Transient fueling issues

[lanebaumann]

Hey guys. I am having some problems with transient fueling and I would like some advice.

The vehicle I am dealing with is a 2003 silverado LQ4/4L80e. Everything is stock and I am currently running open loop SD/MAF blend. The VE and MAF tables have been tuned (Other than some strange fluctuations at idle that I can't pin down).

I have been going over lwrs10's guide on transient fuel tuning (here) and I believe I understand how to begin tackling the tuning. The problem I am running into is on tip-out. I am getting the characteristic rich spike, but then it immediately transitions into a lean spike. I don't understand what I need to do to correct a problem like that. Does that relate to the Boiling time table? Any help would be appriciated.

For reference, here is a good example of the issue that I am having.

Tip out issue.PNG


The tune and log in question.

20_Enh RTT_General Fuelling_2017-12-26_Lane 2003 Silverado LQ4.hpt
2017-12-27_Transient Fuel Tuning.hpl

Thanks!

[5FDP]

Will you even be able to "tune" something out that happens in less than .750 of a second in total?

Can the changes even happen that fast in real life inside an engine though?

[lanebaumann]

Will you even be able to "tune" something out that happens in less than .750 of a second in total?

Can the changes even happen that fast in real life inside an engine though?

What do you mean? Isn't this what the transient fueling tables are for?

[5FDP]

Yeah I know this what they are for but the changes are so rapid for the rich and lean spikes that tuning it is so difficult.

I know you can get them super close but is it possible to predict the exact numbers to use to prevent a rapid rich spike that last only .200 to .300 of a second? The error you are dealing with is so small and rich out is for sure less of a worry than rich or lean in.

From that guide you posted did you try the tables based on how James Linder on page two described?

It could also be worthwhile to smooth the VE a little more too, it may help you. If you zoom in on the 3D Chart your VE still has little dips/spikes throughout. Us the smooth selection function to try and smooth them out.

[ericbedd]

As far as the idle afr swings, I have been dealing with something that might be similar. During idle MAF tuning attempting to get it close to 14.7 afr I had no joy. I would make a 1/2 percent adjustment to the MAF table in the startup to warm idle HZ range. Then it would swing the other way. I ended up getting my VE nailed, then set the Dynamic Airflow High RPM disable to 975 rpm (only set this for MAF tuning) to use the VE to help filter my MAF's unreliable readings at idle. I have cleaned the MAF very well, checked for air leaks after the MAF on the intake, and all checked out. This fix for me has allowed me to get my idle afr in OL MAF/SD right where I want it and with less than .5 afr swings.

[lanebaumann]

Yeah I know this what they are for but the changes are so rapid for the rich and lean spikes that tuning it is so difficult.

I know you can get them super close but is it possible to predict the exact numbers to use to prevent a rapid rich spike that last only .200 to .300 of a second? The error you are dealing with is so small and rich out is for sure less of a worry than rich or lean in.

From that guide you posted did you try the tables based on how James Linder on page two described?

It could also be worthwhile to smooth the VE a little more too, it may help you. If you zoom in on the 3D Chart your VE still has little dips/spikes throughout. Us the smooth selection function to try and smooth them out.

I will work on smoothing out the VE table to try and prevent that from being an issue.

I looked through what James had posted and I am currently trying to emulate his method and get results similar to his. Thanks for the pointers.

[lanebaumann]

As far as the idle afr swings, I have been dealing with something that might be similar. During idle MAF tuning attempting to get it close to 14.7 afr I had no joy. I would make a 1/2 percent adjustment to the MAF table in the startup to warm idle HZ range. Then it would swing the other way. I ended up getting my VE nailed, then set the Dynamic Airflow High RPM disable to 975 rpm (only set this for MAF tuning) to use the VE to help filter my MAF's unreliable readings at idle. I have cleaned the MAF very well, checked for air leaks after the MAF on the intake, and all checked out. This fix for me has allowed me to get my idle afr in OL MAF/SD right where I want it and with less than .5 afr swings.

Whenever I have been tuning the MAF I have been setting the High RPM Disable to around 400 RPM in order to rely solely on the MAF. Are you saying to set it to 975 RPM but still make changes to the MAF table in the idle areas? Assuming the VE table is dialed in as well.

[ericbedd]

Just to be upfront, I'm not telling you to do anything. I tried for awhile with my High RPM disable set to 400rpm with nothing but headaches setting the MAF to get good commanded idle afr. (w/ LC2 WB) I made sure my VE was set really good for idle and up to 4000rpm. On dynamic with MAF disabled my idle is smooth and afr is good even during warm up. Once I disabled the dynamic air (set high RPM disable to 400rpm) and ran solely on the MAF, I had such unrepeatable/unpredictable afr readings in similar temps etc, and the idle quality was poor and since I don't have cats, the hunting made the exhaust smell worse. I played with that long enough. Now for me I had my MAF tuned as well as I could already get it at idle. I didn't just take a stock MAF table and adjust it off a modified VE. So when I set my High RPM fail to 975 rpm to use the VE during idle conditions only, I only needed to change my MAF table in the idle areas -4% at most. The changes really only avg. about -1.5% in total in the idle areas. This is what I did and whether my MAF just won't read accurately in the idle hz or whatever else was causing this. I now have the smooth idle and much better commanded afr setting during idle.

I was reluctant to try this at first because all the literature and pros state to tune the MAF and VE seprately. I do believe this to be true, and I feel setting the High RPM disable to 975 rpm won't effect any MAF tuning off idle. I am glad I finally did this, it might go against the directions, but I have no trust in my MAF alone at idle, and I don't want to run solely SD because I want my Low octane spark table.

Also: The 975 rpm setting is just what I came up with to cover startup down to warm rpm. I will most likely set this lower and lower until I run into my MAF tuning wall.

[jonofmac]

This is a tricky one unfortunately. I've been playing around with transient tuning myself, and it is NOT easy. I spent hours doing trial and error...

It looks like you adjust some KPA rows individually. For example, I got my transient fueling to do a 40 to 80 kpa transient almost perfectly, but a 80 to 20 kpa transient does a similar thing. I had to start moving the 20 kpa around to clean it up.

In your case, your KPA isn't quite a step function. It is almost 2. You have 1 quick one, then it slowly drops a bit more. That could contribute to it a bit, try your best to get step functions, and be prepared for a frustrating time trying to get rid of all these transients, though. I still have more work to do too ha. But I noticed you can't just do a select-all and multiply by +/- % to see what works. It gets it close, then I had to start messing with trouble KPA rows individually