I asked this in the PCM section, but got no responses....

Ok, I run a TNT F1 wet shot, and will be stepping up to a 150 this fall. I have read about being able to use Edit to make the PCM go to a lower timing table by running a dry shot and passing it through the MAF. I want (need) something like this, but for my wet shot.

I remember reading about people using like a 5 hz resistor in the IAT sensor to make the PCM think the IAT was 57* F I guess, maybe celcius. I noticed that the timing tables are in Celcius, not Farenheit. So that 57* F would be about 14* C. Therefor, couldn't we just figure out what size resistor we would need to tell the PCM that the IAT is 90* C (194 F)?

Then just put in the 90* C column how much timing we want taken out? I dont think that we would actually ever see a real IAT of 90* C anyway. Thats seems awefully high.

I just dont want to have to run a seperate file for good N/A and another for safe N20...

Will this work?

 

How low does the chart go?

 

how low? Like how much timing is reduced at the highest IAT? My stock 98' file claims to remove 3* at the 90* celcius reading?

How much timing should I pull to be safe on the 150 shot?

 

Use a 750 ohm resistor. Only problem now is that it pull some fuel out too because the air is supposed to be less dense at 100 F. It works fine with a wet kit cause you can jet the fuel up, but not a dry, you end up starting to run lean.

 

I'm interested in doing this too, wouldn't the timing be retarded all the time if you wired in a resistor?

 

I don't see a table in LS1edit relating to fueling vs intake temp so how do you know that the computer will pull fuel according to the air temp?

 

If the computer doesn't add or subtract fuel if the temp goes up and down then what is the IAT there for? If the temp is 120 one day and 2 the next, you better believe it adds the extra fuel when its colder and pulls some when its hot to keep A/F's correct. Cartek believes the same, heres the link: http://www.cartek.net/tip03.html

Part throtle should be based off of O2's, and WOT should be based on MAF, air temp, RPM, and maybee load. I won't pretend to know anymore then that.

 

Guys, I am talking about taking timing out, not taking fuel out with the resistor.

And I am not talking about running the resistor all the time, just when you are going to spray. Plug it into the IAT sensor like guys do with the 5 ohm one for a temp of 57*

 

The IAT is there for timing adjustment. Seeing as how these cars have a MAF sensor, it does compensate for air density, temperature, etc through the MAF. I guess what I am saying is, there is no proof that the computer uses the IAT sensor for fueling, only timing adjustments. Until somebody provides proof otherwise, I am more inclined to believe what I just said since the evidence is on my side.

Therefore I believe that wiring up the IAT sensor through a relay with a resister than can be switched on and off with the solenoids/relay of a nitrous system would be perfectly fine and not screw up fueling so to speak. Oh yea, I have done this on a wideband to verify my hypothesis that what I have said is correct. Worked great with no fueling adjustment.

 

Cool. Any idea what's the maximum timing you can pull out with this trick? What size resistor?
TIA

 

You could pull out however much timing you wanted by changing the appropriate iat vs load timing cells that correspond to your resistor value.

How is the car runnin Jim?

 

It's not
The motor's been rebuilt and is ready to put back in. I should have it running again by the end of the month.

 

my stock 98' table will only pull 3 degrees at max....

so how do we find out what size resistor will give us the 194* F reading...?

 

Aww, that sucks, but at least it will be running again at the end of the month.

I used a 330 ohm resistor to get me ~80 degrees celcius and just fill in the table accordingly. I just built my device last night and hardwired it in and it works like a charm.

 

Nic00Z28M6'


http://www.kemparts.com/TechTalk/tt06.asp sais:
" As air flows across it, it cools down. The heated wire or film is a positive temperature coefficient (ptc) resistor. This means that it's resistance drops when it's temperature drops. The drop in resistance allows more current to flow through it in order to maintain the programmed temperature. This current is changed to a frequency or a voltage which is sent to the computer and interpreted as air flow. Adjustments for air temperature and humidity are taken into consideration since they also affect the temperature of the heated wire or film. Humidity always affects the density of air since humid air is denser than dry air. No other compensation is therefore needed for this factor. Air temperature affects density since colder air is more dense than warmer air. Many systems use an air temperature sensor to compensate for this factor since similar amounts of air can enter an engine at different temperatures. Some MAF sensors use an internal "cold" wire to send ambient temperature information to the computer. Some use an intake air temperature sensor in the manifold or the intake piping. This sensor is almost always ntc in design (negative temperature coefficient). That is, it's resistance goes up as air temperature goes down. This "thermistor" works just like a coolant temperature sensor and usually has identical resistance to temperature values. By the way, these values are very different from manufacturer to manufacturer and are available in most repair manuals. They are also programmed into scanner software."

That site explains the use of an AIT for fuel trimming perty clearly. You can find quite a few if you do some searches.

You wont find a temp/fuel table in LS1 edit because the air temp/density ratio is a constant which means you wont ever have to change it. The computer knows that if the temp goes up by 1 deg there will specific amount it will increase by.

You can see the match for this at these sites:
http://www.davisnet.com/product_docu.../apnote_14.pdf

http://www.elji.se/kund/apnote_14.pdf

http://wahiduddin.net/calc/calc_da_em.htm

And here is a link for an Air Density calculator using Excel so you can run it on a laptop without a web connection : http://pages.globetrotter.net/equipekcm/densite.xls

Bottom line, the AIT sensor helps determine the density of the air so the MAF can determine the correct airflow and the PCM can add the correct amount of fuel. The PCM will also add or subtract timing based on the air temp in order to keep from knocking at the higher intake charges temps.

 

FinalTA. I have a wiring diagram that I have scanned that shows how to wire up the relay and resistor so it is only hooked up when the N20 system is armed. If you want, I will send it to you. And if you get stuck I can walk you through it.

 

That is a generic site that does not relate directly to the GM LS1 PCM. All of my testing that I have done on this concludes that the IAT is NOT used for fueling on these cars since I can scale the IAT reading from -39 celcius up to 90 celcius with no change in A/F verified on a wideband dyno.

I do not believe this since all of the testing I have done on this concludes that the IAT is NOT used for fueling on these cars. The MAF wires will cool at different rates according to mass air flowed which also includes temperature and humidity as factors.


These sites deal with carburators, not Mass airflow vehicles.


These are great and accurate, but don't have a bearing on this discussion.

I don't believe this for one second. The MAF does all of this except add or subtract timing based on temperature, which is what the IAT sensor is used for. Like I said, I have tested all of my theories on a wideband dyno and the A/F NOR THE REQUESTED TIMING CHANGED AT ALL. Substantiate it yourself if you don't believe me. Run the test with a wideband and after that come tell me that the IAT has any bearing on these vehicles with fueling.

 

FinalTA, just got back in town. Will get it out to you tonight. The pic shows how the relay is latched with the N20 arm switch on.

Nic00Z28M6,
called Cartek today and asked them about their warning for their tech tip. They told me that on factory and mild tunes there was barely enough difference to even show up on the W/B. They also said that they have gotten in some cars that where tuned from other people/places with highly modded tables that it showed up signifigantly. I told them how someone scaled the IAT sensor up and down with the ls1eit and how that would affect it. He said they never did it that way for testing . Only by going up and down in resistor sizes in place of the IAT. They said you can run up and down in the resistor sizes and watch the injector pulse width move up and down very slightly.

 

You can watch the pulsewidth change by just changing resistors because without changing the IAT vs map table to 0 with LS1edit the timing will change, which will change fueling/pulsewidth. Like I said, I guarantee that if you test my theory yourself you will find the same results that I have, changing air intake temp alone with everything else considered constant (timing included) will not impact fueling, period. Hell, the general concensus a year ago was that the volumetric efficiency tables didn't come into play until the MAF was disconnected.