Boost drop and missfire

[Pjhowy]

My mk5 gti started missfiring I plugged it in and read codes for.

Multiple misfires detected
Missfire cylinder 1

I cleared codes changed coil from 1 to 4 and then got code

Missfire cylinder 4

I purchased 4 new r8 coils from awesome gti and still get the same issue, the boost drop has been there since I have owned the car and happens around 4K/5k rpm. I’ve changed DV for the plastic one, new cam follower, and n75 valve at the front of the engine. The car runs nice until around 3/4K rpm when it misfires then after that boost drops from ~19 psi to 5psi at 4/5k rpm.

Any advice would be greatly appreciated as I’m starting to run out of ideas, I’ve removed all boost pipes cleaned and re clamped them but still have issues.

Car was sold to me as stage 2:

HPFP upgrade
Twin intercooler (one infront of other, I hate this I want to change to s3 alloy intercooler)
Basic induction kit that I have changed to a Ramair oversized induction (boost drop still happened before I changed this)
Milltek cat back
Pcv delete (no catch can)

As I said any advice would be brill I have access to vcds aswell so if need be I can run logs. Cheers 

[LC5F]

Hi - are you saying the misfire moved with the old coil pack from 1 to 4 and then with new coil packs the misfire is back but in same cylinder, is that 1 or 4?
Could be a number of things - injector about to die, air leak, even injector seal to head.
The cam cover gasket bolts are only 7lbs torque, but tends to get he-maned down, crushed too thin and eventually goes hard - creating a leak.
Smoke test may be the quickest way to show up a problem.

[Pjhowy]

Yeah missfire moved then got all brand new ones and started missfiring again, I haven’t looked at codes since I put the new coils in so maybe that’s next step, sadly this car loves to not throw codes, took me 30 mins of running full throttle to get a code for the first missfire.

[mjmallia]

Possible injectors.

When I had misfires it was down to the carbon build up on the the intake valves....spent a day taking apart, cleaning and assembly, then she was healthy again.

[pudding]

Have a look at the sparkplugs.  If they're all the same colour, dry and don't have gaps you can drive a bus through, we can out-rule those.

Plugs in the problem cylinders tend to be darker/wetter than the healthy ones, which will help you to narrow things down.

The boost drop could either be the ECU pulling the boost back/closing the throttle due to an issue (usually insufficient fuel flow) or the wastegate isn't sealing properly.

Both conditions usually throw a code, but only if a certain threshold is met or exceeded.  If it's just a momentary dip, that usually doesn't throw a code.

[Pjhowy]

I did think an injector would be the issue due to it pulling back the boost due to the afr leaning out, I took it down the my local mechanic who I know well and he said he will book it in for diagnosis, on the way to the garage it never misfired but still left me with a boost drop at 4/5k.

This could be due to the valves not seating properly also so he will run compression test and if needed clean my valves but to be honest I want that done anyway with the swirl flaps also carbon cleaned with new injectors for peace of mind.

[pudding]

How many miles on the engine?  The valve seats don't usually carbon up enough prevent them from sealing properly. It's just the tops of the valves and the stems that get bunged up.  It's worth asking your chap to do a compression test though, for peace of mind, if you suspect that is a problem.

It could be injectors.  When they start to go, they cause all sorts of running problems.  Sluggish off boost, surging/bucking at low rpms/light throttle, idle misfires and laggy boost.

The injectors are a consumable unfortunately.  Petrol Direct Injection is nearly as big a con as dieselgate.  The problems it causes far outweigh the benefits.

Anyway, have your man look over it and go from there.  Prepare yourself for a chunky bill if the injectors need replacing though.

[Pjhowy]

So dropped it off at garage, bloke came out and took it down the road and it boosted no missfire 😂 first ever time I’ve felt full boost but anyway, it misfired after that and dropped boost, plugged a snap on scanner on and got code P0299 (this didn’t show up on vag-com for some reason) which is boost regulation not reached or something, so we decided to do a smoke test and found my pcv rubber seal wasn’t sealing correctly to my forge delete kit.

He’s got the car now ordered the part and should be able to pick it up later fitted for 80 quick all in, if that fixes all the problems I’ll be over the moon.

Will keep you guys updated because I hate never getting a conclusion to an issue.