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Old 06-02-2015, 09:32 PM   #1
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Default Stalling when hot outside

I am having a strange issue I cant seem to find a solution for. My car has been running and idling great but when it got hot out i found an issue with warm start up. If I drive around and get the car to operating temps, maybe a bit more, then I turn it off and let it sit in the sun for 5-10 minutes when I go to start it up again the car starts then stalls. Sometimes it will start and then if i rev it the rpms will drop down and stall.

If i give it enough gas to not let it stall and drive around a bit the issue goes away.

Any idea what this could be?

Sorry for all the threads recently, I just want to keep these issues seperate
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Old 06-02-2015, 09:33 PM   #2
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is your ait heatsoaking?
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Old 06-02-2015, 09:36 PM   #3
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Heat soaked IAT, pretty common. After you warm up the engine then shut it off, that heat dissipates off and the sensor literally soaks it up. When you start the car, the sensor now reads crazy temps, like 100-150f. But the air going in is actually cooler (more o2), say 80f. The MS injects enough fuel for 150f air, but starts running lean until you drive around, letting the air cool the sensor off to a more accurate reading.

Try changing your MAT air density table under Basic/Load settings, to inject more fuel at higher temps. Doesn't need much, just enough to run properly until it cools itself off.
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Old 06-02-2015, 09:39 PM   #4
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Heat soaked IAT, pretty common. After you warm up the engine then shut it off, that heat dissipates off and the sensor literally soaks it up. When you start the car, the sensor now reads crazy temps, like 100-150f. But the air going in is actually cooler (more o2), say 80f. The MS injects enough fuel for 150f air, but starts running lean until you drive around, letting the air cool the sensor off to a more accurate reading.

Try changing your MAT air density table under Basic/Load settings, to inject more fuel at higher temps. Doesn't need much, just enough to run properly until it cools itself off.
Sounds reasonable enough. I will try that! I hate that I wont know if it woorked until a specific day...........
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Old 06-02-2015, 11:02 PM   #5
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This is textbook lean hot restart like I said in your last thread. It's a combination of the injector dead time changing because they've just sat on the hot head for 15 minutes with no cooling fuel flow, the fuel density changing because it's also sitting in the hot bay, and a itty bitty tiny bit to do with the IAT. Log it, I'd bet a nickel it's not pulling anywhere near as much fuel as you expect.

You can tune this with ASE, increase ASE for hot coolant temps and increase the ASE taper time. Using newer injectors helps a lot, too.
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Old 06-02-2015, 11:28 PM   #6
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This is textbook lean hot restart like I said in your last thread. It's a combination of the injector dead time changing because they've just sat on the hot head for 15 minutes with no cooling fuel flow, the fuel density changing because it's also sitting in the hot bay, and a itty bitty tiny bit to do with the IAT. Log it, I'd bet a nickel it's not pulling anywhere near as much fuel as you expect.

You can tune this with ASE, increase ASE for hot coolant temps and increase the ASE taper time. Using newer injectors helps a lot, too.
I tried a tom of ASE in the past and it did not help. Here is a log I had from before when it was happening. Can you see the issue? In the log it does idle but then i rev it and it stalls.

@curly is it ok to flatten the curve like this?

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Old 06-02-2015, 11:41 PM   #7
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You are not hitting any air temperature related fueling changes in the log you posted.

You need to tune, you are tanking to 10.7 AFR. You are stalling from too much fuel, not too little. Your VE goes from 50 to 100 something, and the AFR follows fine.

Zeroing the air correction table isn't going to do anything but have you running rich when it's hot out.
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Old 06-02-2015, 11:57 PM   #8
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You are not hitting any air temperature related fueling changes in the log you posted.

You need to tune, you are tanking to 10.7 AFR. You are stalling from too much fuel, not too little. Your VE goes from 50 to 100 something, and the AFR follows fine.

Zeroing the air correction table isn't going to do anything but have you running rich when it's hot out.
I will try and get a log of the issue this weekend if the sun ever decides to show its face... As for tuning I truly am trying, I just barely know the first thing about it so I am asking as many question as I can and reading as much as I can. I really have no idea what I should be looking for at this point.
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Old 06-03-2015, 01:10 AM   #9
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Do you understand the premise of speed density tuning, because I'm not sure you do. If you don't, how can I even begin to explain things to you? Would you like me to rewrite the entire manual? The problems you are having are step one tuning problems, and I'm a bit insulted when I have to explain such simple stuff. When you say you've been reading, reading what exactly?

I don't know exactly what is going on with your car, but from that one log you've posted it's evident the car is nowhere near ready for driving. It idles 12.6, and your VE numbers are all over the place. It tanks rich, then lean because your fuel table is potatoes. You can't expect that to work at low load and low rpm on a cold motor.

Mega Miata

Read that, make sure you notice the "older posts" button at the bottom, go all the way to the beginning.
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Old 06-03-2015, 12:36 PM   #10
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^^Chill bro, we all start somewhere.

OP, I made a quite comment minutes after leaving the dyno, dialing in a MSM, well, until it blew a turbo. I may have looked passed your poor base tune.

I'd touch nothing except for fuel, and get that dialed in. Then if you notice a big difference in AFRs on a hot day vs. a cold one, that's when you might change the MAT density table. Notice in the comments however, that this curve is based of the ideal gas law. The big word being LAW. It's physics.

However, at some MATs you'll hopefully never see, like 140+, it's probably ok to lessen that taper (again, after fuel table is nailed), in order for it to maintain idle until it regulates it's MAT.
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Old 06-03-2015, 12:42 PM   #11
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^^Chill bro, we all start somewhere.

OP, I made a quite comment minutes after leaving the dyno, dialing in a MSM, well, until it blew a turbo. I may have looked passed your poor base tune.

I'd touch nothing except for fuel, and get that dialed in. Then if you notice a big difference in AFRs on a hot day vs. a cold one, that's when you might change the MAT density table. Notice in the comments however, that this curve is based of the ideal gas law. The big word being LAW. It's physics.

However, at some MATs you'll hopefully never see, like 140+, it's probably ok to lessen that taper (again, after fuel table is nailed), in order for it to maintain idle until it regulates it's MAT.
The car was dyno tuned and I even had it at a 2nd tuner who looked over the fuel tables so I hope they arent that bad. I always check my AFRs while driving and they seem to always be around 14 when cruising and 10-11 when under full boost.

Is it possible that I have a mechanical issue that is just rearing its ugly head when it gets hot out or is it most likely something in my tables I am missing. Thanks for understanding that this is completely new to me and I am looking into everything you guys tell me so I can keep learning.
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Old 06-03-2015, 12:47 PM   #12
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Well, personally I'd like 11-12 when under full boost, anything below ~11.3-4 should be avoided. Cruise should be in the 15s, but that's really getting picky for good mileage, not a necessity.

I don't think it's a mechanical issue, just needs some more tuning.
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Old 06-03-2015, 12:51 PM   #13
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Well, personally I'd like 11-12 when under full boost, anything below ~11.3-4 should be avoided. Cruise should be in the 15s, but that's really getting picky for good mileage, not a necessity.

I don't think it's a mechanical issue, just needs some more tuning.
ok. I know this was a very financially irresponsible decision (and probably pointless) but I purchased a new Megasquirt PNP 2 so I will use a basemap and load up my current fuel tables that way I know where I am starting from and can make adjustments. I saw its supposed to be mid 80s next week so I be able to data log if the issue happens.

The hard thing for me is right now there is no issue so its hard to learn what I need to fix.
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Old 06-03-2015, 03:30 PM   #14
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You bought an identical copy of what you already have, DIY is not going to tune your car for you, basemaps are NOT for driving the car on, and that was a huge waste of money. You will be miserable till you learn to tune street manners yourself.

We all have to start somewhere, but we all have to start.

Again, I would bet a nickel you are wasting so much time and money because you can't be bothered to sit and read how the MS2 actually works.
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Old 06-05-2015, 03:02 PM   #15
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I requested load based air temp compensation from the developers to have more flexibility to address this problem.

Bias thr table rich and use closed loop fuel to lean it out after start. That's a workaround.
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Old 06-06-2015, 10:19 PM   #16
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I am running open-loop now and I think i may have found out my issue. My AC is pretty much always running (on or off) and I just noticed that it seems my AC fan is controlled by the WLED port and not my cooling fan, it was set to 92 and I noticed my AC would start working at 92 degrees and not the cooling fan. The car cooled down a bit (below 92) and the ac was blowing hot, I dropped the WLED threshhold to 70 and bam the AC blew cold and my idle dropped to 700. Am I going crazy?
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