Weird boost problem.......

[tstrahonja]

My car is very jerky on part throttle..for example if i drive 50 km/h in 4th..and press throttle to 50 % it startts to accelerate slowly..then suddenly boost hits 1.3 bar then drops to 0.5 then to 1 bar and then drops again and now it is running good on part throttle..
I have the Cupra for 2 yrs now and this was happening all the time so i just got used to it..
When on full throttle it overboosts at 1.4bar on 3000 rpm and drops to 1 bar at 6000 rpm
However...
2 days ago when i press the gas car runs excellent as usual but my gauge shows no boost..
On part throttle it shows boost until 0.5bar..then it drops to 0...
And car boosts like usual..
Ive tested all hoses and boost gauge..all fine, no leaks and boost gauge works ok..i used a bicycle pump
My gauge is connected between charge pipe and N75..
Today i tried my friends N75 and everything is the same..
MAF is ok..its new.
The only way that boost gauge can show 0 would be if the n75 is open and letting all the preassure go to the intake pipe....
Ive tried bypassing the N75..so ive disconnected it from wastegate line and from the charge pipe..left it electrically pluged in...pluged the holes so that there are no boost leaks...
Now boostgauge works fine and shows boost all the way....
Maybe my friends N75 is also broken?
Could this be MAP related?

 

[tommy2008cupra]

never heard of boost gauge plumbed in there? try plumbing it on vac lines on left hand side of the engine where there should be a green nipple cut that off and put it on there instead

 

[-=Rob=-]

Me neither, I reckon that could be causing your problem...

 

[tstrahonja]

Well i was driving it like that for 2 years..no problem at all..

 

[tstrahonja]

the thing is when u connect boost gaue be4 n75 it doesnt show vac but only boost..
so when ure idleing it show 0 bar and not -0.8 or something..
today ive connected my gauge to DV line so the boost reading is not affected by n75
when i floor it on 3000 rpm i get 1.8 bar....waaay too much...so that confirms that n75 is working weird.....

 

[-=Rob=-]

Check for a leak on the N75, maybe where you had the boost gauge connected before...
I actually had a similar boost problem like you before, up and down boost on part throttle, I changed the N75 and it fixed it, maybe try another one of no leaks?

 

[tstrahonja]

I did check for the leaks...from N75 to actuator...even try pumping air into wastegate line to observe that wastegate is moving and working..all good
So that leaves me with 2 lines...line from charge pipe to N75 and line from N75 to intake pipe..
Ill check them....

 

[tstrahonja]

So ive checked the boost line from charge pipe to n75...all good
Tried another N75...everything is the same...
N75 just doesnt wont to open wastegate for some reason...
Going to connect vagcom in few hours...

 

[tstrahonja]

,Group A:,'115,,,,Group B:,'118,,,,Group C:, Not Running
,,RPM,Load,Absolute Pres.,Absolute Pres.,,RPM,Temperature,Load,Absolute Pres.,,,,,
,TIME,,,,,TIME,,,,,TIME,,,,
/min, %, mbar, mbar, STAMP, /min, °C, %, mbar,STAMP,,,,

2320 , 78.2 , 2060.0 , 1060.0 , 29.29 , 2360 , 17.0 , 85.5 , 1250.0,,,,,
2480 , 110.5, 2020.0 , 1450.0 , 29.99 , 2560 , 15.0 , 70.6 , 1600.0,,,,,
2640 , 129.3, 2000.0 , 1740.0 , 30.59 , 2760 , 15.0 , 67.8 , 1860.0,,,,,
2840 , 149.6, 1990.0 , 1980.0 , 31.19 , 2960 , 14.0 , 68.6 , 2080.0,,,,,
3120 , 162.4, 1960.0 , 2140.0 , 31.79 , 3240 , 13.0 , 61.6 , 2130.0,,,,,
3360 , 160.2, 1940.0 , 2090.0 , 32.39 , 3520 , 12.0 , 58.0 , 2050.0,,,,,
3640 , 152.6, 1940.0 , 2010.0 , 32.99 , 3760 , 12.0 , 56.5 , 2000.0,,,,,
3880 , 153.4, 1930.0 , 1980.0 , 33.59 , 3960 , 12.0 , 54.9 , 1970.0,,,,,
4120 , 150.4, 1910.0 , 1930.0 , 34.39 , 4280 , 12.0 , 58.0 , 1940.0,,,,,
4400 , 154.1, 1900.0 , 1930.0 , 34.99 , 4480 , 13.0 , 59.6 , 1920.0,,,,,
4600 , 153.4, 1880.0 , 1900.0 , 35.69 , 4760 , 13.0 , 60.0 , 1870.0,,,,,
4840 , 152.6, 1860.0 , 1850.0 , 36.29 , 4960 , 14.0 , 60.8 , 1830.0,,,,,
5040 , 148.9, 1850.0 , 1830.0 , 36.89 , 5120 , 15.0 , 63.5 , 1820.0,,,,,
5240 , 147.4, 1870.0 , 1820.0 , 37.49 , 5320 , 15.0 , 65.5 , 1810.0,,,,,
5400 , 142.9, 1880.0 , 1810.0 , 38.10 , 5480 , 15.0 , 75.3 , 1800.0,,,,,
5480 , 23.3, 1000.0 , 1570.0 , 38.80 , 5400 , 14.0 , 0.0 , 1180.0,,,,,


can someone explain these please...does this look good?
wastegate duty cycle looks weird..too low?

 

[tstrahonja]

anyone?

 

[tstrahonja]

graph seems ok....

 

[Mat]

wish my boost graph looked like that!

 

[tstrahonja]

new problems...
i cant make logs because i hit limp mode every time..
code is 17963..maximum boost exceeded
i have connected boost gauge between boost pipe and n75 valve so i can what is n75 doing..
there should always be boost in that line because n75 is redirecting it to wastegate..however..there is some boost on part throttle...when i say boost i mean boost in the line between charge pipe and n75...for example...driving 15mph in 3rd gear...i press throttle a bit...there is boost..0.1bar..the same second i press full it drops to 0..so n75 doesnt send anything to wastegate..therefore wastegate stays closed and car overboosts...
maf is ok
coilpacks are ok
N75 is ok
vac and boost lines are ok
i am suspecting MAP...giving wrong boost reading...
can it be condensation in ECU?
i am positive that 1 injector gives less fuel than other 3...maybe it got worse thru time..can a faulty injector cause this problem?
please help guys

 

[tstrahonja]

problem solved
it was a weird combination of things that happend...
1st my cheapo 15$ boost gauge broke and was reading much more boost that it actually is...started to read 1.8 on overboost...but no limp mode..so i was concirned....then it got really cold..-10,-15 deg celsius wich tends to make our cars boost even more due to colder air, + the fact that ive put golf5 gti FMIC wich is huuuge ..meaning even more cold air...so naturally it started hitting limp mode...in the meantime 2 of my coils started to play up under boost...
so i bought 2 new coilpacks, put them on, combining with the 4 old ones..solved spluttering under boost, but still limp mode...adjusted actuator a little..was on 13 threads, now it is on 12 and thats it
working excellent
in the meantime bought another boost gauge....reading 1.4 bar on 3000 rpm and then drops to 1 bar and holds....