Patrick G

iTrader: (14)

This is very frustrating. I have been working on tuning my car for months and I still have one nagging problem. My car will not hold a steady cruise between 1000-1200 rpm. It will accelerate smoothly in that range and it will decel smoothly in that range, but at a steady cruise (like going through a school zone or parking lot), the car will buck and shake.

Here's what I've done to try to eliminate this problem.
MAF-less speed density tune.
Base running airflows correct at various temps.
IAC Effective area modified to allow Dynamic Air and Idle Air to match from 0-100 IAC counts.
Spark tables from idle and main tables match at lower rpm levels and loads.
Increased spark timing (32 degrees) for improved idle and low speed driveability.
Throttle cracker trimmed.

OK, here's what I think the problem is: When cruising at 1000-1200 rpm, there seems to be a conflict between the IAC motor and the PCM. I'm sure I'm getting some nasty reversion from my cam at this low rpm level, so that doesn't help either. But at a steady 4-7% TPS, the motor absolutely will not hold steady at this rpm.

Is there a way to limit the IAC from trying to correct above a certain rpm or vehicle speed? Setting the throttle follower and throttle cracker to 0 does not help.

FWIW, I am new an EFI Live newbie, but an HP Tuners veteran.

jimmyblue

iTrader: (11)

That RPM seems like a total mismatch for the cam,
you've got to be in a pretty high overlap still (your
reversion remark). I question why you'd want to
cruise there, though it's y'alls business. It'd be like
me trying to cruise at 800RPM (if the A4 would let
me). Got to be lugging badly with any sort of load.

Can you see this action as misfires? Might need to
pull back the spark substantially at these lower RPM,
higher MAP levels and see if that helps the bucking.
Not at idle, but make sure the just-off-idle has some
reasonably continuous profle w/ RPM, and the load slope
is enough to prevent kick-back as you add pedal.

To see if IAC is involved, just log the IAC counts and
see if they are any different while bucking, and not?

I see no mention of EGR here (in the .sig) and wonder
whether that has something to do with it; like fluttering
about the edges of added-EGR-spark, making an unstable
(or bistable) situation, like more spark = less MAP = quit
EGR = less spark = more MAP.... Left-hand end of the
EGR "pocket" is a steep face at 800 - 1200RPM and cruise
CylAir levels.

I guess I'd try reviewing the logs with an eye to picking
out oscillatory behaviors, and try to figure out the egg
& chicken relation.

Patrick G

iTrader: (14)

Thanks for the response Jimmy. I've logged many, many times. At that rpm where I get the bucking, timing holds rock steady, IAC counts hold rock steady. No EGR on the car any more (FAST 90/90) and it has been zeroed out in the spark tables and turned off in the PCM.

As far as pulling back timing at that rpm goes, I'm not sure if I want to do that. With as much overlap as I have (61 degrees at .006", 10 degrees at .050"), I've found that the motor is happier and crisper with 32 degrees of timing frpm 600-1200 rpm. It gets really soggy with timing in the 20s.

Call me picky, but I've got this motor extremely smooth in the 900-1500 rpm driving ranges. As long as I'm accelerating or decelerating in that low rpm range, the motor is an absolute pussycat. I no longer get bucking when I decel any more. But when trying to hold a steady cruise at anything lower than 1200 rpm, the motor is not happy. Is it something I'm going to have to live with?

1CAMWNDR

iTrader: (21)

I have the same thing on and off between 1,200 and about 1,700 rpm but only in second, third and forth gears at light throttle. And I have a stock cam!! I have HPT by the way. Could it be something with switching from idle fuel cells and drive fuel cells? My car also had no EGR or AIR. Any insight is greatly appreciated.

jimmyblue

iTrader: (11)

That's a good point. You could be flipping between
fuel trim cells if the boundary lies right at 1200RPM.
While most fuel and spark tables are interpolative I
believe the fuel trims aren't. So if you have the
boundary right on your cruise-point, a little RPM
could point you to two fairly different LTFTs and
the wandering could be STFTs playing catch-up.
Do you see the trim cell # jittering between two
values?

You should leave idle cells with any non-idle TPS
(when warm) but if you have the lower RPM boundary
at 1200, you might see Cell0/1 or 4/5 twitching.
Similarly, if your lower MAP boundary lies right about
your cruise MAP, you might boogie 0/4, 1/5 or like
that. And the double whammy, whoa, Mama...

Especially if your trims are very different cell-cell.

Patrick G

iTrader: (14)

Good points on fuel trim cells. Currently, my long term fuel trims are switched off and I only operate off of S-Trims (since I'm constantly making my VE tables better and better). Do you have any suggestions on what to change in my fuel cell boundaries to?

My LTFT matrix is 900/2500/4000
My MAP boundaries are 40/60/80

GuitsBoy

iTrader: (4)

Those are good points about the cells.

While Im here, where shoudl the first MAP division be? Just above or just below idle?

Currently I look like:

RPM: 1000/2600/4000
MAP: 55/66/77

Sharpe

iTrader: (7)

So his problem isn't just right at 1200 RPM.

Patrick G

iTrader: (14)

Problem is between 900-1200, but it's especially bad at 1100-1200 rpm. Think about cruising at very low TPS through a parking lot, a school zone, or cruising on the highway in 5th or 6th gear at low rpm. 55mph in 6th is 1200 rpm so it's pretty important to me.

1CAMWNDR

iTrader: (21)

I will see if I can log the FTCs this afternoon while cruising around. Which parameters can I delete so I can add FTCs? MAF? I am SD so that might work. Spark advance and Retard? The last time I tried to add a different parameter, nothing logged . Guess I deleted something that was still needed.

1CAMWNDR

iTrader: (21)

OK. I logged about 45 minutes of driving between 900-1800 rpm. The slight bucking seems only to be when switching from FTC5 to 6, or while in FTC6. I noticed in the lower gears (1,2, and 3) it switches from FTC 5 to 6 (I think this was when the MAP passes 59kPa). In the higher gears (4, 5, and 6) it switches from FTC5 to 9. I know these were when the MAP passes 59kPa. The switch form 5 to 9 has no issues what so ever.
Any ideas ?

GuitsBoy

iTrader: (4)

I would hazard a guess that if you got your VE table a little more dialed in, the FTC changes wouldnt do so much to bother you. If your LTFTs were all 0, and the VE was correct, it wouldnt matter cause youd be jumping from 0 to 0.

1CAMWNDR

iTrader: (21)

My LTFTs during the monitoring period were between -1 and +2, which I understand to be pretty damn tight. So whatelse do I need to change? And why does it not do it at higher speed/higher load (gears 4,5, and 6)?

Patrick G

iTrader: (14)

OK, here's the deal: My L-trims are zeroed out so there's no jumping from cell to cell. Next as an experiment, I went into total open loop to eliminate any potential fuel jockeying with changing s-trims (even though all my trims are very close to 0). Didn't make any difference...I still get the shakes at a 1100-1200 steady cruise.

I used the Delta Spark function on EFI Live to add or subtract timing while driving in that trouble zone. I was hoping the problem would go away by taking away spark or by adding more. So far, it didn't seem to make any difference, but I'll try it some more over the weekend. The Delta Spark function is super cool because I can ask the computer to lop off 8 degrees and it will take it off from what ever the spark table reads at that certain point. Sure makes dialing in a combination easier.

Ragtop 99

iTrader: (7)

sounds like a job for 3.73s.

Does it occur at all MAPs? If you use a fwy overpass you can test it going uphill and downhill.

Did you test the spark at less than 8* changes, say +/- 3*?

Patrick G

iTrader: (14)

No, it doesn't do it at all MAPs. Mainly around 50-55 KPa. Any greater of a load and it smooths out, any less of a load and it smooths out. As far as the spark delta function, I moved the timing up +1,2,3,4 then down -1,2,3,4,5,6,7,8 (all in 1 degree increments at a time) to see if more or less timing helped. I couldn't see any evidence of that changing timing helped. Even when I forced a certain timing value in there, it would still have a tendency to buck at 50-55 KPa around 1100-1200 rpm.

I think it could still be IAC related. Next, I'm going to disconnect the IAC and see if it still bucks. If it does, then I'll know it's not that contributing to the problem either.