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.