***Need help with idle surging while coming to a stop please***

[WICKEDOWESIX]

Well first off I have a RWD Silverado SS with a 6.0L with the following mods, 228R cam on 112lsa, LT's, CAI, exhaust, Vig 3600 stall, 4.10's. When I come to stops is starts surging really bad to the point where it almost dies. Even if I go in reverse it starts surging too. Any help/tips/ suggestions are greatly appreciated. I will post my tune and a log soon. Thanks!

[Tordne]

Have a look for Throttle Cracker and Throttle Follower threads. Also search for RAFIG on the forum which is for tuning the "actual" idle airflow requirements for your vehicle with mods.

[WICKEDOWESIX]

Also we have tried to make changes to spark in gear and tweek the TF a bit and it solves the problem for a bit but then shortly after the problem still persist.

[WICKEDOWESIX]

Have a look for Throttle Cracker and Throttle Follower threads. Also search for RAFIG on the forum which is for tuning the "actual" idle airflow requirements for your vehicle with mods.

Thanks!

[Tordne]

Definitely do the RAFIG process as a starting point.

Throttle Cracker is the added airflow while moving (coasting basically). While Throttle Follower is added airflow and decay rate based on TPS change.

[WICKEDOWESIX]

Definitely do the RAFIG process as a starting point.

Throttle Cracker is the added airflow while moving (coasting basically). While Throttle Follower is added airflow and decay rate based on TPS change.

Ok we will try that again and see if it fix is it thanks for all the info bro!

[whackem04]

i had problems with my idle and what i did was find a similar tune stock or modified and copy in the idle info and try that if you think your program is off. It helped me alot with a/c surging.

[Mr. P.]

Hi Art - a suggestion, my truck was doing a similar behavior when I would coast down to a stop, the truck would take off and drive fine, and would start and idle fine, but when coasting down the PCM would hunt for idle and always be hitting off the stall saver and the AFRs were cycling rich-lean-rich-lean; what I found (accidentally) was modifying the injector tables made the issue go away for me, I am sure I also need to go through the RAFIG process but for now it's much better behaved. I am referring to the injector pulse width tables, small pulse adjust, and voltage correction tables; there is not a lot of literature/guidelines on these tables, it's kind of a black art :( Also, related subject I found that rescaling my AFR & VE tables made a world of difference in spark and transmission behavior.

Mr. P. :)

[WICKEDOWESIX]

Hi Art - a suggestion, my truck was doing a similar behavior when I would coast down to a stop, the truck would take off and drive fine, and would start and idle fine, but when coasting down the PCM would hunt for idle and always be hitting off the stall saver and the AFRs were cycling rich-lean-rich-lean; what I found (accidentally) was modifying the injector tables made the issue go away for me, I am sure I also need to go through the RAFIG process but for now it's much better behaved. I am referring to the injector pulse width tables, small pulse adjust, and voltage correction tables; there is not a lot of literature/guidelines on these tables, it's kind of a black art :( Also, related subject I found that rescaling my AFR & VE tables made a world of difference in spark and transmission behavior.

Mr. P. :)

Thanks Steve! I will give it a try. Same here the truck idles, revs, take offs are completely fine its just when I am coming to a stop or low mph coasting.

[Mr. P.]

Thanks Steve! I will give it a try. Same here the truck idles, revs, take offs are completely fine its just when I am coming to a stop or low mph coasting.

Yup I reframed my thinking - the cause is that the injectors changed, not because of the change in cam or heads or whatever... the PCM is a little lost on how to run the new injectors correctly at low pulse widths. As you are using a GM injector, I would attempt to find a tune from holdencrazy of a stock application using those exact injectors, and copy all the injector tables into your tune because those values were labratory measured by GM; this may require you go through the AutoVE process again, but at least the PCM will have the info it needs to run the injectors correctly at super-low pulse width situations. In my case I'm screwed because I have modified injectors, so I am experimenting with these tables to get it to act right during overrun.

Mr. P. :)

[Mr. P.]

I'm running COS3 - specifically, investigate the values you have in B4003 & B4004; all values in my B4002 table are set to "1.0" FWIW. Also look at your main VE table in units of "percent VE" and if you have any cells way over stock VE percentages then you might also benefit from scaling the VE and IFR tables down equal amounts; example in my VE table I had a lot of cells at 110-115%, and the highest VE that I see on the stock VE table is 103%, so I took B0101, A0009, and B4001 and reduced them all 12% across the board, and the truck is far more domesticated now in spark, KR, and shift behavior. My IFR was calculated at 9.1 g/sec on the spreadsheet, but now I have it at 8.0 and scaled down the VE tables to match and even though the IFR is not theoretically perfect everything is operating far better, I am pretty sure there are some areas in the PCM code that when it sees sky-high VE's it panics! I need to go through the AutoVE process again now, I'm a couple percent lean in most places, but everything is running far better than before. I'm still working on a BKR problem (I think?) but looking at all those areas is what I did recently and the overrun surging problem went away, and my economy/fuel mileage went from 12.0 to 15.2 at 75-mph lol.

Mr. P. :)