Manual swapped 99 Silverado runability issues

MidRebuilder · March 1

I just finished up an NV3500 swap on my truck. Jumped the NSS and went for a cruise! She’s got a refreshed 5.3 with a nice streetable cam. Man does she scream!

However, on idle, she likes to “hunt” for return to stable rpm after slowing to a stop. Is this due to the ECM not being tuned to think it has a manual transmission? The truck was tuned with the cam when it had an auto, would that tune need to be scrapped in order to run right with the manual? First foray into tuning and I’m a little lost in the concepts.

MidRebuilder · March 1

I would like to add that the truck runs great while driving, it’s just when idling. It also likes to kill itself when turning at idle. I’m sure this is due to parasitic draw from the PS pump

CamGTP · March 1

Ideally yes, you need to flash the computer with a manual OS as a starting point. There are many tables that are different and of course there would be no settings for the 4L60e transmission that is now missing.

Sometimes you can do a segment swap with a same year 1999 4.8/5.3 Manual tune file. You swap the transmission segments but that might not do everything required. If you flashed it to a manual OS, then flashed back in most of the engine side changes from your current tune, it should run like normal with some minor tweaks needed.

Not having the 4L60e right now makes it tougher to tune but not the end of the world, just some things won't work exactly 100% correct. If you kept this OS, you need to disable every single transmission related DTC. The abuse mode for the transmission must be disabled, torque mngt for the transmission must be disabled. Is the systems tab, in the systems options, if there is a "1" in the brake tq mngt tab for GMT-800, that needs to be set to zero.

Probably going to need to adjust a lot with the idle settings. Base running airflow, throttle follower. Perhaps even the idle timing some to make it happy.

All of this is with HP Tuners is what I'm talking about. I assume that is what you'd be using for tuning. Always save your file before you make any major changes here, that way you have something to go back to and work from.