negative timing on Idle

[Silspark]

looking for the reason making timing on idle negative specially with camshaft upgrade

LT4 with 2.31 making almost -5 to -10 timing on idle
L83 with cold air intake make -15 to -10 on idle
L83 with camshaft making -5 to -10 on idle

is thats symptom of air leak and PCM try to correct itself or needing work on torque management also there are shearing the actual RPM less the commanded RPM (happen on D and less on N)

WOT and cruising is perfect even not stalling but with 0 paddle

regards

[Higgs Boson]

Going to have to post a tune and a log file if you want help with it.

[Redline MS]

looking for the reason making timing on idle negative specially with camshaft upgrade

LT4 with 2.31 making almost -5 to -10 timing on idle
L83 with cold air intake make -15 to -10 on idle
L83 with camshaft making -5 to -10 on idle

is thats symptom of air leak and PCM try to correct itself or needing work on torque management also there are shearing the actual RPM less the commanded RPM (happen on D and less on N)

WOT and cruising is perfect even not stalling but with 0 paddle

regards

I'd guess your predicted torque is too high so the PCM uses spark to try and pull the idle down

[Speedforhire]

The LT4 generally pulls timing after a cold start to keep the rpm's up for a very brief time. I think it's less than thirty seconds.

The base idle does not pull timing.

Help us, help you! Post a tune and log for definitive assistance.

[Redline MS]

The LT4 generally pulls timing after a cold start to keep the rpm's up for a very brief time. I think it's less than thirty seconds.

The base idle does not pull timing.

Help us, help you! Post a tune and log for definitive assistance.

The reason the control retards the timing at cold start is to raise exhaust gas temps to light off the cats. This is also done in conjunction with cam phasing. This is why these motors have a loud exhaust tone until it decays off.

[Speedforhire]

.......This is why these motors have a loud exhaust tone until it decays off.......

It would be nice to keep that loud exhaust note to. Once it falls below 800 rpm's it sounds like a sewing machine. LOL!

[Higgs Boson]

i disable all the cat lightoff stuff because i always remove the cats! ;-)

[Silspark]

u r right in cold start exhaust is louder and diving u great tone, and also sometime on Decel but Im talking about normal Temp 180+, before air leak could make negative timing but u can detecting the leak but in GenV is using different methods

[Silspark]

I just log the car with negative timing @idle + stock with tuned files

Please advice

[Speedforhire]

The stock tune you posted does not appear to be stock. What are these tunes from?

[Silspark]

Sierra 2016 Stock

[Silspark]

any advice ?

[GrannySShifting]

The reason the control retards the timing at cold start is to raise exhaust gas temps to light off the cats. This is also done in conjunction with cam phasing. This is why these motors have a loud exhaust tone until it decays off.

I cant find cat lightoff timing tables on a 2017 SS file? Obvious to find on earlier stuff

[s57_s2k]

looking for the reason making timing on idle negative specially with camshaft upgrade

LT4 with 2.31 making almost -5 to -10 timing on idle
L83 with cold air intake make -15 to -10 on idle
L83 with camshaft making -5 to -10 on idle

is thats symptom of air leak and PCM try to correct itself or needing work on torque management also there are shearing the actual RPM less the commanded RPM (happen on D and less on N)

WOT and cruising is perfect even not stalling but with 0 paddle

regards

did you find out what it the issue ?

[Ben Charles]

Negative timing is Bc the ECU uses Tq to control idle (much like older ECUs used airflow) when you INCREASE airflow the ECU pulls timing in an attempt to bring it back

[s57_s2k]

Negative timing is Bc the ECU uses Tq to control idle (much like older ECUs used airflow) when you INCREASE airflow the ECU pulls timing in an attempt to bring it back

Yes you are right , my tps was 13% before cam and after cam it is 18% and it is pulling timing to keep idle at commanded value. is there a way to lower throttle position ? maybe idle torque reserve ?

[Ghostnotes]

Negative timing is Bc the ECU uses Tq to control idle (much like older ECUs used airflow) when you INCREASE airflow the ECU pulls timing in an attempt to bring it back

Ben,

Maybe a stupid question but since i put my supercharger on, i figured i would have to increase torque some to account for the added load to turn at xxx rpm, or should i be increasing air? My thinking was since i already have a fairly large cam the idle flow rates should not change much.

I had the cam tuning spot on but this is kicking my butt a little.

One thing i know for sure is before the SC i could change my fuel trim output STFT/LTFT by changing torque settings. When i was dialing my cam in, I could get real close to +/- 2.0 or so by torque BUT my timing was still a little low. It was not until i dialed my MAF in that the rest fell into place.

[vannatta20]

I have had the exact same issue. Any tips on how to fix this?

[TriPinTaZ]

Have you tried lowering your Virtual Torque tables in the idle area?

[Ben Charles]

Bingo!!! That lowers predicted Tq and will help with idle timing since then it won?t try to fight its self with spark