Desired airflow won't equal measured airflow

[Ryan]

Before anyone feels tempted to post a link to the RAFIG tutorial, please don't. I've already been through it.

Now, I am running a 98 PCM with an A4 and a healthy sized cam. The tune is currently set to OL with MAF enabled (and solely MAF after 1200rpm). The MAF curve provides a reasonably accurate AFR.

My problem lies with the desired and reported airflow values. At the desired idle RPM in Park or Neutral, the car idles properly around 8g/s of airflow. Following the RAFPN table, the PCM thinks the car wants ~2g/s (after ST/LTITs). The values I use in B4307 seem irrelevant, as the PCM constantly reports to want some absurdly low amount of air. Regardless of where the values in B4307, the car still will swing right to 8g/s. The airflow values I am given to use from the trims are nonsensical, and constantly want extreme adjustment. I am right around 80 IAC steps at hot idle.

Now, when I shift into gear, the IAC immediately opens almost all of the way (sometimes it goes to the max of 310 steps). This is highly annoying, as the car has to sit still for some period of time to "learn" back downwards. If it moves before it's learned completely, the idle flares back up to ~1400rpm. The RAFIG process results in the same odd values. The car thinks it wants >22g/s in gear, but idles at the proper rpm (once it learns down) around 11g/s. No matter what values I put in B4307, the car wants more air. If I put what it wants (22g/s), it shows IACDES_B to want 26g/s. As soon as a gear is selected, the desired airflow jumps up, as do the reported airflow values (although they do not go as high). Even after learning back down to the proper rpm, IACDES_B shows some apparently ridiculous number (the learned values also have no effect in B4307).

The trims always point to some nonsensical value. I can't get the desired airflow values (IACDES_B) to match the values in B4307, and I can't get the idle trims to be reasonable.

I have played with the "Idle" section extensively, with no avail. Clearly, the desired airflow values are no reasonable.

Things I know:
The IAC motor is not sticking, nor do I have vacuum issues. I am not confusing units. The fueling at idle is (relatively) normal. B4307 seems to have no effect on IACDES_B. I have not found any PID that seems to add the values to IACDES_B on top of the B4307 (such as throttle cracker/follower, startup friction, etc.).

What tables/parameters effect IACDES_B (or: how can I fix this)? My current tune is attached, and I can gather a log of any PIDs suggested. I've described the behavior shown in my various scans.

[mr.prick]

out of curiosity,
what is your average RAFPN/RAFACPN value?

[Ryan]

Thanks for the reply Mr. Prick.

I don't have a long-term correction for park/neutral with A/C on, so I can't get a calculated PID for RAFACPN. I do have a short term correction PID for both IG and PN with the A/C on.

I have grabbed a brief log to try to show what problem I am having. If you view the log, you can see that my RAFPN shows it wants values of ~2g/s, added to the 3g/s in B4307 (giving about 5g/s of corrected desired airflow). Right around 80C ECT, the engine hits right around 8g/s of airflow, where it will remain all the way up to any reasonable coolant temperature.

The log also contains the short-term correction for A/C on (which I used around 70-75C ECT), but it's not very useful as I don't have a long-term/RAFACPN nor table in to which I can paste the values.

The difference between the corrected airflow value and the reported airflow at which the engine happily idles are pretty significant (between 2.5-3g/s). If I were to flash a new tune with this corrected airflow, it would then "correct" back down to around 2.5g/s after the next RAFPN process.

Sorry for the short log, but the longer I allow it to go, the less corrected airflow the engine calculates it wants (my corrected value from RAFPN and B4307). At full hot, the engine apparently desires around 3-4g/s. I can grab some more data later, but I have to go to work now.

[mr.prick]

try zeroing out your in gear potion of the table,
being an A4 you won`t need that,
then try another log, paste, and add to see if that does anything.
also from my experiences with RFIG being lean will give you high positive numbers.
do you have a WBO2 by any chance?

[TFZ_Z06]

what is your STFT?

[Ryan]

try zeroing out your in gear potion of the table,
being an A4 you won`t need that,
then try another log, paste, and add to see if that does anything.
also from my experiences with RFIG being lean will give you high positive numbers.
do you have a WBO2 by any chance?

I thought it was the M6 cars that didn't need the in-gear portion of the table?

I do have a wideband, but I also have a lot of overlap due to the cam, so I don't have accurate readings. I have gathered that it does not run that lean, as the exhaust doesn't burn my eyes (so not a ridiculously high NOx count), but I've tried to avoid being incredibly rich to the point of a "dumpy" sounding exhaust and smell of hydrocarbons. For what it's worth, the car did the same thing when it was excessively rich.

what is your STFT?

I am in open-loop; my stock narrowband sensor basically serves as an exhaust plug, as it is too far back in the headers for the heater to function properly. The other O2 bung contains my wideband.

[redhardsupra]

i've seen few cars where they showed unrealistically low RAF numbers, they all had some unaccounted airflow (drilled TB, bent back TB, leaks). are you sure that your hardware is 100% healthy?

[Ryan]

i've seen few cars where they showed unrealistically low RAF numbers, they all had some unaccounted airflow (drilled TB, bent back TB, leaks). are you sure that your hardware is 100% healthy?

I checked the throttle body hole, and it is stock size (5/32in diameter). The blade is straight and the throttle body is unported, so I don't believe any excess air is going by the blade.

I don't think I have any vacuum leaks, as half of the lines were replaced when I swapped cams. I can't hear any leaks, and haven't seen any openings in any of the lines, but I will pull them off today and look again for good measure.

I thought that with a vacuum leak that would allow for ~6g/s of airflow would be pretty substantial, to the point of allowing the engine to run with the IAC and the vacuum leak alone, so I taped off the TB blade hole. The engine refuses to run.

Also, a vacuum leak doesn't explain why the car desires unreasonably high airflow in gear, as the leak would not subtract 15g/s of airflow.

EDIT:

After watching the logs a little more today, I put B4307 back to normal values and decided to watch RAFIG/RAFPN. The corrections for both IG/PN are pushing IACDES_B much higher than it needs to be. I can "guess" values for B4307 that, when summed with the corrections, result in an IACDES_B value that is approximately in line with what the engine wants, but clearly this is not the correct way of doing things.

Is it possible to reset the idle trims as it is with the fuel trims? I'd like to see how the trims are gathering their data, or at least see what the car does from a complete reset.

[white01ss]

Have you tried turning off the MAF and running speed density? Might be a good idea to take the MAF out of the equation and see what happens. Lot's of the large cam guys run OLSD. Also, large cams like it a bit on the rich side - what's your target AFR at idle?

[Ryan]

Have you tried turning off the MAF and running speed density? Might be a good idea to take the MAF out of the equation and see what happens. Lot's of the large cam guys run OLSD. Also, large cams like it a bit on the rich side - what's your target AFR at idle?

I can try going into OLSD, but my biggest hold-back so far as been the inability to provide adjustments for weather changes. I am in Texas and it is hot during the day and cooler during the night; it would be nice to not be overfueling during the day or underfueling at night. AutoVE can't compensate for this and as such, I don't think it is the "correct" way of doing things, at least, remaining in OLSD.

Target AFR at idle is whatever the car likes; it's lean, but not overly rich, either. As I mentioned earlier, I have a lot of overlap, so my wideband readings range from 11.5:1 to about 18:1. The PCM is commanding stoich at operating temperature, with the VE table referencing about 1.8 g*K/kPa.

I have a replacement wideband in the mail (failed LC-1 ) so I will try going back to OLSD next week.