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Old 04-28-2014, 12:01 PM   #1
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Hot Start AFR?

Since I've had my AFR gauge, I noticed I go lean (15-15.5) on a hot start. When I start the truck cold, I have a rich ratio (~13.5) which from my understanding is normal. I'm wondering if the lean hot start is normal? This lean hot start condition will lasts while I'm at idle after a hot start. Once I start driving, it goes back to 14.7ish like it should. I have also been having an intermittent hot start problem for the past few months and wonder if this has something to do with it? Could this maybe indicate my IAC isn't working correctly on a hot start? Like maybe the IAC valve is sticking open during a hot start? I'm not sure what the IAC valve is supposed to do on a hot start. Any help is appreciated!
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Old 04-28-2014, 01:28 PM   #2
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open loop (cold start) and closed loop (hot start). The ecu isnt reading AFR through the o2 sensors until the engine reaches norm operating temp then it goes into closed loop
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Old 04-29-2014, 06:32 PM   #4
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Quote:
Originally Posted by fyremanpat View Post
open loop (cold start) and closed loop (hot start). The ecu isnt reading AFR through the o2 sensors until the engine reaches norm operating temp then it goes into closed loop
I understand this. However, when ever I hot start, my truck is in open loop as well and my afr is lean. I was just wondering if this is normal.

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Originally Posted by Vassily28 View Post
Based on my experience, at idle and low rpm my truck is running (at least the monitored cylinder) lean, something like 14.9 to 15.2. On cruise at highway speed, it's running around 14.7.

Your rich ratio at cold start is normal (first 40 sec approx.) cause you're in open loop in an area that is an electronic emulation of the choke.
Thanks for your input. My idle is always at ~14.7 like it should be, EXCEPT when I have a hot start. I am just wondering if anyone else experiences this lean hot start condition like I do.
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Old 08-07-2014, 02:39 PM   #5
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Bump. Any more input?
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Old 08-07-2014, 10:54 PM   #6
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The instructions on my wideband says it takes 30 seconds for it to warm up to give a proper reading. There is a good chance you need to let them warm up after a fresh start even though the motor may be warm still. If it stays lean for a long while you might have an air leak after the MAF sensor. Also noted if your short term fuel trims jump all over the place.
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Old 01-18-2015, 12:54 AM   #7
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Hey Kigmob, did you ever get this resolved? I know you've told me on my long, sad thread that fuel pump and regulator fixed your hot start issue, but I noticed this thread and wondered how this resolved.....thanks!
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Old 01-18-2015, 08:49 AM   #8
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My truck does the same thing but to a much worse lean afr at hit start. It is because I have the turbo placed before the maf sensor. The maf heat soaks after driving. At hot start my air temp is 120F plus. Once it gets cool air again it settles down. The ecu has some bug in it when your temps get too high it starts trimming fuel like crazy. One way around it with a piggyback is the fuel delivery at idle max your Lt fuel trims to all the way rich. I'm assuming aftermarket intake will have this same issue if you aren't cold air.
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Old 01-18-2015, 01:40 PM   #9
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Quote:
Originally Posted by lovemytacolots View Post
Hey Kigmob, did you ever get this resolved? I know you've told me on my long, sad thread that fuel pump and regulator fixed your hot start issue, but I noticed this thread and wondered how this resolved.....thanks!
It actually still does it but I don't think its an issue. It fixes itself after no more than a minute of idling after I start it. And if I start driving it usually fixes itself even quicker. Still kind of weird it does it, maybe its something the ECU is set to do?

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Originally Posted by MadTaco461 View Post
My truck does the same thing but to a much worse lean afr at hit start. It is because I have the turbo placed before the maf sensor. The maf heat soaks after driving. At hot start my air temp is 120F plus. Once it gets cool air again it settles down. The ecu has some bug in it when your temps get too high it starts trimming fuel like crazy. One way around it with a piggyback is the fuel delivery at idle max your Lt fuel trims to all the way rich. I'm assuming aftermarket intake will have this same issue if you aren't cold air.

Thats strange. My MAF is before my S/C so it shouldn't be heat soaking after driving. Unless my engine bay is really hot after driving? I feel like its something normal the ECU does for a hot start. Not sure why. It only last for maybe a minute max for me. So I'm not super worried. And its only at like 15.5 AFR max when it does this. So I think its ok. Just wonder if this is something the ECU is supposed to do or not.
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Old 01-18-2015, 02:01 PM   #10
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Mine used to pull air from the fender. Now I pull air under the hood. I hooked an obd 2 up and you can see the fuel trims go weird while the air is hot. Same thing for me it goes away after a minute. My truck is pretty different than stock so I just need to live with it. Mine goes to 19 for a bit but I have larger injectors than stock. Little scary but it is just idle. It won't do it if I pop my hood.
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Old 01-18-2015, 02:05 PM   #11
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Quote:
Originally Posted by MadTaco461 View Post
Mine used to pull air from the fender. Now I pull air under the hood. I hooked an obd 2 up and you can see the fuel trims go weird while the air is hot. Same thing for me it goes away after a minute. My truck is pretty different than stock so I just need to live with it. Mine goes to 19 for a bit but I have larger injectors than stock. Little scary but it is just idle. It won't do it if I pop my hood.
Well thats good to know. I'm gonna try the pop the hood thing. I removed the elbow as well as did the deck plate mod so mine sucks in hot air too.
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Old 01-20-2015, 11:03 AM   #12
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Quote:
Originally Posted by kigmob View Post
It actually still does it but I don't think its an issue. It fixes itself after no more than a minute of idling after I start it. And if I start driving it usually fixes itself even quicker. Still kind of weird it does it, maybe its something the ECU is set to do?




Thats strange. My MAF is before my S/C so it shouldn't be heat soaking after driving. Unless my engine bay is really hot after driving? I feel like its something normal the ECU does for a hot start. Not sure why. It only last for maybe a minute max for me. So I'm not super worried. And its only at like 15.5 AFR max when it does this. So I think its ok. Just wonder if this is something the ECU is supposed to do or not.
What are your IAT's at the hot start, before it has had a chance to idle?
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Old 01-22-2015, 10:18 PM   #13
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Quote:
Originally Posted by Torspd View Post
What are your IAT's at the hot start, before it has had a chance to idle?
I know they are quite warm in the summer. I rarely monitor IAT's this time of year. Im going to check this weekend and let you know.
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Old 01-24-2015, 08:25 PM   #14
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I have to get a A/F gage " would speed up tuning after mods easier" but I have the MAF CAL and I run 10.1 "10 is stock" at idle and it idles much better, I could tell the difference the first time I started it... Over all runs better with a little more fuel at idle..
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Old 01-30-2015, 12:06 AM   #16
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Quote:
Originally Posted by shr133 View Post
I have to get a A/F gage " would speed up tuning after mods easier" but I have the MAF CAL and I run 10.1 "10 is stock" at idle and it idles much better, I could tell the difference the first time I started it... Over all runs better with a little more fuel at idle..
Quote:
Originally Posted by MadTaco461 View Post
^^^ and makes you ocd over your fueling
My piggyback only controls the 7th injector. I can't add fuel at idle with the 7th. Now if I had the 6 injector upgrade with the FTC or a MAF cal, I could do it. My 7th injector piggyback is an additional injector controller and is designed to control the 7th when under boost. I mean I'm sure I could tell it add fuel at idle but the ECU would just trim the injectors and keep me at whatever AFR it wants. I think as long as it stays around 15-15.5 like it has, I should be ok. Its never for longer than a minute. And even shorter if I start driving and don't sit at idle when I first start up.
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Old 01-30-2015, 03:02 PM   #17
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I wouldn't sweat it. It's kinda a pain to tune closed loop. Since it is idle no load I doubt your egt even increase. I'm way worse than you at hot start
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