E38 Transient Fuel Table Tutorial?

[Michael_D]

I have a lean spot that is engaging KR as I transition from a dead stop to get the car rolling, and also after each shift with moderate throttle input. This is during light traffic type driving. KR is more apparent when I was calibrating MAF (VE disabled), than VE (MAF disabled). It is however still present when in VE mode and MAF disabled. This is not hard acceleration, so PE is not being engaged. Before pulling a bunch of timing or disabling burst knock, I thought I’d play around with the transient fuel tables a bit, to see if there was one in particular I should play with that would help throttle tip in.

Changes to Transient Fuel Mass do not seem to have much effect at all. I moved this from 1.0 to 2.0 and did that did nothing that I can see in the logs.

Looks like there are only two other tables to mess with. 1) Evap Factor: Gas/Alcohol/Blend and Gain. 2) Transient Fuel Mass Gain Impact Factor (five tables).

I understand the concept behind these tables, but am unsure what direction I should go with them, as I do not understand why they would have an effect on throttle tip-in.

I did stumble onto a pretty informative post in FAQ section, and the HPT help menu has some pretty good general info, but the E38 does not appear to have as many transient tables are other ECMs.

This is an N/A LS7, pretty lumpy cam with FAST 102 and a VMax ported 92mm TB. 60# injectors.

[mowton]

As it is tip-in/dynamic related, try increasing the VE in the area's that the lean spot is occurring.....better yet, make sure the VE is tuned within all the drivability areas.

Ed M

[Michael_D]

Hi Ed,

VE cal was my first step. I must have spent close to five hours calibrating the table the best I could using STFT’s, and verifying with my wide band. I worked it till average error % was under 2 in every cell I could collect data in, from idle, off idle and up to 5000rpm. After VE, I addressed idle air. Then I moved on to MAF low and hi / WOT.

I’d rather not have to jack the VE table around to correct these throttle tip in areas if I can help it.

It would be nice to know what effect making changes to the different transient table will have, prior to jacking them around, then taking long drives and collecting data, then doing it over again…. I just don’t understand which direction to take them, and time is the enemy right now. Snow is coming, and the car goes into storage in about three weeks.

I need to collect some IVT data next I suppose, seeing how many of the tables reference IVT.

[mowton]

Hi Ed,

VE cal was my first step. I must have spent close to five hours calibrating the table the best I could using STFT’s, and verifying with my wide band. I worked it till average error % was under 2 in every cell I could collect data in, from idle, off idle and up to 5000rpm. After VE, I addressed idle air. Then I moved on to MAF low and hi / WOT.

I’d rather not have to jack the VE table around to correct these throttle tip in areas if I can help it.

It would be nice to know what effect making changes to the different transient table will have, prior to jacking them around, then taking long drives and collecting data, then doing it over again…. I just don’t understand which direction to take them, and time is the enemy right now. Snow is coming, and the car goes into storage in about three weeks.

I need to collect some IVT data next I suppose, seeing how many of the tables reference IVT.

What's up Mike, sounds like you have the VE settled in, perhaps a bit of timing. I haven't had much luck messing with the transient fuel stuff yet so I can't really help. Will stay around to see if anyone else posts some advise though. Be good...

Snow!!!!!!!!!!!!!!!!! that's why we just relocated down south to enjoy my retirement and be close to the kids. Once our plans were set, the first thing I sold was our snow blower :-) Its 85 degrees today and heading to the pool.....

Ed M

[Michael_D]

One thing I have grown to appreciate, is a damn good VE table. Getting that table dialed in got rid of most surging / bucking I was getting with this lumpy camshaft under 2500 rpm (70 deg seat to seat overlap). 5% error is not good enough, despite what you read in all the “how to” books. I’ve also learned that MAF is pretty much worthless under 3000 rpm.

Timing…… yah…. That’s always an issue for me. Our “premium” is 90 octane. I tried adjusting the Hi table by observing KR, then lowering/smoothing in the KR areas. Tried and tried to do that over the last couple years. Hi spark table got so fugly I just wanted to cry whenever I looked at it. I finally gave up on that tactic and just copied the low table to hi table. Then I went back to the low table and lowered it 4% to get some room. Even running the “low” table for a “hi” table, I still ended up pulling some timing in the off idle/transient areas in the left upper-hand side of the table. I also had to simply change my driving/shifting habits to make sure the revs were up before hitting to go pedal. Grrr…. At least I am not getting KR on the right hand side now, and I can start moving timing up in that area. Just trying to get the drivability areas dialed in now, and will work on WOT timing when I have more time and can get this beast on a dyno.

I’m ready for sun. Trying to find somewhere to re-locate to now. Too much snow where I live for a snow blower. I use a four wheeler with a plow.

[ttz06vette]

I had the same problem with my twin turbo 2007 Z06 which I solved with a combination of transient changes and timing. Took about a month of experimentation but I finally completely got rid of the problem. Here is what worked for me

1.) First I cut the Maximum Mass in half to 1024. This allows the MAF to respond to smaller changes in air mass(reduced mine to 1024)
2.) Next I reduced the "Enable Delay" setting to allow transient to kick in at lower RPM's. I estimated right or wrong that crank reference pulses roughly correspond to RPM's so I used 23 as a setting. You will know if you reduce this too far if transients will kick in during idle.
3.) I then adjusted the Transient Fuel mass impact factor gas table. Basically increasing the number adds fuel in the desired IVT area. Also this table takes into account changes changes in the MAP values as well. So basically I found that increasing at 20 MAP and pasting it down the column only seems to effect the 20MAP region. By increasing the values at 30MAP and 40MAP however I saw the effect in my AFR's. FInd the MAP and IVT area that you experience the tip in most frequently and adjust above and below that area of the table rows. I went from .6900 at 20 MAP to .8995 at 50 MAP then held the .8995 constant at higher MAP levels. I also applied the same percentage change across the higher IVT columns.
I believe this table calculates the amount of fuel left on the cylinder walls. The numbers start high because in a cold engine more fuel sticks to the walls thereby requiring a richer charge. By increasing the numbers I believe the computer thinks there is more fuel sticking to the walls and increases fuel during transient.
4.) I t also experimented with the gain table, but really didn't see an impact unless I dramatically changed the numbers. I believe this table allows you to adjust the impact of the impact table at based on different airflow rates (lb/hr).
5.) Finally I made my High Octane, Base, and Coastdown tables as close as possible in the first 2-3 rows(g/cyl) from 1200RPM up. I brought the High Octane table down the most in order to do this but it fixed the large jumps in timing that I was experiencing during tip-in.

Hope this helps a bit.You may not have to do everything I did to get the desired effect but each of these things had a small impact as I fine tuned the problem. Good luck.

[Michael_D]

Thank you sir!!

That is very helpful! I intend to screw around with these tables today.

[mowton]

Ditto, will think it over this weekend for sure. Thanks for sharing, gotta love this forum :-)

Ed M

[BigDaddyCool]

I've been messing around with transients for some time..... it's hard to pin down.

The shortest solution is to go for a drive (not after you've just flashed it).... but clearly a start or two later, and do some random full throttles....... and look at the overall 'lean spike' you get in percentage. Then maybe add a few percent to that and just multiply the whole 'impact factor' table by the percentage.

At first the car will feel bogged down, but overall it will solve a few drivability issues and the car generally 'unlearns' or 'adjusts' the transients overtime so it will slowly become less of a bogged down feeling and more just smooth.

Another thing to consider with transients is 'temperatures'. Not defined in that area......... oil temps, overall mixed temps. Also the more transient fuel you add, the more fuel 'waste' you get so your economy goes down somewhat.

[ttz06vette]

I've been messing around with transients for some time..... it's hard to pin down.

The shortest solution is to go for a drive (not after you've just flashed it).... but clearly a start or two later, and do some random full throttles....... and look at the overall 'lean spike' you get in percentage. Then maybe add a few percent to that and just multiply the whole 'impact factor' table by the percentage.

At first the car will feel bogged down, but overall it will solve a few drivability issues and the car generally 'unlearns' or 'adjusts' the transients overtime so it will slowly become less of a bogged down feeling and more just smooth.

Another thing to consider with transients is 'temperatures'. Not defined in that area......... oil temps, overall mixed temps. Also the more transient fuel you add, the more fuel 'waste' you get so your economy goes down somewhat.

My problem was low speed cruise tip in/lean. My full throttle was fine. It occurred at lower MAP when cruising in 5th or 6th gear and you lightly get into the gas. Likewise during up shifting during normal driving. Think some of my issue was heat soak due to my sheet metal intake. During these episodes I would see my AFR 's go into the 16's for a second then come back to 14's. Since making these changes my AFR's stay between 13.7-14.7 during these periods.

[Michael_D]

That's exactly what I have been dealing with. I got so tired of dealing with KR, and lowering spark in the Hi table, I just copied the low table over the hi table. Then went back to the low table and dropped spark 4%. Now that I've got VE and MAF dialed in, I figured I'd start bumping spark up. These lean tip in areas are mostly non-existent in any gear now but sixth. But when I raise spark, I get KR again. Not sure if I will have time to screw around with this again. We got snow last night. I might just load the car into the trailer and put it in storage.

[10_SS]

One setting you might want to try changing is the "Intake Volume". I would double it right now, see if that has any impact. It's a relatively new setting and I thought it had an effect on transients. I personally tried playing with all of the other Transient settings with no noticeable improvement... but I have a Whipple and after I reduced the rate of throttle opening just a bit to stop the pressure surge happening between shifts... my problem went away. After all of this, then they added "Intake Volume" so I never had a chance to test it.

[Michael_D]

Where is this "Intake Volume" table? Is it in the transient tab? I'm probably staring at it....

[10_SS]

Where is this "Intake Volume" table? Is it in the transient tab? I'm probably staring at it....

It's under Airflow/General if your OS combo has it. I'm using 2.24.840. Not exactly sure what it will do, and not all OS's have it... the two ZL1 files I compared doesn't.

I would think it has something to do with the timing and impact of transients... but I have no real idea.



IntakeVolume.PNG

[Michael_D]

Bummer... I don't have that table. Mine has the two MAF tables. Latest HPT build.

[redgto4u]

I've been having the same tip in issues...off idle lean spike. The transient tables did nothing for me. I believe there is a post on here where some people had great success messing with the cylinder charge temp filter table. I will be trying the same thing. You mentioned a sheet metal intake. The cylinder charge temp table might be the key. If you look at those tables they relate to ect vs iat. For me I have a fast acting IAT sensor. So sitting at a light my IAT temps goes up to around 110 and when I get rolling they drop fairly quick to 90 or so. The ECT is always around 172. It seems the rate at which it moves from ect to iat biasing is slow therefore the lean spike because the pcm is biasing ect over iat. Since ect is hotter it thinks less air therefore less fuel??

[ttz06vette]

I've been having the same tip in issues...off idle lean spike. The transient tables did nothing for me. I believe there is a post on here where some people had great success messing with the cylinder charge temp filter table. I will be trying the same thing. You mentioned a sheet metal intake. The cylinder charge temp table might be the key. If you look at those tables they relate to ect vs iat. For me I have a fast acting IAT sensor. So sitting at a light my IAT temps goes up to around 110 and when I get rolling they drop fairly quick to 90 or so. The ECT is always around 172. It seems the rate at which it moves from ect to iat biasing is slow therefore the lean spike because the pcm is biasing ect over iat. Since ect is hotter it thinks less air therefore less fuel??

Not sure how the table works but my tip in and lean spot are completely gone so I refuse to mess with anything else. My AFR used to jump to 16.2 during cruise lean tip in...now it is a consistent 13.9.

[Michael_D]

I had the same problem with my twin turbo 2007 Z06 which I solved with a combination of transient changes and timing. Took about a month of experimentation but I finally completely got rid of the problem. Here is what worked for me

1.) First I cut the Maximum Mass in half to 1024. This allows the MAF to respond to smaller changes in air mass(reduced mine to 1024)
2.) Next I reduced the "Enable Delay" setting to allow transient to kick in at lower RPM's. I estimated right or wrong that crank reference pulses roughly correspond to RPM's so I used 23 as a setting. You will know if you reduce this too far if transients will kick in during idle.
3.) I then adjusted the Transient Fuel mass impact factor gas table. Basically increasing the number adds fuel in the desired IVT area. Also this table takes into account changes changes in the MAP values as well. So basically I found that increasing at 20 MAP and pasting it down the column only seems to effect the 20MAP region. By increasing the values at 30MAP and 40MAP however I saw the effect in my AFR's. FInd the MAP and IVT area that you experience the tip in most frequently and adjust above and below that area of the table rows. I went from .6900 at 20 MAP to .8995 at 50 MAP then held the .8995 constant at higher MAP levels. I also applied the same percentage change across the higher IVT columns.
I believe this table calculates the amount of fuel left on the cylinder walls. The numbers start high because in a cold engine more fuel sticks to the walls thereby requiring a richer charge. By increasing the numbers I believe the computer thinks there is more fuel sticking to the walls and increases fuel during transient.
4.) I t also experimented with the gain table, but really didn't see an impact unless I dramatically changed the numbers. I believe this table allows you to adjust the impact of the impact table at based on different airflow rates (lb/hr).
5.) Finally I made my High Octane, Base, and Coastdown tables as close as possible in the first 2-3 rows(g/cyl) from 1200RPM up. I brought the High Octane table down the most in order to do this but it fixed the large jumps in timing that I was experiencing during tip-in.

Hope this helps a bit.You may not have to do everything I did to get the desired effect but each of these things had a small impact as I fine tuned the problem. Good luck.

Hey ttz06 -

I finally got around to messing with this again. Took your advice and basically just used your settings. Wow, what a difference! Tip in KR I was fighting with is almost gone. Just rare instances when at an RPM lower than I should be at when stabbing the go peddle anyway. I am unsure about the part in bold above though. I can't quite follow how you made these changes. I essentially just bumped the entire table up in 10% increments. Twice now...

Now the only KR I'm getting is when I release the throttle and commanded AFR go from PE mode to 14.7. I think I might be able to fix that with the throttle follower. Not terribly concerned about it though.

[SultanHassanMasTuning]

another way to help with tip in enrichment
INJECTOR FLOW RATE VS MAP

give that a try above 1 enriches

[GHuggins]

another way to help with tip in enrichment
INJECTOR FLOW RATE VS MAP

give that a try above 1 enriches

I was about to recommend the same thing. Here's the tables I typically use for cams combined with blowers or forced induction in general. Then of course you need to make sure your injection timing is retarded for these setups as well.