Hondata

2002 Civic Si
Kmanager 4.2.5
Relevant modifications:
3 inch intake with Ktuned velocity stack
OBX race header
Greddy catback
RDX 410cc injectors
lightweight flywheel
stock A3 IM (without the variable intake runners)
Ktuned TPS
MAP and IAT sensors are stock
Stock IAC
Kpro acquired with the car - previous owner didn't know he had it

The issue is that I am experiencing bucking at around 20-30% throttle from about 2k to 2.5k. So this is basically throttle open when exiting a low speed corner. My autocross club loves to throw a tight bend before the finish and I am exiting those corners like a broken lawnmower.

The log shows that my AF is bucking around and no amount of fuel tuning seems to fix this. I disabled the tip in retard entirely because I was actually getting ignition retard rather than ignition advance. Since I've done that, this problem is less bad, but it is very difficult to launch the car smoothly without too much riding on the clutch. The problem manifests itself in every gear except first, although I'm going to guess that first is so aggressive that I don't have time to notice any irregularities.

On some occasions, if I don't get aggressive from the start, I will bog soon after engaging the clutch. Those are pretty dangerous situations especially if you are pulling into traffic. So to compensate, I usually do a kind of "mini launch" to get the RPM out of the problem area as soon as possible.

I've really racked my brain on this one. I thought maybe it was the VTEC threshold, then maybe the target AF and the interpolation from medium load to heavy load, then I though maybe it was the ignition advance, but I just don't know. I even ran more ignition advance, which I think was helpful a little bit.

I've attached the data log. The fluctuations in RPM and the jumps in AFR are exactly where the bucking manifests itself.

I suppose I should qualify this by saying that the car is worth $0 and I am not taking it to a tuner. The closest tuner is good and has done a car for me before but they cost between $500 and $1000 to get the car tuned, and it just isn't worth it on a 15 year old Civic. So any help you can provide me is very very very very much appreciated.

Update - but still looking for input

I "artistically" smoothed the fuel maps and then added about 30% to fuel trim. I knew this would make the AFR very rich, but I wanted to see the effect on driveability. Overall, it was much better. The idle was especially improved. It was very smooth and without any lean popping.

My conclusion thus far is that 1) the race header is leaning out the AFRs substantially compared to the base map and 2) targeting lower AFRs at all points on the fuel map is going to improve driveability.

I've changed my target AFR for low to medium load to 13.7 and for high load to 13.0.

If you can suggest any other general changes based on my setup, that would be great.

Hijacking my own thread, I know, but if more people did this it would be easier to find answers to commonly asked questions.

I cannot tune around the hesitation issue. Rich AFR, lean AFR, more or less advance, cutting the B18 wire on the wire harness, nothing made a substantial difference.

KTuned confirmed that the lifespan of the rotor style TPS V2 is "finite" - I read that to mean about two years. Well I have 50k on mine. New Acuity TPS sensor with Hall Effect operation is being overnighted now from KSeries Parts. If that works and solves the issue, I will post for POSTerity. Haha get it?

The TPS signal looks ok. Battery voltage is all over the place. AF is spiking high in places when the injector duration would not suggest so.
I would guess that it is either the o2 sensor false reading or a fuel system problem (injectors, fuel filter etc).

Thanks for the input. I replaced the fuel pump and the pulsation dampener. I clearly needed a new fuel pump. But the issue remained.

I had NGK heat range 6 plugs. My guess is they were left over from my turbo setup. I threw a set of NGK 8s in there annnnndd...problem solved! The misfiring must have been pre ignition caused by a hot plug and the exhaust popping should have been a give away.

Regarding the voltage, my alternator is literally six weeks old. My check battery light is stuck on despite all systems passing checks. Any thoughts as to where I should look next? Or does it even matter now that the car is running brilliantly?

Remove and clean down to bare metal all the engine bay grounds. Check the fuse box connections from the alternator and battery. Check the fuses are not dirty or corroded.