IAT modding?

[19bonestock88]

So I had a thought... our cars run like crap when it’s super hot out partly due to less dense airmass, but also partly due to the PCM pulling timing back...

Who has tried to trick the PCM into thinking the air charge is cooler than it actually is? My thought is that since the car in closed loop is always adjusting AFR to right at 1 Lambda(14.7AFR), what IAT value it sees during closed loop doesn’t matter much, except for controlling timing advance, right?

I’m guessing that most IAT sensors lave less resistance when hot and more when cold, so skewing the IAT value *should* be as easy as adding a measured amount of resistance to the circuit... I would think that you wouldn’t want to move the value too much, lest you bottom out the IAT table in winter time, but I imagine a nice round 20*F correction should add some timing advance while not setting a fault code...

Now, this would alter the AFR at full throttle (when engine is running in open loop and ignoring oxygen sensors) but I imagine that could be tuned out with a piggyback fuel controller (such as a SAFC)...

Add in an EFIE in the oxygen sensors to lean the mixture in closed loop, and an engine could become much more efficient...

Any thoughts?

[Stubby79]

It will think the air is denser and therefore add more fuel and give you worse gas mileage. (although the MAF Sensor might take priority and it will just ignore your IAT sensor mod) It doesn't just affect ignition timing.

[19bonestock88]

In the short term it would give worse mileage but in theory, with the engine running in closed loop wouldn’t it correct the AFR based on the O2 sensor data?

I considered going the other way for lean burn but I figure I’d have to do a full ECU reset about once a week to undo the “learning” that had been done, which led me to dropping the IAT value...

There’s no MAF to adjust or scale in this car, hence my ability to fiddle with intake designs

[teoman]

Heat the air after the iat?

[twj347]

You really want to know the relationship between IAT and intake temperature in your ECU before doing this. My car has IAT vs Ignition Timing tables in the ECU, but the OEM tables only retard timing above intake temps of 40C. At all temperatures below 40C, there is no adjustment. This means that unless its really hot outside, fudging the IAT sensor calibration is not going to do anything but possibly mess with your AFRs.

[teoman]

It has been some time since i was looking at the iat’s but if i remember correctly, 86 degC was the sweet spot according to one publication.

[19bonestock88]

Originally Posted by twj347

You really want to know the relationship between IAT and intake temperature in your ECU before doing this. My car has IAT vs Ignition Timing tables in the ECU, but the OEM tables only retard timing above intake temps of 40C. At all temperatures below 40C, there is no adjustment. This means that unless its really hot outside, fudging the IAT sensor calibration is not going to do anything but possibly mess with your AFRs.

Ideally I'd like to do some data logging before doing any mod, since I can't access or adjust the timing tables in the PCM due to lack of support... Basically I thought of IAT as a workaround method of advancing the timing some more, which would help both power/torque and mileage at constant speed..

[hat_man]

I seem to remember some Ford ZX2 guys experimenting with a 5.6k ohm resistor in series with the IAT. Was supposed to trick the computer into thinking the temps were 10* cooler. I think the idea was that it would slightly advance the timing (3 degrees or so) but the O2 sensors would return the resulting "rich" mixture back to normal but leave the timing advanced. I'll see if I can find some links and post them in a bit.

https://ecomodder.com/forum/showthre...n-32306-2.html

It looks like Team ZX2 may be defunct. There may be a way to access their archives in this thread....

https://www.feoa.net/threads/teamzx2...hreads.112752/

[19bonestock88]

The issue is that the ZX2s are MAF controlled, IAT isn’t used as heavily to determine AFRs...

But the objective is the same... I wonder if the GM sensor has the same temp/ohm curve?

[hat_man]

That I couldn't tell you. I was looking for my '97 Ranger. Not even sure it's a possibility with the new Ranger.

Let us all know if you find anything out. I'm sure there are other "inquiring minds" that want to know.