Let's discuss Transient Fuel

[Blades]

Ahh, could it just be a software error that the x-axis of gain table says Mass Air Flow (g/sec)? My VE table is really driving me nuts, and the lean-tip in from transient fueling isn't helping.. Its a chicken or egg kinda issue..

I think my error would've been adjusting the calibration of the MAP sensor offset by -1.. 200 linear, 9 offset vs 200 linear, 10 offset. I noticed the other day that the baro was reading 103.. Now, it obviously reads 102.. and the baro readout apparently changes everything. This isn't really on topic to this thread.. I'm just trying to sort out why my VE table went to hell in a handbasket..

[A-Pex]

...

The main things to mess with are the Impact factor and its gain and the boiling time constant and its gain. eg. you can see that in the stock tables as MAP increases (you hit the gas) the boiling time increases (fuel evaporates slower) and also the impact factor increases (more fuel hits the intake surfaces), both of these increases result in the PCM adding more fuel during the transient. You can also see that as MAP decreases the numbers get smaller, resulting in the PCM subtracting fuel for the transient.

Hope that helps,

Chris...

I'm not sure I completely understand the process of impact/evap/gain. Consequently, I have three points of clarification requested...

1) On my C6, the impact factors DO NOT increase with MAP increases. They do however change with increased IAT. Given this, should I try to scale these tables to increase w/ MAP?

2) Impact/Gain: If I'm trying to reduce KR in the transient areas safely (without access to "Accel Enrichment") and thereby trying to enrich the AFR at tip-in (add more fuel), should I be increasing these numbers or decreasing them in the MAP areas where I'm experiencing high AFR and subsequent KR?

3) Evap/Gain: I'm also seeing double digit positive AFR Error % (high AFR) between 75 and 95 MAF (g/sec) during the transitions. Should I increase or decrease the gain in these areas to increase the amount of fuel pumped into the ports at this point and reduce my positive AFR Error?

Thanks in advance!

[jimbos'ss]

sub'd

[mdmbkr]

Why did this thread die?

On my E40 car I get a lean spike when running SD that goes away on MAF only. If I open the throttle slowly there's no spike, it's only when I open it fast. It looks very similar to the charts posted above. The first chart shows quick throttle with a spike, the second chart shows gradual throttle with no spike.

VE table is nicely dialed in.

Not sure how it can be a transient fuel issue if enabling the MAF masks it .. maybe the inherent delays in the MAF? No spikes running MAF only or MAF+VE.

Or maybe disconnecting the MAF affects the transient calculations? My impact table has at least some effect when running OLSD but it's not predictable.

Maybe worth noting is that disabling the MAF causes my traction control to disable as well - I guess it depends on a MAF reading.

[redhardsupra]

MAF does have a little lag. Usually it's not noticeable, because in the stock MAF+SD hybrid SD takes over and compensates quickly. From earlier in this thread, one guy brings up a good point that on ECU's with dual MAF tables, you wanna make sure that the tables blend/transition nicely. I agree from earlier post by eficalibrator that regardless of the airmass estimator in use, all other modifiers work the same, as long as the airmass values reflect reality.

[Wnts2Go10O]

is the gain directly opposite proportional? if so, if i log stft's in the fuel mass gain table and set it up to make the numbers negative then copy/paste %, would that work? accurately?

[ttbestas]

how to change transient fuel tables for e85 fuel? thanks

[12sws27]

The transient stuff is killing my brain....

I'm tuning a 98 GM truck that used to have the poppet GM injectors. Now it has a real MPFI intake with larger injectors. Plenum volume has increased and the injectors positions have changed. So I get real lean tip-in and real rich decel. DFCO is disabled. The lean spikes are short but the rich decel sticks around for awhile.

The transient fueling is bad enough that with out any changes the truck bogs. If I doubly the Fuel To Wall Impact Factor vs. Cool Temp vs. MAP the bog goes away and the lean spike gets smaller. If I go to much over that the truck has a hard time starting.

Should I be playing with boil time too? Should I increase it for rich decel or decrease?

I just need a better understanding of this so I can try and figured it out.

My transient fueling seems to be so screwed up it's hard to tune m VE tables because I think it's throwing my AFR error percentage in my histos off.

[MNR-0]

Personally, I would set it back to stock and leave it. Without controlled conditions and metering devices to tell whats going on your are shooting in the wind. No wonder you are fried!

There are no power gains or measurable mileage gains to be had with messing with this stuff.

Just tune for correct AFR - that is waht washes out everything in the end

[12sws27]

Thanks for the reply.

I ended up leaving transient fueling alone for now. My VE tuning is going well. I was doing something wrong before. I was forgetting to change my secondary ve table to match my primary so I wasn't getting anywhere.

I would still like to better understand these tables and what does what in case VE/MAF tuning doesn't take care of all my transient problems.

[backchannel]

removed

[wyochimneysweep]

I'm lean at tip in and rich at decel. any more info to this out there that i'm not finding?

[wyochimneysweep]

so with going from cast to aluminum heads and intake I should probably decease the numbers in the evap vs temp vs map due to heat transfers faster and the evap will happen faster right?

[benno25]

Bringing up an old thread here.

There seems to be a lot of talk to do with fixing fuelling issues when getting on the throttle, however little of what to correct when lifting off the throttle.

I have a problem where the car goes really lean briefly when lifting off the throttle, enough that you can feel the car stumble when this happens.

What do I need to adjust in the transient fuelling to correct for this?


This is for an LS1 pcm that is now running an LS3 engine.
Also DFCO is disabled, so that is not my problem.

Cheers
Benno

[TheFlyingDutchman]

Benno, did you figure out a fix for the lean spike on throttle lift off? I'm working through this same issue now. I made some changes to the impact factor and the fuel on wall decay tables, which fixed a lean condition on tip in, but made the lean condition on throttle lift worse.

[benno25]

I found increasing the Fuel Boiling Time vs Coolant vs MAP in the low MAP areas seemed to help things the most. I also increased the Impact Factor in low MAP areas.

Also, here is a good link I found explaining how to adjust these tables to get rid of a lean spike on tip in that you may find interesting.
http://www.performancetrucks.net/for...-b3403-451539/

Keep us posted on how things go with your problem.

Cheers
Benno

[TheFlyingDutchman]

still working on this on weekends here and there. Thanks for the advice benno on increasing the evap and impact factor values in the low MAP regions. That advice is getting me closer.

Does anybody know how to translate the airflow values (lb/hr) from the Impact Factor gain and Fuel on Wall Exp Decay Mult vs Airflow tables to engine rpm?

You can observe different transient behaviors at high and low MAP, and this is clear translating between in the values in the tables and the MAP sensor in the car (they are the same), but I'm really guessing when it comes to translating behavior at low/high rpms to the values in the gain tables.

Any help would be greatly appreciated.

[homebuilt]

I have a lean tip in and decel. My valves and intake ports are CNC ported and the ceramic coated (as well as the valves).

I would expect this is going to change the wall film behavior. Would the proper calibration process be to change the transient tables by a percentage accross the board by trial and error until lambda error is reduced? What about the gain tables?

[Bayer-Z28]

Not looking to butt in with a basic question, but you could fine tune the transient fueling after everything else is nailed down 100%, correct? Or would a minute change to transient fueling throw the trims off just a tad? Or is it not exactly enough to pick up on until something has gone past an acceptable level?

[homebuilt]

Not looking to butt in with a basic question, but you could fine tune the transient fueling after everything else is nailed down 100%, correct? Or would a minute change to transient fueling throw the trims off just a tad? Or is it not exactly enough to pick up on until something has gone past an acceptable level?

I my limited experience it seems to. Especially if I'm trying to work on the high vacuum areas of the VE table which I can only get into under transient conditions.

I have a very rich spike on a let off (negative MAP) input. I am thinking I would adjust the Fuel Boiling Time table until the let off is better by adjusting that whole table globally and then come back and adjust the Fuel To Wall Impact factor specific rows that I move to with a positive MAP input until the tip-in is back to where it was.

Is this correct? Basically I'm not clear if the entire Fuel Boiling Time table should be adjusted globally or by the row the transition moves to.