Car calibration question for normal cars.

[Turbo6Smackdown]

Do modern cars (post 1990 say) "learn" their ambient changes? For example air filter changes. A high flow air filter or a really dirty oem air filter. As your filter gets dirty the airflow decreases. So doesn't the maf and o2 sensor see this and pull fuel to adjust the AFR back to normal? Then why do people say a clogged filter makes the car run rich? Tell me why the car's not compensating?
What is one way auto makers use to improve fuel economy? Lean out the AFR of our cars. Then how do high flow air filters improve fuel economy? Wouldn't a high flow filter allow more air across the MAF, sending signals to the ecu to add more fuel to readjust the AFR back to original? If more fuel was needed to accomplish that, how is it helping fuel economy? Wouldn't a clogged air filter improve fuel economy?

I keep getting conflicting answers. Some people say cars don't learn/accept their mods without ecu reflashes, and some people (like hypertech) say you don't need a reflash for minor airflow mods. I tend to agree with the latter seeing as how the whole point of the maf and O2 is to make those adjustments internally.

When I was scanning my Regal GS and my GN, I would change all sorts of shit around and never had a problem with lean or rich conditions. Why do some cars need a re-tune and some do not?

 

[charlief1]

While an increase in airflow does use more fuel, it also produces more power. That means that the engine doesn't have to work as hard to produce enough power to move it down the road. It really depends on the mods that are done and the operating system that the vehicle has.

Think of it this way. If you have a straw to drink out of, and add a second straw, it may drain the glass quicker but it also reduces the time you take to drink, and quench the thirst you feel, faster.

 

[Turbo6Smackdown]

I see. That makes sense. Though why do some cars need a retune just for a filter? If that's the case, how do those cars adjust for dirty factory filters, or clean filters in the winter time? If the car can adjust for that, can't it adjust for a high flow filter then?

 

[pacecarta]

actually his answer isnt close because you question was about going rich not limiting horseposer as he answered but i dont feel like explain it out as it varies depending on what engine management is in place as some pre obd11 (before 96) were map based and some were maf based
a dirty filter will limit hp vs a clean filter , and a clean filter can increase hp within limits and the ecu will just make adjustments , beyond that it could lean the AF and power can drop

for the most part the on obd1 vehicles the ecu ability to adjust is very small and tuned from factory knowing what the engine needs as they built and shipped it and only needing to adjust for altitude and temp changes (usually only 5% or less ) , cut the flow 10% and the ecu wont be able to adjust the tune and with less air and the fuel decrease at their limits it will be richer, increase the flow too much and same scenario ecm cant correct that far and youll be lean

 

[Turbo6Smackdown]

I see. So they do adjust, they're just limited in how much they can adjust then. What did people do with our cars when they first got them? How did those people get away with yanking the filter out of our box and turning up the boost?

 

[NY Twin Turbo]

I see. So they do adjust, they're just limited in how much they can adjust then. What did people do with our cars when they first got them? How did those people get away with yanking the filter out of our box and turning up the boost?

The computer would see the additional air flow and add fuel accordingly.....but only up to a certain point.

After that, air flow would move up past the MAF sensor's ability to read the higher flow. But, that still didn't change the commanded AF. If you wanted it richer you would add fuel pressure or get an aftermarket chip. Without the chip you could add fuel pressure to a point higher than the computer could correct to remove it.

I remember plumes of black smoke coming from TR exhaust pipes at the track back in the early 90's. But this was better than white smoke!

A lot of motors blew-up back then. However, if it weren't for that.......most people today wouldn't have learned anything about fuel injection and forced induction. Let's face it.....most (not all) other Hot-Rodders still have no idea what they're doing.

 

[Turbo6Smackdown]

The computer would see the additional air flow and add fuel accordingly.....but only up to a certain point.

After that, air flow would move up past the MAF sensor's ability to read the higher flow. But, that still didn't change the commanded AF. If you wanted it richer you would add fuel pressure or get an aftermarket chip. Without the chip you could add fuel pressure to a point higher than the computer could correct to remove it.

I remember plumes of black smoke coming from TR exhaust pipes at the track back in the early 90's. But this was better than white smoke!

A lot of motors blew-up back then. However, if it weren't for that.......most people today wouldn't have learned anything about fuel injection and forced induction. Let's face it.....most (not all) other Hot-Rodders still have no idea what they're doing.

So to ensure I'm understanding this correctly, our old stock mafs measured up to what, 255 gr/sec or some shit like that? So past that limit it switched to a predetermined fuel table in the chip? I do remember that, but therein lies where my question really sits - it's this predetermined table. It has a prewritten fueling rate stuck in there; I'm assuming for the flow/mass of air a stock air box w/ stock filter flows. Is this problem people describing with the wrong fueling tables in this section of the chip? Is the high flow filters (or totally removed filters) flowing more air than these predetermined tables can allow fuel for? Love your answer thus far.

 

[NY Twin Turbo]

So to ensure I'm understanding this correctly, our old stock mafs measured up to what, 255 gr/sec or some shit like that? So past that limit it switched to a predetermined fuel table in the chip? I do remember that, but therein lies where my question really sits - it's this predetermined table. It has a prewritten fueling rate stuck in there; I'm assuming for the flow/mass of air a stock air box w/ stock filter flows. Is this problem people describing with the wrong fueling tables in this section of the chip? Is the high flow filters (or totally removed filters) flowing more air than these predetermined tables can allow fuel for? Love your answer thus far.

Whoa, wait one minute. It's been a long time since I've had a stock set-up. Even longer since I've had a stock computer. But let me try to recall.

If we are talking about stock motor, fuel injectors, MAF sensor, and chip.....
Then this is what I think happens. Everything is normal until you pass the max MAF reading. After that the injectors are at 100 percent duty cycle. Any additional fueling after that is all on you! Then it's a matter of fuel pressure.

That's why people used to turn it up at the track and down when they left. If they didn't, the computer may see a rich condition at other driving parameters, and if it couldn't pull the fuel out, it would give you a trouble code. Fouled plugs and a dirty fouled out O2 sensor.

Now, if you upgrade the injectors the fuel table must be correct for the normal driving areas of the map. If nothing else has changed the pulse-widths will be shorter to achieve the same AFs. Maybe the chip burner will command higher AFs in some of the power building areas and even at max MAF. And there still may be pulse-width left at max MAF. But it still won't increase any further because there is no higher readings after a maxed out MAF. This may still require a fuel pressure increase if you plan on going past that.

Now introduce a MAF translator to the mix. Now things begin to get interesting.

Or even better......F*&K the MAF sensor! Get an XFI!