Meph Posted May 30, 2015 Share Posted May 30, 2015 Hey Guys. Ive got a 4.8L installed into my Z with a WC T5 trans, everythings going great, drive nice and runs well. Its an auto ECU and my vehicle speed signal is working. The problem i'm having is if I take the car out of gear it till try to rev anywhere from 1200 to 1700 rpm until you come to a complete stop, then drops to 600 rpm. Seems like an Automatic transmission related issue. Im not sure if Im missing something in the wiring will correct this (allow the revs to drop when you push in the clutch) or if its something to be corrected with HP tuners. I dont have hp tuners to check but had a tuner come to my house and remove Vats and ECU codes and do a little tuning with the car on jack stands. I have a youtube series that covers the build if anyone wants to see it, videos start off kinda crappy and get better over time https://www.youtube.com/watch?v=FodoN_njblM If anyone has any input or ideas Id really appreciate it, -Meph Quote Link to comment Share on other sites More sharing options...
crapforum Posted May 31, 2015 Share Posted May 31, 2015 Lol I just posted this exact same thing in the HPTuners forum. Issue is that your ECM is programed for an auto and it has throttle holds and blah blah blah. Check out my thread, you have to grab spark and DFCO tables from a manual car and transfer them over http://www.hptuners.com/forum/showthread.php?51612-Engine-waits-before-losing-RPM-with-0-throttle Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted May 31, 2015 Share Posted May 31, 2015 Even the manual system needs some tuning: I was getting no engine braking during autocross and tuner reduced one of the idle speed parameters significantly to help. These cars are tuned to allow drop from higher rpm to idle really slow to reduce emissions I think the parameter was IAF-idle air flow, but Im not certain. You can drop it to zero and the car still runs. But it is much more snappy on the throttle and a lot more like an old school cable controlled throttle. If your car is DBW, you probably want to turn down your pedal rate-my car was way too twitchy. Quote Link to comment Share on other sites More sharing options...
Meph Posted May 31, 2015 Author Share Posted May 31, 2015 (edited) Thanks for the replies, I was sure it was something to do with an auto transmission ECU. My pedal swing is pretty short between Closed and WOT but its been driving pretty nice, no twitch. I do notice I have very little fuel cut/ coast down. It will almost cruise in 5th indefinitely at 1300 rpm if I let off the gas Now as a temp. fix before the car get to the dyno for a tune I'm thinking of running a normally closed switch on the clutch pedal that will interrupt the VSS when I clutch in, in theory making the rpms drop to idle as if I were stopped, any thoughts on that one? (maybe even on the gas, vss = 0 when pedal = 0% but VSS will be dynamic when gas pedal is even slightly pressed) Just an FYI its a 2004 4.8L (285 hp DBW edition) Edited May 31, 2015 by Meph Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted May 31, 2015 Share Posted May 31, 2015 (edited) That the twitchiness will only be noticed when autocrossing or at a road course. De-sensitizing that DBW pedal was important to keep my ass under me. I was having trouble spinning the car exiting corners. You can actually program how fast the power comes on and off. And my idle speed was set at 1000 and I dropped it to 700 to help with throttle lift weight transfer. Now that the IAF is adjusted too, the car drives more like a carbed car where you can snap the butterflies shut by coming off the pedal fast. Interesting idea with the switch on the clutch-might steal that if I do a dog box. When I started my build, I got lots of folks warning me not to use the DBW setup. I'm so glad I did. Edited May 31, 2015 by RebekahsZ Quote Link to comment Share on other sites More sharing options...
ktm Posted May 31, 2015 Share Posted May 31, 2015 (edited) Even the manual system needs some tuning: I was getting no engine braking during autocross and tuner reduced one of the idle speed parameters significantly to help. I can't recall if its a decay value that is used to control how fast the engine returns to the base idle speed or its in the fuel cutoff/overrun section (the decay value that is). Edited May 31, 2015 by ktm Quote Link to comment Share on other sites More sharing options...
Meph Posted May 31, 2015 Author Share Posted May 31, 2015 I tried the clutch switch today, it didnt work as well as one would hope. The VSS signal takes a second or two to be processed and will cause a kick in power application to the wheels when its obtained. It will also cause the engine to idle too low sometimes, back to the drawing board. Quote Link to comment Share on other sites More sharing options...
Phantom Posted May 31, 2015 Share Posted May 31, 2015 My LS1 came out of an automatic car but JCI sent it to www.chipsbyal.com and the entire ECU was re flashed to a 2002 manual program. I've had no issues with the ECM. Quote Link to comment Share on other sites More sharing options...
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