Help me understand what happens in PE

[JerryH]

Just to throw this out...

I believe there is an IAT fuel modifier. There would almost have to be. Warmer air will require different amounts of fuel than cooler air. If you really want to be sure, get a resistor and jump the IAT sensor, that way there will be no change at all. A 2200 ohm resistor will show about 90*.

In Krunch's situation (I've had a chance to work on his car real life and know it a little), his car is turbo'ed and his IAT is on the preassurized size of the turbo. He can get IATs up into the REALLY high numbers after a few seconds into boost. No one here would know that unless they knew his car personally.

The IAT placement is a cartuning thing. IMHO an improper place for it, BUT... at this point all the tuning that Dwayne as done to his car reflects this placement and changing it would require some serious bin changes.

I agree with you Eddie, there has to be an IAT fuel modifier there somewhere. That would be a nice table to have. Just imagine... near perfect fueling no matter what the temperature was! There is an equivalent table that we all know of that does it for the spark side... the Air Temp Spark table. Used to lower timing once temps reach a certain point. I use it to raise temps a touch under colder conditions and lower it when hot. This comes after 2 years of playing with the timing tables and seeing how my car trends out with spark needs in different temps.

I do know that there is an open loop A/F by RPM vs Air Mass table that comes in handy for flash KR situations sometimes. In my setup, I zero out that table as it wants to lean things out, often at the wrong times. Could this be the reason BlackGS sees the things he is seeing?

[krunchss]

Thought I had subscribed to this thread...no emails? Oh well...

Just wanted to clarify something Jerry...Placing the IAT between the turbo and my TB was MY idea...not Cartuning's....Cartuning's instructions were, and I quote...

"Just tape up the IAT and let if hang in the engine bay"

???

However this likley explains why Cartuning 0'd out the IAT spark table for 50-60 Celcius...THAT was the range my IAT was in all the time...measuring underhood temp. I guess they figured if they could keep IAT consistent, it was easier for them to tune? Dunno...

There idea sounds worse then my idea, as who would tune their car based on undethood temp? Hence I mounted where I did figuring this would be the best place for it. Some people sais mount it between the turbo and the air filter...well, THAT'S not what my IAT is? Why am I trying to trick my PCM into thinking the incoming air is a LOT colder than what it actually is? The reason why I mounted it where I did as this would give me more control of how much spark I can run, based on IAT. Once I get a decent baseline for spark, I can start to add / subtract spark based on IAT and at what temp I see KR.

Hoping to test out my theory this season :P

Krunch

[BlackGS]

I do know that there is an open loop A/F by RPM vs Air Mass table that comes in handy for flash KR situations sometimes. In my setup, I zero out that table as it wants to lean things out, often at the wrong times. Could this be the reason BlackGS sees the things he is seeing?

So, there is a table in PE mode that sets AFR based on RPM and cylinder airmass? Wouldn't that conflict with the Add vs RPM, and possibly MAF? Is it setting actual AFR, or is it an add/subtract value?

[krunchss]

Not quite sure if I follow your question / statement or not BlackGS...

Here's a snipit I found in a VE / MAF tuning document. Not sure if it applies to your question / situation or not but here it is...

"At WOT, the PCM falls out of closed loop operation. When this happens, it relies on the PE table to set the AFR. The PE table is broken down by RPM, with the values being divisors of the stoichiometric AFR. Hence, if the stoichiometric AFR is the default value of 14.7, a divisor of 1.225 would equate to an AFR of 12:1. This is referred to as the “commanded” AFR. This AFR is not monitored and adjusted by the O2’s."

Krunch

[Perforator]

So, there is a table in PE mode that sets AFR based on RPM and cylinder airmass? Wouldn't that conflict with the Add vs RPM, and possibly MAF? Is it setting actual AFR, or is it an add/subtract value?

I believe the table Jerry is talking about is open loop only, not pe and it's probably some kind of startup table that applies for a certain period of time after you start your car before you go into closed loop.

[BlackGS]

I believe the table Jerry is talking about is open loop only, not pe and it's probably some kind of startup table that applies for a certain period of time after you start your car before you go into closed loop.

Ok, that makes sense.