not to throw a wrench into this whole negative Ltr

[TT_Vert]

ive had my trims negative using IFR and after some reading I decided to set my IFRs back to stock and modify my VE tables. I set IFR back to stock and have driven about 50 or 60 miles and logged. My Ltrims are now +2 or so everywhere BUT even w/ a 13.5 or so AFR (havent messed w/ PE again yet after IFR change)I'm getting zero knock when I used to be able to generate it when I wanted to and my Ltrims are still going to 0 at WOT.. On top of this, my car used to sometimes go to 300-400 rpms as i would come to a stop. This no longer occurs. SO what gives here? This seems to be the complete opposite of what i have read should be happening. It also seems that on tranition airflows, my o2 voltages arent dropping to the double digits and staying there as long as they would before i changed the IFR back. I will post some screen shots of my Ltrim historogram in a bit.

Input please?
for some reason im have some 100s in here that are skewing the average some. I've never seen 100s prior to IFR changes either




Dave


Dave

[Screamn03]

My car has a few areas where the LTFTs are a little positive like yours and under wot throttle I still have 0. I think you have to go out of a certain range for it to start adding fuel under wot (postive ltft in cell 22).

[rattle]

what happens at WOT depends on what the fuel trim was in the cell just before you went wide open. So if just before you went WOT the fuel trim was negative then no modification is made to the WOT fuel ratio. Now if you were in a cell that had a positive trim just before you got WOT then the vcm will add fuel to the WOT fuel ratio.

[Keith@HPTuners]

100's are data errors.

[TT_Vert]

what happens at WOT depends on what the fuel trim was in the cell just before you went wide open. So if just before you went WOT the fuel trim was negative then no modification is made to the WOT fuel ratio. Now if you were in a cell that had a positive trim just before you got WOT then the vcm will add fuel to the WOT fuel ratio.

i though this too so i intentionally went WOT in a cell that had a positive Ltrim and it went to 0 still.

Keith, why do i get data errors all the sudden? I never had any before 2 days ago.
Dave

[Keith@HPTuners]

Using a USB to serial converter?

What is the computer specs and what scanner windows do you have open?

If you use the histo and chart + gauge display, it does use a lot of CPU overhead which sometimes causes data from the serial to be missed.

[TT_Vert]

Using a USB to serial converter?

What is the computer specs and what scanner windows do you have open?

If you use the histo and chart + gauge display, it does use a lot of CPU overhead which sometimes causes data from the serial to be missed.

no its going itno a serial port. No other programs run when the scanner runs. its the same laptop, same OS etc nothing has changed

Dave

[Keith@HPTuners]

Dave, sometimes packets are just lost. Scanning is a very bandwith intense operation. It is possible that 2 devices in the vehicle tried to talk at a very similar time which confused our hardware/software.

Its nothing to be alarmed about.

[TT_Vert]

ok. ill be getting a new laptop soon we'll see if that fixes it. those 100s really skew my averages some times in the historograms.

Dave

[AnotherUser]

Stupid trivia time. Does scanning put any load on the PCM that could cause normal calculations like fueling to take longer?

[GarySmithZ28]

Stupid trivia time. Does scanning put any load on the PCM that could cause normal calculations like fueling to take longer?

The PCM software undoubtedly runs engine management functions at higher priority than OBD scanning functions. My guess is that engine management calculations are guaranteed to complete under all conditions below 8000 RPM.

-Gary

[AnotherUser]

The PCM software undoubtedly runs engine management functions at higher priority than OBD scanning functions. My guess is that engine management calculations are guaranteed to complete under all conditions below 8000 RPM.

-Gary

That would make sense, however programmers do not always do things that make sense. Especially at GM.