Large LTFTs with stock MAF & injectors, why?
08-10-2008, 03:45 PM
#1
Launching!
Thread Starter
Join Date: Jul 2004
Location: Gainesville, Florida
Posts: 200
Likes: 0
Received 0 Likes
on
0 Posts
Large LTFTs with stock MAF & injectors, why? I'm seeing a lot of trims in the range of -10 to -15 and this puzzles me. I know the PCM uses speed density for throttle transitions, but lowering the VE on the speed density tables doesn't seem to affect anything at all.
The car has a stock MAF with screen, original injectors, and correct tables for both. AFR 205s, 11.8:1 CR, 224/229 cam, LS6 intake, stock throttle body and LG longtubes. It runs and drives fine, but the fuel trims are confusing me.
Thanks for any help.
The car has a stock MAF with screen, original injectors, and correct tables for both. AFR 205s, 11.8:1 CR, 224/229 cam, LS6 intake, stock throttle body and LG longtubes. It runs and drives fine, but the fuel trims are confusing me.
Thanks for any help.
08-10-2008, 06:45 PM
#2
Moderator
iTrader: (11)
Join Date: Mar 2002
Location: East Central Florida
Posts: 12,605
Likes: 0
Received 6 Likes
on
6 Posts
With a big cam the intake pulsations / reversion at
lower RPM can make the MAF "double count" the
airflow (same air "hits" the hot wire twice, like). It
can muss up the calibration some. If you see a
MAF airflow g/sec that's a lot higher than Dynamic
Airflow g/sec at low RPM, maybe this is it.
lower RPM can make the MAF "double count" the
airflow (same air "hits" the hot wire twice, like). It
can muss up the calibration some. If you see a
MAF airflow g/sec that's a lot higher than Dynamic
Airflow g/sec at low RPM, maybe this is it.
08-10-2008, 09:12 PM
#3
LS1Tech Sponsor
check for exhaust/intake/vacuum leaks....
__________________
06MonteSS / DiabLew Tune
2014 Camaro 2SS/RS - LS3, 6-speed manual, short-throw performance shifter, NPP dual-mode performance exhaust, 1LE front splitter, ZL1 rockers, Z28 Rear Spoiler, all paint-matched Red Rock Metallic, BMR strut tower brace, Cold Air Inductions cold air intake, Apex Motorsports, Inc. catch-can, Custom DiabLew Tune
www.diablewtune.com -- www.diablocustomtune.com -- www.diablocustomtunegm.com
06MonteSS / DiabLew Tune
2014 Camaro 2SS/RS - LS3, 6-speed manual, short-throw performance shifter, NPP dual-mode performance exhaust, 1LE front splitter, ZL1 rockers, Z28 Rear Spoiler, all paint-matched Red Rock Metallic, BMR strut tower brace, Cold Air Inductions cold air intake, Apex Motorsports, Inc. catch-can, Custom DiabLew Tune
www.diablewtune.com -- www.diablocustomtune.com -- www.diablocustomtunegm.com
08-10-2008, 11:04 PM
#4
With a big cam the intake pulsations / reversion at
lower RPM can make the MAF "double count" the
airflow (same air "hits" the hot wire twice, like). It
can muss up the calibration some. If you see a
MAF airflow g/sec that's a lot higher than Dynamic
Airflow g/sec at low RPM, maybe this is it.
lower RPM can make the MAF "double count" the
airflow (same air "hits" the hot wire twice, like). It
can muss up the calibration some. If you see a
MAF airflow g/sec that's a lot higher than Dynamic
Airflow g/sec at low RPM, maybe this is it.
08-11-2008, 09:07 PM
#6
Launching!
Thread Starter
Join Date: Jul 2004
Location: Gainesville, Florida
Posts: 200
Likes: 0
Received 0 Likes
on
0 Posts
With a big cam the intake pulsations / reversion at
lower RPM can make the MAF "double count" the
airflow (same air "hits" the hot wire twice, like). It
can muss up the calibration some. If you see a
MAF airflow g/sec that's a lot higher than Dynamic
Airflow g/sec at low RPM, maybe this is it.
lower RPM can make the MAF "double count" the
airflow (same air "hits" the hot wire twice, like). It
can muss up the calibration some. If you see a
MAF airflow g/sec that's a lot higher than Dynamic
Airflow g/sec at low RPM, maybe this is it.
Unless I'm greatly mistaken, both an intake and exhaust (before the O2s) leak would cause the ECU to inject more fuel, not less.
Why would it be running off the secondary VE and low octane tables? The changes I made to the high octane map certainly showed up in logs of timing advance.
08-11-2008, 09:57 PM
#7
FormerVendor
iTrader: (9)
Join Date: May 2003
Location: Jacksonville, Fl
Posts: 1,573
Likes: 0
Received 0 Likes
on
0 Posts
It sounds like you are running Closed Loop MAF Fueling. The negative trims indicate an uncalibrated VE table. By definition, (in stock form) below 4K rpms the pcm is blending airflow measurements between the MAF and Map sensors. The turbulent readings the MAF gets below 4K rpms that Jimmy was describing necessitates putting the vehicle in Speed Density or simply put, make the MAF fail in order to calibrate the MAP sensor.
This failure state, that GM never intended to be used by Tuners hacking into their proprietary software with aftermarket tools, will default the vehicle to the backup VE table for the MAP sensor in the case of a 98-00 like yours.
I would recommend you upgrade your 99 OS to an 02 (alleviating the reduced resolution of the backup VE table as 01+up did away with this table-compare the two and you will see what I am talking about) and put the vehicle in OLSD and tune the MAP sensor (Main VE table) and then re-enable the MAF and calibrate it accordingly.
This failure state, that GM never intended to be used by Tuners hacking into their proprietary software with aftermarket tools, will default the vehicle to the backup VE table for the MAP sensor in the case of a 98-00 like yours.
I would recommend you upgrade your 99 OS to an 02 (alleviating the reduced resolution of the backup VE table as 01+up did away with this table-compare the two and you will see what I am talking about) and put the vehicle in OLSD and tune the MAP sensor (Main VE table) and then re-enable the MAF and calibrate it accordingly.
