Can we modify stock ECT scaling on Injection Timing, or why not?

Perhaps another newbie question, but can anyone tell me why it is suggested to leave this table alone (especially in the lower temps)?

*using Cringer / Silversurfer77 as reference. I have not found threads that explain it.

I am no expert... but just as a generalist the factory tables seem extreme to me.
Can any temp difference effect flow rates as much as 125 crank degrees?

I am also in Ohio.. and subject to bipolar weather.. but even with a fairly mild winter I'm seeing up to 100deg timing difference on warmup.

I can't point to specific data, but the engine just feels/sounds bad until it is near normal operating temp.

This could absolutely mean that I have the timing set wrong at normal temp... but I really think it is close.

Dunno... discuss. =P

when the engine is dead cold the factory has injection alot earlier so fuel can sit on the valve longer to help heat it up before entering the chamber, u can play with ect normal it if u want if it makes startup better if ur loosing too much out the exhaust when it opens the intake valve

I find it depends on the cam. More aggressive needs to be set closer to operating temp especially if a blower's involved. You can use colder engine temp trims or engine response to set it up. For those something like this -

Attachment 142811

Quote:

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Originally Posted by 07GTS

when the engine is dead cold the factory has injection alot earlier so fuel can sit on the valve longer to help heat it up before entering the chamber, u can play with ect normal it if u want if it makes startup better if ur loosing too much out the exhaust when it opens the intake valve

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Oh okay, that makes more sense than what my tiny brain was thinking.

Also makes me want to change it even more because I'm probably blowing a lot of that fuel right out.

The Truck Norris cam isn't super aggressive but the overlap is there.

And Injection Timing has been absolutely vital to making it run well.

Thanks again GHuggins.
I actually snuck 20 off as a test but now I'm not afraid to tighten it up more.

Yes as others have pointed out it is about getting fuel atomized which is hard to do naturally when cold. So leaving it on the back of the valve helps the fuel to heat a little bit. And the hotter the fuel, the more easily it will atomize.

I do also believe there are other several reasons for this.
1) While the liquid fuel (not good) may be in a puddle on the valve, as soon as that valve barely cracks open during overlap, there is going to be quite a large vacuum sucking that fuel in and causing "mechanical" atomization by the sheering force of air and fuel going in. So this another way to assist atomization.

2) Since catalytic converters don't work until they get up to the proper temperature, the OEMs can speed this up by short circuiting the fuel to help heat the cats up more quickly. This is important to understand from the OEM viewpoint since the majority of pollution is caused during cold start ups.

Check out this see through catalytic converter in slow motion...pretty cool...I mean HOT!
https://youtu.be/ekQcy6GN1pM?si=1xu7QxFWi2Msj5D0&t=176

In my experience, cammed N/A LS motors have no issues starting cold. Hot starts are always more of a pain to sort out. So can you mess with this table? Sure...will it help cold starts...I doubt it? However, I would be interested in anything you discover from testing, so please be sure to post back!

Quote:

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Originally Posted by Cringer

In my experience, cammed N/A LS motors have no issues starting cold. Hot starts are always more of a pain to sort out. So can you mess with this table? Sure...will it help cold starts...I doubt it? However, I would be interested in anything you discover from testing, so please be sure to post back!

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It's not so much for the startup as it is for the driving or transient fuel gain from it. I've had them so advanced going in behind other tuners that raw fuel was running or being spit out of the tail pipes during a cold start. Actually had a customer drop one off in my yard and it killed all of the grass where I cranked it up the next morning and had it idling logging for the cold start. This was the worst I've seen, but it was a BIG cam and had straight fuel coming out the tailpipe.

Boosted engines with cams greatly benefit from it too. Usually a quick throttle stomp when coolant temp gets around 80 to 100 F will show if it's needed or even driving it around when cold. If it's having problems running or stumbling then it's most likely a problem. I've had some boosted cammed motors that I've actually flat-lined and they cold started and took throttle just like they were hot.

It is primarily for cat lightoff like you said. Doesn't have "that" much to do with fuel atomization from being cold like we all think...

I should probably attach a disclaimer to this part because... blah blah blah.
Don't do this at home kids.

But for the sake of sanity and science I went the extreme route.
Settings are 'flatlined' aka equal across all temps.
Attachment 142952

Note: the cats were gone on this truck long before I came along.

Cold start / run is greatly improved and I have noticed zero negatives over the course of 1-2 days.

Quote:

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Originally Posted by TragicMike

I should probably attach a disclaimer to this part because... blah blah blah.
Don't do this at home kids.

But for the sake of sanity and science I went the extreme route.
Settings are 'flatlined' aka equal across all temps.
Attachment 142952

Note: the cats were gone on this truck long before I came along.

Cold start / run is greatly improved and I have noticed zero negatives over the course of 1-2 days.

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Very interesting results. I guess we are all full of crap with our speculations haha! Thanks for testing and sharing!

Quote:

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Originally Posted by TragicMike

I should probably attach a disclaimer to this part because... blah blah blah.
Don't do this at home kids.

But for the sake of sanity and science I went the extreme route.
Settings are 'flatlined' aka equal across all temps.
Attachment 142952

Note: the cats were gone on this truck long before I came along.

Cold start / run is greatly improved and I have noticed zero negatives over the course of 1-2 days.

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i done that on my last engine seemed to help very cold starts on E85 also, just keep eye on cold start fueling if its gone leaner then before ur not burning all the fuel right but if it stays as it was then all good

Quote:

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Originally Posted by 07GTS

i done that on my last engine seemed to help very cold starts on E85 also, just keep eye on cold start fueling if its gone leaner then before ur not burning all the fuel right but if it stays as it was then all good

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This is important. I use wideband and trims to adjust it even though everyone tells me that's impossible.......

Quote:

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Originally Posted by GHuggins

This is important. I use wideband and trims to adjust it even though everyone tells me that's impossible.......

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on the thought of odd stuff i was dealing with a e38 last year that uses OL fuel trims so even tho it was a cold start i wanted to add more fuel to help with immediate drivability but it used trims before they were enabled to bring it back closer to stoich, never found out what triggered it as i couldnt turn it off and just use OL fueling before the 02's were enabled like normal

Quote:

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Originally Posted by 07GTS

on the thought of odd stuff i was dealing with a e38 last year that uses OL fuel trims so even tho it was a cold start i wanted to add more fuel to help with immediate drivability but it used trims before they were enabled to bring it back closer to stoich, never found out what triggered it as i couldnt turn it off and just use OL fueling before the 02's were enabled like normal

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It's probably been removed or just wasn't defined for that OS, but there should have been a setting to use stft's for open loop in regards to an (on/off) type of switch.

This is the whole reason I argue being able to use trims to dial in open loop tables or at least the IVT table. The OE did just that on a lot of platforms, so why can't I? Granted "initial" open loop - as the engine is stumbling to life if you will - is an entirely different scenario!!!

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Paste Special Add then smooth for what it's worth - usually requires 2 passes ;)