off idle lean issue?
I installed the 60o hp go efi on a basically stock vortec 350 about 3 months ago. From day one I've had an off idle lean issue. Any time I'm cruising and let off the throttle completely then get back on the throttle the afr will go to 16,17,18, and sometimes almost 19. The engine will stumble and recover a second later. this also happens when taking off from a stop light. Ive changed both fast and slow accel settings as per fi tech customer service with no noticeable improvements. I now have the fi tech installed on the 6.0 ls that I recently installed in the same vehicle. The vortec 350 had roughly 300hp and the new motor should be in the neighbor hood of 450hp. Im having the same issue with the new motor.... Are there any other settings that i should be looking at that would affect the initial throttle opening?
What are you using for fuel supply and do you have a pressure gauge? Can you send a datalog?
I’m running a frame mount 255lph fuel pump mounted close to the take. I have the computer set at 100%for the fuel pump. So no pwm. I have not checked fuel pressure yet. Would be nice if fitech included a port to check fuel pressure... It seems to maintain the afr fine at all other throttle positions including wot so I was thinking that fuel pressure should be adequate. I have turned fast accel up as high as it will allow and have not noticed an improvement. I’ll work on a log and get it uploaded.
I know this will probably have nothing to do with your lean tip in condition. You could possibly have too much fuel pressure at 100% PWM. Get a gauge with thread on back. Fitech offers one for cheap. Drill and tap one of the front unused port caps. Even better, make a hi pressure braided line and mount gauge inside. Fuel pressure is often overlooked. An internal pressure gauge is the number 1 thing I wish Fitech would add. Then we could log it.
When you log, make sure engine is up to operating temperature and show some idle time along with lean tip in.
Hi Fuse1977
I too have the AFR spike just leaning into the throttle gently my car almost dies AFR goes up to about 20 then its good
I have a big cam so very low Vac of 6 I have tried all the things Kirk at fitech told me accelerator pump and fast acc also min and max DTPS ACC
My IAC is at 7 warm
Feels like no fuel but have pressure even change relay and pump and wires.
So did you sort your issue?????
I have heard guys talk about raising the IAC steps to 10-15 on wild cams such as yours. Don't know if that will help, but couldn't hurt to try.
I would suggest never mounting any live "fuel pressure" gauge inside the passenger area.. You need an isolator or an external mount. There are in fact instances where lines have ruptured or started leaking pushing raw fuel into the compartment and igniting..
Quote from RandyO on December 21, 2018, 6:35 pmI would suggest never mounting any live "fuel pressure" gauge inside the passenger area.. You need an isolator or an external mount. There are in fact instances where lines have ruptured or started leaking pushing raw fuel into the compartment and igniting..
I recently ordered an electronic fuel pressure gauge from Speed Hut. Says Fitechefituning.com on the gauge. Pretty cool and very impressed with the quality. I will be posting a video very soon.
I have a theory and possible patches. I wrote a PLC program to run my 70 Nova on natural gas. I wrote the program with several subroutines that are software equivalents to the multiple mechanical circuits in a carburetor. There is a subroutine at idle that meters the fuel and adjusts the airflow via IAC to operate the engine to an RPM setpoint. Then, once off idle, the fuel is metered solely to a target AFR. I think the software problem is the handoff between the two subroutines. I wrote a patch loop in my software to monitor and adjust for a smooth transition. I had a supervisory loop that set the max AFR. Fitech also has this. It's the "max deviation from target AFR" in the pro tuning menu. Factory is +50%. I just changed mine to +30%. I noticed that although the AFR got too lean to burn at 20.6:1, that was the max it would get. When the AFR gets that far out of whack, the PID loop tends to over-react and make the AFR too rich. To FiTech and any other EFI package credit, a variable speed / power output machine dramatically varying in output is damn near impossible to control but just so much. The software must anticipate changes sometimes to keep up. You didn't notice the finer points because carbs run relatively sloppy all the time. They tended to run rich during transition times so you wouldn't have a glitch. Plus, carbs are so much simpler, they were more reliable in that respect. I also changed the AFR setpoint from 1100 RPM to 940 RPM. My manual transmission engine idles at 950. I haven't seen the FiTech program, but it might not be mapping well under 1100 with that setpoint. It has gotten better, fwiw.
Quote from Novafitech on August 4, 2019, 2:15 pmI have a theory and possible patches. I wrote a PLC program to run my 70 Nova on natural gas. I wrote the program with several subroutines that are software equivalents to the multiple mechanical circuits in a carburetor. There is a subroutine at idle that meters the fuel and adjusts the airflow via IAC to operate the engine to an RPM setpoint. Then, once off idle, the fuel is metered solely to a target AFR. I think the software problem is the handoff between the two subroutines. I wrote a patch loop in my software to monitor and adjust for a smooth transition. I had a supervisory loop that set the max AFR. Fitech also has this. It's the "max deviation from target AFR" in the pro tuning menu. Factory is +50%. I just changed mine to +30%. I noticed that although the AFR got too lean to burn at 20.6:1, that was the max it would get. When the AFR gets that far out of whack, the PID loop tends to over-react and make the AFR too rich. To FiTech and any other EFI package credit, a variable speed / power output machine dramatically varying in output is damn near impossible to control but just so much. The software must anticipate changes sometimes to keep up. You didn't notice the finer points because carbs run relatively sloppy all the time. They tended to run rich during transition times so you wouldn't have a glitch. Plus, carbs are so much simpler, they were more reliable in that respect. I also changed the AFR setpoint from 1100 RPM to 940 RPM. My manual transmission engine idles at 950. I haven't seen the FiTech program, but it might not be mapping well under 1100 with that setpoint. It has gotten better, fwiw.
I like what you are saying. I started this site to learn more myself, then it became a troubleshooting site with install and user error. Now it seems a portion is moving towards advanced topics and issues. I see lean to rich spike issues all the time. Some have been able to modify the VE tables to lesson the effect. In effect giving the Fitech a head start.