Manual trans vette real bad bucking issues, tried evverything(or at least I think so)

[GrannySShifting]

Tried disabling M6 spark smoothing, forcing it open loop rich and lean, added and took timing out nothing seems to really affect it. zerod out all the throttle crackers and followers to see if airflow from there was contributing to it, nothing seemed to change it

Any other ideas? Its a 427, with an unknown cam, and a no name throttle body. Before straightening out other stuff on tune cust said he doesnt remember it bucking that bad, but flash the original program in it still does it

Timing real jerking when it starts doing it (timing from where frame 310) but when I held timing constant with controls it was way worse (locked timing log)

Only other thing Im thinking is SD, if maf reading is erratic enough to do that, but the gms/cyl value isn moving around mor ethan .02 which wouldnt make it read in wildly different areas of timing table. Maybe burst knock pulling it out when it does that

[POWERZONE]

Smoothing spark advance with smooth transistions. Same with fueling, smoothing VE with smooth transitions general helps the majority of the time.

The VE and Spark advance tables need work.

Just look at your VE and Spark advance tables and imagine them running linear or on a curve. Its going to be jagged with severe drops and peaks(especially when combined with over/under speed) like the scan.

[MikeOD]

If you log spark and IPW when it's bucking (log IPW with some resolution after the decimal)...if one of them is moving...figure out why...if it's injector pulse width, look at the VE table...if it has a drastic change there...smooth that portion of the table out and that will stop...if it's spark advance, smooth the timing table there out...if that doesn't fix it (they're both smooth and it's still bucking)...give it a good bit more timing right there (that cell and the neighboring cells...then smooth in the cells neighboring the neighbors)...try 40 degrees or maybe even more if it's at very light load. Also make sure it's actually at Lambda 1.0...not way lean or way rich.

If that doesn't cure it...is it a FAST 102mm intake? Make sure there's no manifold leaks (internal between runners and the plenum and external)...if that doesn't cure it...I'd do a few more mechanical checks...make sure the pushrods aren't too long make sure the plugs are OK and gapped correctly...after that...report back.

[GrannySShifting]

Smoothing spark advance with smooth transistions. Same with fueling, smoothing VE with smooth transitions general helps the majority of the time.

The VE and Spark advance tables need work.

Just look at your VE and Spark advance tables and imagine them running linear or on a curve. Its going to be jagged with severe drops and peaks(especially when combined with over/under speed) like the scan.

Just compared to original file after you said somethign about VE table, and somehow I have that original jacked up VE table in this thing. I was playing with the airflow values mostly for a while and must have went one too far back when trying stuff

Checking it out later with a VE table not a VE hillclimb

New o rings in it because they were too small and leaking (LS7 manifold)

[GrannySShifting]

VE is pretty close again. Thing is still a bear to drive sometimes.

I feel like theres an airflow error on the bottom end of things because when you clutch out it is super tricky to catch or it wants to stall or flare. Car makes you feel like you forgot how to drive a clutch. Did I mention it has some no name Chinese throttle body on it

[GrannySShifting]

Frames 1991, 1874, 987 (timing was jumping around and was fine, tiny bit more throttle and timing went up and steadied but started bucking?)

Hard taking off with clutch at 445, 290 for example. I think ve may be a little heavy in low rpm high load area although wideband doesnt say so

[POWERZONE]

I just tuned a car that had killer jerking and bucking especially when downshifting via 2>1 and cruising around 1st or 2nd.

It was pig rich with too much timing. I cleaned up the VE and made it as smooth as possible, I did the same with all spark tables and MAF.

No more bucking. Now it does not always come out that perfect, but at least the customer was happy.

[GrannySShifting]

I have zeroed out everything I can think of cracker/follower not moving at all, everything looks smooth as far as I can tell 40kpa to 65kpa 1300-1900 rpm, AF pretty spot on with STFTs with SD7 file, SD8 file I tried it in open loop richer in that area, thinking O2 might be happy at 14.7 but overlap at light throttle maybe screwing with it it needs to be ran closer to 13-13.5 - acted same

Noticed timing jumping around a couple times in SD8 log, but theres 4 times as many occurances of it bucking bad with timing pretty steady @38 degrees, tried adding and subtracting up to 7 or 8 degrees both ways no change. This thing is a basketcase, and Im starting to think theres more to the TB than anything

[GrannySShifting]

more examples of stuff that doesnt work, EOIT changes, idle proportional fueling, spark smooth turned off

Frame 1615 can see rpm bucking

[GrannySShifting]

No one have an idea?

[Russ K]

Since your idle KPA is 67-68, your cam has a lot of overlap (probably 15-20*). So that explains the bucking. And most likely has a light weight clutch/flywheel, causing the poor take offs. Also a light weight clutch/flywheel will make the bucking worse.

Russ Kemp

[GrannySShifting]

More than that prob, its a 440-450 inch engine LOL