bucking/surging as low eng speeds

**EC_Tune** · 03-22-2006

Set the coolant value to enable to 284 deg F.

EC

**S2H** · 03-22-2006

Originally Posted by EC_Tune

Set the coolant value to enable to 284 deg F.

EC

dont forget about the clutch DFCO as well....also set it to 284 deg F

**5_Liter_Eater** · 03-23-2006

Well I drove home with the idle sparks set to the main sparks and that didnt make a real noticable difference. This morning I drove in with the DFCO disabled (set to 284 degrees) and my clutch transition was already at 284 degrees as is the stock setting. Still bucks/dives going from zero to little TPS and is much more noticable at low speeds at ~1500 RPM's.

**S2H** · 03-23-2006

try putting it in open loop and adding or taking away a bunch of fuel...
many times when spark doesnt make a difference..it ends up being a fueling issue

**ramjudd** · 03-24-2006

Hey guys

Good thread going. I'd like to figure this issue out!! I have tried everything except set the Throttle Craker Enable to 100 and Disable to 20 per A&A tuning as posted a few entries up. I have tried variation of this with no affect. Peter in Au suggests it just may be a matter of the huge cam lope, no getting around it. I would like to add an observation of the most recent scan of this bucking- the spark does jump around on some of the instances, but it jumps UP instead of tanking low. Sow I have a steady spark scan of 22* until the bucking then it will jump as high as 30*. Not so sure smoothing this will fix anything because on many of the bucking scans I have a flat line spark curve, flat nice AFR of Stoich, no other oscillation of any scanned PIDs. WTF?? Sure would like to hear from someone that has fixed this.....keep the info coming. I would like to swap tune files with some of you to compare notes. email me [email protected]

Robert

**EC_Tune** · 03-24-2006

When it's bucking what is your dynamic airflow doing?
MAP?
Cyl/air too.?

Could be bouncing around on the VE Table pretty irregularly. You may want to flatten out the VE table around idle a bit more.

EC

**ramjudd** · 03-25-2006

good suggestions, and I have been monitoring these pids closely. ROCK STEADY. I mean totally solid MAP, g/cyl, timing, AFR, TPS, etc. This is what makes this problem so difficult to solve. And even with solid scans, I still make changes to various tables (VE, timing, throttle cracker) to affect some sort of change, good or bad, so I know what tables affect this symptom. I am still a bit lost.

Robert

**S2H** · 03-25-2006

I've been working on an ls1 04 GTO M6...with a 232/234 cam..and its bucking...but only in lower gears..
no problems in 3rd or 4th... just 1st and 2nd...
we've thrown spark at it..and taken it away..we've added fuel and leaned it out...
taking away spark made it buck harder but adding didnt change it at all...
on fuel ..leaning it out made it worse..and richening it up helped..but it also was so pig rich that it stumbled at idle and died everytime he let off teh gas...and idle has been ROCK SOLID...

I'm kind of at a loss here too right now..usually I can fix it..but this one wont go away..and its starting to drive me nuts..
I've had solid rollers that drive like a stock cam..
we've played with throttle cracker and follower tables with no success...
we have the idle spark and high/low octane tables with all teh same values everywhere to make sure its not juming between the 2 tables..
and teh spark seems to only be changing a max of 1*-2*...usually bucking with no spark changing or just 0.5* worth.....

this car I'm having problems with is also an aluminum Flywheel and a spec 3..so I'm starting to wonder if its Driver Error as I have never driven the thing and I am just teh passenger seat tuner...

**EC_Tune** · 03-25-2006

The 427 C5R with F1R procharger I've been working on has this happening to it at about 1200-1600 RPM at very light throttle even on the dyno. Bucks & kicks like crazy. It's usually around 45 Kpa MAP. The car idles at 60 Kpa.

I have done all the things SE has done to no avail. I think it's just irregularities in operation for big cams. They just don't play nice just above idle at light throttle.

EC

**LosLS2** · 07-21-2006

Same exact problem here. I don't have a blower but I idle at about 55Kpa and jump back and forth between the 800 and 1200 cells. No problems there. My bucking is happening in the 1600 to 2000 cells and at various Kpa depending on the gear that I am in. With all of these tables and cells w/in each table, there has to be a fix. Also, I had a bigger cam and went to the one that I am currently running in my sig and have the same problem (a little less pronounced). I am tuning in OLSD w/ WB and 2bar SD OS. I am also using a Spec 3 clutch. The dfco is disabled. The OLFA is at 1.0. My idle timing table and timing tables all match up. Could this whole thing have to do with the injectors and the tables for that? I am running 60#'ers. It seems that no one is having this problem with stock injectors. Correct me if I am wrong.

Also, is it normal, from a role to have a lean spike (17:1) when you nail the throttle and enter into PE in the VE table? If not, what do I need to do to fix it? I can't add fuel to the VE table because if it enters PE earlier then the cell will be pig rich?

**LosLS2** · 07-21-2006

I just noticed that the amount of timing shown on my scan does not match what I should be commanding from high/low octane timing tables in the area in question. The values are closer to those of my idle timing table (only in the problem cells). I copied the applicable rows for 1400RPM and up to the idle tables from my main spark tables and will see if that does anything.

**TSDuke** · 07-21-2006

Mine doesn't buck too bad, but subscribing to thread for info.

**MNR-0** · 07-21-2006

Log your inj. pulsewidth at dile and coming to idle. If you are getting surge, check to see your injectors arent playing havoc. If they are, set your VE values at idle and just off idle to be within +-2 of each other, preventing the large swings in injector modulation. I ramp my VE values up around idle very slowly, then off idle, faster to prevent lean spots.

So, if you idle at 60kPa at 860RPM, set you VE values for all adjacent cells within +-2 of each other around that load point and blend it in to the rest of the VE. At 800RPM from 55-60-65 ramp them by 1. At 1200 ramp them by 2. From 60kpa 800-1200RPM they should be no more than +2/3.

You only need enough spark to maintain idle. 22* is a good start. Also make sure your overpseed/underspeed corrections arent over-reacting by lowering the stock values by 50% up till +-100RPM then blending to stock from there.

I also copy over my main spark table to my idle advance tables and increase my follower decay rates in the 1st columns. Ive found increasing the rate of decay removes the IAC from interfering with fuelling much quicker. Also the cracker table, Ive zeroed min 400-800-1200 up till 36mph then blended the rest in there. At idle, and coming to idle, I dont want the IAC motor to be interfering with my base airflow.

Oh, and finally, with all cammed cars I tune I run them in open loop till 1200RPM. The O2s dont meter AFR well at low airspeed with large overlap cams and will flood the engine. Disable closed loop when tuning idle and the VE.

If you have enough spark, decent AFRs by VE tuning and control over your injectors at idle, there is no reason why you can't have nice steady idle transitions.

**LosLS2** · 07-22-2006

Is it normal, from a role to have a lean spike (17:1) when you nail the throttle and enter into PE in the VE table? If not, what do I need to do to fix it? I can't add fuel to the VE table because if it enters PE earlier then the cell will be pig rich.

**WS6FirebirdTA00** · 07-22-2006

well, some of that is the time it takes the car to respond to the change in throttle as well as for the exhaust to be filled with the cyl charge it is now commanding. If you have the VE fully tuned and its all within reason, dont worry. Although mine really doesnt spike lean that bad, I woudl assume you need to do some more ve tuning.

**LosLS2** · 07-22-2006

I have been fishing around for the solution to the lean spike. Is there a way to tell the pcm that it must enter PE in the 80Kpa+ sells? If there is, could someone tell me exactly where I should look for that? Under the PE tab I was set to PE enable at 15Kpa which doesn't make sense. I can't find were you tell it what throttle position it needs to be in for the PE to enable. I appreciate the help. I am so close to having this thing dialed in nice.

**WS6FirebirdTA00** · 07-22-2006

just look further down, you will see where it says tps enable for pe

**MNR-0** · 07-22-2006

Originally Posted by LosLS2

Is there a way to tell the pcm that it must enter PE in the 80Kpa+ sells?

Yes. Power Enrich|Power Enrichment PE Enable and set MAP to 80kPa. It wont enter PE unless your MAP is greater than 80kPa.

**LosLS2** · 07-23-2006

found'em guys. Thanks. It's like when you are sitting at your desk and cant see something that is rght in front of you. You just have to walk a way for a bit. I found it this morning.

**checkmate** · 07-27-2006

Originally Posted by MNR-0

Oh, and finally, with all cammed cars I tune I run them in open loop till 1200RPM. The O2s dont meter AFR well at low airspeed with large overlap cams and will flood the engine. Disable closed loop when tuning idle and the VE.

If you have enough spark, decent AFRs by VE tuning and control over your injectors at idle, there is no reason why you can't have nice steady idle transitions.

How do you setup OL only till 1200rpm?

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