cold start stall in gear

[fastslvblkcar]

To start with I am running a speed density only tune using the factory map sensor. I did not change the OS. Engine has a mild cam, intake and exhaust. When ambient temps are 80?F and above I have no issues at that point. Temps recently dropped in to the 50's and 60's at night. My problem is... I go out to the truck in the morning and start it up and pull it out of the garage and everything is fine. I put it back in drive and it is fine, as soon as I start pulling out of the driveway, it stalls. I drove all of the way to work (17 miles city and highway), after 10ish miles on the interstate I turn off and it stalls at every light unless I hold the throttle open some. I pulled over this morning and it tried to stall so I let the intake air temp warm up to above 80?F and I had no more stalling during the rest of my trip (of which which was short and IAT did not have a chance to cool off. Looking at my logs, I see no excessive rich or lean condition causing the stall. The only thing that I am seeing that makes a difference is IAT. What info do you want to see to get a better idea? Or do you have an idea already?racing timing 28 6500rpm-2 cold idle correction att.hptmorning stalling.hplevening no stall.hpl

[kevin87turbot]

Your IAC is working really hard to keep it running. At the end of the morning data log, it's around 165 when you come to a stop.
You need to adjust the throttle body opening such that the IAC is around 40-60 counts when the engine is up to operating temp and in Park. You'll likely find that you have to adjust the throttle body screw by at least 1 full turn to get the IAC into its designed operating range.

[fastslvblkcar]

The problem with that is that the throttle plate is already almost completely closed. I have checked for intake leaks with a smoke machine and found no leaks cold or hot.

[blindsquirrel]

No, you need to open the throttle blade with the screw to decrease the IAC counts.

[fastslvblkcar]

I was thinking backwards apparently. When I set this up It was 90 ambient.

[fastslvblkcar]

well it warmed back up but I did adjust it. are any of you seeing a difference with this depending on ambient air temp? do you have to adjust it for winter and summer?

[kevin87turbot]

well it warmed back up but I did adjust it. are any of you seeing a difference with this depending on ambient air temp? do you have to adjust it for winter and summer?

You can typically just set it and forget it. Although, I've had a couple of aftermarket throttle bodies that the screw vibrated loose after being driven for a while. A little Loctite fixed those up...

[fastslvblkcar]

That must be what is going on. I set the throttle plate in February when it was in the 20's and 30's and it was doing great even through the summer when it was over 100 for highs. As soon as it cooled back off for a week it started playing this game. I will try the Loctite and see how that does. Thanks for the help!

[K-fed]

After you adjust the set screw for your throttle body blade, you have to do a tps reset

[fastslvblkcar]

It has now cooled back down to the 30s and 40s overnight and I am having the same lean issue. I changed the intake over the summer and had some pretty exceptional gains in low end torque and picked up a half second 1/4mile time. I changed from the stupid but nice looking sheet metal intake, to a stock intake from a 2008 Suburban so essentially a TBSS intake. A little refresher, this is a 5.3 with a 218, 227 duration and 523,524 lift cam from jegs p/n 200578 and some ls6 springs. This also has shorty headers and quiet mufflers. Other than this, it is a stock engine. This is a speed density system as well. Here is the tune and a warm start log. I will get a cold start log in the am. Also, I did adjust the IAC and reset the TPS when I installed the new intake. It now sits at ~60 +/- 5 at operating temperature.

[fastslvblkcar]

I did adjust the IAC.

[fastslvblkcar]

Here is a log at 49F ambient. Initially it looks good and is rich for a few seconds then goes pretty lean. It was a little warmer this morning than I expected but it still went lean. After the engine is warmed up, even in open loop tuning mode, it doesn't run lean.

[fastslvblkcar]

Here is another one that went way lean after startup.

[Fast4.7]

Cold air is denser. Without a properly functioning MAF what you are seeing happens often. You can adjust the IAT fueling table stuff, but its going to take some experimentation and you will likely make it worse. Even with a MAF my short term fuel trims will run +6% or so with a cold engine. Then again thats why the 02 sensors are there.

[Fast4.7]

Going back to what I was saying last night. I have tried to fix this slight issue in my tune on two different engines in the same vehicle. Here is what mine does even with a MAF in place and well calibrated. Evap purge solenoid is commanded off during the datalog via the control so that it is not messing with the fueling. Mine is lean until the thermostat opens and starts to heat soak the intake. Once the intake heat soaks to where the engine was tuned when it was hot, the lean trims start to go rich. As the intake continues to heat soak above the temperature the engine usually sees when driving around it starts to go rich. The wideband stays very close to stoichiometric but the trims move in response to the fueling change. I wish I knew exactly what IAT tables to change and how to log the required changes, but at this point it has been a guessing game. This is the closest I have had the trims during a log from cold start to heat soaked. The stock engine as GM provided it on the stock tuning would swing from +12 to -12 as the intake heat soaked, so even GM did not have it right. This is a L31 based engine in a 97 Express van. The stock L31 on the black box had the widest swing. The 0411 PCM tamed it a bit. The current engine is a ~500 hp 383 with aluminum heads. I have probably tested 50 different setting changes to help with the condition. It is actually using the IAT compensation data from a 2004 6.0L van right now. Seems GM improved this over the years, but it could still be better. 6.0L data is not going to be the same as a SBC, but the air cleaner housing is in the same place and the two engines heat soak equally. I think the 6.0L data improved things slightly because GM tightened up the variance in later models for cleaner emissions standards as well as the fact the aluminum heads on the 6.0L are a better match than the data for my stock engine with cast iron cylinder heads. If anyone has any experience with this part of the calibration; I am open to suggestions as well. I think more bias toward the IAT at lower flows might help it as it is heavily biased toward the CTS. That being said I got tired of messing with it and it runs nearly flawlessly. For the first 3-5 seconds the engine is also very rich, the pre-heated wideband shows 0.70 lambda immediately after it starts. Grey smoke out of the pipe, but once it runs for 5 seconds it cleans up and runs at 0.82 lambda and tapers off smoothly to 1.00 as the commanded air/fuel ratio drops and the short terms enable in open loop. I have not figured out why the PCM commands air/fuel ratios in the 3s for the first second or two either, but it did it with the stock 0411 PCM file as well on the 350. I would like to lean that out a little too, but it is not something I usually have to mess with and not sure which of the cold startup tables to adjust.

Cold Start Idle Log.hpl

[Fast4.7]

One other thing worth mentioning is that my STFTs do not start to drift lean until the open loop commanded air/fuel ratios start to approach stoichiometric. When they are still in the low 13s before the coolant temp sensor starts to heat up the STFTs are actually pulling fuel. I have considered adding fuel to the open loop air/fuel ratio table and delaying closed loop until a higher temperature, but I would rather get it fixed properly adjusting the IAT compensations. I plan to mess with it more after I swap to the 7137 Pro Flo knock off and 102mm TB on a 102mm to 92mm adapter. Intake and fuel rails are on the way to me and I already have the TB and adapter from a different project engine. Came off a LS I bought from a failed swap that I put the DBW TB back on. When the intake is on with GM injectors with good data, I will re-visit this myself.

[Fast4.7]

I will data log from a cold start in the morning, but I believe both problems have been solved that I mentioned above. I was able to really lean out the enrichment post startup. I was also able to mostly correct the fuel trim drift as the IATs increased. Previously my fuel trims only drifted noticeably near idle, above idle at cruising speed and accelerating down the road they were never an issue. I was able to take a few stabs at it today given that it was cool enough outside that the engine cooled off very quickly. I spent most of my day outdoors anyway, so I figured why not try to fix this annoyance after posting about it. Looking at both banks individually from the log from this morning the fuel trims dropped roughly 10% from cold start to heat soaked. Looking at the total fuel trim numbers, both short plus both long terms added and then divided by 4 the numbers ranged from +5.5% to -3.9%. This evening starting the engine with the coolant temperature at 74*F and the IAT at 68*F the overall average fuel trims held from about +2 to -2% throughout the whole 20 minutes it ran from cool to heat soaked. They still had the ~5-7% split left to right like most GM engines seem to. To me that is making headway! Tomorrow morning is supposed to be very cool. Will try to re-verify the results from this evening.

Stock 2002 350 Van
2002 Express Van 350 IAT CTS Blend.jpg

Stock 2004 6.0L Van
Stock 2004 Express 6.0L IAT CTS Blend.jpg

Custom
Custom IAT CTS Blend.jpg

Difference Custom vs 2002 350 Van
IAT CTS Blend Difference Custom to 2002 Express.jpg

As for the afterstart enrichement, I made a drastic cut to the Initial Adder vs ECT table (Multiplied by 0.25) as well as the Decay Delay (Multiplied by 0.25). As a result the afterstart is now commanded at about 8:1 to 10:1 vs 3:1 and the overly rich mixture starts to decay out after only 20-30 crankshaft revolutions vs 80-120 revolutions. At 1,000 rpm at startup, 120 revolutions is over 7 seconds. Nobody I know uses full choke for 7 seconds on an engine that is 60*F and already running. On a carbureted car with an automatic choke the vacuum pull-off leans the engine out instantly by partially opening the butterfly the instant vacuum comes up. I will see how it starts in the morning after an overnight soak. It is 50*F now outside and the forcast is 39*F at 8:00 am.

I completely do not understand why GM had such a rich choke air fuel ratio. No wonder this engine has always had a rough startup. I actually pulled 3 different 0411 Van calibrations to verify it had not been tampered with. At 46*F the multiplier was 0.449 at 68*F the multiplier was 0.320 and that is added to an already 20% richer open loop air/fuel ratio. It was completely drowning the 350 in fuel even stock.

I figured out how to do the above cold start change, reading a couple of OLD posts on here. The IAT blend was just taking more time to study what the differences were in what I had tried and looking at the data closer to see where the problem lied. That far left cell on the IAT table is where the engine idles at. Even on the 04+ van the fueling correction was mostly CTS at idle. It took a drastic change to shift the bias toward the IAT. The IAT practically alone was causing the swing. I started the engine hot at 180F and heat soaked to 140 IAT. It ran slightly rich. I then popped the hood and let the air intake cool off. When it restarted the CTS was still reading close to 180F and the IATs were 70F. It immediately went lean. Now the the fueling is heavily biased toward the IAT.

[Fast4.7]

The verdict is in. If your fuel trims yoyo with IAT temperature changes, decrease the Charge Air Bias table values. I will decrease my values a little more and see if it tightens up the fueling even more. My total average variance dropped from 9.4% yesterday morning to 5% today. It was slightly colder today as well and typically the colder the IAT the worse the lean spot has been in the past.

Running 2004 6.0L Bias
Old IAT.jpg

Running Custom Bias
New IAT.jpg

After removing a lot of the after-start enrichment the engine still fired up and easily idled cold. It could actually stand to have some more removed.

https://youtu.be/TGxcwd-P06g