heat soak on IAT

snillet · Post by **snillet** » Tue Jul 18, 2006 2:17 am

On the car in questrion for me the problem excists with stock ECU to

, i have NO IDEA why the sensor is positioned where it is actually.

But i will move it.

renns · Post by **renns** » Tue Jul 18, 2006 8:32 am

RTD is a metal (platinum) temperature sensor. Usually a low value like 100 ohms and has very small changes per deg C.

RTD's are also have a positive temperature coefficient and usually have a very linear characteristic curve as opposed to the NTC sensor's logarithmic curve.

Roger.

Keithg · Post by **Keithg** » Tue Jul 18, 2006 12:16 pm

good discussion, here. I am having the same problem. Heat soak. It is exacerbated in traffic. I cannot locate the IAT to be outside the ingine compartment, so there will always be heat soak. I have ducted around it to make sure that the wash off the radiator does not affect it directly, but radiated heat will eventually.

Interesting that the use of no IAT is possible. The code forces a aircorr of 100 when it is disconnected. Maybe a better approach would be to turn it off during boost. I'll hack that up and see how it works for me. Ambients of 95F cause 110F on the road and 120-140 in traffic especially with A/C.

Like Snillet says, the stock ECUs seem to have figured out how to deal with heat soak. I looked on the wife's car and it has an IAT in a similar position to what I have done in my MS'd car. ie. it will rise with wash off the radiator/condenser and it does not run lean in hot temps. Stag_Matt and I have discussed this a lot before and 'things' have been tried that deal with heat soak and such. I poorly coded a version a few weeks ago and tried Matt's suggestion. While I think it would work on his car (N/A), If I coded it correctly, I think a boosted car has a slightly different requirement.

Subie4me may be on to how the OEMs deal with it. Definitely off in boost, but 'adjusted' somehow during run. Maybe use it to a certain threshold and flatten it to 100 when IAT is greater than 90F? As it is, heat soak makes my car really tough to start and I need to try something.

I am running a boosted 2.0L 4 cyl.

KeithG

superchargingmachine · Tue Jul 18, 2006 12:35 pm

One idea is to use 2 sensors and an output from MS going through a switching relay. I was going to try this but I am worried about the jump in IAT that will occur at the switchpoint. I was going to stick one IAT in the aircleaner for off boost running and one in my cross over tube for on boost.

Maybe a better way would be to just use the IAT in the air cleaner and tune AFR on boost with my WB???? Or allow the cooler IAT before the turbo to enrich AFR's on boost.

keithmac · Post by **keithmac** » Tue Jul 18, 2006 2:32 pm

I had an IAT of 71c today in traffic! Car compensated very well for it though using full time EGO correction and an IdleVE that can be changed by input from the EGO correction routine it`s suseptible to Wideband failure.

Do agree hot re-starts at the worste, I have a timer running for 30 seconds (same as ego timer) for my IdleVe routine (14:1 afr), the normal Table VE`s are equivilent to 12:1 on a hot engine so this richens it up a fair bit and combats most heatsoaking.

Maybe have a countdown timer that`s started when the ECU powers on that will lock the IAT value for 30 sec to a minute if the IAT is above a threshold (30 deg c?).

I`ve found a few occasions where the IAT reads 40+c on a hot restart and the car is lean, but 3 minutes down the road the AIT is still in the same region but the AFR`s are spot on, so you can`t take the temps as gospel when it comes to detecting heatsoak, Wideband seems to be the only true way of testing the mixture but they`re not active during startup.

snillet · Post by **snillet** » Tue Jul 18, 2006 11:18 pm

In slow traffic my IAT value usually is around 75-85deg C

.
baaaaad.

chicksdigwagons · Post by **chicksdigwagons** » Wed Jul 19, 2006 8:06 am

subie4me wrote: As I understand it, as the air gets hotter it is less dense. This requires less fuel to get a desired AFR. Problem is , that hotter air makes a turboed motor more prone to detonation. The last thing I want to do is take away fuel due to the hot air and further compound the problem. The extra fuel helps to prevent detonation. For that reason, I have NEVER used the IAT sensor on any of the megasquirts that I've done. I also didn't use it on the link plus that I have on an offroad car. Maybe you need it on a street car, but you do not need it for offroad use.

You're on the right track I'd say, But for a road car that needs daily drivability this isn't really feasable. Furthermore, unless your car is tuned on the fringe edge, you should have plenty of fuel in boost to make this a non-issue. On a race destine car, a fringe tune may be the difference between winning and losing however.

Also, I think it is may be possible to alter the IAT correction to flatten out above a certain threshhold to preven pulling more fuel after a peak temp to help exactly the issue you're describing. Might be something worth forwarding to Phillip and James. If you're using the later MSnSE code there is a IAT related boost taper, which to me is probably a better solution to detonation than adding fuel when IAT warrant.

snillet · Post by **snillet** » Thu Jul 20, 2006 2:15 am

Now i suddenly got an angle on the "traffic jam hiccup" that i experience...

Since the hotter air is less dense and you need less fuel at that point, it´s MOST LIKELY the acceleration enrichment that causes the hiccups when the traffic slowly rolls/stops/rolls a little again/stops and so on.

Since the enrichment is set in milliseconds , it´s not corrected against temperature ?

subie4me · Post by **subie4me** » Thu Jul 20, 2006 12:00 pm

chicksdigwagons wrote:
subie4me wrote: As I understand it, as the air gets hotter it is less dense. This requires less fuel to get a desired AFR. Problem is , that hotter air makes a turboed motor more prone to detonation. The last thing I want to do is take away fuel due to the hot air and further compound the problem. The extra fuel helps to prevent detonation. For that reason, I have NEVER used the IAT sensor on any of the megasquirts that I've done. I also didn't use it on the link plus that I have on an offroad car. Maybe you need it on a street car, but you do not need it for offroad use.
You're on the right track I'd say, But for a road car that needs daily drivability this isn't really feasable. Furthermore, unless your car is tuned on the fringe edge, you should have plenty of fuel in boost to make this a non-issue. On a race destine car, a fringe tune may be the difference between winning and losing however.

Also, I think it is may be possible to alter the IAT correction to flatten out above a certain threshhold to preven pulling more fuel after a peak temp to help exactly the issue you're describing. Might be something worth forwarding to Phillip and James. If you're using the later MSnSE code there is a IAT related boost taper, which to me is probably a better solution to detonation than adding fuel when IAT warrant.

The driveability is just fine without the iat, and hot starts are never a problem. IMO not using one affects mileage more than anything else. That is more of a concern on a street driven car than offroad.