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2016 octavia cxx engine underboost

Posted By Blackdog Sunday, September 08, 2019 11:03:39 AM
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Blackdog
 Posted Sunday, September 08, 2019 11:03:39 AM
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Having some heartache again. 65 plate octavia 1.6tdi cxx engine code with an under boost problem.Back story with car bought through English auction by trader and when arrived it had underlying problems. Trader wrote to previous owner and got a call back from him. Apparently the car had developed this fault and 5k later he called his losses and auctioned it.
Not sure what exactly he got for his 5k but new turbo was one thing.
Car has 75,000 miles and appears otherwise in very good order.
Now to where I'm at!
Leak tested intake system and all is good.
Vacuum checked and present.
Blanked both egr valves for testing and have temporarily had them mapped out.
Ran with exhaust off and front lamda sensor removed to eliminate dpf and exhaust restriction.
Visibly checked throttle flap on intake manifold for functionality.
Tried some bits from another working car just for eliminating, maf map sensor and n75 valve.
Timing all checked and pinned spot on.
Nothing obvious broken under rocker cover all 16 rockers intact and cams visually look good.
Wiring from n75 to ecu and fuse box load tested and all good.
Suspected faulty turbo so had it sent to be tested, was told some signs of carbon were present so had it reconditioned calibrated and refitted.
Car is still no better, where do I go from here?


Assumption is the mother of all f😨😱k up's!!!!!
Blackdog
 Posted Sunday, September 08, 2019 11:15:55 AM
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Just to clarify this car has the big aluminium cooler as the inlet manifold and I've not yet had that flow tested.Also to note the car feels lazy all the time and the fault logs in 4th gear around 2000 rpm wot.
The boost is at around 2000milibar at this time and I believe it should be around 2300.
If I bypass the n75 and pull the turbo wide open I can achieve maximum boost in 4th gear at 1750rpm wot so mechanically the ability to make boost is there.
Some vac readings at turbo actuator vacuum pump pulls 29 ins hg consistently measured at n75 supply side.
26ins hg at actuator on idle and 16 ins hg at actuator on full throttle before fault logs.
I'm starting to lean towards fault in ecu not commanding n75 enough but would appreciate some opinions


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McTech
 Posted Sunday, September 08, 2019 4:46:35 PM
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BD

Have you had a scope on the control of n75 PWM? Whats the duty cycle like at WOT? Do they relate?

Has this engine got intake runner flaps? (I have no access to data at mo)

Old fashion internal resistance test on n75 comparison with new.

So I guess its an underboost fault code... any FF with it.

At 16hg WOT is the actuator a full reach or is 16 still too much?

Si


I O, I O, its off to work I go!
Blackdog
 Posted Sunday, September 08, 2019 5:04:48 PM
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No access to scope although I see signs the n75 has been scoped by previous garage. Heatshrink on the wires.Can't just remember about the duty cycles at the moment I've confused myself so much with this I'd be guessing trying to remember.
No manifold runner flaps on this engine just a big aluminium water-cooled intercooler as an inlet manifold.
Yes underboost fault code. Ff?
At 16hg the rod is about 70% boost


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McTech
 Posted Sunday, September 08, 2019 5:40:47 PM
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FF - freeze frame.

I guess if 5K has been spent its got a new n75 (what make?)

Supply volts at n 75 OK?

I'd want to know duty cycle and PWM at n75 - actuator test and vac gauge might show something???

Sunday night time for liquid sedatives.....Smile

I O, I O, its off to work I go!
Robski
 Posted Sunday, September 08, 2019 6:18:47 PM
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No mention of scan tool, DTC(s) inc FF data or any test methods i.e. 'leak tested intake' ..... how ??

Rob.
Blackdog
 Posted Sunday, September 08, 2019 8:29:11 PM
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Mctech freeze frame data not to hand but il get hold of it. I can get the car to fault most runs in 4th gear slight uphill and wot. Freeze frame rpm always around 2000 rpm and map always around 2000mbar.Yes supply voltage at n75 tested. Battery + on 1 pin and load tested. Ecu controls ground to n75 wire load tested between ecu and n75.
Yes n75 also replaced and genuine, swapped another from one of the owners stock to be sure.
Will run actuator test with vac guage when time permits.
Rob codes read with delphi as it's what I have, verified with vcds when at the tuners.
Smoke tested intake, no leaks but blanked egr valves later as we couldn't prove they weren't sticking intermittently.


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K And R
 Posted Monday, September 09, 2019 4:05:03 AM
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BD

"Smoke tested intake" at what pressure ?


"No access to scope although I see signs the n75 has been scoped by previous garage" about time you had access to a scope .


As for it being scoped before, punture marks etc does not prove a scope has been used.


Kev.

ps. about time you updated your open thread,s


"If you dont KNOW how it works, don,t try to test or fix it"
Monday, September 09, 2019 5:01:29 AM by K And R
Blackdog
 Posted Monday, September 09, 2019 5:14:16 PM
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Kev smoke tested at 15psi.
Not had time to get missing data today but will soon.
Will tidy up other threads now.


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K And R
 Posted Monday, September 09, 2019 5:28:40 PM
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bd

"The boost is at around 2000milibar at this time and I believe it should be around 2300." Kev smoke tested at 15psi."


I know 15psi and 1000millibars (1 bar) are near enough the same but WHY use mixed system, it,s stupid.


That,s how NASA fucked up the hubble.


Kev.

"If you dont KNOW how it works, don,t try to test or fix it"

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