Mellon

hey guys, I've been a lurker here for ages but just now registering to make a post so hello to all

I drive a 91 dodge stealth r/t tt that's modified a bit. One of the common mods we do is rid ourselves of the restrictive stock MAS and replace it with a GM MAF and MAF translator box that converts the GM airflow signal back over to Kharman so our cars can use that data.

I've been noticing lately that my a/f is shifting greatly with the weather changing from 18 to 40 degrees and back. I don't have this problem at all with the stock MAS that has a built in IAT and Baro sensor.

with the GM MAF, when it's cold I go super rich we're talking 10.0 a/f and when it warms up I go as lean as 12.5 which is death to my car and quickly sets off knock counts if I stay in it for any lenght of time (pump gas)

my question is..does the Delfi brand LS6 (zo6) 3.75" GM MAF have a built in IAT sensor or not? I was under the impression that it had it's own built in and could compensate for temp changes and automatically calculate that into the airflow signal it forwards on to my ECU.

I know for a fact that the MAF-T (translator) box sends a fixed IAT and Barometer signal .. IAT of ~80 degrees and baro ~95 to my ECU, so if the GM MAF is NOT correcting the signal with an internal IAT/Baro then that explains my a/f shift with the weather.

foff667

iTrader: (2)

im 99 % sure it does.

slow

iTrader: (7)

it does have a built in iat sensor, but it is not used on the calculation of the maf output, but has 2 wires to the pcm for the iat sensor. that is why its a 5 wire vs 3 wire sensor.

Ryan

Mellon

ok, so it has a built in sensor that sends that IAT info to the computer which you guys refer to as the PCM??

if that's the case then that would explain my problem.. the built in IAT isn't doing anything for me since the MAF-T box is sending a fixed value for IAT and Baro to my car's computer (ECU) right?

Another_User

You probably aren't getting any value for your IAT. I have no idea what kind of wiring you are dealing with, or what kind of PCM, but you probably need one of these:
PAC5889 - Wire harness adapter for PACE 85mm MAF or LS6 MAF 5-wire to LS1 MAF 3-wire
I saw that on the Pace site...I have no idea if any sponsors make a similar device, but I am sure they do. Unfortunately they did not come up first on my Google search. If your PCM can handle a seperate IAT input you can just use that neat-o adapter.

Mellon

well from the GM MAF the wires go to what's called a MAF-T which is just a box that gathers the GM airflow signal and converts it to the Kharman type signal with the stealth/3000's ECU uses. It also gives a fixed IAT and baro signal to the ECU. Normally the stock MAS for my car gives the ECU airflow, a real IAT and Baro, not a fixed signal so that it can compensate for weather changes.

Mellon

what role does the IAT play on your cars? Is it used in the fuel calculation at all or is it used for soley for other things.

Another_User

It is used in fuel calculation.

Mellon

interesting....some suggest that the stock IAT it is NOT used for fuel calculation on the stealth's but it sure does seem like it.

Mellon

do you guys know of any technical documentation of the GM MAF.. I'm trying to learn all I can on it.

TurboBob

iTrader: (1)

Some technical followup.

The Mitsu cars use a Karman Vortex airflow sensor. It is a VOLUME flow sensor so the ECU (PCM) also requires Barometric and Intake Air Temp sensors so the ECU can calculate air MASS FLOW.

The Translator for the Mitsu's provides fixed value signals for the IAT and BARO signals since the MAF is a MASS FLOW sensor itself.

The QUESTION is: Is the signal from the MAF (GM LS1/LS6) correct at all temperatures? Or does the GM PCM use the IAT sensor to correct the MAF value?

My data/documentation says that the MAF sensor signal is accurate vs temperature. My experience agrees.

Perhaps Harlan could comment........

TurboBob

Another_User

I think it uses the IAT to correct, but I am not 100% positive. Regardless, the GM MAF is very particular about how it is mounted in the intake, and what the shape of the intake system is. Any changes will require a recalibrated MAF table.

TurboBob

iTrader: (1)

Yes, there is the sensitivity to airbox and filter, but they are using a MAF Translator. The "MAFT" for the mitsu cars has 5 dials instead of the 2 that the LS1 version has as well as 2 tuning modes. Mellon is also using an 'eManage' unit which is a fancy MAF signal tuning device. So the calibration is not the issue.

The root of the question is: Does the IAT affect the PCM's calculation of Mass Airflow from the MAF sensor. My data says it does not. (meaning that the MAF Sensor signal is accurate vs temperature)

Bob

samz28

well you kinda sorta need the IAT for speed density mode. If the MAF is out of range of failed, you can't run speed density without the IAT based on principle.

At some points i believe the MAF is not ready the car ls1 ecm may run in speed density mode I'm guessing other cars need this ability too, say if its -20C outside and the maf is a popsicle, it may take a bit to get online and accurate so yeh fallback to alpha-N or speed density. i spose if you have a map sensor that would be speed density, if only a tps then alpha-N


iat is really good for determining if you are doing a warm cold start or a cold cold start (IAT VS ECT) to not flood the motor too much or lean and not start.