I do have an autotap and an interceptor. I also have lots of pre mod datalogs too.

Right now I modify the MAF signal using my DTEC which uses RPM and Load (MAP signal), but I am just doing it accross the board at 5% right now.

My goal is to change my DTEC MAP to get a 0.0 LTFT accross the board .

My question to you WOP is do you know how LTFT cells are based? Are they RPM or Load based?

My LTFT has went from 13-20 to the 0-5 and the occasional 8. Needless to say I am out of the range needed to get the 0171 (which is 20)

 

So how do it modify the fuel curve if it just plugs into the MAF only? If it doesn't know your RPM or Engine load ?

 

Zin
LTFTs are scaled in a "grid" of "cells" (usually 16 cells in a 4x4 grid) that is referenced to RPM (x) and LOAD (y). So it's BOTH!
As RPM and load increase your LTFT will be maped/read from a higher cell. (again typically 0-15) So when you observe your LTFT value change dramatically, it's not that it's "learned" a new value- it just moved into a different cell!

So are you talking 8 at idle? or at a steady road load?
All that is saying is the system is having to trim your steady state AFR (at that RPM and LOAD) by adding approx 8% additional fuel from the base calibration- in order to minimize your emissions. -10% to +10 % is generaly considered the "normal" range but some engines normally go beyond that in some cells.

Either way the closer it is to 0 the closer you are to stoich ratios (14.7:1) as you drive. This AF is optimal for complete combustion and optimal cat efficiency. The LTFT has to be "pegged" at 20% (the upper clamp on the LSJ calibration) for a full 2 minutes (in a "weighted" cell) before it would set a P0171.
Very common anytime you are getting "unmetered" air into the engine

HTH
WopOnTour

 

At a steady 70mph in 5th gear on a flat road the LTFT is about 2-3. This can jump up if I am accelerating to about 8 (probably to a new LTFT CELL).

I can be driving without any MAF trickery and my LTFT will be at 18.7, then if it hops to 19.5 the P0171 DTC is tripped. I have watched it happen probably 10+ times.

At Idle will bounce around between between -2 and 2.

Is there any way with a TECH2 to see what LTFT cell I am in or any way to figure it out by detuction?

 

Well based on what you are saying Zinner, what you are doing is definately going in the right direction! Good Job!
What I (and others) have found however is you eventually start running up against the rationality DTCs (but maybe NOT if you limit your rescaling efforts to only 5%)

Sounds like what you are doing is EXACTLY what needs to be done to at the very least keep the P0171 from failing (and MIL OFF) with the K&N CAI. But keep in mind that generally the DTC will only FAIL if you are in a "weighted" cell (those most commonly observed when idling and when driving at normal steady state road loads) So you may still be able to have some "play room" to optimize your AFRs in some of the upper range cells.

Additionally because it is a TYPE B DTC it may show a FAIL state, yet wont illuminate the MIL until the diagnostic executive observes a FAIL on 2 consecutive trip cycles.

And YES, the TECH 2 (and even going back to the TECH 1 days) will always display the current LTFT (aka block learn) cell number. Obviously this is extremely important when using a scan tool in a diagnostic capacity. (Typically in snapshot mode over a consistent drive cycle) Maybe I will drop a line to Todd at Aeroforce and see if there's anyway they could add "LTFT cell#" to the Interceptor PID list. It certainly would make the gage more useful when diagnosing trim related faults. Doesnt the Autotap show LTFT cell????

WopOnTour

 

http://www.c5forum.com/diy/ltft.php

Hope this help ...

 

Cool I do have an autotap so I will find that value and add it to my config for my car.

 

Hey ZOOOMER, welcome to the Cobalt world!

If you extend the harness on your AFC so we don't have to pull the headlight out to make changes, i might be interested in it.

I do still have one on my Impala and it works good. Nice adjustability.

 

How many "cells" does the Cobalt PCM have? If you don't know, guessing will get us no where! The L67 has 3! The LS1's, 20+ Get my point.

 

No, what's your point?
Some ECM/PCM calibrations use a separate "idle" map using cells (usually 17 to 20 in a 2x2 grid) and influenced mostly by P/N and AC clutch state. Others, (like the L67) use an "abbreviated" trim map. So what?
What really matters is the cell's contents (LTFT value after trimming) and to be able to identify when it "switches" cells to observe THAT particular cell's value. (in order to dfferentiate the possible change in LTFT from just a cell change)

So the # of cells used or the table structure is really quite irrelevant. What really matters is trim value observed with the cell you're currently IN!

While it’s no substitute for wideband tuning or anything, you can at the very least use the existing trim value (or averages) as a basic indicator for DIY MAF translation.

Regards
WopOnTour

<EDIT>The LSJ appears to use cells as high as 36 for "road load" conditions and cell 27 for idle.The only "anomaly" I have observed with the LSJ is a wierd "special" LTFT cell (cell 28?) that becomes active whenever it hits it head on the rev limiter. (still havnt figured out EXACTLY what it's all about yet)

 

Actually, I'm glad you asked. The AFC does in effect know your engine load. It has 13 adjustments for MAF frequency range. The higher the engine load, the more air it uses. Higher air usage means higher MAF frequency. Since the AFC has adjustments based on MAF frequency, it can be tuned for various ranges.

 

Zoomer you're right, BUT since our car is forced induction, the pressure around the MAP is rising quickly, so the MAP has even more influence than the MAF on the injector pulse width.

 

All of the MAF-T's from Intense as of monday will ship with the connectors making it plug and play. And you won't need to remove the headlight to make adjustments.

Tim

 

^^^^^^^^ What about injector connectors too?

 

We are still working on those. Hopefully we will have some news regarding those in the near future.

 

Still no P0171 with a slight tweak of the maf signal. I have actually changed the map a bit. I am running about 1.9% correct in the low load area, 2.7% in the medium load and 3.9% at 100% load.

I just got an wideband as well and I am showing about 12.8 to 13.0 AFR at WOT, with a 3 inch pulley.

I have only made a couple runs and I might actually try another free air calibration.

 

Recently I got this very CEL 3 times with my current setup (10% larger injectors along with merely no MAF correction percentage). Because I downgraded from 42 to 37 lb/hr injectors so the PCM saw a lean condition for a couple of days, then I think it compensate for it.

 

I got it today on the way home from the track. Almosy 6000 miles on the Injen and nothing until now. I've had 3 runs on the dyno prior to this and my a/f ratio's have always been rich, I mean 10 rich. (I know this thread is a month old....oh well)