Tibo

iTrader: (15)

I know it has been covered before, but I did not find enough useful information. Here is the setup:355 ported TPI 10:1CR, 26 lb/hr inj., Hot cam, ported TFS heads, headers, 3.45 gears and a T-5. All run on the 730 $8D code.

I am able to drive the car quite well with the blms between 124 and 130. It idles nicely in closed loop at 750 rpm and 35-40map. Part throttle accel is good, even gets 25mpg mixed. I am running a toned down and tweaked ANHT spark table. The .bin file started out life as a super_AUJP_v3 file before I started tuning it. I have 0 emissions.

The jerking occurs when I am at lower rpm's (<1600) or am driving lightly and have just shifted. The car will jerk. Sometimes, if I stay very steady on the throttle with no movement the bucking will stop. I can also accel out of it OK. I have tried playing with the VE table as well as the spark table. I have looked at the TPS% to enable DFCO vs RPM, but it is already down to 1.95-1.17%. Should I lower it more?

What should I look at next? Go back to spark tables or VE tables?

3.8TransAM

Make sure you are not lean in the affected area.

Make sure its not electrical/mechanical in nature(bad wire/plug/cap/rotor)

Try taking away some timing from the are as well as adding/subtracting fuel.

I would turn off DFCO temporarily to see if it helps/eliminates the issue. Can be violentish feeling when it comes on after cutting fuel depending on setup.mods.tune.

Is this in 5th gear at 20mph? When and what gear or any at same speed?

Also IAC functions may have to be tamed down as well.

Possible PID for oxygen sensor also...........

later
Jeremy

RednGold86Z

iTrader: (1)

This is a very common problem with a manual transmission. I'm currently fighting it myself (on a 1L 3 cylinder), and have almost completely eliminated it, but not quite there.

I've deduced that the main causes are spark advance, MBT (timing for best torque), and engine mounts.

The spark timing control is pretty much the only reasonable way to control it. IAC could be used a little, but it will sort of drive the car for you if it's not right.

The main problem, as I see it, is that there's usually a steep slope for timing in the RPM direction, but a relatively flat slope (for most tables) in the MAP direction. My efforts have been in reversing that a little. The lower MAP points can get more timing, and the lower RPM (middle to low MAP) can get more timing, and the upper part of that RPM range (like 1600-1800) can get a little less timing.

Basically, most timing tables have a compromise in the idle area to get a flat, and somewhat less than MBT, spark curve. The system I'm working on has a separate table, completely, for idle (with very low timing for both idle stability control range, and catalyst warming), but in order to reduce jerk, it has to blend somewhat with the main table (the main table contains the compromise for blending, since it's used the instant that the throttle is opened). This blending is the bigger problem, as it usually contains the problem that I stated above. I've also been applying a large filter to + changes in spark to reduce the rate of advance increase. Seems to help.

The rubber engine mounts just aggrivate the problem, by allowing the observed RPM to change even more.

Hope you can get something from this.

dimented24x7

iTrader: (2)

RednGold, have you had any experience with any derivative RPM control routines? GM threw them in some of the PCMs for when a manual is in use and I was curious how hard it was to set them up. I had all the same issues with bucking when the TCC was engaged, and I can only assume itll be even worse with the manual.

Ronny

iTrader: (1)

as a side note. i just dropped in the EBL with the timing tables of what i believe was a 89-92 F body with auto trans(EBL.bin). the bucking is really bad. was not such in my old bin(pre EBL). i will hope it is the LEAN condition i am working on in VE1-2. the timing tables i believe are much more aggressive that that i was running in 7747 from first glance. manual trans for me.

RednGold86Z

iTrader: (1)

I think the GM derivative RPM control is to compensate for dwell and spark advance in a 4 ref pulse per revolution system, which inherently wont respond at all to immediate RPM changes, but, if you see a change, you can anticipate equal change. If you're calculating spark advance on just a pair of pulses a long (relatively long) time ago, than delta RPM will tend to knock or break parts when it's negative.

I don't know of any other application for it. Can you enlighten me?

Tibo

iTrader: (15)

I did go ahead and try a few of your suggestions. I turned the TPS% to enable DFCO vs RPM down to 0.00 for all values. This helped out alot, however, it did not totally eliminate the problem. I have the bucking at fairly ordinary RPMs. I shift at 2500-3000 RPM and have the 3.45 gears. So the problem is deffinatly not because of me shifting into 5'th at 20mph.

My table is set up as you were describing. I just remember the way that the vacuum advance distributor worked on one of my previous engines. Low RPM and MAP get high advance. So I should subtract spark? I have "0" knock always.

I am never lean enough in any of the areas to throw up a flag. I also have an open loop setting that I use with the same results. The open loop runs at .900 on the O2.

RednGold86Z

iTrader: (1)

Could I see your spark table? How about a log specifically of that problem.

0 knock doesn't mean more is better. MBT is "best" but sometimes, for drivability sake, you have to blend weak timing areas into the map, unless you have an algorithm do it for you (which it doesn't have).

RBob

iTrader: (1)

You could be switching in & out of the closed throttle (CT) SA table. If the values between the main SA & CT SA tables don't match up between the 2 it gets ugly. And getting them to match isn't always easy as the MAP for the main table varies.

RBob.

Tibo

iTrader: (15)

How should I go about posting my spark table? I use tunerProRT. I can make an attachment or send it to you. I do not know if I can take a screen shot.

"You could be switching in & out of the closed throttle (CT) SA table. If the values between the main SA & CT SA tables don't match up between the 2 it gets ugly. And getting them to match isn't always easy as the MAP for the main table varies."

I have checked that before and I redid the table before I tried lowering the DFCO setting. In tunerPro the ct sa and sa tables are right by each other right? Is the closed throttle SA table the longer one or the shorter two?

Z69

The idle spark table has a 1500 rpm qualifier and 15 mph IIRC.
Which xdf are you using?

RednGold86Z

iTrader: (1)

A screenshot is fine. Or just zip your bin and xdf together and attach it here or something.

Do you have rubber engine mounts? Just curious. I think part of the jerking is aggrivated by a direct link between engine and tires, with a soft link between engine and heavy vehicle.

devilfish

Intreseting. I got the exacy same probleme last year. My car is a 1991 corvette manual with hotcam and TF heads.
No matter what i did on the tune i could not get rid of the jerking under 1800 rpm.I could get it better, but not perfekt.
I drove like this for a hole summer I whas close to give up..
Then one day a injector started to leak. I changed all to new injectors and the jerking trouble disapeard. So make sure all the mechanical is good to go before you get crazy with the tune.

THanks

RBob

iTrader: (1)

You mentioned in your first post that it may be DFCO. To check just disable it. There should be a temperature enable term, max it out.

For the closed throttle timing table, look in a dat alog for a jump in timing. If the timing jumps 4-5 degrees or more, that will cause a jerk in the engine. The closed throttle table is a 2d table based on RPM.

Devilfish has a good point, Multec injectors. If you are running used from '89 through '92 in the f-body's. If those are the injectors you have in the engine I would replace them on general principle.

RBob.

Tibo

iTrader: (15)

I dropped the DFCO down to "0.00" for all values and it helped as stated in an earlier post. I will go ahead and disable it though.

My injectors have maybe a few thousand miles on them. They are the 26 lb/hr ls1 injectors that slp sold a year ago for like $100.

I did see a few jumps in spark where it is idleing and "jerking." I will triple check the spark table, but I thought, they were perfectly in sync. Is there a way to disable the CT SA table?

3.8TransAM

Also.

For some reason alot of people severely cut down the time between DFCO engagements.

Stock on most bins I have seen is 2.0sec between cut outs.

Dropping this too much more than 1.5 for me is nothing but an annoyance and often leads to the same type of bucking.jerking you are talking about.

Real on/off tendency

later
Jeremy

Z69

No, but you can make it so it adds zero to the SA.
Stock, no SA is added in when at normal op temp and SA is pulled when it gets hot.

RBob

iTrader: (1)

Should be good to go on the injectors.

The sparks jumps during idling is normal. It is idle stabilizer SA.

The closed throttle (CT) table is used whenever the throttle is closed. Even if the vehicle is moving. What can happen is that during coast with a light touch on the throttle, the ECM can switch between the CT table and the main SA table.

Look for jumps in the data log during that period of time.

To disable the CT table need to make a change to the code. Change the BHI to BRA.

That way it will always use the main SA table. As the code is different for a lot of the BCCs, I can't give you the exact location in the BIN to change. The BHI op code is $22 with a BRA op code being $20. Just need to change the 1 byte to disable the closed throttle SA table.

RBob.

dimented24x7

iTrader: (2)

GM seems to be using it for when a manual is in use. If the vehicle is in motion and some parameters are met, then a derivative term is calculated based on what the RPMs are doing. I can only assume its to dampen out bucking or rapid RPM changes. There doesnt really seem to be anything in there to anticipate any of the needed timing.

Im sort of leery of trying to use it as it can go from dampen to encourage, and more if its not properly set up and the system enters positive feedback. Theres also the wild card of a sloppy drivetrain, which could probably make things quite interesting.