IAT messing-up my idle AFR

[Engine_HP]

Hello guys,

I found that there is a huge split in air/fuel ratio bitween hood open (iat reading 60*F) and hood closed (iat reading 130*F)

here are some readings i wrote done:

IAT vs AFR @ idle
80*F AFR was 13.3
87*F AFR was 13.5
95*F AFR was 13.7
100*F AFR was 14.2
110*F AFR was 15
120*F AFR was 15.3
130*F AFR was 15.7

is there any IAT vs Fuel Mult table in hptuners to correct my afr at idle ?

Thanks

[SSUte01]

If your IAT is accurate, and what I mean by that is that if your IAT is an accurate representation of the temp of the air your actual engine is breathing then you need to model the ECT/IAT (MAT) bias more accurately.

If the IAT thermistor is simply heat soaked and not giving an accurate representation of the air being induced by the engine then you need to more accurately measure it (i.e. IAT location) and repeat your results. If it is still leaning out then you will need to refer to my point above. Any changes to the bias will require airflow/airmass re-modelling.

I am not all that familiar with specific Camaro OS, but I believe the 'bias' (MAT) is strictly IAT on pre-01 or 02 OS, so to tune it you would need 01 (I think?) + OS. I'm sure someone will chime in if I'm incorrect. There's some monster threads on here about ECT Bias (search that from soundengineer) and if I remember correctly something from WS6FireibreTA00 entitled "end to SD Issues" or similar. Both are related to ECT Bias.

To summarise and give you a starting point: GM's methodology for compensating for the reduction of available O2 in hot, less dense air, is over zealous. So, instead of going rich when less air is available, GMs modelling in this particular instance is to over-compensate and the end result as you have seen is to go lean. In general terms, values in the bias closer to 1 decaying down towards IAT as dynamic airmass increases. Not dissimilar to that of GMs effort, I personally have had success increasing values (compared to GM) i.e. biasing more towards the ECT at low airflows and decreasing the values (compared to GM) at higher airmass. The exact modelling is extremely difficult to achieve as effectively you are trying to solve a 'circular problem', for want of a better term.

Enjoy!

[LSxpwrdZ]

To correct this you need to relocate the IAT sensor or upgrade to a 01-up OS like SSute01 said. Your '99 is IAT based only and when the IAT heat soaks due to radiator heat and underhood heat it will falsly report high temp readings to the PCM. The air isn't actually that warm... Moving the IAT sensor into the intake manifold or in front of the radiator to where it can't heat soak will cure alot of your issue.

I battled this issue on my 98 and was bound with the IAT only readings because you can't put a 01-up OS in a 98 PCM. So relocating the IAT sensor GREATLY helped this issue.

My current car is a 02 model and I've played around with the BIAS table enough now to keep AFR's pretty consistant for my setup.

[Engine_HP]

thanks guys for putting ur time to help me through,

Btw im tuning OLSD.

Going to a newer OS will charge me more credit for licening and RTT (thats too much money ).

im sure the IAT is reading correct cos when i see the iat rise in the scanner i go and pup the hood put my hands on the lid near the iat senser and YES i feel heat not like when the iat was reading around 60.

where is the BIAS table located for the 02 modles is it: Engine > Airflow > General Airflow > Cylinder Charge Temperature ??

attached is a pic of what my 1999 looks like

[LSxpwrdZ]

While it will warm up some it's not to the extent of the iat readings or the car wouldn't lean out like it is. Basically in SD the PCM needs to know the barometric pressure and temperature to calculate density. If the IAT is the key thing changing in that calculation and is throwing the a/f off then it is over compensating for the hot air that actually isn't so hot.

One other way around the issue is to play with the IAT sensor calibration under Eng. Diag. tab. You can alter the temps it is reporting to somewhat give you more consistent AFR.

[jimmyblue]

You know that the IAT responds to ambient conditions.
But the air inside the duct is drawn from elsewhere and
is not as hot as the MAF body, airbox body or whatever
(unless you have a really poor air path). This is the root
of the discrepancy.

If you were equipped and interested, putting a thermocouple
in the duct just before the TB would show you the reality
and let you decide whether simply relocating will be better
for fidelity. Or just cut and try.

Too cool an IAT reading says more air mass and richer in
effect. Which is less likely to cause grief, just lose MPG.
I am very happy with mine located outside the engine bay.

[Asylumwarp]

How does putting it in the intake manifold really help? wouldnt that heat soak it too? I know its plastic, but hey, plastic conducts heat too.

[LSxpwrdZ]

The reason putting it in the manifold will help is because it's getting constant airflow across the sensor and isn't close to the radiator which causes most of the heat soak. Alot of people have been having great luck putting the IAT sensor where the EGR tube would normally go. Also a charge temp senor that is used in the typhoon and syclones works much better than the stock LS1 sensor. Responds much much quicker to temp change and is somewhat shielded from external heat sources.

[Asylumwarp]

Are they building a egr blockoff plate with a grommet to fit the iat sensor?

[gn2beatu]

x2 on the typhoon sensor. Im using that one currently, and moved it to the intake in my truck too. Make sure you re-calibrate the sensor in your tune. The easy way is on cold start. Get a reading of the outside air temp EX: 32 degrees. Turn on ignition and see what new IAT is reading. EX: 44 degrees. Calculate the differance 32/38= .84 I then multiplied the entire IAT temp table by .84 and rechecked and it was within 1 degree. I then started the car and brought it up to temp. I disconected the the EVAP tube on top of the manifold and duct taped a meat thermometer where it hung down into the intake. (need to tape it to stop vacuum leak) After it got a stable temp, I compared that temp to what the scanner showed when warmed up. It was only off by 2 degrees, so the scaling was close enough for me. Hope that helps.

[Engine_HP]

Thanks Guys,

I get what u mean, i will transfer the IAT to the front of the raidiator outside the engine bay and see how it gose,

btw i finished DYNO tuning my car http://ls1tech.com/forums/dynamomete...ottom-ls1.html

[Engine_HP]

took ur advice guyz moved the iat to the slp cold air intake.

no complains till now.

[gn2beatu]

Good choice for location. Make sure you calibrate the sensor. Sometimes they are off. After your car sits overnight, take a temperature reading of the outside air. Then load up the scanner without starting the car and see if it matches. If it doesnt, calibrate the sensor. Ex: if outside air is 34 and sensor reads 39 degrees, then multiply the whole IAT temp scale by .8718 (thats like saying you want it to be 87.18% of the current temp. When done with that, then re-check the value. Always do it to the whole table. I have seen them off by as much as 18 degrees or more, so it pays to calibrate it.

[eficalibrator]

Good choice for location. Make sure you calibrate the sensor. Sometimes they are off. After your car sits overnight, take a temperature reading of the outside air. Then load up the scanner without starting the car and see if it matches. If it doesnt, calibrate the sensor. Ex: if outside air is 34 and sensor reads 39 degrees, then multiply the whole IAT temp scale by .8718 (thats like saying you want it to be 87.18% of the current temp. When done with that, then re-check the value. Always do it to the whole table. I have seen them off by as much as 18 degrees or more, so it pays to calibrate it.

So what kind of adjustment does that multiplication give you at 0 degrees? What about -20? Or even at 120? More bad internet advice, sorry.

[LSxpwrdZ]

On the IAT thing... I'm still trying to figure out what the column axis is. % isn't quite resistance. Maybe I will try to map out what is what with a variable load on the IAT circuit with a little logging to determine what % is what resistance.

[vette_c6]

i dont think relocate the IAT is the right sulotion ,,

i think you have a problem getting heat when you close the hood ,, is a problem

i was just scanning a car SD with F1C and supercharged cars are much hotter then N/A car

there must be a problem ,,,
because the sonsor is reading correct ,,

when you close the hood , , you have a heat

good luck by transfaring the sensor

keep us update

[LSxpwrdZ]

Having tuned hundreds of cars I can assure you there is a heat soak issue on most FBodies. Yes there is heat in the engine bay that will heat up the cylinder charge temp but what the sensor reports is sometimes excessive and is indicative by AFR's going lean. If the air was actually as hot as the sensor reported then the density would be calculated correctly and the AFR wouldn't have gone lean. This is why changing to a better sensor that stays in the airstream to keep heat soak down or moving the sensor away from the radiator to keep the readings more inline.

The biggest problem I see with these cars is ones that have the "Free Mod" of cutting the bottom of the airbox out to allow more airflow through the filter... What this does is allow radiated heat to rise and catch right in the airlid like a hot air balloon. The temp sensors are usually located right in the kneck of the lid. This hot air doesn't always equate to the incoming air that makes it to the cylinder. Moving the temp sensor into the intake like I said earlier or putting it in the piping right before the throttle body will ensure airflow passes over it at all times instead of being stagnant like the stock location has it above the radiator.

[domestic rice]

Well I just posted about this and then found this thread so guess I will ask here. Why does a modded car have these problems but stock/light mods dont? I never had this high IAT / Hot start problem before I put on the heads and cam. I see here I cant mess with the BIAS on my 99. Has anyone had any luck with the IAT Sensor Cal? Any tips or tricks to it? Not really looking to relocate the sensor, but guess if there is no other option I will have to.