NefMoto > Technical > Tuning > Boost before fmic + k04 hybrid stage2
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Author Topic: Boost before fmic + k04 hybrid stage2  (Read 932 times)
Dejw0089
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« on: June 21, 2025, 06:26:18 AM »
Hi.
Anyone measure pressure before fmic with bigger turbo (or maybe k04 hybrid)?
I move my map sensor to place before fmic and have weird readings.
It is possibile i have that "restricted" inlet hose?
2.5" inlet pipes. Or i cant mount sensor in that place?
I have 2550+ readings over 5k rpms with 0 WG opened.
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aef
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« Reply #1 on: June 22, 2025, 11:16:18 PM »
you confusing things?

mapsensor between turbo and fmic = hot side = usually higher pressure
inlet pipe = no pressure = should have as less vacuum as possible
0% WG = no N75 working = base pressure = spring pressure only

usually you should have a good fmic (google bar plate vs. fin tube) with now pressure drop
on the intake side of your turbo you should have as no restrictions.
your turbo is happy if you have no high pressure on the pressure side and no high vaccum on the inlet side.

please tell us about your problem again. logs?
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Dejw0089
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« Reply #2 on: June 24, 2025, 04:28:19 AM »
Quote from: aef on June 22, 2025, 11:16:18 PM
you confusing things?

mapsensor between turbo and fmic = hot side = usually higher pressure
inlet pipe = no pressure = should have as less vacuum as possible
0% WG = no N75 working = base pressure = spring pressure only

usually you should have a good fmic (google bar plate vs. fin tube) with now pressure drop
on the intake side of your turbo you should have as no restrictions.
your turbo is happy if you have no high pressure on the pressure side and no high vaccum on the inlet side.

please tell us about your problem again. logs?

I change two smic to fmic and regenerate k04-023 to hybrid stage 2 and have mounted map sensor after turbo - before intercooler.
And now make logs and map readings over 5k rpm hit map limit (2550+) but have mounted gauge in mainfoald and show 1.3bar so difference is 0.2 bar + and my question is : It is normal?
I ask only because I dont want blow up brand new turbo.
I know here are many people with great knowledge.
So first I must move map sensor before throttle plate after intercooler back and should measure pressure before additionally?
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aef
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« Reply #3 on: June 24, 2025, 04:41:25 AM »
0.2bar pressure drop over the fmic is good and totally fine

mount the pressure sensor on the cold side where it has to be and start logging
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Dejw0089
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« Reply #4 on: June 24, 2025, 08:20:21 AM »
Quote from: aef on June 24, 2025, 04:41:25 AM
0.2bar pressure drop over the fmic is good and totally fine

mount the pressure sensor on the cold side where it has to be and start logging
Ok thanks for advice Smiley
I mount it back and start logs and tune forward.
May ask one question? Should I change MAF to the brand new if isbstill OEM? Car is from 2002.
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Dejw0089
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« Reply #5 on: June 30, 2025, 07:10:01 AM »
Ok I move sensor back after intercooler and before throttle.
And now maybe you can give me a tip what can cause that insane boost in mainfoald.
First log is with unpluged hose to WG.
Second is with connected and it is posible that turbo can handle high boost without N75 opened on high rpm-s?
Sorry for my english Sad i know it's bad.
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aef
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« Reply #6 on: June 30, 2025, 07:45:18 AM »
unplugged hose or unplugged connector on your n75?

working as designed i would say
you have to tune your boost pid tables

add throttle plate to the logger
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fknbrkn
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« Reply #7 on: June 30, 2025, 07:50:27 AM »
this caused by faulty wastegate flap or poor quality turbocharger at all
n75 also could be the reason
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Dejw0089
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« Reply #8 on: June 30, 2025, 08:00:18 AM »
Quote from: aef on June 30, 2025, 07:45:18 AM
unplugged hose or unplugged connector on your n75?

working as designed i would say
you have to tune your boost pid tables

add throttle plate to the logger
Unpluged hose. It should only open on spring or I in mistake?
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Dejw0089
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« Reply #9 on: June 30, 2025, 08:06:07 AM »
Quote from: fknbrkn on June 30, 2025, 07:50:27 AM
this caused by faulty wastegate flap or poor quality turbocharger at all
n75 also could be the reason
Can you explain?
Can poor quality turbocharger make to much boost ? Wastegate flap is new and is still K04 Hybrid so size is same as K04-023
Yes N75 could be reason and I buy brand new pierburg and wait to receive it.
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aef
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« Reply #10 on: June 30, 2025, 08:17:02 AM »
If you unplug the hose it will make all the boost it can possibly provide.
Either your Intake is collapsing or your wastegate is pushed open because of weak WG spring.

Unplug the N75 connector and log basepressure please.
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Dejw0089
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« Reply #11 on: June 30, 2025, 08:46:56 AM »
Quote from: aef on June 30, 2025, 08:17:02 AM
If you unplug the hose it will make all the boost it can possibly provide.
Either your Intake is collapsing or your wastegate is pushed open because of weak WG spring.

Unplug the N75 connector and log basepressure please.
Ok but why if I disconnect N75 it work ok but if I unplug hose to WG it isn't work?
If I unplug hose only spring is used to build boost so I should have low bost on all RPM-s range?
Why unplug connector change basepressure read?
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fknbrkn
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mk4 1.8T AUM
« Reply #12 on: June 30, 2025, 09:25:16 AM »
mid-range overboost could be fixed with PID tweaking but high-end where it pulls 1.4+ boost with 0% wgdc caused by non-machined wg port usually
another words: this hybrid sucks

try to bore out wg port for a bit
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Dejw0089
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« Reply #13 on: June 30, 2025, 10:19:40 AM »
Quote from: fknbrkn on June 30, 2025, 09:25:16 AM
mid-range overboost could be fixed with PID tweaking but high-end where it pulls 1.4+ boost with 0% wgdc caused by non-machined wg port usually
another words: this hybrid sucks

try to bore out wg port for a bit
Ok I try sort it out because I think I am missunderstanded. If I unplug N75 (cable) I have 0.4 bar to 0.6Bar at end RPM's (7000)
If I unplug WG hose i have spool peak (weird) boost ~(2Bar) and then goes down to 0.6Bar (6500rpm)
If I have conected all as it should (N75 etc) I have boost higher than I should even with 0% N75 so it isnt only turbo problem because in other causes boost it isnt very high. Only with N75 connected boost when reach 1.4 bar is still high to 7k rpm's. In other situatons with N75 not connected properly over 5k rpm's I have 0.6 bar so why you tell me this turbo is bad?
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aef
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« Reply #14 on: June 30, 2025, 01:14:14 PM »
Quote from: Dejw0089 on June 30, 2025, 08:46:56 AM
Ok but why if I disconnect N75 it work ok but if I unplug hose to WG it isn't work?
If I unplug hose only spring is used to build boost so I should have low bost on all RPM-s range?
Why unplug connector change basepressure read?

please learn how a turbo and n75 works
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