Could someone please help me with this surging?

[LosLS2]

I have made many posts about this problem over the last year. I recently swapped my 60# Motron injectors for some smaller 42# Lucas injectors with the hopes that this would resolve my surging issues. It did not make any difference at all. I have read, searched and tweaked the tune with very little good results. The only thing that seems to help is when the problem area (40 & 45KPA at 1.6 & 2.0K RPM cells in the VE table @ 4-8% TPS) is made rich like in the range of 13.0 to 13.2 AFR. I'm not sure if that is the solution or not. It seems like a band aid. I really wish that I new what I should be scanning to find this particular problem. Some have said that the answer is in gettng the VE table dead nuts. Not for me. Others have said that the answer is in the RAF (it is dead nuts). Not for me. Others have mentioned timing. Not for me. Others have mentioned the Throttle Cracker and follower tables. These tables are magic for me and I cant seem to figure out what it is that I should be scanning in order to determine which way I should move which cells. Please look at my tune. It is called 2bar 98z28 surge fix smoothed because I got the VE table dialed in and then smoothed it. As for the surge fix part of the name, that is just wishfull thinking. Some background.

I am running in Open Loop Speed Density and I am tuning with an LM1 wideband that is logging thru the EGR. I am using the 2 bar SD upgraded OS simply for the improved VE resolution. I am not using forced induction or any special MAP sensor. My mods are listed in my sig below. I don't think that it is the cam as I had a slightly larger cam before and went down to the current cam and have the same exact problem. PLEASE PLEASE PLEASE HELP!!!!!

I am receptive to anything at this point. Please post a config that I could use to scan the correct PIDs, custom or not.

[WS6FirebirdTA00]

you can give this a shot, might want to try some lower timing values. I would say something around 36-40 or so. Also, did you dial your idle air in from a cold start? My car responds best with an AFR around 14.4:1 or so in areas where it likes to surge. Also, what is your IAC at during a hot idle.

[LosLS2]

you can give this a shot, might want to try some lower timing values. I would say something around 36-40 or so. Also, did you dial your idle air in from a cold start? My car responds best with an AFR around 14.4:1 or so in areas where it likes to surge. Also, what is your IAC at during a hot idle.

I just up'd the timing on that tune just trying anything before I posted it and it didn't really make any difference.
Yes, the RAF is dialed in from 60F (cold for Florida) to 212F column.
IAC counts start of high and work their way down to just below 60 by 190F (operating temp).
I will try the tune posted and post up later.
THANKS for the help.

Also, if there are any configs that you would like for me to log, I would appreciate them.

[LosLS2]

Unable to open the file. It says that it failed the validation check.

[LosLS2]

Figured it out. I was on an old version.

[LosLS2]

OK. I dropped in the test tune. I think that it feels better while first getting into gear and slow roll outs in 1st gear. As far as the bucking/surging goes, it is still there. No change at all.

I logged the RAF using the LTIT+STIT method. I noticed something really funky. I was watching the LTIT In Gear/AC Off PID and it was at like -0.14 and the Idle Adapt (STIT) was at like -0.30. My Custom PID which is supposed to add the two together is reading like -3.45 lb/min. I am not a math wiz but I know that -0.14 + -0.30 is not -3.45. It should be like -0.44 lb/min right? Not sure what is happening.

Please provide a config that I could use in order to help isolate the bucking and surging and explain the issue with the STIT+LTIT.

Thanks in advance,
Los

[LosLS2]

I just had a thought based on something that RussK said in another thread, He mentioend that the blade on the TB should not be drilled and that the set screw should not be turned in. My TB is not drilled but I did have to crack the blade open with the set screw. Being as though my car is being tuned in OLSD and there is no means for the computer to meter the amount of air coming in, this leads me to believe that this could be part of my problem. I am curious if others that are experiencing the bucking/surging ALL have either of these unmetered methods of allowing air into the motor. This is probably causing a vacuum leak type condition due to the unmetered air. Now, how do you drop the IAC count in order to get it in the 40 to 60 count range?

[SSUte01]

I logged the RAF using the LTIT+STIT method. I noticed something really funky. I was watching the LTIT In Gear/AC Off PID and it was at like -0.14 and the Idle Adapt (STIT) was at like -0.30. My Custom PID which is supposed to add the two together is reading like -3.45 lb/min. I am not a math wiz but I know that -0.14 + -0.30 is not -3.45. It should be like -0.44 lb/min right? Not sure what is happening.

Thanks in advance,
Los

Are you using lb/min or g/sec for all calcs that may explain an anomoly? If -0.14 and -0.30 were lb/min and added together to get -0.44 lb/min quickly converted that would be ~-3.4 g/sec which coincedently is approx what you have.

AFAIK a well dialled in RAF will bring your IAC counts into line as well. I had some issues initially once I fitted a BBK and once my RAF was dialled in to get my count where I wanted to allow for movement due to weather ect I had to move the set screw about a 1/4 to a 1/2 turn. This may go against advice given to you, however mine wasn't even in contact and the way I see it why have an idle screw that isn't even contacting the blade. Anyways end result good idle and good return to idle count ~30 (smaller cam than you)

I also had a very similar surging issue about 1500 rpm and 45kPa and for me it was a combination of a few things, proportional fuelling (not an issue for you as OL) min inj PW, transient fuel, and defualt PW (my values now ballpark like those suggested to you by Mike WS6 as he suggested elsewhere) but the main culprit was a lean area and not very lean at that coupled with too much timing. Added a small amount of fuel and little less timing and I cannot replicate the issue that bugged me for months as it varied with extent that it occured.

Cheers

[WS6FirebirdTA00]

I just had a thought based on something that RussK said in another thread, He mentioend that the blade on the TB should not be drilled and that the set screw should not be turned in. My TB is not drilled but I did have to crack the blade open with the set screw. Being as though my car is being tuned in OLSD and there is no means for the computer to meter the amount of air coming in, this leads me to believe that this could be part of my problem. I am curious if others that are experiencing the bucking/surging ALL have either of these unmetered methods of allowing air into the motor. This is probably causing a vacuum leak type condition due to the unmetered air. Now, how do you drop the IAC count in order to get it in the 40 to 60 count range?

That isnt a problem, I have never had an issue like this and I have done the same things on several cars. There is no other way to get the IAC counts down without cracking the blade or drilling a hole.

Try out this config, put in your WB though if you are using something different. Get an idle log from a dead cold start and then start a log when you are in the areas of surging. Then post up.

[LosLS2]

OK, I downloaded the cfg file and changed the PID's around to fit my WB thru the EGR method. The only one that I am not sure of was the actual AFR Error vs VE Histogram. There was a filter that referenced sensor 120 I believe which would be the WB on the IO unit. I cut and pasted my custom PID between the brackets in the place of the sensor. It doesn't look pretty. Looks like this now [([PID.2811]/0.625)+10]>7.4 Do you think that it will work like this or did I do something wrong?

Thanks again for all of your help!!!!!

[LosLS2]

Are you using lb/min or g/sec for all calcs that may explain an anomoly? If -0.14 and -0.30 were lb/min and added together to get -0.44 lb/min quickly converted that would be ~-3.4 g/sec which coincedently is approx what you have.

AFAIK a well dialled in RAF will bring your IAC counts into line as well. I had some issues initially once I fitted a BBK and once my RAF was dialled in to get my count where I wanted to allow for movement due to weather ect I had to move the set screw about a 1/4 to a 1/2 turn. This may go against advice given to you, however mine wasn't even in contact and the way I see it why have an idle screw that isn't even contacting the blade. Anyways end result good idle and good return to idle count ~30 (smaller cam than you)

I also had a very similar surging issue about 1500 rpm and 45kPa and for me it was a combination of a few things, proportional fuelling (not an issue for you as OL) min inj PW, transient fuel, and defualt PW (my values now ballpark like those suggested to you by Mike WS6 as he suggested elsewhere) but the main culprit was a lean area and not very lean at that coupled with too much timing. Added a small amount of fuel and little less timing and I cannot replicate the issue that bugged me for months as it varied with extent that it occured.

Cheers

What injectors are you running? Could you list mods?

There are many many people trying to work out this very same issue. Any specific info would be greatly appreciated. I wouldn't mind seeing your tune in order to compare it to mine and maybe learn something as examples go a long way towards explaining things for me.

Thanks in advance.

[SSUte01]

Little bit like comparing apples and oranges given you're a stroked LS2 with a considerably larger cam and I am stock cubed LS1. But anything to try and help out. Best advice is to listen to the experts but feel free to compare if you wish

Mods

218/224 114LSA 0.525
Milled heads 10.9:1 CR
BBK 80mm TB
42lb 'Green Top' Delphi injectors
CLSD (open lood idle)
Full exhaust
OTRCAI

[LosLS2]

WS6,

See attached log and the last tune that I used. I did a cold start log and dialed in the RAF pretty close this morning. I accidentally didn't save it but I did get the values into the RAF table on most recent tune listed below. Now, this tune has not been altered for this log so feel free to make changes based on this most recent log.

The surging and bucking can be seen in frames 1152 to 1167 or pretty much anywhere that the TPS is at about 7% and the inj duty cycle is at 4% with the RPMs just over 1700.

Thanks!

[WS6FirebirdTA00]

I assume that you have it setup to log the WB through EGR? What is the relation in voltage vs afr?

[LosLS2]

Crap I don't remember. Here is the formula though for the custom PID: ([PID.2811]/0.625)+10
Is that enough information? I can tell you that the log and my LM1 display appear to be reporting the same AFR values.

I had to remove the filter that you had in the AFR Error vs VE table as subing in this formula [([PID.2811]/0.625)+10]>7.4 where I replaced sen.120 between the [brackets] did not work. Maybe I did it wrong. Let me send you the redone cfg file so that you can use it to view the log. It's in my laptop.

[LosLS2]

Here is the updated cfg file that I had to use based on the one that you sent me originally.

[WS6FirebirdTA00]

that was an old filter I had in there for when I was droping frames, never did take it out haha

[WS6FirebirdTA00]

try this, take a log and every time it starts to surge insert a marker (press the m button)

[WS6FirebirdTA00]

also forgot to mentino that those areas you saw surge the AFR was in the 15's, which WILL make the car surge.

[LosLS2]

Wow, I didn't even get a chance to look at this log. Would the change to the RAF or the Follower table effect the VE table? Yesterday's log was actually rich in those areas. Oh, I did pull a little timing in that area and I think I am going to pull more. Would maybe lowering the timing cause me to go a little lean? I thought that it was the other way around. Anyway, I will give this a try and leave the timing alone until I see if this helps.