Real lean then real rich when zipping the throttle...

[LS1_Dragster]

I've asked this before but never got the answere but what causes the AFR go lean as soon as you hit the throttle then go pig rich afterwards?

I've messed with Fuel Dynamics B3406, B3401 and b4326 but I just cant seem to get it to respond right.

This is for my firebird, 454, 0411, 01270003 OS

[joecar]

Play with fuel dynamics (transient fueling) again, but do the opposite of what you did.

[5.7ute]

Lee, do you have the .cax file that gives you the impact & boiling time modifiers?
Transient fuelling is a black art at the moment which I will be turning some more time to once I have some desired airflow research done. But the basics are.
Increasing B3406 will increase the amount of fuel injected during tip in, since this tells the pcm that x amount of fuel will adhere to the port walls & not make it to the cylinder.
Increasing B3401 will also increase the amount of fuel injected during decel since it tells the pcm how long this fuel will take to evaporate from the walls into the cylinder.
Since airflow, ECT & manifold pressure dictate the evaporation rate the modifiers will be essential.
Also you need to ensure that a minimum pulsewidth limit isnt being hit during decel causing your rich condition.

[swingtan]

Further to that....

• B3406: Impact Factor
  
  Is a fuel correction "adder", so it increases the amount of fuel injected. It is calibrated via ECT and MAP to allow for different corrections based on temp and load. This table tends to have greater influence on smaller throttle movements rather than slamming the throttle open.
• B3401: Evaporation Time
  
  Tells the PCM how long it takes for the fuel left on the wall to make it into the intake charge. Again, this is a "correction" factor, not an actual figure for the evaporation time. Higher numbers here will extend the time that B3406 is used for as it indicates a longer evaporation time correction is needed. again, it tends to have more influence on smaller throttle movements.
• B3426: Stomp Compensation
  
  This tells the PCM to inject additional fuel when jumping on the throttle. Think of it as a pump jet in a carby based engine. As would be expected, bigger numbers = more fuel.
• B3428: Stomp reduction
  
  This tells the PCM the rate at which the "stomp compensation" is ramped out. Higher numbers result in a raster ramp out.

So for a lean tip in, I would look at....

1. Increasing B3426 to give a slightly rich spike at tip in spike
2. Adjust B3428 to blend the rich spike into the normal commanded fuel. Fir the spike goes, rich-lean-commanded, increase the factor to stretch out the rich spike. If it stays rich too long, reduce the factor to lean it out quicker.

For the rich spike at throttle close....

I wouldn't worry as much, but it can cause issues if you are running CL and the STFT's pull lots of fuel just prior to the throttle being snapped open. You could try reducing the values in B3406 and B3401 for the cells effected. This would normally be in the very low MAP cells, but may need some correction higher up to "catch" the rich spike earlier on.

If you really want to try it out, you can also mess with the Injector timing to mess with dynamics. The basic rule here is...

• the earlier the injector fires, the more time the fuel has to evaporate

So an early injector event results in more of the fuel being used for the intended induction event. ( IE. less fuel left on the wall )

I've done some testing with firing the injector just after the inlet valve closes. Doing this you can pretty much zero out the impact tables, but you may also miss time the throttle stop fueling as the injector has fired before the PCM signals it needs stomp fuel.

I've also fired the injector as the inlet valve opens, it makes the stomp fueling pretty good, but needs lots of work on the impact tables to get things working.

Also remember that at full song, the injectors will be open for longer than the inlet valve is open......

Simon.

[LS1_Dragster]

Thank your guys VERY MUCH for the lessons. This will help me out a ton.

5.7ute - I did find the cax file today and downloaded it.

Question: Whats the difference between B3406 and B9000? Also B3401 and B9003? And should they be the same?

I've messed with the injector timing at the race track with the dragster. I proved to myself that this does indeed increase performance. Look for my posts on this subject.

Now as far as I know, increasing the the values in table B3702 and B3703 causes the injectors to fire sooner? I suppose the reason this helped so much is because of the larger cam and allowing the fuel to be injected sooner to work in concert with the valve opening sooner.

For some reason with the firebird I have to increase these values substantially for it to run good. With the stock values it sputters and pukes when trying to rev the motor. Right now it starts at 3.5 and goes to 7.6!

Thanks again, I would like to see swingtans post become a sticky.......

[5.7ute]

Some of those tables are copied in the .cax with the different table id. You could edit the .cax file to remove them, but it is not really necessary as when you change one, it will change the other. If you like, you could post up the .cax file you are using & I can edit it to remove the double tables & place the rest in the dynamics folder.

[BlackGMC]

Further to that....

• B3406: Impact Factor
  
  Is a fuel correction "adder", so it increases the amount of fuel injected. It is calibrated via ECT and MAP to allow for different corrections based on temp and load. This table tends to have greater influence on smaller throttle movements rather than slamming the throttle open.
• B3401: Evaporation Time
  
  Tells the PCM how long it takes for the fuel left on the wall to make it into the intake charge. Again, this is a "correction" factor, not an actual figure for the evaporation time. Higher numbers here will extend the time that B3406 is used for as it indicates a longer evaporation time correction is needed. again, it tends to have more influence on smaller throttle movements.
• B3426: Stomp Compensation
  
  This tells the PCM to inject additional fuel when jumping on the throttle. Think of it as a pump jet in a carby based engine. As would be expected, bigger numbers = more fuel.
• B3428: Stomp reduction
  
  This tells the PCM the rate at which the "stomp compensation" is ramped out. Higher numbers result in a raster ramp out.

So for a lean tip in, I would look at....

1. Increasing B3426 to give a slightly rich spike at tip in spike
2. Adjust B3428 to blend the rich spike into the normal commanded fuel. Fir the spike goes, rich-lean-commanded, increase the factor to stretch out the rich spike. If it stays rich too long, reduce the factor to lean it out quicker.

For the rich spike at throttle close....

I wouldn't worry as much, but it can cause issues if you are running CL and the STFT's pull lots of fuel just prior to the throttle being snapped open. You could try reducing the values in B3406 and B3401 for the cells effected. This would normally be in the very low MAP cells, but may need some correction higher up to "catch" the rich spike earlier on.

If you really want to try it out, you can also mess with the Injector timing to mess with dynamics. The basic rule here is...

• the earlier the injector fires, the more time the fuel has to evaporate

So an early injector event results in more of the fuel being used for the intended induction event. ( IE. less fuel left on the wall )

I've done some testing with firing the injector just after the inlet valve closes. Doing this you can pretty much zero out the impact tables, but you may also miss time the throttle stop fueling as the injector has fired before the PCM signals it needs stomp fuel.

I've also fired the injector as the inlet valve opens, it makes the stomp fueling pretty good, but needs lots of work on the impact tables to get things working.

Also remember that at full song, the injectors will be open for longer than the inlet valve is open......

Simon.

I know this is a rather old thread, but this is exactly the info i was needing, thank you for posting!

[mowton]

I have a question relative to the STOMP parameters. As I tune in both EFI Live and HP Tuner, is the EFILive STOMP factors basically the same as the Steady/Non-steady Dynamic control (MAP/TPS), which as I understand calculates the rate of airflow change and "blends " in the VE predictions to compensate for transitions until the MAF "catches up"?

Thanks,

Ed M

[swingtan]

The way I see the "stomp" compensation is that it's a correction factor for the amount of fuel that will stick to the walls of the intake when suddenly opening the throttle. It's main purpose is to alter the "Impact Fuel" calculations to increase the correction fuel, stopping the lean out condition on fast throttle open. The technical explanation is that at high manifold vacuum, fuel evaporates faster than at low vacuum, so during a transition from high vacuum ( closed throttle ) to low vacuum ( open throttle ) the amount of fuel available to the intake charge reduces. This lean-out is normally taken care of by the Impact factor corrections, but on fast transitions, it's more of a "step" than a ramp. The Stomp corrections increase the Impact Factors at this time.

The easiest way to think when using the table, is that bigger number mean more fuel on quick throttle openings "stomping on the pedal". To tune it, log commanded and WB fueling and look at where the throttle is stomped open. If the transition from cruise to PE mode is slow and has a rounded leading edge, then more stomp may be required. If the leading edge shows and overshoot that then returns to PE commanded, then there is too much correction. Of course, this is just a basic guide and individual engine may like a slightly lean stomp or slightly rich stomp. Neither is the over all "correct" setting, the correct setting is what makes the engine perform the way you want it to.

Simon

[mowton]

The way I see the "stomp" compensation is that it's a correction factor for the amount of fuel that will stick to the walls of the intake when suddenly opening the throttle. It's main purpose is to alter the "Impact Fuel" calculations to increase the correction fuel, stopping the lean out condition on fast throttle open. The technical explanation is that at high manifold vacuum, fuel evaporates faster than at low vacuum, so during a transition from high vacuum ( closed throttle ) to low vacuum ( open throttle ) the amount of fuel available to the intake charge reduces. This lean-out is normally taken care of by the Impact factor corrections, but on fast transitions, it's more of a "step" than a ramp. The Stomp corrections increase the Impact Factors at this time.

The easiest way to think when using the table, is that bigger number mean more fuel on quick throttle openings "stomping on the pedal". To tune it, log commanded and WB fueling and look at where the throttle is stomped open. If the transition from cruise to PE mode is slow and has a rounded leading edge, then more stomp may be required. If the leading edge shows and overshoot that then returns to PE commanded, then there is too much correction. Of course, this is just a basic guide and individual engine may like a slightly lean stomp or slightly rich stomp. Neither is the over all "correct" setting, the correct setting is what makes the engine perform the way you want it to.

Simon

Simon,

Thanks for the response. I think we may be saying the same thing. The only confusion I am having, is there a difference in the Wall film/Evaporation tuning (both EFILive and HP Tuner have those tables) and the airflow charge compensation for larger throttle opening/closure transitions.

As it has been explained to me, large throtle transitions (unsteady) "contaminate" the MAF airflow reading as it has two voids to fill...the manifold and the cylinders. To this, not all the air being registered by the MAF is actually entering the cylinder, so fueling calculations would be inaccurate. To compensate, the PCM "validates" the MAF against the calculated SD value (VE) to make sure it is within a specifc tolerance level. If not, it uses the VE developed fueling to essentially "override" the MAF until the transient airflow event returns back to a steady state condition and MAF data is accurate again. Should this "override" task ocurr for a specific period of time, then the PCM fails the MAF (bad) and reverts to SD using the VE calculations.

To this, HP Tuner has a set of parameters (MAP and TPS) which are used to define this transition period. And as I said above, both have the Wall/Film/Evap Transient fueling tables. So to my feeble brain, the wall film/evap seems to be for actual instantaneous fuel delivery "compensation" due to valve timing, heat soak etc. and the other is to establish an accurate Air Flow model so IFR can be developed.

So after all this...sorry so long Does EFI Live give you the means for setting that MAF/VE blending except for the Filtered MAF High RPM disable/enable?

Thanks again

Ed M