Once the EPA realized what was up GM got into trouble for having an emissions defeating device installed and ended up disabling it in all subsequent cals where the code is present.

As an aside, it's worth noting that cat overemp protection code can prevent continuous operation of lean cruise mode. If the model determines cat temp exceeds safe limits it can (depending on the code) force 14.7:1 AFR and / or adjust timing to cool the converter and prevent meltdown.

Remember: Emissions, Economy, Warranty, Driver Experience. I know of only one bin in a camaro that was lean cruise enabled (there may be more) but it had a 90 second delay. That was probably long enough to pass emissions test, then got better MPG for cooperate avarge... interesting stuff!

Since warranty is no longer a factor we need to change priorities
[Remember: Emissions, Economy, Warranty, Driver Experience. Should be
1. Driver Experience.
2. Economy or Power. refer to number one.
3. Emissions when in a state that requires it...

Global Warming is caused by Catalytic converters! Look at the spike in Global Warming and it is same time Catalytic converters were put into play.

[dyeager535]

Assuming the bins are valid, AKUN nor ARJX have the PE delay timer set above 0. ANTY and ANTZ do, 3 seconds seems the average. My Dad has said he noticed the difference between the delay and no delay, FWIW. And he had no idea I had changed it.

[EagleMark]

Just looked at stock ASDU that came in my 1990 2wd Suburban with 3:73 gears from factory(because I have another asdu marked 2:73). PE delay time 0 but delay was set until 2800 RPM mine was changed to 1500 RPM
Stock AFR for PS enabled was
0 RPM 13.60
400 RPM13.60
13.60
13.20
12.70
12.70
12.70
2800 RPM 12.70
3200 RPM 13.20

So it was not that much, mine are set to all to 12.50 and read 12.80 on wideband leaving stock PE added spark at 1.41...

[RobertISaar]

Global Warming is caused by Catalytic converters! Look at the spike in Global Warming and it is same time Catalytic converters were put into play.

LOLOL.

a lot of the (natively) MPFI masks don't have any type of provision for a PE delay.

[1project2many]

For many years trucks lagged behind cars in development. Trucks used massive monolithic converters until 95. Cars were switched over to honeycomb style much earlier. It might be revealing to correlate converter type and wet vs dry manifold type.

Some current models operate at stoich at all times and I know of a few which are able to compansate for mechanical fuel adders such as AFPRs by bringing an afr as rich as 10:1 back to stoich, and quickly!

[JeepsAndGuns]

Ok, I'm sorry. What is stoich?

[RobertISaar]

http://en.wikipedia.org/wiki/Stoichiometry

for a gasoline engine, roughly have 14.7 parts of air to 1 part of gasoline, by mass.

factors such as alcohol content/additives will skew that number though.

[JeepsAndGuns]

So basicly its the standard 14.7 air/fuel raito?

[EagleMark]

So basicly its the standard 14.7 air/fuel raito?Right! 14.7 to 1 AFR is Stoich...

[RobertISaar]

if you want a simple and perfectly correct explanation:

it's providing the exact amount of fuel for the amount of air in the cylinder, so that when combustion is complete, there is no leftover fuel or oxygen.

[EagleMark]

The perfect mixture for emissions! Catalytic converters were designed for stoich. Narrow band O2 sensors were designed for stoich.

Not perfect for fuel economy.

Not perfect for maximum HP.

Now that direct injection is being built into new cars they can run leaner for better economy while cooling combustion chambertemperaturess, how does this effect the perfect mixture? It must pass emissionss, so stoich is no longer perfect?

[1project2many]

The stoichiometric number represents the amount of "stuff" required to make a balanced reaction. It doesn't mean the reaction is happening. For example, stoichiometric AFR pumped through a cylinder with the spark plug disconnected results in no reaction and extremely high HC counts from unburned fuel. Now, in theory all cars must maintain a stoichiometric ratio which on the surface means DI is only helping reduce unburned HC's and possibly reduce NOx from high combustion temps due to more complete reaction. It's possible that stratified charging and turbulence are allowing an overall leaner AFR but the EPA has been known to go after carmakers caught violating the sanctity of 14.7:1.

My personal feeling is this is a real dynamic political game right now. IMO GM and ChryCo are playing exactly by EPA rules with AFR while using projected higher CAFE standards as a lever to make changes. Powertrain engineers right now are saying "Yes, we can get the remarkable mileage you want but you're not going to like how the car drives when we're done." Service Bulletins say many of the driveability complaints with new cars aren't "problems" at all but behavior deliberately included in the programming to attain better economy. If disapproval for CAFE is high enough maybe it will be relaxed some.

[JeepsAndGuns]

The perfect mixture for emissions! Catalytic converters were designed for stoich. Narrow band O2 sensors were designed for stoich.

Not perfect for fuel economy.

Not perfect for maximum HP.


If 14.7 is the optimal raito, then why would you want to go to something diffrent? It was always my understanding that running too rich, your simply wasteing fuel, because only so much can be burnt before the combustion cycle is over. If you have more than can be burnt, your just pushing it out the exhaust (black smoke) and wasteing it. Go even higher and you foul out the plugs.
Leaner I figure could be ok, but too much and you start running hot and run the risk of damaging/melting engine parts. How much leaner from 14.7 can you go and be safe? On the 7747 of yours running the highway lean mode, do you know what raito it is?

[EagleMark]

If I knew all those answers I would be an engeneer in Detroit.

But look at PE (Power Enrichement) and then AFR when in PE and you will see AFR closer to 12 to 1

Look at fatory enabled highway lean cruise and you will see AFR closer to 16 to 1

Safe lean cruise? Depends on engine and load on car. Robert says he runs 16.2 to 1 AFR with no issues when I was asking the same question when enabling highway lean cruise on my Suburban, which you can set in XDF on 7747. But a Suburban is much heavier and has areodynamics of a brick compared to his car. So my max is 15.9 at high MAP kpa down to 15 to 1 AFR lower MAP kpa and set MAP kpa to disable Highway Lean Cruise at 69.xx like when pulling a mountain grade.

[RobertISaar]

yep, lean cruise i shoot for 16.2:1, anything beyond that and lean misfires can happen due to the variability of the fuel around here. running that high, i managed 37.6MPG on a ~450 mile trip this summer. not bad for a 21 year old midsize car that has since been retired.

PE: 11-12:1 for boost, 12-12.5:1 N/A, depending on the exact engine. there are always exceptions to the rule though.

and NEVER a PE delay. :nono:

[1project2many]

If 14.7 is the optimal raito, then why would you want to go to something diffrent?

Well, you need to get your head clear on this. 14.7 is a ratio that makes the best balance of what comes out. It is not the optimal ratio for making the engine run. As engineers learn more about combustion they're figuring out how to make the engine run better on leaner mixtures, but many engines run best at mixtures richer than 14.7. Old stuff like the 304 and the IH 345's like a mixture around 12:1. The old GMC 60 degree V6 truck family had huge bores and liked mixtures as low as 10:1. Look through forum after forum and you'll find questions like "My engine runs great in open loop but when I enable closed loop and try to run at 14.7 it's got problems." It takes a little more work to make an old engine run at a leaner mix.

Not all fuel is burned in any cylinder and a richer mixture is used to get more fuel and more oxygen together so they're likely to burn. Unused fuel is wasted but the total amount of fuel burned (and power made) is higher than at 14.7:1. Larger bore engines with tall piston tops and large amounts of cast iron tend to keep fuel from burning at the outer areas of the piston and cylinder. Lean mixtures can burn well but the temperatures produced tend to make NOx which is harder to clean up than HC and CO.

I've got to run, but if you look around for "rich best power" , "lean best power" and "BSFC" you might get some good reading.

[93V8S10]

Maybe another way of saying the same thing is that 14.7 is the optimal ratio in chemistry, not necessary the optimal ratio for the engine.

[EagleMark]

and NEVER a PE delay. :nono:Yeah, really! PE delay, How Rude!

If I put my foot in it it's becaue I want power. Why would I want PE delay? That goes back to OEM priorities, not mine...

[gregs78cam]

My Camaro idles real smooth and cruises nice at around 15.5:1.

[Six_Shooter]

In my Datsun, I have it tuned (no highway lean cruise mode), to run at between 15 and 16:1 while at a steady state cruise.

[EagleMark]

How do you do that? So it must be open loop? Is that a Code $59 thing?

[Six_Shooter]

Yes, I'm running open loop, no, not just a $59 thing. I seem to get better milage and drivability in open loop, though, I only tried closed loop briefly, I decided that I wanted to get the VE tables and such in better shape before enabling CL again.

[JeepsAndGuns]

Hopefully not to get too far off topic, but I have always wondered exacty why does a lean mixture make a engine run hot?

[EagleMark]

You know you ask questions that drive me nuts sometimes because they are so simple I can't answer them! It has also caused some of the best learning threads we have had! Just so you don't misinterpret that, it is a good thing. :thumbsup:

Lean in itself does not make an engine hot, certain leaner than stoich mixtures can actually cool an engine because of there lean condition leave a thin barrier against cylinder walls and when ignited the extra heat from more oxygen and less fuel never hit the walls. Combustion happens in mid air if you will. More air (oxygen) then fuel is what causes leaner mixtures to be hotter. This can be measured in Exhaust Gas Temperatures (EGT). So exhaust valves will be the first to go if to lean. People think the pistons will melt a hole. That is not true, that is caused by detonation when a mixture is to lean for to long (or other reasons) and fuel is ignited before the spark plug fires, like ignited from a hot exhaust valve or glowing tip of spark plug, then you have a two way flame front in combustion chamber reaching full combustion way before piston has compressed, like knock because of to much timing on steroids.

Richer, more fuel has a cooling effect from more fuel evaporating or actually wetting the walls of cylinder which is to rich because you are wetting rings and things with fuel taking away the oil protection. Ever have a carb engine and the oil smells like gas? Ever notice proper tuned EFI engine oil stays cleaner longer and does not smell like gas?

[JeepsAndGuns]

You know you ask questions that drive me nuts sometimes because they are so simple I can't answer them!

:laugh::laugh: :innocent2:

I have been accused of asking lots of questions before...lol
I just like knowing as much as I can, even if my memory only lets me remember so much of it.

[daleulan]

Emissions are affected greatly by how close to stoich you can keep. I can't overemphasize how greatly. I generally calibrate using lambda, so lambda = 1 is stoich, below 1 is rich. Anyways.... catalyst efficiency is greatly affected by the averaged lambda going in. On the inlet of the catalyst, assuming that the fuel in question wants a lambda of 1.0 for best conversion efficiency, I like to see lambda staying from between 0.96 and 1.04, but with an average of 1.0000. If you run an average lean shift of 1.002 what will happen is that the conversion first looks good, then after a period of between 20 and 200 seconds the NOx goes to hell - it'll rise from say 5ppm exhaust out to 250ppm. The 250ppm might meet 1995 emissions standards but not 2011. So the trick is to put an oxygen sensor after the cat and use it to learn an offset for the front sensor. That works in steady state, but not in transients. The postcat sensors are often used for fuel control, especially for US emissions levels but also on EU vehicles as well.

For transients, it is most common these days to run an adaptive oxygen storage model for catalyst oxygen management. When you go through a transient the ECM estimates the oxygen imbalance from the engine and calculates a revised step-and-ramp for the front sensor (or in extreme case, an open loop AFR step) to restore conversion efficiency. But what you first try to do is eliminate as many transient air-fuel excursions (open-loop) as possible through careful calibration. You basically need to map out not only steady-state volumetric efficiency (needed even on an ECM with a MAF), but also thermal models that include a lot of stuff. Normally three airflow estimates are used - MAF, speed-density, and speed-alpha (throttle angle), and used in different operation modes. Filtered MAF is normally used for steady-state. Speed-density and speed-alpha are all weighted in with the MAF reading in different transient modes, depending on which weighting tracks the real airflow better. Read the Delphi paper on 'Thermal and Pneumatic State Estimators' and it explains a lot of this. Then you do the air transient estimation calibration.

Then if you're dealing with a liquid film, then you need to dial in fuel puddling. These days that's normally done with a physically based compensator (commonly an X-alpha compensator).

I guess normally my order for calibration is roughly this. I do it always on an AC motoring dyno. It takes at best a few weeks and at worst a year or two to do.

1. Enter in the base engine and sensor information
2. Calibrate steady-state VE, first pass, plus MBT and knock limited timing, and engine torque at MBT, first pass.
3. Calibrate transient air temperature model
4. First-pass calibration of fuel injection timing
5. Recalibrate steady-state VE, reconfirm engine torque.
6. Calibrate transient air flow model
7. Calibrate transient fuel flow model, engine warm
7.5 - Calibrate engine drag, frictional, and parasitic load (alternator/AC/power steering) torque, Refine engine torque map.
8. Calibrate idle controller for reasonable idle return; this usually needs to be revisited on-vehicle. Also calibrate engine trag torque.
9. Calibrate accelerator pedal feel with a 'reasonable' calibration. This needs to be revisited on-vehicle.
10. Calibration of catalyst temperature model, steady-state.
11. Calibration of front lambda, step, ramp for emissions. If goal cannot be met, consider using timing retard for emissions if EGR is not available.
12. Calibration of postcat setpoints and gains for emissions.
13. Repeat calibration gathering for different coolant temperatures to refine temperature models, air/fuel shifts, and ignition timing shifts.
14. Run engine dyno emissions test to see where you are. If this is an engine test cycle (ETC, WHTC, HDDT) then you have a good idea where you are.
15. Calibrate easy DTC's - rich/lean/sensor
16. Calibrate hard DTC's - sensor drift, emissions

The more complicated the engine is and tighter the emissions laws are, sometimes you end up 'looping' trying to get something tuned up right so you can go on to the next step. Another challenge is that if you find a software bug, you may need to go back and recalibrate a bunch of stuff once the software guys or gals fix it. When you add VVT or VGT that adds another level of complexity because there is now not just one optimum solution - there are several.

[EagleMark]

That is the new best first post I have seen! :thumbsup:


So the trick is to put an oxygen sensor (http://shop.ebay.com/i.html?_nkw=oxygen+sensor) after the cat and use it to learn an offset for the front sensor. That works in steady state, but not in transients. The postcat sensors are often used for fuel control, especially for US emissions levels but also on EU vehicles as well.
and I know know why there are post cat O2 sensors!

[POZE]

Rumor is Honda will release a 60:1 next year in the states and currently using it overseas. I will ask more questions from the source.

[1project2many]

Anyone know what the overall lean ratio of the CVCC engine was? How about the 49 state 91 - 92 Civic with WBO2?