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I'm helping a member out with some tuning and we ran into something very odd. I also noticed something between Tunercat and Tunerpro that I don't quite get.
I'm tuning in the ANJF broadcast code, but it's typical for others...
1. Tunercat vs Tunerpro
The open loop %change to AFR vs coolant temp, for whatever reason, has different values between Tunerpro and Tunercat for the same bin. There appears to be about an 8.5 point offset between the two. Not sure why that is. The open loop %change vs MAP tables match eachother.
2.) So on this member's situation, I'm watching the commanded AFR shown in TP diverge tremendously from what the ECM should be commanding based on the bin values.
Where A = coolant temp table value and B = MAP table value
What's happening is that when he gets to temperatures over say 68F, the commanded AFR that TP reports gets increasingly leaner than what this formula calculates it should be based on the bin values. The bin values suggest a commanded AFR of 13.39, but TP is reporting a commanded AFR of over 15.
The MAT reading is remaining constant while I'm observing this. MAP is holding constant at about 35 kPa. So the only thing I see varying is the coolant temp.
So the question is, what else could be driving the open loop commanded AFR besides coolant temp, MAP, and air temp?
I went back and re-read RBob's posts... The man is still a legend... RIP.
Turns out my Open Loop AFR calculator tool incorrectly was using the formula for Power Enrichment.
When I converted my tool to reflect his formulas, everything matches. TP's reported commanded AFR matches the calculated AFR exactly... but after it settles in.... which then raises another question...
His TP data starts when he starts up the car at ~61F coolant temp. I then see the commanded AFR start out at 11.4:1, then over the course of about 1.5 minutes, it gets up to the final commanded AFR that matches the calculated AFR of 15.39.
In the factory ANJF bin, the start up enrichment decays out after 4 injector firings. But this decay doesn't start until 25 injector firings. So at ~1000 rpm, at one injector firing per revolution... isn't that like 1.5 seconds? 25/1000 * 60 = 1.5 sec? 1.5 sec to start the decay out, then a few milliseconds for the actual decay to occur?
Certainly not over a minute anyway.
So why does it take over a minute to reach the final commanded AFR?
Also referred to as after start fuel.... These get decayed out in a short period of time. About 2 minutes on a cold engine (say 40* F). and within a few seconds on a hot engine.
RBob.
So I guess this explains what I'm seeing in the TP data. The question now is how is this decay calculated?
I experimented by going into closed loop much earlier.
It does go into closed loop as commanded (I see the INT start to move), but the after start fueling is still in force. The INT drops abnormally until the after start fueling decays out and he gets up to 14.7:1.
The member I've been helping has been giving me TP data of the car starting. From that data I could figure out how long it was taking for the startup enrich to decay out to the commanded open loop AFR, since I can now successfully calculate start up AFR and open loop AFR.
Basically it was taking about ~85 seconds.
In the linked post by Elky, says
Assuming 1000 RPM after startup, there will be 1 injector firing every 60ms, so the 50 injections will occur in 3000ms (3 seconds). After that, enrichment decay begins, but it does not happen all at once. Decay only occurs every 4 injections (Scalar 0x41E), until the enrichment has been decayed to =0.
Conveniently enough, the member's car idles at ~1000 rpm immediately after startup.
At the coolant temp he starts at, his factory ANJF bin calls for 25 injects on the table Startup Enrichment Decay Delay vs Startup Temp (0x441).
ANJF also calls out ~19.7% on Startup Enrich, Decay Amount vs Startup Coolant (0x44F)
So I stared just playing around with the numbers and when did the following calculation, I got...
(25 x 19.7/100)/.06 = 82
Where the .06 is the 60 ms at 1000 rpm that Elky mentioned above.
I'm thinking the 82 calculated vs 85 actual can't be a coincidence... the 3 second difference being maybe in the idle rpm fluctuating up a little here and there and/or some rounding error.
The only puzzling thing right now is if I increase the RPM in the calculation, I would expect the decay time to be shorter, but it actually increases, which doesn't make sense.
So either I'm not thinking about something correctly, or this 82 vs 85 really is a huge coincidence.
