RCP Phx
NAXJA Forum User
- Location
- Phoenix,Az
It did pass, but trying to move forward (on my own) in the mean time! I figure "if I can't tune my computer to my engine, I'll try and tune my engine to the computer"!
Just a couple of comments, and I understand that many know these points already, but I just thought I would chime in based on my experiences tuning these motors.
Fuel tuning:
Strokers need bigger injectors, roughly in proportion to the increase in displacement. I typically recommend 27 lb/hr injectors, but then again, there are many choices in the 24-27 lb/hr injector range, and typically 24# injector brand X will not flow the same as 24# injector brand Z. Sounds somewhat trivial, but this makes it difficult to predict fueling needs given a specific build based on previous tuning experience. In general, I've seen a wide range of fueling requirements on what I would consider are very similar builds.
Don't assume that the fueling is close based on how the Jeep drives or looking at the fuel trims. The JTEC engine controller has a range of authority of +/- 33% for short term and long term fuel trims which means a total range of +/- 66% . The long term fuel trims in most calibrations are only applied to closed loop operation, however in some (not many) calibrations one of the long term fuel trim cells is applied to open loop fueling in the positive direction. Also, there are 153 fuel cells in your main fuel lookup table, while there are only about 22 long term fuel trim cells, so the long term fuel trims are very "choppy" compared to the actual fuel look-ups. What this means is that your tune can be quite a bit off, and the ecu will learn the fueling to some degree, the short term fuel trims will keep the engine running around lambda 1 in closed loop, but typically this will not help you at high engine loads while in open loop.
Regarding evaluating the air fuel ratio, looking at a air fuel ratio gauge while driving the Jeep will not help us much as far as tuning goes. It is better than doing nothing, and will certainly give us an idea if we are grossly rich or lean, but the engine is mapped in rpm and map cells, and logging provides a way to accurately evaluate the air fuel ratio through most of these fuel map cells.
The SCI data stream is capable of 500 bytes per second update rate, however not so with the generic OBD2 data stream which is what SCT and other scan tools typically use. Since there is not a readily available and reasonably priced tool that can log the factory SCI data stream, the next best thing is parallel logging the signals being fed into the JTEC, and this is what I recommend. Using the generic OBD2 data stream, you will typically see about one to four updates per second, polling three or four PIDS, that is not very useful. Alternately using a Zeitronix ZT-2 logger as an example, you will receive about forty updates per second for each channel logged. By tapping into three wires of the JTEC, map signal, cam position signal, tps signal, you will have a high resolution logging solution. To measure the air fuel ratio error, we need to eliminate the factory fuel trims. Unplugging the stock O2 sensors will prevent the JTEC from going into closed loop. Disconnecting the battery power from the JTEC for at least a minute will clear any fuel trims. Once those two things are done, measured air fuel ratio will be a result of base fuel pulse width calculation without any influence of fuel trims.
Contact Ryan Hogan too. he did all of my tuning. Great Guy and really dialed in the stroker.
Is this Chris?