ri-vette

any ideas why when i drive it spikes leans 16.9 and i feel a hesitation? only happens when driving around town. in first and 2nd gears around 2,000 rpms. WOT no problem. i recently had it tuned for other issue i had. i have a procharger stock boost. i have a wideband and fuel psi gauges.

tblu92

Are you using your MAF and front 02's ??? If so your ECM is constantly trying to achieve the Stoich AFR of 14 .68 during P/T-----If that is not happening---either your maf is reading wrong or your front 02's are reading wrong----need to know more about your tune and your mods---Do you have LT headers ??
ALSO where are you getting the lean spike of 16.9 ?? If you are getting that only when lifting off the throttle--this is a common occurrence--- When you LIFT offthe gas--the ECM kicks in the DFCO table "decelerantion fuel cut off" where the AFR spikes way lean as the fuel is shut off to get better MPG's---Many tuners with majorly modded engines
will turn the DFCO off to get more accurate AFR readings and no spikes-

mowton

A dollar says they didn't touch the VE......

Ed M

ri-vette

i bought it back to the turner and he said its not that bad. he thought i was releasing the throttle at one point. so needles to say its still doing it. whats VE

mowton

VE = Volumetric Efficiency -- how much the cylinder is filled; 0% = empty and 100% = full (can go higher but thats another thread :-))

Your car operates under 2 different airflow models..

1) Mass Air Sensor -- measures the density of the air being consumed by the motor and reports back to the PCM Airmass converted to an oscillating signal called MAF Hertz (hz). The tune has airmass values assigned to specific hz break points and the pcm uses them for airflow values. This values are in Grams/Second which it uses for its Air to Fuel ratio calculations...excellent and accurate during steady state airflow; cruise, wide open throttle etc.

2) Volumetric Efficiency -- Instead of a specific sensor, the PCM reads other sensors like Manifold Absoulte Pressure (MAP), Intake Air Temperature (IAT) etc and a table called VE to calculate the Airmass in Grams/Second. The table fairly large (much larger than MAF) and is referenced to RPM and MAP (engine load) It is precisely tuned using steady state data to provide the PCM a second means to determine airflow and if the airflow is correct from the MAF. VE can "correct or bias' the airflow value if not within a "tolerable level".

The best example for this is when you tromp on the pedal and there is a huge inrush of air passes the MAF and into the manifold. Because the manifold wasn't "full" to start with, some of that air is not making it into the cylinder which is what the PCM has to know in order to inject (Injection Pulse Width) the right amount of fuel to meet the commanded AFR. When the PCM goes to the VE table and calculates what the cylinder airmass s/b, it will see a difference and help smooth through (bias) that difference by adding or subtracting using the VE table.

Hope this helps

Ed M

KoreaJon

That made my head hurt.......

KoreaJon

mowton

"Not that bad"......kind of a messed up response in my books. I would like to hear "its ok" or "lets take a look" rather than that

It could be decel as tblu92 stated above.

Ed M

PS -- sorry for the head spinning