Engine IAT sensor resistor mod...

why is your MAF Sensor reading wrong, why dont you just drill a hole in your intake to for your sensor.

IAT sensor resistor mod...

I've posted my AEM CAI onto ebay and pretty much resolved to just sale it and be rid of it. The problem with it was that it was causing the engine to run lean b/c the MAF sensor was getting an inaccurate reading - lots of detonation in middle rpms.

I'm generally not too keen on the idea of messing around with stuff like this.....but......

I was thinking - adding a resistor to the IAT sensor would cause the ECU to think the incoming air is colder than it actually is and inject more fuel, which would correct the lean mixture.

Good or bad idea?

Thoughts, opinions, any feedback at all is welcome.

Yes, I am trying to find a cheap fix - but this does seem like it might work. Something like 200 or 400Ω.

Late,
Trav

I'm using this forum as my virtual/mental scratchpad, so just ignore this if you don't wanna read it. You know...the whole therapeutic self-talk thing or whatever.

The density of air in kg/m^3 increases by about 1% for each drop of 5ºC.
So, ideally, the ECU would inject about 1% more fuel for each 5ºC colder.

The IAT and ECT sensor work by increasing resistance as temperature decreases, but it is an exponential curve. At 68ºF (20ºC) there is no correction. Resistance at that temp would probably be around 1.5-3kΩ. At 32ºF (0ºC), the resistance would be around 4-8kΩ, whereas 104ºF (40ºC) would show around 0.8-1.5Ω.

So:
0ºC 4-8kΩ
20ºC 1.5-3kΩ
40ºC 0.8-1.5kΩ

That's about the limits of temperatures I'll see around here.

Anyhow - on re-thinking, I'd say a 1kΩ resistor would do well. At 40º, the ECU would think it was around 20º colder and richen the A/F mix around 5% or so. And at 20ºC, would probably only cause the ECU to think it was 5 or 10ºC which would richen 3 or 4%.

Perhaps a 2kΩ resistor would be more appropriate. I think I'm going to try both to see...if the intake doesn't sale, i.e.

On vehicles with a MAF sensor, there is a little screen or some kind of mesh (on the Corolla it is plastic) to straighten the airflow out so there's not as much turbulence. Helps the air to be hitting the MAF sensor in a direct straight line. Aftermarket intakes don't have that, so there's a lot of turbulence and consequently, the MAF sensor tells the computer that X amount of air is entering the engine when actually it's more. That ends up with a lean mixture. The only fix is to somehow find a way to trick the ECU into injecting more fuel.

I just hate the idea of doing the IAT sensor mod....because.....

Well - it's just so friggin gay with all this "+20hp" crap all over ebay which is a total load of BS!

Late,
Trav

For all intents and purposes, the IAT resistor mod should work - I think. I'm curious what kind of impact colder temps have on timing - SHOULD be minor if any....just don't know the logic of the ECU here. I do know that adding a resistor to the circuit won't make as much of a difference at low temperatures. AHA! a potentiometer would be a good idea with this....adjustable resistance. SNAP!

Things to consider:

1) The EVAP system monitor can't run without a cold start. The ECU determines what a cold start is by comparing the ECT and IAT - if they're within 8ºC (15ºF), then it's a cold start. Probably would cause an OBD-II readiness flag - how big of a deal is that?? If there were a problem with the EVAP, the check engine light probably wouldn't illuminate...dunno about that.

2) I do know for a fact the MAF sensor was getting an inaccurate reading between 1800-2800rpms @ 1/2 - full throttle b/c that's where I was detonating. That probably(?) was b/c detonation doesn't usually happen in high rpms b/c there isn't enough time in the combustion cycle. But maybe the MAF sensor was getting an accurate reading at higher rpms. The only way to know is by using a wideband O2 sensor (not an option) or knowing the flow dynamics of the airstream inside the tube (also not very likely).

HA - I guess the only way to find anything out is just to try it and see - if the stupid thing doesn't sale.

Late,
Trav