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I have a Nissan GTR with about 1500hp that I street drive on motec M150 ECU. It is running on 6x ID2600 injectors and I had a question regarding closed loop fuel control in the area where the car is just coming out of idle. The car idles around 1000rpm and I have found that there are certain areas of the VE table Less than 60kpa that I can adjust to get the car to idle really well but then cause the part throttle driveability to suffer and vice versa. With the large injectors and long sample time with low exhaust mass I found it best to disable closed loop under 1300rpm and under 55kpa so that with the infrequent samples I wouldnt get a continuous rich to lean cycle.
Rather than disable closed loop under 1300rpm are there any other things I can try to get closed loop working a bit better in the 1000-1500rpm range at low throttle?
You shouldn't need to disable the closed loop control to get good results. It's all about choosing a suitable gain for the closed loop control, as well as a sensible period at the exhaust mass flow you're seeing at idle. For the GTR engine I tuned for pikes peak I was using a period of 2000 ms at 2.5 g/s and 1500 ms at 10 g/s to give you some idea of numbers that I found worked well. I also use a gain of around 70-75%. What you're wanting to do is give the change in fuel delivery sufficient time to actually register in the exhaust gas and be detected by the lambda sensor. If you have it right you should track target closely with no wild oscillations.
I'm a little confused however as you shouldn't be using the same zones for idle and light throttle cruise - They are typically pretty independent and exclusive of each other. You may find it beneficial to have slightly tighter break points around the idle transition area for both rpm and MAP, and lastly check what your cam targets are doing around this point just to make sure there isn't something weird going on with the cam control that's causing weirdness with the engine VE.
Spent some time on this yesterday and today and made some positive progress and have closed loop working down to 900rpm, idle is around 1000rpm with the large 282 cams and 4.1 displacement motor.
After watching the cold start webinar it clicked that most of the trouble spots were during warmup and was able to spend some time with the Coolant Temp Volume and Coolant Temp Fuel AIM tables which I didn’t adjust after making the switch from ID2000 to ID2600 injectors. I was able to tweak the VE table and the coolant temp volume to work together better with closed loop as they seemed to have been fighting each other a bit prior.
I will also look at adding some more granular rows and columns to the VE table to avoid the overlap as well as look at the cam control around the 50-70kpa area as well next.
As far as closed loop around idle I have the period set to 2000-2200ms and the gain is 80%.
Cam Advance is set to zero until 1500rpm and 125kpa as well
For coolant temp fuel comp I essentially had to add some fuel until around 40deg C and then pull some fuel out from 40-60 deg. Probably need to tweak the VE table some more and add distinct break points at 55, 60, 65, and 70 Kpa as currently they are set at 50 and 75.
One last question - there is a slight drop in the idle and lambda when I go from park to gear during warmup - I couldnt find a specific table or setting to address this, any thoughts?