Im the first.

[misnblu]

Thought Id be the first to post on this section.
Here is a link for the information and specs of the LD9 (2.4) engine in the third generation z24's.
Lets see some more tech stuff on these threads, that would be nice.
Misnblu

[mtomas]

Good call on the info!

[misnblu]

Thanks man.
As time goes on, Ill have a lot more to contribute to the forums.
You should see me files on all kinds of subjects, not just import or domestic.
Misnblu

[misnblu]

Here is some very technical information from somewhere. I think RoboGeek posted this, not sure but explains plenty about the IAT mod and other related things.
Enjoy


Ok.. there's so much misinformation I just gotta post this.

First.. the IAT mod that everyone sooms to constantly discuss and what is sold on EBay as a 'timing kit" is a complete scam. Being someone who regularly tears PCM codes apart I can tell you that NOWHERE does the IAT sensor do anything to timing. What the sensor does is provide one part of a formula for something called "speed density" Think of it as a way of guessing how much air is flowing into the engine. This is used in a corrections table to calculate BPW (base pulse width) which is basically the injector pulse width.

BPW = BPC * MAP * T * A/F * VE * F33C * BLM * DFCO * DE * CLT * F77

Where: (everything labeled "term" is from a lookup table)

BPW = Base pulse width in milliseconds
BPC = Base pulse constant term (table lookup, basic engine air and FI
calibration plus EGR calibration)
MAP= Manifold absolute pressure term
T = Inverse air temperature term
A/F= Inverse air/fuel ratio term
VE= volumetric efficiency term
F33C= Battery voltage compensation (for the effect on FI open/close delay
and fuel pump delivery)
BLM= Block Learn Term (what the ECU has learned from the O2 sensor)
DFCO= Decel Fuel Cutoff Term (when to turn fuel off on decel)
DE= Decel enleanment term (when to lean instead of cutoff)
CLT= Closed loop correction term (result of O2 sensor Proportional/
integral closed loop)
F77= Turbo boost multiplier (if used)

Now if you notice the "T" in the formula is the IAT sensors contribution - its actual number is from a 2D table.
Now also note that the "T" is a multiplier and that there is another multiplier named "BLM" - that is the Block Learn Multiplier which is in simple terms what the O2 sensor has seen as far as rich/lean conditions.
So if the car has an incorrect IAT reading and is making ther O2 sensor read rich the BLM number will compensate for it - net effect = 0.

Now as far as spark - there are only a few things used to calculate that. Spark tables are fixed (static) tables which can only be modified by changing the PCM program. Sparks main tables are:

Spark Table (RPM vs Vacuum Signal in kpa) (3D table)
Power Enrich Spark (RPM vs Added Spark Advance)

There are some knock retard tables and some other things but those are the main ones. Notice there is nothing about temperature. Some PCM's use a table that modifies spark vs coolant temp but I have yet to see one use IAT.

So I hope that clears stuff up a bit..



Theres 2 different things the PCM usually uses for calculating stuff offsets and correction factors.

An offset is usually added to the number that needs adjustment, while for correction factors, the number needing correction is multiplied by a correction factor. This difference is important when tuning the PCM for bigger injectors because the Injector Size value is a correction factor, but the Injector Offset vs. Voltage is an offset.

Funny thing is I HATE MATH!! lol



Well, since you guys kinda understand this let me go a little further and explain how this mod can actually help performance.

There are 2 kinds of open loop. Right after a cold or hot start, a scan tool will report that the PCM is using open loop fuel control. Once the PCM decides that conditions are right, it switches to closed loop fuel control. But even after this switch, if you lean on the throttle hard enough, the PCM will switch to power enrichment (PE) mode, which is another form of open loop. In PE mode the scan tool may report that the PCM is in closed loop, but it should also report that learning is disabled. Learning disabled means that the PCM is ignoring the O2 sensors, which is the same as saying that the PCM is using a version of open loop fuel control.


Whether the engine is in closed loop or open loop, the PCM will jump to the PE fueling tables when you really lean into the throttle. So how does the PCM decide exactly when it needs to use the PE tables? By looking at another table, naturally. There is a "WOT" table that tells the PCM how far open the throttle must be (as measured by the TPS signal) for the engine to need the PE tables. The only table input is RPM. For example, at 2000 rpm the table might say that the TPS must be at 66% (in other words, 66% of full throttle) for the PE tables to kick in, but at 4000 rpm only 38% TPS is needed for the PE tables to kick in. Note that the "WOT" table is used for many high-load conditions other than wide open throttle. WOT is just a convenient label to refer to the conditions needed for switching to the PE tables.

So what happens in PE mode? It works like this: the PCM bases PE fueling on the same 14.7:1 AFR it uses for closed loop. The PE vs. ECT lookup table supplies an enrichment factor based on coolant temperature, and the PE vs. RPM table supplies an enrichment factor based on RPM. The base pulsewidth is adjusted by the factors chosen from these tables when the PCM decides conditions warrant it. Wait a minute, you say, what about the BLMs and INTs? The O2 sensor signal is not reliable at the richer-than-14.7:1 air/fuel ratios used in PE, so PCM ignores the O2 sensors and disables BLM learning. So what are the BLMs and INTs doing during PE mode? Unfortunately, for the BLMs the answer depends on where they were the instant before the PCM decided that PE mode was necessary.

If the PCM calibration is generally good (BLMs near 128), or generally rich (BLMs are smaller than 128), the PCM will set the BLMs to 128 during during power enrichment (even if it was 108). But if the last BLM before the switch to power enrichment was 132 or bigger to compensate for the calibration being too lean, the PCM will use that BLM during WOT instead of 128, even if it's 160. GM did not want to let the engine go lean when you dip into the power!

This is where the IAT mod comes into play..
If the PCM had to adjust the BLM numbers to make up for the IAT being miscalibrated or tweaked then the BLM tables will be less than 128. That causes the PCM to use 128 as the WOT reference. The combination of going from part throttle to WOT if its just right will actually improve performance as the excess fuel burns out and it passes through perfect calibration points. This does not work all the time and is not repeatable which is why its not generally used. However ECT is.. that was the basis of many OLD performance chips.

The PCM bases PE fueling on the same 14.7:1 AFR it uses for closed loop. The PE vs. ECT lookup table supplies an enrichment factor based on coolant temperature, and the PE vs. RPM table supplies an enrichment factor based on RPM. The base pulsewidth is adjusted by the factors chosen from these tables when the PCM decides conditions warrant it. The O2 sensor signal is not reliable at the richer-than-14.7:1 air/fuel ratios used in PE, so PCM ignores the O2 sensors and disables BLM learning.

just wanted to throw a little more fuel on the fire for you guys..




Author unknown, I think.



Misnblu

[misnblu]

Here is the second half of the post.

wow.. this post came back from the dead!!

Since this was posted we found a little more info..
The newer OBDII PCM's have a few more spark tables - or things that use the tables for their own algorythms. Its mostly emissions stuff and as most things are when it comes to the computer - spark is subtracted from total advance.

I dont think I posted it in here, but I hooked up a timing light (snap-on digital advance) and marked a reference point. Then I read the timing with the IAT on. Removed it and replaced with a potentiometer (100k). Went throught the whole range and only managed to make my exhaust smell like rotten eggs..
Timing didnt advance... Including total timing

add this to the FAQ if you want..



First of all, I am not trying to write the things that RoboGeek said again, so I am only trying to explain the thinks in other way and learning something good with all this explanation that RoboGeek have posted before.
So, Please be free to correct me.

So, If I understand the whole idea, this is the explanation in other way:

You talk that modern cars have two main forms to process the computing of the BPW, mainly named open and closed loop.

Supposing that most of the OEM oxygen sensors are not wide range O2 sensors, from 12.8:1 AFR to richer conditions it goes to erratic readings, we can call open loop procedure, to a process that depends in all the inputs to generate an answer, in this case the BPW. That is, any condition where the readings from the O2 sensor goes out the specified numbers in the tables or a forced situation that change loop process function.
For example, cold or hot starts and some engine AFR enrichment conditions.

In the other way close loop procedure , is when a feedback process appears in scene to affect the answer due to the inputs and previous answers by itself. So it is a bi-stable system, that correct is functions by the inputs (BPC, MAP, T, A/F, VE, F33C, DFCO, DE, F77) and the outputs (BLM and CLT)

Ok, many of the upgrades done to an ECU, are made with power in mind as acceleration, top speed, etc.....

So, modifying the tables and/or add some offset to current factors, of N/A ECU programs, we can obtain the outputs needed, forcing a controlled power enrichment mode when it is really needed to make the gains we expect.

And we introduce factor corrections where major factor affects the needs of the engine, like boost of a supercharger or a turbo.

Finally and if I understand good, the IAT sensor introduce changes in the BPW, modifying the AFR not the spark timing at all. Because spark timing depends on other variables like vacuum and rpm, and are located in fixed tables as RoboGeek say. That is the reason that IAT trick (relocating this sensor in the front bumper of the car to reach cold air) only generate an offset in the variable "T" making the AFR richer, making that more gasoline will consume by the engine. That is right, but without the enough spark timing, rpm signal, manifold pressure and other factors that would be apply to improve the average of the BPW, more power can't be done by the engine. This trick maybe could be useful when a WOT situation forces a PE mode releasing a little more gas.

!!!!!Either way, IAT trick or eBay IAT timing trick only makes the engine waste more gas and make less power.!!!!!!!!!!

when it comes to boost (like a GN) they use a different multiplier added in (F77) That compensates for the needed fuel load. Modifying a stock non-boosted PCM you wont have that luxury - that part of the programming is nonexistant. So your best bet is a 2 or 3 bar MAP sensor, then modifying the tables that the computer uses for fuel trims. Once you have those close then you can tweak the PE mode and the WOT mode.

In open loop (cold) it runs from fixed tables, using coolant temp as a reference point. Once the O2 sensor has had several crossover events (swinging from below .45v - above .45v) then the computer kicks into closed loop. It also goes into a form of open loop (warm) at idle when the O2 sensor drops below 600ºF or so..

The IAT is only used in the calculating of the air density.
A MAF car uses air temp and airflow in grams/sec for fuel calcs.
A MAP car uses air temp and Volumetric Efficiency to calculate it.

Also remember.. if you do the Ebay thing, the PCM will 'learn' eventually that the sensor is off. The O2 sensor, reading rich, will cause the PCM to adjust the fuel trims leaner. Which means you accomplished nothing by doing it.

relocating it doesn't hurt anything.. unless its in direct sunlight. It will still read close enough to the true air temp to be accurate. Remember, only warm blooded creatures or devices that are warmer than the surrounding air are cooled by airflow - The IAT is at the outside temp at a total standstill or moving - unless it gets wet. Then you get evaporative cooling and that will cool the temp it reads down some. Fortunately wind chill has no effect on cars or you would never be able to start one in winter (shut up cali and florida people ).

My IAT is convienently wire tied to a harness near my batt.. just because I'm too lazy to drill a hole
( I have a WAI so those temps are close too)



Misnblu

[RoboGeek]

YAY!! another forum to post in!!!

yea.. my PCM guru here ;D

If its electronic, I can make it smoke!

[misnblu]

Robo, you are the expert on OBDI and II, why not post some information on that here in the forums?
Ive got a couple of your technical articles in my files too and Im not sure, isnt the one above from you too??
Glad your here as your expertise is always welcome.
Btw, how are your projects coming along?
Misnblu

[RoboGeek]

yea.. those were from JBO trying to clear up some misinformation that was being preached as facts.

The things that start as one persons incorrect opinion and get repeated and turned into de-facto information just amazes me sometimes. I think that post was going to cause damage, which is why I made it such a long one.

[misnblu]

It was a great post and because of your insight of the post, made me a more knowledgeable person.
Now if only I could have a better understanding of the obdII system.
Thanks for that post Robo. If I would have know it was yours, I for sure would have given you the credit.
Any type of article like that, I do give credit to the person that made the article.
Misnblu

[RoboGeek]

Wait till OBDIII hits..
Its going to use the same setup basically as Onstar uses.. your car will constantly transmit emission info to transponders and if your car is polluting you will recieve a notice to report to the local smog station. Obviously this is gonna be done in Cali first - they are prototyping it there right now..

Here's whats scary.. remember the rental car company that charged you for speeding by using the onstar tracking system? And you've heard of photo radar right?
OBDIII will be capable of monitoring your position and speed and transmitting that to the nearest PD for a nice speeding ticket in your mailbox. You speed through several jurisdictions or multiple times and you could have thousands of dollars in tickets with just one trip.

Big Brother is watching...


**EDIT**

Here's some OBDIII info..
Something this article doesn't mention is that there will be a provision on the PCM to allow law enforcement or anybody with access to disable the vehicle. This is mainly for high speed chases where the cops could send a signal and kill the car.


OBD III
Have you heard anything recently about OBD III? Michael McCarthy of CARB shared some of the latest news about what's happening in this area.
“We paid a contractor to build up a couple of mock cars with remote transmitting systems and demonstrate that it was technically feasible to have a system that sends out a remote transmittal when the check engine light comes on,” said McCarthy. “A pretty basic contract since there are already systems like On-Star and LoJack.”

This prototype system was built by GM Hughes Electronics, and uses a roadside transmitter to interrogate vehicles as they pass by. The system is reportedly capable of retrieving information from eight lanes of bumper-to-bumper traffic whizzing by at speeds up to 100 mph!

“The concept is to stop requiring smog checks for every passing car and only test the failing cars. It would likely be a voluntary system - when you buy the car you could choose whether to go to smog check every two years or pay $xxx and never have to go to smog check,” said McCarthy. “You would, however, have to push a button on the dash once every three months that would send a signal that identifies your vehicle and the status of the check engine light. If you forgot to push the button you would probably get a letter in the mail telling you to press it or bring it in for inspection. If you pressed the button while the MIL was on, you would probably get a letter in the mail saying you have 60 days(?) to correct the problem and press the button again. If the MIL came on and you got it fixed before you pressed the button, you would never get any notice in the mail. There would not be a continuous signal identifying the location of the car or anything like that.”



Since this article a few things have been changed. This was originally for emissions but has evolved into much more. Including a 'black box' that stores accident info - like speed, braking, accelerometer forces etc. No more lying and saying you was only doing 20mph ;D

[misnblu]

Thanks robo, Ive copied and pasted to a folder for future reference.
See Import Tunerz, more information for the Library.
Misnblu
Thanks again Robo, oh, and a link to your site with more information please.