Lean hot restarts... IAT heat soak

http://www.diyautotune.com
Post Reply
User avatar
BigLoukaT
Dont Question My Nissan Knowledge
Posts: 879
Joined: Sun Jul 23, 2006 11:03 am
Location: MA

Lean hot restarts... IAT heat soak

Post by BigLoukaT »

My IAT sensor is about 6 inches away from the throttle body, in the engine bay. This past weekend was the first time I have driven my DIYPNP SOHC turbo more than 5 miles away from the house (put 300 miles on it in one day :D ), and hadn't popped the hood after each drive or let the car cool down after driving as I had previously been while driving for the sole sake of tuning. I was actually driving the car to get somewhere lol.
After turning off the car and keeping the hood down for 10 mins (getting gas) to 1.5 hours (grubbing), the next time I started the car idle afrs were very lean (16-17:1) until I could get out on the road and get some air flowing both in the engine bay and over the sensor in the pipe.
I seem to remember reading somewhere that the best placement for the IAT sensor is as close to the throttle body as possible. Of course, when searching this issue on the msextra forums, it seems this problem is widely known; the solution seems to be manipulating the non-linear MAT correction to correct at the heat soaked temps and/or moving the sensor downstream of the I/C but outside of the engine bay. It's too bad I didn't run into those threads in all of my reading on megasquirt before modifying my piping for the IAT sensor.
Any other ka-t's here place their IAT sensors in the engine bay and run into this issue? This weekend I'll be doing some logging after running/stopping with the hood down, and see how bad the IAT heat soak actually is. Then I'll probably get to playing with the MAT correction table.
I was also thinking of trying header wrap or reflective heat tape around the sensor/pipe to see if I could isolate the sensor decently from the engine bay radiant heat.
Anyways, I guess I'm not really asking a question (besides polling other ka-t users on this issue), but maybe this will serve to remind others to keep their IATs outside of the engine bay on the first round to avoid heat soaked lean restarts.
1990 S13
Boosted single slammer
MS DIYPNP
npx from 240sxforums wrote:i figure from my very limited knowledge about the 240 and under the hood about cars in general i would follow the sr20det trend.
User avatar
BigLoukaT
Dont Question My Nissan Knowledge
Posts: 879
Joined: Sun Jul 23, 2006 11:03 am
Location: MA

Re: Lean hot restarts... IAT heat soak

Post by BigLoukaT »

clearly this isn't the hottest topic on ka-t.org right now, but just to follow through:

I looked at some logs I took after shutting the engine down and keeping the hood closed, coming back every few minutes to power up MS and check what the IAT temperature is at that point. Within ten minutes, IAT reached 130 degrees (75-80 ambient, 91 at shutdown), and then I stopped bothering to check.

I put some exhaust wrap around the sensor/pipe to see if I could at least slow the heat soak down a bit, and it didn't seem to make a difference on a followup run cycle. I also messed around with the MAT correction table (maxed it out), which did not really help enrich the lean idle during the heat soak condition. Obviously at this point, the answer is to move the IAT sensor to a place that is unaffected by the underhood temps.

My IC pipe setup is admittedly probably the worst for heat soak on shut down... it's a steel pipe, painted black, that routes around the upper radiator hose.
1990 S13
Boosted single slammer
MS DIYPNP
npx from 240sxforums wrote:i figure from my very limited knowledge about the 240 and under the hood about cars in general i would follow the sr20det trend.
User avatar
p00t
Encyclopedia-Nissan
Posts: 1170
Joined: Sun Aug 28, 2005 10:27 pm
Location: Detroit

Re: Lean hot restarts... IAT heat soak

Post by p00t »

My only comment would be that if that is what you are seeing on your logger then that should be the correct temp of the air going into the engine. So if your tables are setup correctly (do they work the way you think?) it should actually help because you are more accurately measuring the air going into the engine.

If you are saying that the sensor heat soaks and reads higher than the temperature of the intake air, then I would argue that you are using the wrong type of sensor. Isn't it an open element type?

Shorthand:
-Sensor type?
-Correction tables?
Current Experiment: Project Twin-Charge 2022
User avatar
Matt Cramer
KA-T.org Sponsor
KA-T.org Sponsor
Posts: 934
Joined: Mon Sep 15, 2008 5:34 am
Contact:

Re: Lean hot restarts... IAT heat soak

Post by Matt Cramer »

Open element sensors do still have some thermal mass, and can get heat soaked a bit to where they pick up some heat from the tube they are in and give a false hot reading. Depending on what firmware you're running, there may be a way to tune around this.
Matt at DIYAutoTune.com - Megasquirt ECUs, fuel injectors, wideband O2 sensor systems, and more
Nissan plug and play engine management now in stock!
User avatar
p00t
Encyclopedia-Nissan
Posts: 1170
Joined: Sun Aug 28, 2005 10:27 pm
Location: Detroit

Re: Lean hot restarts... IAT heat soak

Post by p00t »

Matt Cramer wrote:Open element sensors do still have some thermal mass, and can get heat soaked a bit to where they pick up some heat from the tube they are in and give a false hot reading. Depending on what firmware you're running, there may be a way to tune around this.
The reason I asked Matt was that on your site you sell a closed element sensor which you label for IAT use. If he has a lot of heat soak this type of sensor is going to make this problem really stand out. Basically it becomes an intake pipe temperature sensor instead of an IAT. If he car is sensitive to heatsoak he should be using the open element type GM sensor.
Current Experiment: Project Twin-Charge 2022
User avatar
BigLoukaT
Dont Question My Nissan Knowledge
Posts: 879
Joined: Sun Jul 23, 2006 11:03 am
Location: MA

Re: Lean hot restarts... IAT heat soak

Post by BigLoukaT »

p00t wrote:My only comment would be that if that is what you are seeing on your logger then that should be the correct temp of the air going into the engine. So if your tables are setup correctly (do they work the way you think?) it should actually help because you are more accurately measuring the air going into the engine.

If you are saying that the sensor heat soaks and reads higher than the temperature of the intake air, then I would argue that you are using the wrong type of sensor. Isn't it an open element type?

Shorthand:
-Sensor type?
-Correction tables?
IAT sensor is the GM Open Element. I believe that the sensor is picking up the heat from the pipe (which gets to be too hot to touch if engine is shutoff and the hood is left down). Eventually, the afrs get back to normal at low MAP while driving and the engine bay sees some airflow (high MAP running seems to be unaffected by the heat soak, I haven't confirmed that on a datalog yet, but I suspect I'll see MAT drop during a pull as the airflow over the sensor increases and overcomes the residual heat from the pipe). I would agree that for the first periods of time after I start the car while hot, and don't start driving, that the air in the engine bay is pretty close to what the sensor reports. However, I can see a higher temp "bias" while driving at low MAP values that affects my intended afr. Gair correction gets down to about 90-93% during the heat soak periods.
Correction tables are pretty much zeroed out... Ideal gas law is 100% and the MAT non-linear correction is zeroed (after I didn't see enough of a change in running condition while the sensor was soaked)
Matt Cramer wrote:Open element sensors do still have some thermal mass, and can get heat soaked a bit to where they pick up some heat from the tube they are in and give a false hot reading. Depending on what firmware you're running, there may be a way to tune around this.
I have seen some talk on msextra about the blended CLT/MAT correction on certain firmware, but have not yet tried it out. I've been concentrating more on getting the rest of the tune straightened out. I was hoping that the non-linear MAT correction would give me enough slack to avoid the heat soak lean condition, but it didn't pan out... I was finding that I had to continue correcting for MAT temps at idle that I would see occasionally on a boost pull, and don't want to correct in the latter situation (where the pull was good and afrs were where I expected).
Also, I haven't yet moved from the 3.0.3u (I believe) that the basemap was made on... I've been meaning to get around to doing that but didn't want to fix what isn't broken yet while still getting the initial tune settled.

I'm sure I'll experience the heat soaked sensor again on Saturday... I have a drift event (first of the year for me and first on ms) when I'll run hard for 2-3 minutes and sit in a line of cars waiting to go next. I think my hood latch will get some exercise this weekend :D
1990 S13
Boosted single slammer
MS DIYPNP
npx from 240sxforums wrote:i figure from my very limited knowledge about the 240 and under the hood about cars in general i would follow the sr20det trend.
User avatar
BigLoukaT
Dont Question My Nissan Knowledge
Posts: 879
Joined: Sun Jul 23, 2006 11:03 am
Location: MA

Re: Lean hot restarts... IAT heat soak

Post by BigLoukaT »

The heat soaked iat didn't hamper my day at all... I was really worried about idling after a run with the hood down but it didn't really seem to affect my afrs between runs. Looks like the problem really only presents itself when I leave the hood down for more than a few minutes without air flow/engine off. I'll move the sensor over the winter.

Besides all of that, I'm loving MS... didn't touch the laptop/tune all day:
Image

Image
1990 S13
Boosted single slammer
MS DIYPNP
npx from 240sxforums wrote:i figure from my very limited knowledge about the 240 and under the hood about cars in general i would follow the sr20det trend.
User avatar
sdaigle240
Belongs To The TOP CONTRIBUTING MEMBERS!
Posts: 4670
Joined: Wed Oct 17, 2007 9:53 am
Location: CONN.

Re: Lean hot restarts... IAT heat soak

Post by sdaigle240 »

thats whats up.
airman wrote:I'm all about spreadsheets. Bitches love spreadsheets.
schmauster920 wrote:I shall cast my own pistons in the sands of time, then forge them in the depths of hell.. as funds allow
Image
hy35 18psi Build Thread: viewtopic.php?t=38784
RIP MJL best friend of 20 years and the man who showed me 240s
User avatar
emo_tactical9
Belongs To The TOP CONTRIBUTING MEMBERS!
Posts: 3086
Joined: Tue Sep 18, 2007 3:21 am
Location: Bowling Green, KY

Re: Lean hot restarts... IAT heat soak

Post by emo_tactical9 »

The GSLender firmware ignores the IAT on cranking. You should try it, it has great idle control also.
Just call me Adam.
95 240: DIYPNP and T28.
08 Honda Fit
84 200sx: Sold after almost 10 years.
My file hosting:Calum,MegaSquirt,FSM
User avatar
BigLoukaT
Dont Question My Nissan Knowledge
Posts: 879
Joined: Sun Jul 23, 2006 11:03 am
Location: MA

Re: Lean hot restarts... IAT heat soak

Post by BigLoukaT »

sdaigle240 wrote:thats whats up.
Thanks bud, that was about 30 seconds before realizing the brake fluid was too hot to work haha
emo_tactical9 wrote:The GSLender firmware ignores the IAT on cranking. You should try it, it has great idle control also.
I'll keep that in mind... I actually have less of an issue strictly starting the car, as I do with the 10 minutes (or more depending on air flow through the engine bay/speed of driving) of lean idling/low throttle driving after the restart.
1990 S13
Boosted single slammer
MS DIYPNP
npx from 240sxforums wrote:i figure from my very limited knowledge about the 240 and under the hood about cars in general i would follow the sr20det trend.
Post Reply