ZO6 Bryan

As the title says. I think it is just different rpm/load parameters. But how are they used in the calibrations of other tables. Reason I want to know is I am trying to tune a freinds cam heads car and it is really rich at idle. This is after we SD tuned it then re-enabled the MAF. In just SD mode it wasn't bad but would still surge at idle. Has anyone experiment with changing the switch point of the O2's at idle to lean out a big cam car. I am think of changing the "O2 rich/lean vs. Airflow mode" but not sure which airflow mode to change or if I should touch this table at all.

brad8266

iTrader: (23)

Did you tune the MAF table? Once you plugged it back in the car runs primarily on it rather than the VE table.

ZO6 Bryan

I was thinking the same thing. I haven't been able to scan it since he said the problem started although I have seen it run since he reported the problem. It surges and loads up on fuel then dies. We tried to just unplug the MAF so it would go back to SD mode but it did no better. But I think you would have to unplug the MAF and reset the fuel trims because it has learned the probably maxed out LTFT's already.

ZO6 Bryan

I still want to understand the "Airflows Modes" regardless.

brad8266

iTrader: (23)

Well airflow works in 2 different ways. If you use the MAF the MAF when properly calibrated to the PCm will measure the amount of air flowing through the engine. The PCM can take that airflow amount and calculate how much fuel to add to reach the desired AFR.

Without MAF youu are using the VE table to predict airflow. It uses a RPM vs MAP table to provide airflow back to the PCM. When in SD the sensors are not measuring airflow but rather they predicting what the airflow should be at the different rpm vs map values. Then the PCM can calculate how much fuel is needed.

ZO6 Bryan

I'm familiar with all that. I was talking about the Airflow Modes 1-16. When is the engine in which mode? These are defined in the "Mode vs. Airflow" table and refered to in several other tables.

muncie21

iTrader: (14)

You PCM breaks airflow (measured in g/second) into the engine down into zones, or modes as described in the OL&CL tab of tuners. These zones are used in CL fueling to oscilate the O2s at idle and while running. Depending upon how much air is coming into the engine (what zone the engine is in) it adds/subtracts different amounts of fuel to make the O2s swing.

You can re-allocate these zones to meet your specfic needs. For example I log the G/sec my engine uses at steady state cruise and give it a specific zone#. I then lower the O2 switchpoints (both O2s) for this zone number, in an attempt to get better gas mileage while cruising.

SSpdDmon

iTrader: (10)

It sounds like you are looking for the answers in the wrong places.

1) Did you adjust idle timing at all? Cam'd cars usually like a little more timing than stock depending on the setup.

2) How close did you get the VE table and did you use a WBO2? You say it wasn't bad in SD. You need to be more specific than "it wasn't bad." Was the AFR close to what you commanded?

3) Did you alter the MAF table once you re-enabled the MAF? If not, you need to tune for the MAF the same way you tuned for the VE (WBO2_AFR/Commanded_AFR=AFR_%_Error).

Surging that still is around after timing and desired airflow have been dialed in is usually due to the IAC. Those airflow tables have nothing to do with the NBO2's and the airflow mode they are in. It sounds like you're confusing the two...

ZO6 Bryan

1) Yes, it is idling with 25 deg advance

2) The VE table was great and all the LTFT's were +/- 2 or 3
Used the LTFT' and STFT's to get it there.

3) No, Haven't touched his MAF table after re-enabling the MAF

And the idle LTIT' and STIT's are +/- 0.50
IAC is at about 40-50 steps at idle

It was idling well in SD mode at 1050 RPM's. At less RPM than that it would surge in gear but not in neutral.

BTW cam is 232/236 580/580 112 +2
Same cam that is in my car but I have a 6 spd and don't have the problems he is having. I spent a lot of time on the VE table in my car and used my VE table as a start point for his car. Then further modified it to suit his car.

And the Airflow modes DO have something to do with the NB O2's. Why else would there be a "O2 rich/lean switch point voltage vs. Airflow mode table"?

SSpdDmon

iTrader: (10)

My point was, the surging you're seeing is most likely due to the IAC if the spark and AFR are correct. Idle in gear should be up closer to 28* of timing. P/N is good around 24*. The airflow mode table affects the switchpoint of the O2's. Altering the switchpoints used might affect the AFR a half a point...but that's about it. Desired airflow sounds good at +/- .50. IAC counts might be a little low as well as in gear timing. Any way you could post a .bin file so we could look at what all is going on? Maybe I can shoot you a few spark maps that'll help you get it down to 850-900 rpm w/out any surging....

ZO6 Bryan

This is what I was thinking. So if the car idles at about 12 g/sec this equates to Airflow mode "8" according to the Mode vs. Airflow table.
Then if I go to the O2 switch point vs AF mode table and lower the switch point voltage in AF mode "8" it should not try to load up on fuel so much at idle. Does this sound right?
Or possibly rather than changing the switch point voltage it would work better to lower the idle proportional base so it doesn't try to swing the AFR so much to get oscillation at idle. Going from a stock 20% rich/lean swing to more like 15% This is in the "Closed loop proportional idle base vs airflow" table I'm refering to.

ZO6 Bryan

I could post it tomorrow. His .bin file is in my laptop and I left it at work tonight. I didn't differentiate between neutral and "in gear"" when I set his idle spark advance. I did play with the spark and idle rpm and AFR using the bi-drectional controls in HPTuners while the car idled in gear. And it would stop surging if I brought the idle up to 1050 rpm OR if I commanded an AFR of 15.5:1 Changing the spark didn't seem to help much past 25 deg.(using the bi-direct. controls)

jimmyblue

iTrader: (11)

Airflow Mode "bins" regions of airflow into a more
convenient (for the PCM) index and then this is
used as described to set O2 switchpoints, prop
fuel etc. I guess it was easier than using straight
air values, or perhaps it provides some degree of
freedom or mapping.

I have set all of my O2 switchpoints somewhat
lower in the low Airflow Mode cells. Can't say as it's
bought me anything but then again, neither has it
bothered me. I figure maybe it has given me some
margin against header-induced O2 laziness. My
fuel trims haven't been bothered by going to the
headers.

Thing is, the O2s still want to swing about stoich
(as measured by exhaust oxygen content). Sure, 300
is leaner than 500mV but not by a whole hell of a lot.
And a cam that blows a bunch of fresh air into the
exhaust at low RPM, is just corrupting the sensor
output because it's whacked the chemistry that
the sensor presumes. If that's the root of it I
doubt the airflow mode and switchpoint fiddling
are going to provide the way out.

Surging gets worse when the mixture is bad, and
when the sensors are slow. But there are a bunch
of contributors - short idle spark, bad idle airflow
targets - that can be in it as well.

The spark value I think is less key, than its taper
with RPM. What may help you is, at RPM below
idle setpoint to make the spark kick up - catch
its fall, so to speak.

The MAF table seems to me to be unrealistic at
the low end. I have measured 85mm MAF outputs
of about 2500Hz, free air. That would claim to be
moving 5 g/sec, when in fact moving none. That
is about half of my actual idle airflow. Big error.
The MAF is not heavily weighted in the airflow
calculation at idle, but it doesn't take much of
a portion of that 50% (or so) wrongness to taint
the calculation. Add to this, that the MAF will
"double sample" the air if you have significant
reversion pulsation down low.

You might want to try logging the Dynamic
Airflow PID with the MAF in and out, and the
engine running at idle-range RPM. How different
are the reported values? Likewise look at the
applied spark, is it being put different places?
If you run open loop idle commanding 14.7:1,
are you getting different fueling between MAF
and no MAF?

Personally I tend to trust the MAF up top but
even GM doesn't trust it down low. If you see
the Dynamic Airflow really discrepant between
the modes, try pulling the MAF table toward
the SD tune values.

muncie21

iTrader: (14)

The switchpoint voltage won't affect the drivability very much, if any.
As for the proportional base, take a look at your O2s. If they are banging (also referred to as railing) between the top/bottom values then you have too much proportional fueling. Remember there's a proportional fueling table for both idle and running.

ZO6 Bryan

Tired to post the file but got a "file is too big message". What am I doing wrong? I zipped it first.

ZO6 Bryan

I got a chance to scan his car tonight. LTFT's were railed at +18. Well that explains that. Put it back in SD mode and did a quick SD tune of just the 3 cells it is in a idle. Idle is great and surging is gone. Didn't get a chance to see what happens when we turn the MAF back on yet.

dynocar

Just my 2 cents added to a lot of good info here concerning idle surge.

Spark, it helps to set your idle spark cells at a constant number, like 25, in all of the areas around and especially lower then your idle RPM. This will prevent the spark from changing with an idle surge which can then contribute to a vicious looped idle surge problem. If the idle is surging, monitor your spark to make sure that it is stabalized and not a contributor.

Open loop, I am much quicker these days in setting permanent OL with header/cam applications due to call backs because of the O2s intermittantly running too cool, causing an over-rich condition which then contaminates the O2s causing them to malfunction even more, another vicious loop. OL just requires much more careful tuning. I much prefer CL but if there is any indication of O2 trouble while tuning, you can bet that it will be an even greater issue later.