power loss at 4000rpm

[muff1991]

hi all, car seems to boost up as normal, but as soon as it hits 4k (ish) it literally cuts the power, or shall I say reduces it dramatically for a good few second accompanied by the DV psshh as if ive just let go of the throttle (i haven't)! if i keep the throttle pinned.. the power will all of a sudden come back around 4.5k (ish).. and rip the last bit to red line.

I have VCDS but am new to it, and don't know exactly what to start with.. - i defo have no codes on auto scan

This issue started (or i noticed it) the same day i noticed my cold start issue... depending on temperature outside, either engine starts then cuts out, or engine starts and runs but has laggy throttle until 2k revs then picks up normal. (obvs until 4k haha). I'm sure its related somehow.

any advice is appreciated.

[pudding]

Data log a 20 minute drive from cold, and then chuck the csv file into Excel for analysis.

You can only log 12 channels at once, so do a couple of runs.

On run one, choose these measuring blocks.  I can't remember the exact names of them, but something like :

Engine speed
Fuel rail actual
Fuel rail specified
Low pressure fuel pump
MAF
Boost pressure actual
Boost pressure specified
Intake Air temp
Throttle angle
Lambda regulator

On run 2, go with:

Engine speed
MAF
Throttle angle
Boost Specified
Boost actual
Lambda
Throttle angle
Ignition retard cyl 1
Ignition retard cyl 2
Ignition retard cyl 3
Ignition retard cyl 4

From the data you should be able to spot anything obviously wrong.  See if boost and rail pressure specifieds and actuals match.  The ignition retard should be very small numbers.

Massive ignition retard, boost request not meeting target, big lambda adjustments, fuel rail pressure drops etc can all cause the symptoms you described.

[bobby_fodge]

It's not the clutch slipping and then biting again?

[muff1991]

@Pudding thank you very much for such a full detailed process.. exactly what i was hoping for :-) I only see this post today! at which point.. over the weekend, i replaced the cam chain cover gasket (as you know, I done the job twice) and found out afterwards I couldn't use the same gasket.. i think its a 1 trip pony... sooo small oil leak!

possibly related.. and I have to put my hands up here.. but when replacing the gasket, i only went and found that the bottom center bolt of the cam chain cover was loose! last time i must of twizzled it in with the skinny T30 extension by fingers and when torqueing up the 7 bolts.. i must of torqued the T30 right next to it! felt like an absolute plumb mate!!

Anyway, while doing this, cleaning everything up.. I replaced the VVT cam adjuster solenoid. (the sensor going into the cam chain cover) as someone had broken the electrical plug on it previously. I had temporarily repaired it months ago and the car run great! but with the heat, it was brittle and snapped again. so put a new one in and jobs a gooden.

so with all that said.. this weekend I achieved and replaced:

a new VVT cam adjuster solenoid fitted
an oil leak free cam chain cover
an ECU reset as the battery was disconnected for a few hours
a tiny tiny tiny air leak in the bung on the inlet manifold (part of the Forge PCV delete)

took the car for a drive afterwards, once it had warmed up and cam chain had some oil squirted all over and i gotta say.. it drove perfect! more low down grunt.. power just hits and goes.. traction light was wanting to slap me up side the head, and it pulled smoothly all the way through from 2k - 6k! in 2nd and 3rd gear! It bypassed 4k cut off i was getting like it wasn't even a thing!!!

so I'm pleased to say with a mixture of all those, its fixed. whether it was down to a small boost leak, small oil leak loosing crank pressure, dodgy VVT cam adjuster solenoid or what I personally think most of all... is a good ECU reset! whichever the cause, if not a bit of all.. its done and I'm very happy.

my only concern or doubt with the fix.. is my cars been acting very weird in the colder temperatures and the power at 4k could sometimes be intermittent depending on warm or colder conditions. This weekend after the fix, when i drove it was 12 degrees Celsius. so come the colder whether in the next week or 2 i will tell better. no doubt ill be back for more help otherwise haha. (although the way it was behaving.. its fixed  )

@bobby_fodge thanks for the suggestion.. as always I'm more than happy for anyone to throw ANY clue or ideas around as it all helps with diagnosis. but the clutch is feeling solid (for now  )

thanks again for the input.. @Pudding I am still going to do these logs once i get the chance! just to see if everything is behaving anyway.

[pudding]

Sounds like you might have sussed it! A non-functioning VVT adjuster would certainly cause problems! 

I can't remember if the VVT defaults to full advance, or full retard (NEVER go full retard, lol) with the solenoid plug disconnected but if locked onto full advance, great for low and midrange, not so good for top end.   If it locks onto full retard, it'll be gutless low down but OK up top..... in theory.  Either way, the engine won't run great if it's not working.

Keep an eye on it.

Mine's been the same way for 18 months now, it prefers the summer!   That could point to a weak fuel pump or under reading MAF, but all of it's been replaced.  So yeah, I need to log my own car at some point 

A slipping clutch would register as a blip on the rev counter and no gain in acceleration or mph, and you'd hear it as well!

[muff1991]

its weird, because the VVT solenoid would throw the EML as open circuit, when it had disconnected/slipped off (obviously). but whether it was connected or not with the EML on as open circuit or not.. the car drove the same. the car even drove fine for months before with it like this, which is why I kind of ruled this sensor/solenoid out when the problem started.

But I defo think, a mixture of that new sensor (think its the N205 for anyone who doesn't know what I'm referring to) plus its new firm connection and the ECU reset (battery disconnected for a few hours) has certainly done the trick! But like I said i will tell better if its solid when I drive it next with the outside temps being mild ish (under 10) as it was intermittent and im sure outside temp may have had something to do with it. But it got to the point it become more constant problem.. it was so bad! I even got a mate to film holding a boost gauge and you could literally see the boost needle drop then bounce around ( up and down, like an N75 issue) but replaced that to find nooo difference!

Measuring the MAF is something I want to do as well.. I read it should be around 10g/s when holding the revs at 3000rpm.. not sure if this is stationary or driving though?

funny you mention fuel pump too, as back in the summer last year (when all was running great) I heard a small whining coming from the pump, only when I was sat in neutral in the traffic, I was leaning over the seat and could defo hear it was the pump. But the second I revved it would disappear, it only done it a couple of times, and haven't heard it since! so maybe an underlying issue with that too! possibly something to do with the cold start issues lol

maybe related too.. so last of all.. in the summer my drivers door wouldn't unlock every time, it was playing up! to the point I would have to use the key to unlock it.. put this down to the locking mechanism thing, but then all of a sudden after a few months.. it started working again.. and still working fine now! wtf lol