Tuning larger LT-5 cams - ZR-1 Net Registry Forums

XfireZ51 · 05-29-2011

Thought I would share one of those tuning "mystery" stories. Sometimes you've got to play detective. I have been busy tuning my LT-5 for the last 2 months. Over the winter I added a set of ported cylinder heads (AFR or Trick Flow don't make DOHC 32V high flow heads) and decided to take advantage of the additional airflow by installing larger single pattern intake cams. This is all on a stock block 5.7L LT-5 motor w 1 7/8" Watson headers and 3" Magnaflow exhaust. These babies LOVE to breathe. Very much a top end motor. Not much tops an LT-5 at full song around 7000rpm IMO.
Anyway, have been playing with the tune for a couple of months when I noticed the BLMs are not updating. The LEARN flag is OFF although motor was going into C/L. I thought possibly there was a problem with my new copy of TPRT 5.0. I also "noticed" that the bin where all this started had a Checksum that reset, IOW it went beyond the 65xxx. I do multiple changes to a bin but none were of the kind that should affect LEARN control. Or so I thought. It took me a couple of days of eliminating the parameters that had changes between the bin that DID work from the bin that DID not. It turned out to be coincidence that the Checksum reset at the same bin change but had nothing to do with the LEARN staying off. Using Craig's Ostrich 2.0 and Mark's TPRT 5.0 really made the sleuthing a much more effcient process. Still took me most of the morning today BUT I finally got it. With the larger intake cams, you invariably get the rich smell at idle and I had lowered the O/L change v CTS table to take some fuel out. Apparently the code doesn't like too much fuel pulled out because it appears to prevent LEARN from turning on. Essentially you are running O/L although the ALDL says you are in C/L.
Made the change to the bin, download and bingo LEARN ON. I re-input the stock values but for grins I would like to find out how much I can decrease fuel before re-creating this issue again. Maybe one of the hack gurus can tell us what the logic is behind this outcome. After going thru this, I thought I would have LOVED to have an ECM bench.

05-29-2011	#1
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,709	Tuning larger LT-5 cams Thought I would share one of those tuning "mystery" stories. Sometimes you've got to play detective. I have been busy tuning my LT-5 for the last 2 months. Over the winter I added a set of ported cylinder heads (AFR or Trick Flow don't make DOHC 32V high flow heads) and decided to take advantage of the additional airflow by installing larger single pattern intake cams. This is all on a stock block 5.7L LT-5 motor w 1 7/8" Watson headers and 3" Magnaflow exhaust. These babies LOVE to breathe. Very much a top end motor. Not much tops an LT-5 at full song around 7000rpm IMO. Anyway, have been playing with the tune for a couple of months when I noticed the BLMs are not updating. The LEARN flag is OFF although motor was going into C/L. I thought possibly there was a problem with my new copy of TPRT 5.0. I also "noticed" that the bin where all this started had a Checksum that reset, IOW it went beyond the 65xxx. I do multiple changes to a bin but none were of the kind that should affect LEARN control. Or so I thought. It took me a couple of days of eliminating the parameters that had changes between the bin that DID work from the bin that DID not. It turned out to be coincidence that the Checksum reset at the same bin change but had nothing to do with the LEARN staying off. Using Craig's Ostrich 2.0 and Mark's TPRT 5.0 really made the sleuthing a much more effcient process. Still took me most of the morning today BUT I finally got it. With the larger intake cams, you invariably get the rich smell at idle and I had lowered the O/L change v CTS table to take some fuel out. Apparently the code doesn't like too much fuel pulled out because it appears to prevent LEARN from turning on. Essentially you are running O/L although the ALDL says you are in C/L. Made the change to the bin, download and bingo LEARN ON. I re-input the stock values but for grins I would like to find out how much I can decrease fuel before re-creating this issue again. Maybe one of the hack gurus can tell us what the logic is behind this outcome. After going thru this, I thought I would have LOVED to have an ECM bench.