Cold start issue , scaled injectors

[MStefak]

Here in Ontario Canada weve had -30 to -45 Celcius weather lately.

After scaling injectors ( double AFR , halve IFR ) I am having massive fueling issue with cold starts. If the truck sits for any length of time ( even 45 to an hour ) it doesn't want to start. Im assuming that doubling the AFR has caused this issue . Would cutting the open loop fueling in half fix this ?

2008 6.2 Sierra with a magnacharger and 103 lb/hr injectors

[SSUte01]

Log IVT and see where you run into troubles and make the target OL multipliers the same as what they would've been if you hadn't scaled. I'm guessing since the scaling you're reporting a different IVT and therefore commanding an inappropriate target AFR. That all said that's extreme temperature and wouldn't have thought that too much effort would've been made modelling those conditions by GM.

[DSteck]

Might be the injectors themselves.

[MMGT1]

Log IVT and see where you run into troubles and make the target OL multipliers the same as what they would've been if you hadn't scaled. I'm guessing since the scaling you're reporting a different IVT and therefore commanding an inappropriate target AFR. That all said that's extreme temperature and wouldn't have thought that too much effort would've been made modelling those conditions by GM.

Check your cranking fuel, I bet yours is commanding something ridiculous like 9 or 8 AFR for starts in cold temps. Aim for 12 to 12.5 for cranking fuel and see how it does

I just had a look at a stock file and if yours is stock, its aiming way too rich in the lower temps

[MStefak]

I had the same thought , commanded afr hits 1.x at times. Clearly way to rich . But which table to I change the cranking fuel or just the OL? Just OL correct ? Because the cranking fuel will multiply the OL ?

[MMGT1]

I was into an LS2 that was aiming low 9's when cranking. I changed it in the Cranking fuel mult vs time and pulled VE in the 90-105 range, 400-800rpm. Fires a hell of a lot quicker but have a slight oscillation after cold start I am trying to figure out, but it is a hell of a lot better now. Hot starts are perfect, purrs like a kitten. Cold start settles within 15-20 seconds but it is kicking my ass man. 100% SD tune. I am going to try setting cold temp idle to 1K and have it fall back to 850 as it heats up to see if that will get this one in line.

[MStefak]

The oscillation is the spark , I have the same issue. Check out the catlight off tables and such, ive noticed that something pulls a bunch of timing right after startup. My idle spark is set at 15 and cold start spark jumps around 6-9 degrees. Im suspecting it might be the startup flare control though need to mess with that as well.

I get a very cammed sound as the spark swings for about 20 seconds and it calms down when cold.

[MMGT1]

The PCM has no idea what gear it is in, so p/n tables are referenced. I have the catlight off for p/n 0ed out already so I will try getting rid of the rest. Long tubes, no cats... yada... yada... but yes exactly as you described there, timing is dropping and rising, I just cant find what is doing it! As I said too, hot start no problem, coolant under 50*C and its doing this. I just cut the start up flair control in half and going to see if it helps too

[MStefak]

I think it's the flare spark , only numbers I see with adders and sub tractors that equal my spark after start up are the flare control so it makes sense. Even try changing the startup over speed and under speed table to force it into " run mode" sooner "

[MMGT1]

Yup, your on the right track there bud. Cutting flair spark in half calmed it quite a bit. Next chance I get we will tighten it a bit more, but it looked really promising. I suggest you go the same route there and see how yours does

[MStefak]

It will have a positive effect on mine im sure , I just need to figure out the fueling when its super cold out.

[MMGT1]

Fuel, Open Loop, EQ Ratio... look there

[eficalibrator]

That all said that's extreme temperature and wouldn't have thought that too much effort would've been made modelling those conditions by GM.

..and you would be wrong. All OEMs spend a LOT of time dialing in cold start. We actually spend more time on this than we usually do at "normal" conditions simply because it takes so long to get right and you only get one or two tries per day per car.

Check your cranking fuel, I bet yours is commanding something ridiculous like 9 or 8 AFR for starts in cold temps. Aim for 12 to 12.5 for cranking fuel and see how it does

I just had a look at a stock file and if yours is stock, its aiming way too rich in the lower temps

It looks rich in the table, but that's not reality for the flame in the cylinder. At cold temps, a lot of the fuel that is injected never even evaporates. We compensate by adding extra to make up for this lost fuel. How much extra must be added varies with temp AND engine hardware. Once you modify the engine, it's up to you to fix cold start. Never mind that the numbers "look rich". Just get the actual AFR for combustion around 0.8-0.9 lambda at startup. This WILL require extar fuel at cold temps.

[SSUte01]

..and you would be wrong. All OEMs spend a LOT of time dialing in cold start. We actually spend more time on this than we usually do at "normal" conditions simply because it takes so long to get right and you only get one or two tries per day per car.

No doubt. Its the same for us non-OEM types for the same reasons for cold start, I was referring to the -30*C or colder type temps that I was surprised would get the same amount of attention simply based on the prevalence of those temps and difficulty (and cost) in replicating them, but if they do, good to know.

[MStefak]

its still trying to figure out why this is happening after the injector scale .. which table is the cause oif the issue, because once its close to operature temp everything seems great. But the ciolder it gets the more of an asshole the truck becomes. Ive swung all the fueling tables both ways , individually and it appears it may need more fuel at cold start as I came to today. But the issue is is stinks when it starts. I see the commanded AFR at 2 or 3 at times ( and considering my AFR is doubled that means im commanding half of that which means 1 or 1.5 at times) I havent figured out how the ECM is figureing out crank fuel.

[MMGT1]

Its -45 here today and here is my table now, perfect starts, not making my tail pipes black and not making my eyes bleed anymore! Ill post a screen shot... I got the table from a guy on LS1 Tech and it worked amazingly well. So mine ended up being in the OLFA table, so yes Greg... lol

OLFA.jpg

And when I said "Aim fr 12-12.5" I should have added.. WITH A WIDEBAND, yes

[MStefak]

Our platforms being different make the variables that calculate our fueling completely different.

My E38 uses IVTs with OL fueling. My open loop fueling is pretty well twice yours currently and then there is my cranking fuel which will add to it somehow .. in which im still trying to figure out.

Warm ( anything say above 0 celcius ) it fires on the second turn starts strong and idles well. We will see how the added fueling works tomorrow morning when it hits -35 again.

Id still love for someone to chime in on how the hell I change how the IVTs are calculated so my scaled injectors stop screwing with it ..

[DSteck]

Id still love for someone to chime in on how the hell I change how the IVTs are calculated so my scaled injectors stop screwing with it ..

We can't yet, as I said before.

[MStefak]

Then this is something that is being worked on ?

[DSteck]

Hence why I said it's in their queue.