FR-S "Pulsing" While Accelerating
 

After installing my UEL header, over pipe, HKS Legamax catback, and OFT Stage 2+ off the shelf tune my 2015 FR-S has developed a problem where it will "pulse" or "surge" when the engine is under load (such as going up a hill) while accelerating moderately with 30-50% throttle. The problem is still present, but not nearly as severe/noticeable when accelerating on flat ground. It does not occur at all with 75-100% throttle.

According to my OFT there are no stored codes. I do not hear any exhaust leaks. The car doesn't shake or rock violently or anything like that. The engine speed simply rises and falls a few hundred RPMs while still increasing (kind of hard to explain...). The A/C is not on when this occurs. It does not occur when getting moving from a stop, only when accelerating moderately with the clutch fully engaged.

My car has been sitting for the past 6 months because I have been unable to drive it for medical reasons. My last fill up was in March with Shell 93. Before parking it in my garage I added some gasoline stabilizer/preservative. I have taken it out and driven it around the neighborhood every other week or so to keep the tires from getting flat spots and for "fun".

Does the ECU require time to "relearn" after flashing a new tune and this surging is just it "learning"? Maybe it's just from old/bad gas?

It could be one or both of those.

I'd suggest you (or someone) take it out and run it for a few hundred miles, then put some fresh gas in it.


humfrz

Does it do this at a certain engine temp?

Engine temperature doesn't affect it. It's just as bad when the engine is cold as it is when the engine is hot from driving around all day

Slipping clutch?

I'm thinking crap gas as well.

It doesn't do it under WOT. If it was the clutch slipping, then I'd assume it'd be really bad at full throttle, but it doesn't occur at all. My car only has about 50,500 miles on it on it, so I hope the clutch isn't bad already.

That's what I'm leaning towards too. The stabilizer/preservative I used claims to keeps gas "fresh" for at least a year. I have about 1/3 of a tank left. I'll try getting some fresh 93 and see if it goes away or is at least reduced from diluting the old gas.

The surging doesn't seem like misfires, at least not the kind I'm used to from my turbocharged VR6. If they are misfires, then I'd expect there to be some codes stored. I'll try to get a video.

I did some reading about the D4S fuel injection system in these cars and could the pulsing possibly be from the car switching back and forth between port and direct injection?

For example, it's most noticeable when driving up a long steep hill in my neighborhood. The engine is under high load since I'm going up a hill, but I'm only giving it a moderate amount of throttle because I don't want to drive like an ass in a neighborhood. The car is in third gear at about 3000 RPM going 30 or 35 MPH.

Could the car be thinking, "I'm under load, direct injection time! But wait, I'm only getting 20-30% throttle so I'd better switch to port injection. Man, this load won't let up so it's direct injection time!" and keep going back and forth and won't make up its mind? This doesn't happen at all at WOT, which I believe is direct injection only, so the car didn't have the option flip flop on the fuel injection method.

I've got an identical situation: steep hill, 30mph.
Stock 13 FR-S.

Grinds right up the hill without surging or acting weird in any way.

The tune looks like a significant variable.
Stock ECU will go through a re-learning period after you disconnect the battery.
Though I've never noticed surging soon after an unplug.

What version tune? I am running the v2 stage 2 tune and I have noticed what you're describing before so I'd venture it is the tune causing it. I haven't tried the v4 tunes yet so maybe they're better.

You have an OFT give us a datalog:bonk:

try modify engine load limits


i got nice results and very smooth car, on NA petrol, with those Wayne's engine load limits


800 .88
1000 .90
2000 .92
2200 .95
2400 1.07
2500 1.11
3000 1.10
3800 1.02
5000 1.55

I'm running the stage 2+ V4 tune. My car should meet all requirements (catless header, premium fuel, etc).
I forgot about that ability... I'll get a log next time I drive the car.
I'll give these a shot.

A datalog will tell us if you have an exhaust leak or tune problem in a heartbeat, should be thye first thing you do next time for future reference.