Need help analyzing data on tracing bucking gremlin in car>>

[WS6Fury]

The car has always bucked pretty bad for some odd reason, and seems to have smoothed out a little bit with the new intake and heads combo, but it still be there.

Everything is in check, no spark changes, no bouncing IAC, afr is a little lean when things are hot, and when running rich it tends to calm the bucking a bit.

I attached 3 log files:
a) I subtracted from the follower table to see if any affect, made it worse
b) I added to the follow table (from base line), seemed to not be as choppy but a longer duration, but still there and varies
c) w/ follower same as b), I subtracted from the cracker table.

The only thing I see bouncing around is the dyn air flow, and the idle cracker air flow pids. (Don't mind the afr, or bouncing wbo2 reading, pretty hot here today)

The bucking is when I'm cruising between 1600-2200+ at constant speed, w/ TPS below 8. Just look for the flat TPS reading and will show where it starts to buck every time.

Can someone help point me in the right direction on this to see what else to adjust maybe?

[MNR-0]

My 2c worth is this...

1. Zero out the cracker table
2. Add more fuel at cruise, to say something around stoich (14.7)

You can run upwards of 36-40* timing there, so I'd crusie at 36* advance as well, blending in to idle at 1000RPM (butnot too fast a ramp, or you will be bucking on light low RPM throttle)

Good luck

[colamotas]

Yeap, bucking is usally a sign of not enough timming advanced in that area of the spark map. The 1800-2200 is really low for that area. You should increase it signifcantly, just watch for knock. Take it up about 4 degrees and then check it.
One question what does how is tps representiave of bucking?

[WS6Fury]

TPS is only showing how much I'm stepping on the gas. If I'm on the throttle say 8+ the bucking isn't really there, it's more of a light surge.

TPS <8 which is light throttle to keep a speed when follwing a car is where most the issues arise.

I do agree the cruise cells in VE table need to be richened up, but this is OLSD and this will happen all the time here in NJ with the swings in temp. Yesterday just happened to be a really hot day, so things were running lean.

If I do bump up the spark in cruise cells, is there anything I need to do to the Idle Spark Advance tables?

If I zero out the cracker, do I have to redo the RAF?

Is there anything else that can be pointed out in the logged tables, or maybe something else I need to log to show?

[colamotas]

I would say no on altering the idle spark cells, unless you wanted to smooth the transition, but at idle you shouldnt even see those areas ie no load

[WS6Fury]

Ok, tried two more things on the car this past week, and none seem to make any matters better or worse.

I zero'd the cracker table except the 400 and 1000 column, since the car doesnt even cruise that low ever, and I zero'd the follower airflow table from 3.5% down. The car didn't seem to like the follower aiflow changes, but has since then seemed to calm down a bit after zeroing out.

I attached the log for viewing pleasure. From everything I can see, the follower table is still adding some air, the dyn cyl air is the only pid that fluctuates. Everything else logged is rock solid when the car is bucking/surging.

so what else can I try outside of spark, which is the next animal to tease?

[WS6FirebirdTA00]

have you added fuel? Zeroing throttle cracker under 1000 is going to do NOTHING helpful if you are at 1600-2200 with the bucking

[MNR-0]

Leave the follower table alone. Making wholesale changes like that indicates you may not have thought it through what it does. For your condition, it would have exacerbated the problem.

You are looking at the wrong area. It is not idle that is your problem when cruising.

If at cruise at say 2000rpm you maintain a steady spark of around 40* timing and your dynamic airlfow is static, then look to fuel.

[WS6Fury]

At around 2krpm the spark is at 29*. So this will be the next area to modify and see if any positive result.

Fueling does seem to help if running around 13afr or less, but robs my bottom end power and gas mileage, so trying to keep this at stoich if I can. Ultimately if I have to run it richer when all else fails then so be it (maybe lean cruise mode can be activated for 6th gear cruising... have to read up on this)

Cracker is zero'd from 1000rpm on up.

[WS6FirebirdTA00]

You need to keep it at or just below stoich in most cases to prevent the surge.

[WS6Fury]

What causes would make the dyn cyl air fluctuate +/- 0.40? I'm assuming this should remain steady at cruise correct?

Did a few more tests, but to no avail, I've gotten up to 38* spark so far, working slowly from 29* (in high/low octane tables only) and it seems the surge or buck is a little more bumpy/choppy now. It was a cool morning so the AFR was at or below stoich in the cruise cells.

Are there any other areas to look in the tune I may have missed or just don't know to use yet?

[MNR-0]

Could be anything, from dropping compression in a cylinder to a vacuum leak

If you are holding steady spark advance, steady AFR and steady load/speed and you are still getting surging at 14-14.5AFR, then I'd bet your sensors are out or something electrical/mechanical is breaking down on you.

Check your coils/plugs/leads
Check for vacuum leaks
Do a leakdown test
Do a cylinder balance test

And if that doesn't work, flash a stock calibration back in and start again

[WS6Fury]

Could be anything, from dropping compression in a cylinder to a vacuum leak

If you are holding steady spark advance, steady AFR and steady load/speed and you are still getting surging at 14-14.5AFR, then I'd bet your sensors are out or something electrical/mechanical is breaking down on you.

Check your coils/plugs/leads
Check for vacuum leaks
Do a leakdown test
Do a cylinder balance test

And if that doesn't work, flash a stock calibration back in and start again

Wow!! My heart just sank
I did have a similar problem before heads and intake were installed, tried everything under the sun, but to no avail still surging. So I want to say that would eliminate any vacuum leak as everything on top was removed and reinstalled.

My next step will be cylinder balance test and misfire logging, see what's going on. I assume this will tell me if there is an issue with spark or something quirky with the cylinder.

God I hope not!!

[mcw75]

Could be anything, from dropping compression in a cylinder to a vacuum leak

If you are holding steady spark advance, steady AFR and steady load/speed and you are still getting surging at 14-14.5AFR, then I'd bet your sensors are out or something electrical/mechanical is breaking down on you.

Check your coils/plugs/leads
Check for vacuum leaks
Do a leakdown test
Do a cylinder balance test

And if that doesn't work, flash a stock calibration back in and start again

My car had the same issue at 1000-1500 rpm. Changed the plugs out and it seems fine. No bucking/surging in about 50 miles so far. I think one of my plug wires was pulled loose or barely hanging there. Plugs looked good when they were taken out.

(Sorry for bumping the old thread)

[S2H]

Fueling does seem to help if running around 13afr or less, but robs my bottom end power and gas mileage, so trying to keep this at stoich if I can. Ultimately if I have to run it richer when all else fails then so be it

you could be having a false rich reading...
you need to try pushing your injector boundary timing to a later pint so that no so much fuel blows out the exhaust before it can be used in combustion.

I'd be willing to bet that with your cam and overlap so much is going out the exhaust that your wideband reads the unburnt fuel as a rich state...so do your narrow band sensors...


when you push the EIOT(End of Injection Timing) to a later point, you can help stop the "short circuiting" of the fueling at lower rpm's, which leads to a more true AFR reading at lower rpm's...which may reveal a true fueling issue.

you will have to do a little retune on the VE if you move this injector timing...and you have to be careful not to go too agressive or you will be spraying all the fuel directly into the cylinder and washing down the cylinder walls with fuel....

I found that I have had some good success with moving it about 10%-15% later...usually you dont see anything significant past that point.

smaller overlap cams require less...bigger overlap cams require more...

I have 18* of overlap on my cam...ended up moving it right around 10% to see some results.

[Frost]

Hey Scott... You see the date on the post you quoted

[S2H]

lol...well... I hit the "new post" button...and this one came up... must have been a glitch...LOL

I was answering it from my phone anyways trying to kill some time...

I have a buddy that was looking for this kind of post..so it wasnt a waste..

[WS6FirebirdTA00]

Scott, are you talking about all the injector timing values?

[WS6Fury]

Wow! Lol, yeah my post is pretty old here!!

It's funny cause I was looking up cylinder balance test as I think I have an injector issue or something and this came up. Starting to work on my car again after a 2 year hiatus and giving up on the LC-1.

A good point Scott made, regarding the injector boundary timing I found it in editor, but am confused about where and what to modify in the three fields "boundary", "normal," and "makeup."

I'm about to install a NGK wbo2 so I'm hoping this will help me with my tuning sessions.

Anyone local to central Jersey by chance?

[Higgs Boson]

What if I am already super rich at idle? I would much prefer to get my AFR in line with injector data than forcing OL at idle.... Do I need to make EOIT an earlier value?