What do you guys think, any advantages or just problems? This resistance value should feed the ECM a constant temp of about 30F. This mod usually adds timing to domestic cars. MM should have and answer for this one.

 

Problem is that on the rx8, high resistance means high intake air temp

 

So add one in parallel.

 

so make the car think it is to cold, and it goes into the limp mode..

beers

 

the stock PCM adds a metric ton of timing as it is

 

Best mod is to put a 1.5k ohm resistor across the terminals of the battery.
Use your tongue to secure it.

 

Not sure what temperature would have to do with the ECU going into "limp mode". Usually, the biggest factor for determining whether or not to go into "limp mode" is excessive knock. If this were true, I don't think Mazda would be able to sell the car in about 1/2 the states in this country where it gets cold.

Open loop mode, on the other hand, is dependent on temperature, but not IAT. The ECU monitors coolant temp to determine when to go into closed loop mode. The thought is that once coolant temp is up, then cat temps should be at normal operating temperatures. Once this happens, O2 sensors along with MAF and IAT come into play when adjusting injector pulse width for proper A/F ratios. In open loop, only MAF and IAT are used to roughly determine A/F ratios.

The OP does have an interesting idea. This is a very commonly used trick in domestic and Honda applications. SLP makes one for LS/LT applications, and they are as close to a factory GM tuner as it gets. They're the ones that made the Firehawk.

 

Its not an interesting idea.
Well, maybe it was in 2001.

Don't post. Search.

 

On my way to the garage.

 

put the f'ing resistor down and step away from your car.

 

hey guy i just bought this mod online and its this wire thingy, im not sure where to put it. it says on the instruction to put it in the IAT (intake air temp) sensor plug. can someone please tell me where that plug is on the RX8. Thank you

 

You'll shoot your eye out kid

 

HERE is a photo of an RX-8 IAT, its part of the MAF sensor. Be sure to take photos of how you install that thing.

 

This idea seems to be encountering heavy resistance.

 

This thread has quickly been demoted to Fail status. Surge chips are a must buy.. see sig.

 

I bet this mod is good for like 60hp! am i close to what ebay told you? Please throw that resistor in the trash and leave the car alone. If you want power then please do it the right way.

 

I’ve been having a VERY long and involved IAT conversation with a forum member. At the risk of being attacked for contributing, this is my opinion. It is only my opinion and should be valued at what you paid for it, that is, zero. In addition, I do not work for, nor do I represent any company or product although I’ve got a lot of opinions there as well.

Ok, stupid disclaimers aside-

I started helping a bud with a FI kit convert from Int-X to PCM based fueling. One of the very first things I targeted was the AIT sensor that had been moved from the MAF sensor to after the intercooler. The idea was a good one with the Int-X as you can actually use IAT to do something as charge temperatures climb and the you can allow for different IAT calibrations (different NTC or PTC theremistor transfer curves for the nerds out there).

I banned the non-OEM IAT used in a non-OEM location when using the stock PCM to fuel. Here is why-

I’ve not confirmed this, but I believe the PCM uses IAT to trim the MAF value supplied by the MAF sensor. MAF sensors are fantastic things. They measure stuff going by (mass air flow) by measuring how much heat that stuff can carry away from the hot filament in the MAF sensor. They are not terribly affected by things like barometric pressure. However, they do need a temperature differential between the wire and the mass going by to actually transfer heat (and thus produce a signal). Think of it at the extremes, if the mass passing by is exactly at the same temperature as the filament there will be no heat transfer no matter how much mass goes by the sensor element.

If the above theory holds, then the MAF system needs to know IAT at the MAF sensor element to properly correct for the actual temperature across the MAF sensing element at any instant in time. That instant in time thing will come back later. The IAT input to correct MAF either comes from an IAT sensor internal to the MAF sensor itself or that IAT sensor that sits right next to the MAF sensing element and is actually part of the MAF sensor. I DO NOT KNOW THIS FOR A CERTAINTY, but I assumed the IAT sensor sitting next to the MAF sensing element (and included in the Denso MAF sensor itself) was the one being used to sense IAT to correct sensed MAF to true MAF.

If I am right in the above, please do not move the IAT or otherwise muck with it as you will muck with the MAF system as a whole.

Now, back to the “at that instant” comment above. The other bone I had to pick with the moved IAT was that it (1) was not guaranteed to have the same temperature versus resistance curve of the factory sensor and (2) the one being used was a fluid sensor. Sure, you can correct the IAT sensor calibration in the PCM (via reflash) for a different IAT sensor but now you are doing custom reflash work on your car. As for the sensor being a fluid sensor, those things have a much higher time constant than the epoxy covered thermistors normally used for sensing air temperature. Liquids are a more abusive environment and tend to have higher thermal inertia so they require a more robust sensor (that is bigger and slower to react). Anyway, these sensors delay any temperature information from getting to the PCM and, when it gets there, it is likely to be wrong. IAT moves fairly quickly in an FI system so a slow sensor with inertia tends to smooth out the actual temperature swings and thus does not provide timely or correct information.

These are just my opinions. Given that there was no down side to using the OE system, I did not investigate moving the IAT. I tended to control timing as a function of IAT by looking at how it affected load at wide open throttle on FI applications. This approach is not perfect but does seem to work reasonably well.

I do not tend to stay current on threads so please feel free to PM me if I can be of any assistance. This is how I found out about this thread.

Thanks, Lola

 

sounds reasonable.

 

yeah the end of the discussion - for anyone not getting it yet- is dont play with the IAT. leave it alone

bill it is the one included in the maf assembly- that little brownish bulb thermistor

 

Ah, I didn't actually read what you wrote...

I thought you were talking about using an induced dry system.

I.E. wet jet placement but send a driver signal to the MAF telling it that it has instantly become 40degrees cooler when the nitrous hits.

 

Thats true, unless of course the car had maps for -230 degrees farenheit

 

Yep, it is connected to the two terminals on its side of the sensor and seems to be completely isolated (electrically) from the MAF electronics. It's that isolation that made be think the correction was being applied by the PCM (again, assuming the MAF side electronics do not have their own dedicated thermistor). I'd go looking for the correction table in the firmware but I'd literally go nuts trying to find everything that strikes my curiosity. To keep sane, I've tried to focus on finding the stuff I needed to get my projects running right. My brain already hurts from doing that.

 

I don't think you're going to find a trim table.

I just connected a 2k potentiometer to spoof to my IAT and ran the wire/potentiometer into the cabin. I then monitored MAF output and IAT sensor realtime from the Cobb Accessport while I twiddled the temp. First test was at idle, where MAF rate is 6-7 g/s. Stepping from 81degF -> 175degF did nothing to the MAF reading. It also did nothing for the calculated load reading (22%). I also did tests at load with the same result. As I expected, IAT did not do anything to MAF readings.

If thats not proof I don't know what is. My opinion is that the IAT sensor should be mounted post-intercooler to let the ECU know actual temps so that it may appropriately adjust timing/mixture to control detonation. MAF's already compensate for ambient temp with an internal control circuit in the sensor itself.

On another note, I also just removed the Pettit MSD IAT (yes, it is IAT and not fluid) sensor I had and replaced it with my own custom one. I took a brass pipe fitting with compatible threads for the Pettit UIM, cut the stock IAT thermistor bulb out of the MAF, and transplanted. Here's a pic the result: (Original Pettit/MSD IAT sensor on right, new one on the left) Now the ECU can read post intercooler intake temp as accurately as stock and be tuned appropriately.

 

Joff,
Nice job on the testing. I stand corrected. I guess it is time to go looking for IAT trim tables in the firmware (for me at least).

Did you happen to notice if there was any IAT impact on mixture or injector duty cycle? I suspect you will only see this at open loop but it would give an indication of the presence of IAT related trim tables.

Did the PCM throw a code or CEL when you manipulated the sensor? I would think the PCM does boundary checking for a failed sensor and it might be helpful for those thinking of mucking with it to know how far they can go.

This also means stock PCM based IAT can be used to trigger Methanol injection as well as a function of load, rpm AND post IC temp. I best get to laying out that next widget.

Thanks and nice work!

 

It definitely did something to the mixture or timing even at closed loop idle -- When I would quickly cycle from 175degF to 81F the idle would slightly stumble or surge. If I did it slowly, nothing happened. The input is definitely used in the PCM, but just not for adjusting MAF. I tried to watch the AFR also while tweaking it in a drive test, but its already bouncing around enough that I couldn't really visually correlate a difference.

No CELs were thrown. I would expect it might throw one if I gave it a short or an open circuit, which I didn't.