Boost cutting out

[vwmike1991]

Hello, new to the forum so please be kind.

Recently picked up my Mk5 and been having a baaaad time with the little f***er.

After a cam chain inc guides, cam follower (which was so bad it had a hole in), cam belt and water pump, cam position sensor inc wiring repair, mot, service and brakes sat waiting to go on I now have a boost cut issue.

The car spools and seems to hold pressure fine but sometimes when the car is loaded up and on full chat it cuts the boost and like coughs cutting all of the power for a few seconds then cracks on giving it the big licks. Am I right in thinking my diverter valve is on its last legs? Only had this problem many moons ago on a 2.5T focus and that was the boost control solenoid.

The car is completely standard and only done 78K but I think it was left to its own devices by the previous owner who had it from new who must of only replaced things when it was undrivable.

The battered little turd is a great laugh and a world away from my DSG R I just need to get to the bottom of this as its going around Oulton park before too long and I refuse to get passed by my mates redtop corsa when it throws a wobbler and doesn't want to pull anymore

[Ytee]

I can't help with the solution I'm afraid, but I did have the exact same thing happen on track yesterday. It's been fine ever since. It was seriously hot at the time and I suspect it was some kind of turbo self-protection or similiar shinanigans. No warning lights though. I'll read the codes when I get a chance to see if anything popped up.

[muff1991]

welcome to the forum mate.
it could be the DV, PCV or any other boost leak related areas! start there first!
The first things that popped into my head is a faulty N75 valve (boost controller) & possibly a worn inlet cam or HPFP tip... especially if the cam follower was smashed to pieces!

[flyGtiGuy]

Recently picked up my Mk5 and been having a baaaad time with the little f***er.

I feel your pain... Scrapping mine because it's turned into a money pit.  Hope yours fares better! 

It had similar issue which turned out to be the DV - visibly cracked when I got it off.  Also caused it to make an exhailing sound when coming down from a hard rev.

Have you started with the basics and checked all the hoses for cracks/loose connectors?

Good luck!

[ROH ECHT]

Are you certain it is a boost loss? And not a fuel loss?
I am suspicious of the CF which had a hole in it and what damage it made on the intake cam's tri-lobe.
Have you got VCDS for looking at fuel data? You know someone who can?

[bajric98]

Have you looked if your PCV valve is in good condition?
I changed my PCV yesterday and noticed a big difference in how smoothly the engine was running now!
Also my boost is not cutting out anymore, but I'm not sure if it is the new PCV that fixed that issue. I guess time will tell

[vwmike1991]

Hi everyone, thanks for the warm welcome and the replies I have managed to change the DV over and it seems to of fixed the issue, holds boost strong and no more surge between gears so roll on track time and we shall see if it cuts!

The DV that was removed was a pretty old unit but seems to be OK not great but not totally shag**d either PCV was next on the list anyway with time I'm planning to work through the known weak spots over time and try my best to make it a solid car.

I don't think its a fuel issue as surly that would throw a code or cause rough running? Still no codes on the scanner so my fingers are crossed.

DS2500 pads fitted with pagid everywhere else today just an oil change before oulton and that's it throw it on the circuit and see which barrier I can punch it through :).

Its no more a money pit that my old accord type r which this was bought to replace really just this is actually usable below 6000rpm, do miss the V-Tech though ....

[vwmike1991]

So after changing the DV to the newest revision and things getting better, last night whilst exchanging blows with a v90 on a private run way .... It let me down and cut the boost again.

I am properly stumped now theirs no signs of anything being amiss no codes no management light etc just 10-15 seconds of sweet f all before going back to normal.

It only happens when its open wide and fully loaded up on the throttle boosting away till it randomly has a change of heart and takes it all away from me.

Since last posting its had a new cam chain and belt, fuel pump thingy lol, brakes, fluids, x2 oil changes and various random bits of maintenance so its not exactly in a state of disrepair anymore.

I've sat reading posts all day and pretty much everyone replaces the DV and that sorts the issue, am I missing something?

[ROH ECHT]

I don't think its a fuel issue as surly that would throw a code or cause rough running? Still no codes on the scanner so my fingers are crossed.

The fuel system doesn't store a code sometimes.
CEL or Dash Lights are only for Safety and Emission related codes. All others will be stored/saved for when read.

My LPFP (in-tank electric delivery pump) had failed. Data showed it dropping to 1.2 bar while having a 4 bar minimum target....and no stored codes.

Symptoms; Under full load/throttle, it would boost quite high but not have much power. Then near 5k rpm it would backfire and nose dive from the cutting of power. No codes at all were stored. Sometimes a failing G410 sensor will cause it to cut power when the ECU doesn't receive an accurate or any pressure report. And why it is called a thrust sensor by some...but it is the low fuel pressure sensor. It is mounted on the side of the HPFP/rail pump.

If you want, you can check if the PCV is holding boost pressure. Disconnect the PCV-to-manifold tube where circled. Wipe the oil from it and blow into it with a good bit of force. It should seal 100%...if not it is allowing boost pressure to escape.

[vwmike1991]

I'll have to check the fuel thing properly when I'm next out in the car I'll plug my Carly in and monitor things (I'll try I'm useless really).

With the PCV would it not show when the engines running to remove the dipstick and see if the car struggles?