Engine bogging in WOT after gear change
 

Hi to all,
I have a problem and I don't know how to proceed...
I have a 2015 86, 45k miles, HKS supercharged by 4k miles. Since last week the car was working fine without any problems, I use it as a daily with 1 track day a month (full day or a full weekend).
Recently I have a strange issue, after changing gear near the rev limit in wot the engine stops climbing the rpms for a second and if I keep my foot down eventually the rpms start increasing again.
This happend to me like 4 times, it's not persistent.

My engine modifications are:
-Hks supercharger
-Hks oil cooler
-Hks spark plugs
-Avo 3 bar MAP sensor
-Hks EL headers with cat (GT Spec)
-Milltek overpipe 2,5"
-Custom front pipe 2,5" no cat
-Custom catback 2,5"
-Greddy oil pan baffle
-Ecutek Tune

Stock injectors and fuel pump. I think the problem is mechanic because since last week the car was running fine, the only thing that has changed is the external temperature (like 35°C) No CEL or whatsoever.

Here is the log of a 3rd gear pull
https://datazap.me/u/gt86forcenew/lo...?log=0&data=15

Here is the log of the problem, 2nd to rev limiter, change to 3rd gear, back in wot, rpms stops climbing, i keep my foot down for a couple of seconds until the car starts pushing again and after that I stop accelerating.
https://datazap.me/u/gt86forcenew/lo...?log=0&data=15

My tuner unfortunately it's not available until the end of the month and I want to have other ideas about what the problem might be.

Sorry for the english, It's not my first language.

Seems like your AFR is off; you are leaning out. Rpms are climbing just not as aggressively, right?

Your AFR is like 16-17 initially before it drops to your target.

https://datazap.me/u/gt86forcenew/lo...7&zoom=129-181

Exactly! Any idea why or what to check? :cry:
First time happend during a track day, but only once... I've done like another 30 /40 laps that day with no issues.
I'm thinking fuel pump or injectors but it happens only after the gear change... if one of this things is broken maybe the problem should be in a specific rpm range.

I would be concerned because that is pretty lean, right? If it is intermittent then it is hard to say. For the record, I’m learning how to read these so real novice, so don’t take what I say as Bible.

This seems to show that you are WOT but actual trottle position was reduced to 15%. A safety net maybe:

https://datazap.me/u/gt86forcenew/lo...6-210&mark=113

Here the fuel rail pressure seems to drop:

https://datazap.me/u/gt86forcenew/lo...2-239&mark=152

Fuel pump is going? Fuel starvation during aggressive shifts with a low fuel tank? I really don’t know.

Buy some MAF cleaner, clean your MAF, ensure your MAF is sealing correctly, and then give her a go.

Both of the last 2 major issues I've been directly related to with difference FI kits both traced back to the AFR's going mad off of MAF seal/cleanliness issues.

Is your tune speed density ??


Can you log manifold pressure a lot of aftermarket map sensors go bad


Do you have blow off valve if so check its operation carefully. And for leaks or damafed or loose hoses. Have you clamped all the hoses under intake manifold ?

He did log MAP, right?

https://datazap.me/u/gt86forcenew/lo...34&zoom=95-212

What do you think about my comments? Was there a drop in fuel rail pressure because of a mechanical problem or was that by design/tune or a safety net?

Haha yeah he did log map, too late at night.


Its looks ok


Something weird going on with fueling though the di fuel pressure changes with injector opening time and rpm.



He should probably lookat checking low pressure fuel pump, although low fuel pressure usually effects top end more


Check the di computer is grounded and any intake or exhaust leaks usuall suspects

Thanks for the replies!

Just a couple of questions, I'm dumb and not very mechanically inclined :D

@steve99
Yes the car is tuned in a hybrid speed density using MAF on low rpms, or at least that is what my tuner told me.

Low pressure pump is the one in the tank right? By top end do you mean? My problem seems to be at the top end, over 5,5k rpms. By more do you mean that the problem should be more accentuated?

I need to check for exhaust leaks in the headers right? The rest of the exhaust system should not interfere or not?

By DI computer do you mean the injector "ECU" correct? I have to check if everything is connected or?
I don't have the knowledge/tools to disassemble and bench test the computer. If it's a cpu problem my only option is to replace it, but i want to keep it as my last option...

@Irace86.2.0
Yeah i am a little concearned because as you say, it seems really lean. I'm also trying to understand how this things work..


A faulty DI Injector can cause this problems? I have a friend who just changed one because the seal broke, but his car had a CEL and was making popping sounds.


First thing i'll check for leaks and clean the MAF to see if anything changes, but usually i'm not that lucky.

Yes di computer is injector ecu under bonnett


Yes check for any exhaust leaks before or near o2 sensors once you get say meter past o2 is not going to effect readings.


Check for intake leaks or leaks due bov not sealing correctly


Check map sensor reads 1 bar ie same as atmospheric with ignition on but motor off.


When engine running you usually see something like 0.3-0.4 bar at idle if its more than that its likely got some form of leak



Its difficult to diagnose hybrid speed density as we dont know what the parameter setup is ie where changover occurrs from maf to sd or any other custom tables in use it might be triggering some weird boost related cutout but if its run before for a fait period ok on this tune ist very likely hardware fault

I would get your log to your tuner. As @steve99 said the hybrid MAF/SD tunes require more fine tuning.