During my drag racing this weekend I identifed an issue that I think was the culprit behind my less than expected times. Aparently when I sit and idle my car the intake air temperature sensor becomes heat soaked, and reads erroniously high (like 145 degree high). I have a table in my tune that pulls timing as a function of intake temp. With intake temps at 145 degres at the beginning of the run I was seeing up to 7 degrees of timing being pulled. This is an issues I've never noticed or seen before while tuning because usually my tuning is while driving, and the sensor doesn't get heat soaked when the car is moving and air is flowing.

I bought a different type of sensor to try out, and I may even try a different location for the sensor. The factory sensor is plastic bodied and mounts in a grommet in rubber. My sensor is metal bodied, and mounts in aluminum. I think this is the root cause of the problem. The aluminum is transfering heat to the sensor body, causing incorrect readings. I'm going to try out the factory sensor, and maybe even move it to a diff location.

Here is my intake setup. What is not pictured is that it is now header wrapped. I overlapped the wrap 3/4 width on each wrap, so its probably equivalent to double wrapping it. I used two 50' rolls on the intake.

It should have several layers of heat protection. Ceramic coating, aluminum pipe, ceramic coating, and double thick header wrap. This is the reason I belive the temp sensor reading to be erronious. I am considering not even putting the sensor in the intake, but putting it down in the cavity where the filters pick up air from. Thoughts? Currently the sensor is in the Y where the two sides come together, only a few inches from the throttle body.

 

Nice car. Miata's are never gonna be good dragsters because you can't have a road course car & drag car in the same vehicle. They're polar oposites. You already know this I'm sure. Anyway, as to your problem; yes you can move the sensor to an area that sees truer ambient air temperatures. Also, under hood measures like covering the headers, wrapping the fuel line, hood heat evacuation ducts,...etc., is helpful.

 

kevin, use efilive cos5 w/ a0014 table

 

Its an RX-7, not a miata. I'm not that gay. Kidding, kidding. I know I'll never be able to hook at the track. I have 14k/12k springs so there is no chance of ever hooking like a real drag car, but I want to at least get to the bottom of the IAT issue.

I cannot use COS5 with my PCM. There is not a COS5 for an 04 GTO PCM. Which pretty much sucks, and I've petitioned to have them create one for over a year now. What does A0014 table do? I figure I coudl also modify the IAT timing table to not pull timing, but I don't think I'm real keen on that idea.

 

The heatsoak should only hurt you if you are in OL. If you are using O2 sensors/MAF the error is being accounted for and the IAT isn't doing much inside of the fueling calc!

 

I run in full open loop, speed density all the time.

 

OK, then nice RX7. Move the sensor. If daily driving is a concern, then make a harness that allows the sensor to be mounted in the stock location, for normal driving & out in ambient temps during drag racing.

 

If you are confident in the ability of your knock sensors to pull timing, you can try reducing the amount of timing being pulled from the IAT table.

What I've done with my Camaro (speed density, full time open loop) is move the IAT sensor to a little black box I keep behind my headlight. My fueling stays more consistent overall (especially when idling in traffic) since the IAT sensor is reading a more accurate ambient reading than sitting in the intake tract around lots of hot stuff.

 

Hi Kevin

It might be a girly car but I bet it goes.

What I did is relocate the sensor down be low the radiator. You need to find a place that does not heat up when the car sits still. The air going to the engine at idle travels down the center of the pipe. There is very little flow at the side where the sensor is. If the pipe heats up the element that in the center of the cage get hot and reads hi. If you find a sensor that is longer and goes deeper in the pipe with a smaller element there will be less of a problem.

What I did if find a place that did not heat up during sitting. The radiator adds the most under hood temp. Heat rises so if you mount the sensor below it and in the intake airflow I think that is the best you can do. There are just 2 wires to extend.

Good luck

 

Update: I moved the sensor to the volume that the air filters pull from. I drove the car for about 45 minutes really hard, stop and go, to try and get everything really hot and heat soaked. The ambient temp was 65 degrees, the sensor read 65 degrees with the car cold and off. With the car fully warmed up, it read 70 degrees while cruising. With the car all good and heat soaked at idle for 20 minutes and the highest it read was 80 degrees.

All in all I consider this a big improvement. 15 degrees over ambient vs 65 degrees over ambient. The 15 degrees over ambient I think is actual temp of the air entering the filter. The IAT drops within 15 seconds of getting the car moving, so I think its real.

Success is mine! LOL!

 

Congrats on Solving the problem. Question though , wouldn't the header wrap keep the heat in the tubes ? I mean i understand that it help keep external heat out but wouldn't it do the same thing to the heat that eventually builds up internally ?

Reason I am asking is I have heat problems 90% of the time in our weather lol