Post-Tune Engine Stutter at Peak Torque

[kefi]

Jesus that post I made on tables and reductions is confusing.. to clarify:

There's three tables that limit boost:
1. Boost limit based on atmospheric pressure
2. Boost limit based on IAT2 temperature
3. IAT2 compensation for the atmospheric pressure table (the first table)

It will use whichever of the first two is lower at any point in time. Ideally, you aren't hitting the limits inside of the IAT2 table. If you aren't and are thus are using the limits from the atmospheric pressure table, the compensation from the third table kicks in, lowering the limits of the first table.

Note the large increase (in most spots) in limit on the PA table vs the IAT2 table:

These tables are largely responsible for the massive change in power from season to season. The boost limit keeps going up all the way down to 32F.

This is all unrelated to OP, though. OP probably is hitting fuel pump limit like Hondata said.

 

[aldksgo]

Jesus that post I made on tables and reductions is confusing.. to clarify:

There's three tables that limit boost:
1. Boost limit based on atmospheric pressure
2. Boost limit based on IAT2 temperature
3. IAT2 compensation for the atmospheric pressure table (the first table)

It will use whichever of the first two is lower at any point in time. Ideally, you aren't hitting the limits inside of the IAT2 table. If you aren't and are thus are using the limits from the atmospheric pressure table, the compensation from the third table kicks in, lowering the limits of the first table.

Note the large increase (in most spots) in limit on the PA table vs the IAT2 table:

These tables are largely responsible for the massive change in power from season to season. The boost limit keeps going up all the way down to 32F.

This is all unrelated to OP, though. OP probably is hitting fuel pump limit like Hondata said.

Interesting.

I've sent you a PM Kefi.. not sure but I might've found something similar to OP or something else gone wrong

 

[AnotherFK8]

@kefi @aldksgo @martindtjr @Hondata

Thank you all for your input

Whilst running on the stock tune I did find on the IC hoses had slipped a touch, maybe that’s happened again. I’ll try and see if the pipes are attached firmly as a first.

Then, I’ll run the datalog tonight and seen what the values are doing (boost actual vs target, fuel pressure/pump duty).

Will report back soon!

Cheers

 

[aldksgo]

Let us know!

I too experienced negative behaviour last night.

Couldn't hit beyond certain boost as mentioned. When reaching whatever boost it wanted to stay at, I could very audibly hear loud air escaping noise from in front of my steering wheel.

Turns out that most likely some clamps were not buckled down properly on the rubber hose (for PRLs kit) that connects and bends to the throttle body. Can clearly see now that it is not mounted correctly, so I will need to have that taken care of.

 

[boosted180sx]

without having data, it is hard to say but it sounds like your fuel pump too

 

[02SilverSiHB]

without having data, it is hard to say but it sounds like your fuel pump too

yeah, I was going to say the same...sounds exactly like the fuel pump...like no one saw @Hondata reply about it

 

[AnotherFK8]

@boosted180sx @02SilverSiHB

Thanks for the info. I'll get the datalog on it tonight and see if I can forward some graphs over.

I messaged the tuner to see what troubleshooting they did. They said it's unlikely to be the fuel pump as they've ran more aggressive tunes with similar setups on 100+ FK8's, some 400BHP+. Of the all the FK8's they've tuned none of them have had this problem. Their first guess was to check the boost lines, which I'm about to do shortly.

 

[boosted180sx]

tuners knows that not all engines are created equal.
here in the states, there was a recall for a LPFP issue. I wonder if that is a thing over there? That may be a possibility also.
maybe the car is sensing knock in that area and pulling timing, giving you the sense of a stutter feeling?

The reason why i dont think its a boost leak is because of what you said in your first post.

- Flashing back to stock and retesting. No clicking or stuttering noted.

a boost leak doesnt all the sudden disappear because you ran a stock tune.

 

[AnotherFK8]

tuners knows that not all engines are created equal.
here in the states, there was a recall for a LPFP issue. I wonder if that is a thing over there? That may be a possibility also.
maybe the car is sensing knock in that area and pulling timing, giving you the sense of a stutter feeling?

The reason why i dont think its a boost leak is because of what you said in your first post.

a boost leak doesnt all the sudden disappear because you ran a stock tune.

It's funny you should say that. I know some US spec cars have had issues with their transmissions and have had pump recalls too. Mine seems to be one of the only UK models that has the transmission issue, I'll get onto honda to see if my LP pump needs changing. (My VIN isn't showing as a recall but I've heard that some cars are part of it without being flagged).

Regarding the boost leak, what you're saying makes sense. I wasn't able to check the IC inlet pipe either way. Ktuner isn't showing any knock during the pulls but if it's split second it might not show up.

I'll get a few data logs recorded tonight.

 

[kefi]

I keep forgetting about that damn recall. It's crazy cause I'm starting to see a looot of people running into these mysterious fuel pump issues too.

 

[AnotherFK8]

Managed to get a couple of screenshots. Sorry about the resolution, the windows laptop I use isn't great.

At the point of stuttering at 4200RPM, there seems to be; a drop in fuel pressure (then a slow rise back to full pressure), AFR blips towards lean (max I saw was 12.2, otherwise sitting comfortably at 11.7/11.8), TC press and target begins to tail off roughly in that area.

 

[kefi]

Managed to get a couple of screenshots. Sorry about the resolution, the windows laptop I use isn't great.

At the point of stuttering at 4200RPM, there seems to be; a drop in fuel pressure (then a slow rise back to full pressure), AFR blips towards lean (max I saw was 12.2, otherwise sitting comfortably at 11.7/11.8), TC press and target begins to tail off roughly in that area.

Definitely sounds like the fuel pump. You should be able to see the fuel pump duty cycle from KTuner as well. If it stays at 100% for more than a half second or so it's gonna drop fuel pressure and cause everything you see.

If your fuel pump is OK but hitting 100%, the only route is lowering max air charge or upgrading your pump. You could change AFRs too, but not recommended for anyone but experts.

 

[AnotherFK8]

Definitely sounds like the fuel pump. You should be able to see the fuel pump duty cycle from KTuner as well. If it stays at 100% for more than a half second or so it's gonna drop fuel pressure and cause everything you see.

If your fuel pump is OK but hitting 100%, the only route is lowering max air charge or upgrading your pump. You could change AFRs too, but not recommended for anyone but experts.

Sorry, should have included duty cycle too. Looks like it's not consistent, rising steadily to around 28%, dropping a little and then continuing onwards. But then with some it rises without stopping (the stutter varies with each instance I've noticed, sometimes it's more pronounced than others).

 

[kefi]

Ah, fuck. I was hoping it wasn't that. You're reaching turbocharger targets, but your fuel pump is seemingly failing to keep up for unknown reasons. You should be seeing somewhere around 75-93% duty. Maxing at 24% FPD plus dropping that much fuel pressure at WOT is a problem.

Even with light throttle blips, I'll hit 30-50%. Every time you punch it, it shows the exact same pattern and hits the same invisible ceiling. This tells me strongly there's a physical fuel pump issue.

There's an active recall for pumps and tons have been coming here lately. I see you're already aware.

Just to double check myself here, there isnt anything different about your pump duty readout, right @KTuner ?

nevermind, I'm dumb, thats the INJECTOR duty cycle

 

[boosted180sx]

im sure that is the injector duty cycle and not fuel pump

Sponsored