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Thread: Timing and Fuel not following maps on light throttle run

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2017-12-08 01:38:47
Timing and Fuel not following maps on light throttle run
So, I was doing some datalogging to establish a baseline for tuning my SR20DET (S13) and the data is not adding up to what I was expecting to see. I did a light throttle pull to 6200 rpms being careful to keep it in vacuum for the whole run. (Throttle held at 30%) So, here's what's odd. When I plot ignition timing vs. load or AFR vs. load the points don't coincide at all with the timing and fuel maps. For example: at 6000 rpm the ECU is reporting a TP of 120 which is clear off the map (map only goes to 104) this should be full boost territory, but with the light throttle it's actually still in vacuum. The AFR is 10.5 which is probably correct to the TP and RPM, but the timing is at 30 deg. It also looks like it is staying in closed loop up to 4800 rpms and 96 TP. Again this should be full boost territory, but its running 25 deg of timing instead of the 10 in the map, and the AFR is 14.5 when it ought to be below 12 at that load and rpm. Can anyone tell me what's going on? I'm thinking there is a secondary table in the ECU that compares the calculated TP to the TPS reading and ignores or modifies the TP before accessing the maps.
Engine setup:
Stock S13 SR20DET, stock t25, top mount log manifold, stock maf and injectors, FMIC, greddy knockoff intake

Pics of data.

2017-12-08 07:40:41
Let me see if I can at least embed those images for yah.

2017-12-11 20:35:05
I found the problem. I was using the wrong memory location for logging TP. I had TP pointing at 41DE and apparently the correct address for an S13 redtop is 4292. Now the logged timing shows up spot on to the ignition map and the load values look a lot more reasonable. I'm guessing 41DE pertains to just air flow or just rpm but not the full TP calculation.
2017-12-11 22:37:03
Oh wow, good find. Sorry I'm no help with this sort of thing. I hope you can continue to make good progress now.
2018-08-19 02:22:38
TP value sanity check
I'm hoping someone who has tuned a redtop SR20DET with stock MAF and injectors can confirm what I am seeing in my recent datalogs.

Since I don't see any option for attaching a pic, I'll describe it. What I'm seeing is that the MAF voltage maxes out at 5.11v @ 7000 rpm and 73% throttle, and TP=76 (but the stock TP fuel and timing scale goes to 104)

Applying the common calc for TP~(Q*K/N) /256 along with the K and VQ values from the rom it looks like the 6 or so cells in the highest load, highest rpm region of the fuel/timing maps would not every be used since the MAF voltage is maxed out before you'd ever get to that part of the map. In order to reach the last load column of the map (TP=104) the MAF would have to be maxed out at 5000 rpms. So effectively the last load column (104) can only be accessed at 5000 rpm or below and the 2nd to last column (92) can only be accessed below 6000 rpms. Does this sound right?
2018-08-19 08:27:38
Yah, that sounds right to me. OEMs like to put a margin of safety in everywhere, and that includes the resolution of their tuning maps.
Maybe someone else can confirm though, I've not tuned with that type of setup before.
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