IAT Sensor Failure mode?

[pontisteve]

On GM cars, what happens if the IAT sensor suddenly goes to either full resistance or no resistance, and the IAT PID logs either -40F or full hot?

Will the computer actually use that data? Or will it do something like Ford's Failed Memory Effects Management, where it assumes the sensor is bad, and just plugs in a number that's reasonable?

This car is set up with an IAT mod that when you flip the nitrous activation switch, a relay is supposed to alter IAT temps. I can see in the datalog that the temp goes to -40F, which should pull 5 degrees of timing. However, it does not. I'm theorizing that the computer is failing the sensor, since it goes all the way to the bottom of the temp scale, and therefore the computer doesn't alter timing like it should.

[SSUte01]

Check all the multipliers for Spark, it depends on OS, but some have another multiplier set to zero so you never get the spark reduction from the open IAT circuit. There's no 'sanity' check on the data from the primary sensors that I'm aware of, if the PCM is logging -40, then it's using -40.

[pontisteve]

Yeah, I did check the multipliers. The RPM multiplier is set to 1 at the 170+ coolant temp I am running, and the Air temp vs RPM table was set to all 0's down in the lower coolant temp regions. I'm pulling 5 degrees in the primary IAT table everywhere below 0 degrees F. So I figure that would be 5 x 0 = 0 degrees pulled, right?

Or is 0 in the modifier table representing "no modifier", meaning it should pull 5 degrees without modification?

Either way, I tried setting those zero's to all 1's in those lower temp ranges, and it didn't work. The car still does not pull timing. The only thing I could think of was perhaps a failsafe mode for the sensor. Are you positive there is no sanity check?

Any other ideas why this thing isn't pulling it's 5 degrees? (or any degrees for that matter).

[SSUte01]

Are you able to post the tune? I can't say for certain why or why not it doesn't work, I've seen some things work in one OS that doesn't in another. I assume you're logging the IAT Advance PID

[planethax]

I would not fail the sensor, set it more for -20 then take your timing out from there down.

[pontisteve]

I am logging all the Advance PIDs, and nothing happens. I'm logging base advance and total advance, and they are the same. The IAT spark adjustment tables simply are not doing anything to timing.

I don't know anything about GM's Failed Sensor strategy, and was hoping to hear what happens in the background with GM cars. My guess would be that the sensor fails and the computer ignores it, and that's why the timing isn't moving. Also, this is probably why when guys do the IAT modification trick to retard the timing for nitrous, they don't use the very end of the IAT range. Instead, they shoot for somewhere near the end, but not maxed out. Like 0 degrees instead of -40, etc.

My understanding is that it's typical to use a high temperature instead of a low temperature to pull timing, so this car might have wiring issues with the resistor used anyway. But it seems to me that targeting 0 degrees or so would be a good way to do this in Florida, since the car will never actually see 0 degrees IAT here. Or maybe -10.

Tune attached.