Effects of EVAP when VE Tuning with STFT

[juyanith]

I'm working on tuning VE using STFT and I wondered about the effects of the EVAP system on fuel trims. Right now, I'm disabling MAF, LTFT, DFCO, CFO and PE then logging the STFT in a histogram. I edit the VE "table", update the equations using EQ <> VE and repeat.

I think I'm on the right track, but I got to thinking about the LTFT cells and how cells 21-36 were used when EVAP was closed. Most of time the cells I see are 0-15 (EVAP open), which could mean that a little bit of fuel vapor is being added. Would this matter as far as using STFT to tune VE?

I don't think it would matter much but eliminating another variable might help reduce the number of iterations to get VE sorted out. Does anyone do anything about this or am I just crazy? I started looking at the differences between the histograms if I added filters for the fuel cells but wanted to know if I should just let them average out.

Thanks.

[ajamesbond007]

If you are tuning the VE, make sure you disable the EVAP or it will skew your data. Maybe not a whole lot, and make in just certain areas, but definitely eliminate that variable

[juyanith]

I don't think you can disable EVAP within the PCM, but maybe I'm wrong. I don't really want to remove it either. Am I just asking a dumb question?

[ajamesbond007]

I am not sure if you can tune the PCM to disable EVAP, but check your scanner controls. I forget what that function is called, but it is where you can control idle, tranny, things of that nature with you scanner. IDK with gen 4's, but with gen 3's you can command the EVAP not to purge. Try that and see if you are able to do that.

[DSteck]

Filter out fuel trim cells above 20. That's what I do.

[juyanith]

Thanks, that's what I was doing (filtering out data when fuel trim cells were above 15). However, isn't that when EVAP is open? My understanding is that 16-19 are idle and 20 is decel. I don't really think filtering the other way would work as the car spends most of its time in the lower cells. Oh well, if that's how the car normally operates I guess it doesn't really matter.

[carlrx7]

my car is usually below 17 when driving which means its always open.

at startup is when im at 37, thats why my stft's are high. seems backwards to me.

this is the table i thought the evap operates.


EVAP Open
0 - 15 defined by the LTFT RPM and MAP boundaries
16 - Idle PN (AC on)
17 - Idle PN (AC off)
18 - Idle InGear (AC on)
19 - Idle InGear (AC off)
20 - Decel

EVAP Closed
21 - 36 defined by the LTFT RPM and MAP boundaries
37 - Idle
38 - Decel


-Carl

[DSteck]

The description in the help file doesn't make sense to me, but filtering the way I suggested has worked for me.

[fast400]

Can't you just unplug the EVAP purge plug??

[schpenxel]

Can't you just unplug the EVAP purge plug??

Sorry for the old thread bump....

BUT, can someone confirm if the evap solenoid is unplugged, and the error IS reported, that it will not make "corrections" to fuel trims based on the LTFT Purge reduction factor table?

Also, if I want the Reduction Factor table to have zero impact to fuel trims, would I set it to 0 or 2?

[Engnineere]

I have the exact same question as above, and per usual there's no answer and I can't find a similar thread anywhere...