MK5 Golf GTI

All Things Mk5 => Mk5 General Area => Topic started by: JoshB on May 21, 2022, 03:21:34 pm

Title: Down on power…
Post by: JoshB on May 21, 2022, 03:21:34 pm
So it started about 2 months ago, I didn’t really notice it at first, it was actually my other half that mentioned it felt slower than usual. Then one day going up a hill in 6th, I had to drop it into 5th to make it go… very unusual, but it still generally pulls quite well.
There’s a loud induction/whistling noise and the exhaust definitely sounds boomier.
I did have some gold/brass coloured flecks in my oil filter when I changed it last week (only about 5-6).
Cambelt was changed on Thursday and there’s no change.
I’ve inspected the DV (rev G) and PCV this morning, both fine.
Checked the inter cooler pipes and there’s no oil around the seals (looking toward the front of the car, the metal pipe on the left does move about in the clip, is this normal?)

Been out for some runs with the CarScanner app (sorry I don’t have VCDS) and come back with these.
(https://i.ibb.co/84qzs6R/BC19-C785-891-C-4-FC1-9487-B62328-FC8-D2-F.png) (https://i.ibb.co/MZ5qhvr/157-EDA0-B-D0-BE-4112-AA96-6-E85-D636-CB78.png)

It didn’t feel like I’d lost any boost, no kangaroo’ing etc, but I did occasionally feel the power go a bit wavey if you like. Seems to be making good boost still so I’m confused…

Any help is appreciated.
Title: Re: Down on power…
Post by: JoshB on May 21, 2022, 05:31:30 pm
Just been and took the air box off as I thought the whistling might be down to a cracked airbox. Nothing there.
It idle’s a bit erratically, hunts between 730 and 770rpm, is this normal? Occasionally drops to 690.
I tried disconnecting the MAF and the revs dropped, bogged down a touch but quickly went back and if anything idled better without the MAF. Brought the P0100 code up but cleared when I plugged it back in. Still no fault codes…
Oh and the “calculated boost” sits at -11psi at idle…
Title: Re: Down on power…
Post by: ROH ECHT on May 21, 2022, 06:32:22 pm
Generally, when you unplug the MAF, you want to give it a few seconds to stabilize. If it does so...this points to an air inlet leak, or a failed MAF.

With a diagnostic tool, I.e. VCDS or capable OBD, you can check mass air report data and bring that data back to be questioned. You could also look for confirmation of air inlet leaks within the fuel trim data as instructed here;


Title: Re: Down on power…
Post by: pudding on May 22, 2022, 02:27:37 pm
Exactly the same symptoms as mine. It's OK when in boost but the throttle response getting into boost and driving around town is horrible, it's like driving with the handbrake on.  It used to pull itself along easily on the motorway and like yours, I also have to drop down a gear just to maintain a constant speed.

I changed the turbo yesterday and it made zero difference.  I data logged MAF, boost, lambda, both fuel pumps, VVT, intake temp etc etc over a 30 min drive and absolutely nothing wrong, everything in spec.

The brakes aren't dragging.

I'm at a loss now. My next areas to try are replacing the green boost O-rings as the new turbo is a bit noisier than it should be, and checking the throttle body.  Whilst stabbing the pedal with VCDS up, I did notice a quite a bit of delay in the throttle body responding.

Partially plugged cat is another theory I have.

Bloody car  :grin:

P.S Occasionally mine tries to stall when pulling up to a junction then recovers, and this whole issue is intermittent as well.  Some days it's a missile, and some it's a complete slug. The fact it's capable of normal performance, even if temporary, suggests it's mechanically fine.  No idea what is going on as logging shows nothing and there's never any fault codes.  Tiny long term trims as well, <2%.

I'm nearly at the point of handing it over to a diagnostics place, but if I've fired the parts cannon at it, I'm not sure they'd find anything wrong either  :grin:
Title: Re: Down on power…
Post by: ROH ECHT on May 22, 2022, 05:07:28 pm
Sometimes after much searching, some found tiny leaks in the oddest and unlikely places. From seams in the intake manifold to a brake booster diaphragm. Good luck with it, guys.
Title: Re: Down on power…
Post by: JoshB on May 22, 2022, 07:03:51 pm
I’ve ordered a new MAF sensor just in case, bang that in first then go looking for intake leaks.
I’m pretty sure it is an intake/inlet leak as like I say, it’s making the typical induction sucking/whistling noise.

Thanks for all the pointers!

Shame a new turbo made no difference to yours Pudding, as soon as you said about the turbo I started looking at K04 hybrids…!
Title: Re: Down on power…
Post by: G-olf on May 22, 2022, 08:31:05 pm
If they are full throttle logs in a single gear and i'm guessing they are, then maybe it looks like its dumping its boost? If this is the case then something must be telling it to do so.
As with most turbo cars,  expect a spike above target, perhaps dropping slightly below as the system gains control then to follow its requested reasonably close.
A bit like a torque curve on a dyno plot with an initial spike on spool
Perhaps try again with the requested boost also plotted on the graph?
I don't think it should jump around as much as that graph shows, someone on here will be able to advise you better  :happy2:
Is the map sensor reading something like you would expect?
Title: Re: Down on power…
Post by: pudding on May 23, 2022, 08:38:44 am
OK, so this is interesting.

This morning before setting off for work, I did a basic settings throttle adaptation in VCDS and the car was an absolute rocket ship for the entire one hour journey.  All of the symptoms described by Josh and myself, completely gone. It's the best it's driven in months.  It was like holding a dog back on it's leash. A night/day difference to how it was on Saturday & yesterday.

With the throttle being the primary driver input, it makes sense if that isn't functioning correctly it will kill the performance. I just need to figure out now if it just needs a clean, or replacement. Hopefully not the latter as they're about £300!

Based on this, I think I can safely out rule any general mechanical and fuelling issues  :laugh:

@JoshB (https://www.mk5golfgti.co.uk/forum/index.php?action=profile;u=102442) it was worth doing the turbo anyway as the shaft had about 1mm of in-out play (the new turbo had zero play in any direction), which is why there was gold crumbs in the oil. It wouldn't have been much longer before the wheels started rubbing on the housing.  I also discovered 2 of the manifold to head bolts were finger tight, so no regrets there  :happy2:
Hats off the Borg Warner. The turbo put in 170K miles before getting to that point, not bad at all.

If your scan tool can do a throttle adaptation mate, give that a try.  If you have cruise control, see if the speed adjustment on that is more responsive than the throttle pedal, just as another experiment.

Title: Re: Down on power…
Post by: JoshB on May 23, 2022, 09:58:30 am
As I said I’m going to try and have a look round the inlets today, but as above, it’s like its struggling to breathe almost. Everything from the turbo side suggests it’s healthy, so the only other thing I can think of is fuelling. R-Tech did recommend I fit the stronger HPFP internals when it was remapped, but only if I went to map4/5, which I haven’t yet, I’m still at (or was) 250bhp/280ftlbs.

I can’t monitor fuel adaption unfortunately, it’s either HPFP internals or VCDS this month…
Title: Re: Down on power…
Post by: pudding on May 23, 2022, 10:27:27 am
Internals won't hurt regardless, but VCDS is also worthwhile.  Its exactly what you need in situations like this, or maybe OBD11 as that can do a lot as well.

Well good luck with yours, it's gotta be something simple.

In an attempt to sort mine, I've ordered a used MK7.5 Golf R throttle body off ebay.  They're actually closer to £500 now, not £300.  Inflations a killer.






Title: Re: Down on power…
Post by: JoshB on May 23, 2022, 02:04:31 pm
I thought about the throttle body, like you say, there’s some pretty clean ones on eBay for £40-£50.
Had a good look round the engine this morning and there was nothing obviously leaking, but to be fair I didn’t spray any parts or poke around too much (don’t like running it without the airbox on…).
Did another couple of logs and every looks hunky dory… but the cars feels like it’s flat up top.

(https://i.ibb.co/PYh06ZC/C74-B2264-58-F9-493-D-B5-C2-60618-D99-D206.png)

Just the bottom one, the short term fuel trims seem to be all over the shop, nice and flat under “normal” driving, but plant my foot and it sinks to -8% and then jumps to +5% when it catches up. And that’s the theme, it’s mostly between 0 and -10%. I’m hoping the new MAF cures it but I’m still leaning towards an inlet leak somewhere because of the noises.
Title: Re: Down on power…
Post by: rich83 on May 23, 2022, 02:15:56 pm
Internals won't hurt regardless, but VCDS is also worthwhile.  Its exactly what you need in situations like this, or maybe OBD11 as that can do a lot as well.

Well good luck with yours, it's gotta be something simple.

In an attempt to sort mine, I've ordered a used MK7.5 Golf R throttle body off ebay.  They're actually closer to £500 now, not £300.  Inflations a killer.

I'm not sure the "parts canon" is the most economical way to find out what the issue is but it might work  :signLOL:

Mine sometimes feels like the boost comes and goes when on full throttle which is a bit sh*tty. I think the hpfp could do with replacing as I am putrefy sure if I logged it the fuel rail wouldn't quite be keeping up with the demand. That's what it feels like to me anyway.
Title: Re: Down on power…
Post by: pudding on May 23, 2022, 02:50:19 pm
I thought about the throttle body, like you say, there’s some pretty clean ones on eBay for £40-£50.
Had a good look round the engine this morning and there was nothing obviously leaking, but to be fair I didn’t spray any parts or poke around too much (don’t like running it without the airbox on…).
Did another couple of logs and every looks hunky dory… but the cars feels like it’s flat up top.

(https://i.ibb.co/PYh06ZC/C74-B2264-58-F9-493-D-B5-C2-60618-D99-D206.png)

Just the bottom one, the short term fuel trims seem to be all over the shop, nice and flat under “normal” driving, but plant my foot and it sinks to -8% and then jumps to +5% when it catches up. And that’s the theme, it’s mostly between 0 and -10%. I’m hoping the new MAF cures it but I’m still leaning towards an inlet leak somewhere because of the noises.

The throttle body p/n has changed, yet again, to: 06F133062AG, making it the 6th revision!  I just got the newest one I could find on ebay.

You'll be lucky to see anything obvious.  GTIs like to hide the issue away for you to find like an Easter egg hunt, the little sh1ts!

10% lambda swings aren't too bad.  When mine does it's annoying thing, the short term swings were plus/minus 15-20%, which felt like horrible flat spots and wavering power delivery on gentle acceleration.

So yours is more of an issue up top, rather than down low?
Title: Re: Down on power…
Post by: pudding on May 23, 2022, 03:09:09 pm
Internals won't hurt regardless, but VCDS is also worthwhile.  Its exactly what you need in situations like this, or maybe OBD11 as that can do a lot as well.

Well good luck with yours, it's gotta be something simple.

In an attempt to sort mine, I've ordered a used MK7.5 Golf R throttle body off ebay.  They're actually closer to £500 now, not £300.  Inflations a killer.

I'm not sure the "parts canon" is the most economical way to find out what the issue is but it might work  :signLOL:

Mine sometimes feels like the boost comes and goes when on full throttle which is a bit sh*tty. I think the hpfp could do with replacing as I am putrefy sure if I logged it the fuel rail wouldn't quite be keeping up with the demand. That's what it feels like to me anyway.

Tell me about it.  Not my preferred method of diagnosis!

I've been quietly looking to upgrade to a MK7.5 Clubsport or a TCR, but after looking at the prices of those things, I've decided to keep the MK5  :grin:  So really, what I've done here is a proactive canon firing to buy it some more life  :grin:

Yeah probably worth a logging session.  I got weird behaviour like that when I was mucking about with 2+ maps.  It was a mixture of K04 surge and fuel pump not keeping up, in spite of it being a Loba.
Title: Re: Down on power…
Post by: rich83 on May 23, 2022, 05:46:12 pm
Definitely. Gonna re-buy VCDS ((stupidly sold it 6 years ago)) (gonna get the NET version) this summer so will be able to log it.
Title: Re: Down on power…
Post by: G-olf on May 23, 2022, 08:15:57 pm
It may be worth a phone call to them, explain whats happening. They will point you in the right direction.
Have you tried it with the other map settings? maybe one with less aggressive settings and is it still the same?
Retarded timing can sometimes make it feel flat?
What about an air leak before the MAF? something which it can't fuel for? Just ideas


Title: Re: Down on power…
Post by: pudding on May 24, 2022, 09:52:19 am
That's the good thing about VCDS, you can log up to 12 measuring blocks at once, but that isn't enough for the full picture, so I do two runs.

Run 1: For general fuelling and boost health.

Engine speed, MAF, intake air temp, Lambda requested, lambda actual, current fuel pressure (LPFP), fuel rail requested (HPFP), fuel rail actual, Boost pressure requested, boost pressure actual, throttle position.

Run 2: For checking detonation as the engine will be fully up to temp.

Ignition advance, knock regulation (ignition retard) cylinder 1, " cylinder 2, ", cylinder 3, " cylinder 4, engine coolant, VVT angle requested, VVT angle actual.

If you enable 'Turbo', you get instantaneous readings, rather than the slower non-turbo refresh rate, which can help if you feel the requested and actuals are slow to match.

With that you will get an overall picture of what the engine is up to.

I normally just load up the logging, close the laptop lid and go for a 30 min drive.  Get home, save the log file to my desktop PC and assess the results over a glass or 5 of wine.

I might also get a cheap windows tablet and use VCDS's gauges for some live monitoring action.





Title: Re: Down on power…
Post by: JoshB on May 24, 2022, 01:25:27 pm
I’ve just been out doing some data logging, got the screen below? Can anyone help???

(https://chrisduke.tv/wp-content/uploads/2015/04/dangertomanifold.jpg)
Title: Re: Down on power…
Post by: pudding on May 25, 2022, 08:32:23 am
Lol, is that a Fast & Furious reference?  :grin:
Title: Re: Down on power…
Post by: JoshB on May 25, 2022, 10:04:57 am
So I replaced my MAF sensor last night, and it actually made a difference. Not massive but deffo pulls stronger and smoother, but the reading has also gone down quite a bit. Was previously around 220g/sec, but with the new sensor it peaks at 160g/sec, but as said it’s now a bit faster…

Had a good look round the engine bay and spotted a couple of things.
1) This bracket between the coolant and brake fluid reservoirs has snapped which beans the pipes are free to bounce around. Not sure if it matters but it’s not good. Unfortunately the bracket is attached to some sort of plastic tube that the pipes go down inside. Not sure how the hell you're supposed to replace it.
(https://i.ibb.co/C1MN0Xf/12-F92-D8-D-AD00-4583-B254-DEB59-A4-B60-E3.jpg)

And 2) I noticed that my HPFP was covered in oily petrol. The connector in particular was full of fluid (smelt more oily than petrol). I’ve never had the pump off so not sure if it’s normal to spill a bit when you replace the cam follower? I didn’t do it. The underside of the airbox was also covered, you can see some on the vac pipe to the PCV above. But according to my logs, the fuel rail is getting 125bar, and it doesn’t weep on idle.
(https://i.ibb.co/ZXgt1gG/25-AF9-B4-E-836-C-4413-889-E-FE554352-CC59.jpg)

Again, I’m not sure if any of this matters but it’s things I’ve noticed if it jogs anyones thoughts?
I’ve sent an email to R-Tech last night, see if they reply and see if they can fit me in for a diagnostic.
Booked in for all 4 wheels refurbing and trying to sort my rear calipers before I tried to sort this… turning into a right money pit…
Title: Re: Down on power…
Post by: pudding on May 25, 2022, 02:06:22 pm
220 and 160 g/s would roughly equate to 270 and 200hp respectively.  Strange that the new MAF is reading considerably lower.  Did both tests hit the same rpm, in the same gear, and both full throttle etc?

Can't see the pics currently but oil around the HPFP and under the airbox could be a PCV issue or a torn O-ring on the HPFP?  They can get pinched quite easily when sliding the pump back into it's hole.

Money pits indeed, but once sorted they're damn good cars.  I've been putting off the wheel refurb for years as it's the final cherry on top, which my car doesn't deserve until it starts behaving itself  :grin:
Title: Re: Down on power…
Post by: JoshB on May 25, 2022, 08:40:16 pm
Well I think I’ve got to the bottom of it, but not fixed yet.
Was digging around in the engine bay and wiggling all the vacuum pipes until I finally heard a hiss. Found this little bugger right under the HPFP off the brake booster. Another symptom was the engine bogs down if you pump the brake pedal at idle.
(https://i.ibb.co/gtSzTmC/CC7-D01-E2-5158-4887-AD0-A-ED2-A61-A63-D54.jpg)

It pulled off with ease. It looks ok and there was no obvious signs of damage to the pipe but I instigated a “repair” anyway, PTFE tape solves leaks on my radiators!
(https://i.ibb.co/xLygT3G/3416572-B-212-D-4-A27-A6-C5-6213398-EA111.jpg)

Took some getting back on and stopped the hissing. And whilst I was fiddling, Phil from R-Tech rung me up to reply to my email. Had a good 20min chat (much appreciated!) and he thought it was definitely a vacuum leak somewhere. His first question was actually if someone had changed the map, and luckily I’d actually checked that in the morning! As soon as described the leaky oil he was adamant it was the top PCV pipe.

Looked fine to me but I’d heard they go brittle, a single wiggle resulted in catastrophic failure…
(https://i.ibb.co/Ld7xzwX/5-B3-F158-A-9-DA5-4-F90-AADC-3-CB67-D80384-B.jpg)

So I instigated yet another professional engineering repair.
(https://i.ibb.co/2FVxhSw/2353-A6-A6-EDE7-4465-809-C-65-CF882-E8-E89.jpg)

I’ve instantly gained about 50ftlb’s of torque. Can trigger the traction control light again!
It still not back to where it was but loads better. New brake booster hoses and PCV hoses are in the post.
I’ll report back when fitted, although I’ve no idea how the hell you’re supposed to get that bottom PCV hose off, I can’t get my hand in.



Title: Re: Down on power…
Post by: pudding on May 26, 2022, 08:57:43 am
I replaced the bottom PCV hose on mine last year and it's actually not too bad a job.  Mine was almost plugged with baked in carbon deposits and it snapped in half like a dry reed, so well worth replacing that.

Yep, the oily mist on your HPFP sensor is from the PCV.  Either a cracked top hose as R-Tech said, or gasket/O ring related.

Glad to hear it's finally on the mend  :happy2:  Strange that a vac leak that big wasn't flagged by the ECU.  Normally get 'system too lean' codes and really big long term fuel trims.
Title: Re: Down on power…
Post by: rich83 on May 26, 2022, 09:10:55 am
Glad to see you are making progress
Title: Re: Down on power…
Post by: JoshB on May 28, 2022, 04:40:26 pm
Go on then, any tips on how to get the bottom PCV hose off? I literally can’t even get my hand on there. I don’t have to take the inlet manifold off do I?

(https://i.ibb.co/TcgQxbL/6120-B27-B-DFB4-4-F05-A18-A-70-FCD0-BADDC9.jpg)
Title: Re: Down on power…
Post by: ROH ECHT on May 28, 2022, 06:05:26 pm
As Pudding said; Mass Air report will vary depending on which gear each pull was done with.
Also, it may have been leaking (in the locations you've discovered) more so during one pull than the other.
Disconnecting the breather tube from the filter housing has its difficulties for it being a tight spot, but I managed with giant hands. And since you are replacing it...do not worry about damaging its clips on the end.
Title: Re: Down on power…
Post by: LC5F on May 28, 2022, 08:01:38 pm
I replaced mine when my manifold was off  - it split in the same location while taking it off
Can you get to it from underneath - past the oil filter and intake hose?
Title: Re: Down on power…
Post by: JoshB on May 28, 2022, 09:19:07 pm
All done! Managed to get a finger on the top and a wood chisel underneath. I couldn’t believe just how brittle both pipes were. Full of gunk and full of cracks, managed to get some Febi Bilstein parts for under £30 and they fit perfectly, just have to keep an eye on them in future. Obviously these were the original parts so some black plastic being subject to heat cycles over 17 years, they’ve done OK I guess. I just can’t believe the whole PCV system can cost you like 50bhp.

Just glad it was something so simple in the end. And it doesn’t shake anymore on idle. Thanks for everyone’s help!
Title: Re: Down on power…
Post by: pudding on May 30, 2022, 08:33:51 am
Yeah it's not a bad job that pipe.  I just did a classic reach around behind the runner flap motor and managed to get it off.  If the pipes are that bunged up with crud, I hate to think what the oil separator in the filter housing looks like.  Next time my intake comes off for injectors/walnut cleaning, I think I'll be sticking a new one on.  R-tech have mentioned in the past about those getting clogged up and causing running problems.

Title: Re: Down on power…
Post by: G-olf on May 30, 2022, 07:27:57 pm
Its nice if you can find the problem and its not too expensive to fix  :smiley:

So this looks like another thing on the maintenance/check list.
What happens with that bottom pipe? Blocks up with crud??
Title: Re: Down on power…
Post by: JoshB on May 30, 2022, 08:47:06 pm
Its nice if you can find the problem and its not too expensive to fix  :smiley:

So this looks like another thing on the maintenance/check list.
What happens with that bottom pipe? Blocks up with crud??

It wasn’t blocked up completely but it was full of gunge. It’s probably down to the ribbed nature of the tube, if it was smooth it wouldn’t allow as much build up. I noticed Awesome GTi sell an ECS (?) Tuning silicone replacement kit, which for £86 I was tempted with. But then I read all the shocking reviews…
Title: Re: Down on power…
Post by: GilesWoodward59 on May 30, 2022, 10:30:47 pm
Interested to know why the ECS kit is no good? Looks like a sensible fix - although not cheap.
Title: Re: Down on power…
Post by: JoshB on May 31, 2022, 02:08:44 pm
Interested to know why the ECS kit is no good? Looks like a sensible fix - although not cheap.

For starters it’s a silicone hose. Oil and silicone don’t mix…
Title: Re: Down on power…
Post by: pudding on May 31, 2022, 03:29:10 pm
You can get oil & coolant resistant silicon hoses, but quite honestly, given the original one lasts 13+ years.......