N75 fault? VAGCOM experts welcomed!

[sion_kwl]

Hey Guys, Got what feels like a misfire at peak boost (3-4krpm), vagcom turned up today so I went and ran some logs.

Checked misfire count, nothing. checked knock detection and nothing out of the ordinary, so I checked boost pressure, and it's overboosting by approx 2-300mb vs requested pressure.

I've been checking for boost/vac leaks for the last few days and there isn't one, and there's no tears in the solenoid pipes. Turbo and wastegate were recently replaced as that was destroyed (symptoms were there beforehand too) so I'm now suspecting the N75 itself.

can anyone think of anything else I might have missed before I fork out?

 

[Bigjohn84]

If you think ur getting a misfire log in to engine then messuring blocks, then block 15-16 then you can see what cilinder is having a misfire

Sorry just seen you checked that lol

 

[Gaz7]

Logged on 115 to verify overboost ? I.e requested vs actual ? Also, any variables, new turbo/ actuator ? Unplug n75 and log what you boost to

 

[sion_kwl]

yes logged 115 to find that, and 114 to check duty cycle. duty cycle was 95% solidly, boost went from about 300mb under boosting to 300mb over boosting, if I were to guess I'd say the n75 was sticky (old turbo blew oil through almost all the vac lines) and yes it's had a new turbo and wastegate recently.

I'll log one tonight with it disconnected.

 

[Gaz7]

Actuator only run would confirm whether you're just needed to adjust actuator,

Standard actuator (new one) ? Should see about 5 psi I think

 

[sion_kwl]

consistent 4.7-4.8psi all the way through the run, so I'll order an n75 and see how that goes

 

[Gaz7]

Yeah, sounds like a good bet !

 

[sion_kwl]

Well, wasn't the N75. replaced that and it's still doing it :/ could failing coilpacks cause boost spikes without misfires? that's the only thing that hasn't been changed now...

 

[Gaz7]

Have you check lambda corrections and lambda figures ? Injector durations etc. And check timing pull. Knock sensor. Might be fueling. Pumps like dying off 80-120k

 

[sion_kwl]

I'll run some more logs later tonight/tomorrow.

 

[sion_kwl]

for the sake of a fiver I think I'll change the fuel filter too, I'm up to 130k pushing stage 2 and I doubt its been changed.

 

[Bigjohn84]

If you need a lambda sensor I have a brand new Bosch one £93paid £30 posted to anyone, someone else is Intrested but won't get back to me till tonight so first come first served

 

[sion_kwl]

That's not a wideband sensor is it?

 

[Bigjohn84]

Mate I'm not sure when it comes to sensor I just but the best one lol

 

[Bigjohn84]

Not really supposed to post stuff like that on hear if you need anymore info just let me no mate

 

[Bigjohn84]

It's a wideband mate I just checked online, it's ok as someon else wanted it but I'd thought I'd ask you just incase

 

[Gaz7]

Brilliant. Paid £93 for one literally last night John

 

[Bigjohn84]

Lol sorry mate lol

 

[ibizacupra]

Well, wasn't the N75. replaced that and it's still doing it :/ could failing coilpacks cause boost spikes without misfires? that's the only thing that hasn't been changed now...

if you are changing n75 because of misfires you are barking up the wrong tree

coil packs, plugs usual suspects
maf can also cause
as can issues on valvetrrain
as can lean running from weak fuel pump and/or under reading maf

 

[Gaz7]

Bill, I think he changed the n75 because of over boosting. Says it "feels" like a misfire, but misfire counter doesn't show anything on VCDS.