GTI (K04) Fuelling Issue? Advice Wanted, Datalogs Inside.

[davisharr]

So I have been chasing what I think is a bit of a fuelling issue with my 2012 GTI for a while now, and it seems to be getting worse. I have also recently had a cold start missfire issue come up, that I am unsure if it is related, or completely separate. Looking for some advice from the community if anyone would be willing to take a peek, I finally managed to get it on a datalog as it is very inconsistent when it happens.

First off whats done to the car for reference, here is all the engine stuff:

• Stratified K04 Pro-tune 91 Octane
• HPA Motorsports Stage 3 "Extreme Performance" DSG Tune
• APR Carbon Fiber Intake
• Unitronic Factory Mount Intercooler kit
• CTS K04 Turbocharger
• CTS 3" Catted Downpipe
• CTS K04 Turbo Outlet Pipe
• CTS Throttle Pipe
• Bosch 4 Bar MAP Sensor
• Go Fast Bits DV+

The car was tuned for the K04 setup almost 2 years ago, and datalogs all looked healthy before, so something physically with the car seems to have changed. The car has 165,000 Kms as it sits right now.

I was doing a routine datalog a few months back, just to check out the general health of the car, when I noticed that the fuel rail pressure actual, was dipping quite a bit bellow the fuel rail pressure target parameter. At first, I did not think too much of it, as AFR's look good, STFT looks good, and I am not an expert, so perhaps I was over thinking it, so I just let it be. Here is that log to take a peek at...
https://datazap.me/u/mk6gtiguy/march-22nd-intake-manifold-fuel-trim-diag?log=1&data=6-28

When the car was tuned, I was told an important parameter to keep an eye on is STFT, and through Cobbs suite, anything within .85, and 1.15 is probably acceptable, as of recently, every once and a while, maybe 1/10 pulls, I see the STFT peg itself at 1.25, which I have been told means it is adding as much fuel as it can, and is probably an indicator of a fuel system issue. This is when I started really getting concerned, and here I am asking for advice! It does this inconsistently enough that it was very hard to capture on a log, but consistently enough that if I take the car out for a hard drive, it will happen at least once, you can feel it too, the car is way underpowered when this occurs. Here is that log where I did finally catch it today to take a look at: https://datazap.me/u/mk6gtiguy/april-27th-datalog?log=0&data=6-28

Funny enough, when I finally did catch this STFT spike in a log, the rail pressure dip I noticed earlier did NOT happen during this particular pull, but also that its requesting less rail pressure as well.

So far, because I was due for them anyways, I have done the fresh plugs, coil packs, and a fuel filter, as baseline items as a starting point. I also cleaned my MAF, and smoke tested the car for any boost leaks. last carbon cleaning on this car was done 30,000 KM's ago, car has never thrown an actual CEL for any of these issues, The car does feel like it may be down on power and response a bit, but its hard to tell for sure with the butt dyno, so if it is, it must be minor or I am sure I would notice it a lot more. The car still breaks traction in 3rd gear, and most of the time feels quite nice to drive, but something feels off about it, its idling rough, and it feels almost like its working harder to give me the same performance it used to if that makes any sense.

I would love any thoughts from the community and potentially people who know what they are looking at a bit better than me, before I begin to just throw parts at it. Is there any common failure points you might look to on these cars that show these symptoms... etc. I really do appreciate any thoughts, and thank you in advanced!

 

[GIACUser]

Given all the info you supplied fresh coil packs are something I would do just because.

The ECU is pulling down some timing starting at 4970 rpm in cyl2, then by 5234 rpm it is pulling timing down in cyl 1-3, which is just about the time the thing should really be pulling so your butt-dyno may have felt the difference, assuming you normally get zero timing pull. The ECU continued to pull that timing untill you let off the gas at 5943 rpm.

What gear were you in?
What was the air temperature that day(roughly)?
Was this a first run or was car already hot?
Do you have any datalogs that show what things look like when the car is running right?
What plugs did you put in and what did you gap them at?

 

[davisharr]

Given all the info you supplied fresh coil packs are something I would do just because.

The ECU is pulling down some timing starting at 4970 rpm in cyl2, then by 5234 rpm it is pulling timing down in cyl 1-3, which is just about the time the thing should really be pulling so your butt-dyno may have felt the difference, assuming you normally get zero timing pull. The ECU continued to pull that timing untill you let off the gas at 5943 rpm.

What gear were you in?
What was the air temperature that day(roughly)?
Was this a first run or was car already hot?
Do you have any datalogs that show what things look like when the car is running right?
What plugs did you put in and what did you gap them at?

Coil packs and cleaned air filter solved all cold start missfire issues. Fuel trim issue still exists, both pulls in 4th gear, both pulls on 10 Deg Ambient days. Car was well and warmed up, like 30+ min drive warmed up before both. Plugs are NGK_BKR8EIX gapped to .026 as recommended by tuner. Some timing pull is normal for this car and our garbage local fuel, here is a very healthy log from about 2 years ago, exact same list of mods to engine and exact same tune at time. https://datazap.me/u/mk6gtiguy/k04-revision-12-4th-gear-wot-0?log=0&data=6-28

 

[davisharr]

Still battling this, really getting discouraged, at this point I have no idea what the cause could be, as it's so intermittent. The car will drive like a million bucks for 45 mins, then you floor it to pass someone on the highway, almost die because the car is making no power, and then next time you floor it its perfect again... It does seem to be related to where you start flooring it, from 2,500 3,000 RPM like a dyno pull the issue will very rarely if ever come up, downshift and floor it from 4,000 like when passing, and its more likely, but far from guaranteed to happen.

 

[GIACUser]

Still battling this, really getting discouraged, at this point I have no idea what the cause could be, as it's so intermittent. The car will drive like a million bucks for 45 mins, then you floor it to pass someone on the highway, almost die because the car is making no power, and then next time you floor it its perfect again... It does seem to be related to where you start flooring it, from 2,500 3,000 RPM like a dyno pull the issue will very rarely if ever come up, downshift and floor it from 4,000 like when passing, and its more likely, but far from guaranteed to happen.

Its too bad we can't get a log of when it actually happens so you have data that reflects the issue, rather than a log of the good runs. Intermittent issues always take longer to solve, don't give up.

The log you posted looks like a more normal run. Ambient temps perfect for turbo weather (50 degree F). As for the timing pull, if it were fuel related I would expect to see more consistency in timing retard across cylinders. Only significant pull under load is in Cyl 3 when you first get on it and it clear up quickly, then when you are in most load Cyl 1 has some pull none of which amounts to much in terms of lost power in that run.

I don't think your sparkplugs are the issue, should be ok. You could go with a 7 heat range if it is that cool where you live in the middle of summer. If you pulled the plugs to check them, did they all look the same in terms of color?

I would say, go out and see if you can get a log (record) of what happens when it falls on its face. Sorry, I don't have better advice, but that is what I would try to do.

 

[davisharr]

Its too bad we can't get a log of when it actually happens so you have data that reflects the issue, rather than a log of the good runs. Intermittent issues always take longer to solve, don't give up.

The log you posted looks like a more normal run. Ambient temps perfect for turbo weather (50 degree F). As for the timing pull, if it were fuel related I would expect to see more consistency in timing retard across cylinders. Only significant pull under load is in Cyl 3 when you first get on it and it clear up quickly, then when you are in most load Cyl 1 has some pull none of which amounts to much in terms of lost power in that run.

I don't think your sparkplugs are the issue, should be ok. You could go with a 7 heat range if it is that cool where you live in the middle of summer. If you pulled the plugs to check them, did they all look the same in terms of color?

I would say, go out and see if you can get a log (record) of what happens when it falls on its face. Sorry, I don't have better advice, but that is what I would try to do.

Sorry if I was unclear, but one of those firs two logs does show it. This one: https://datazap.me/u/mk6gtiguy/april-27th-datalog?log=0&data=6-28

Click on the STFT parameter and watch it peg itself to 1.25. That's what's happening. Boost is still good, timing pull is still reasonable enough, but car is trying to richen itself up and not getting the fuel it needs for some reason. Or at least thinking it's not.

 

[GIACUser]

Sorry if I was unclear, but one of those firs two logs does show it. This one: https://datazap.me/u/mk6gtiguy/april-27th-datalog?log=0&data=6-28

Click on the STFT parameter and watch it peg itself to 1.25. That's what's happening. Boost is still good, timing pull is still reasonable enough, but car is trying to richen itself up and not getting the fuel it needs for some reason. Or at least thinking it's not.

STFT is high but by itself does not indicate any fall off in power. In fact I don't see anything on the graph that looks like a big departure from your other graph or anything that looks like power fell off while you had the throttle down. Perhaps I am missing something. The one that you linked as an example that shows the issue does have a little lower boost on top with a bit more timing pull but nothing of any big difference that would feel like power fell off.

 

[GIACUser]

The only other thing that I could think of seeing what appears to be a pretty much normal power graph but driver feels the cars forward motion diminish when it should still be pulling stronger. Worn DSG clutches slipping, I have actually had that happen to me. Really could not feel it at first but I was doing dyno runs and we were able to graph the problem because we could log the correlation between torque and boost. In this situation my car still felt like it pulled ok but It could not put out the numbers we had been putting down consistently in the past weeks. It was slipping and I eventually rebuilt my DSG at what would have been about 112,000 km after running my GTI with K04 etc for more than have of the miles on car.

 

[davisharr]

Nah I know DSG slip, it's not that. It's something fueling, or electronic control related for sure. 1.25 in Cobb suite is the max amount of fuel these ECUs can add, you can then see it begin to lean out a slight bit in AFRs, and the throttle close a few %, then I get off the gas.

At this point it could be a number of things, but I'm thinking of the folowing as options...
- LPFP
- LPFP Controller
- HPFP
- Fuel rail pressure sensor

Less directly related things but who knows:
-Carbon buildup
-AFM
-02 Sensor...

So as you can see, I can't narrow it down. It could be any number of things, I listed, or something else completely.

What makes it so hard is that it's both intermittent, and not catastrophic, as in no hard fuel cuts no Codes... etc. But it's bad enough I don't want to beat on the car. Because I fear it's risking leaning out and causing damage.

I have a long hwy roadtrip tomorrow, I'll log a few pulls and try get a more obvious example.

Thanks for trying to help!

 

[kosmaras]

Not sure how helpful this is, but have you experienced misfires up top? Your log is indicative of valve float...Boost increases and MAF G/S decreases.

 

[davisharr]

Not sure how helpful this is, but have you experienced misfires up top? Your log is indicative of valve float...Boost increases and MAF G/S decreases.

Never experienced any missfires at all, it doesn't break up, it sounds fine, it just makes notably less power. I also wouldn't expect valve float to start so low in the RPM, it looks like my fuel trim issue and notable power loss starts about 4,700, and actually begins to end at 5,800 or so right where you see the boost raise. I imagine something in the computer is seeing we have the fuel capacity, and adding boost back, though that level of higher boost doesn't match what my "healthy" pulls look like, and the MAF G/S lowering is interesting. Not sure if you are onto anything or not, but still appreciate you point that out, perhaps it could be a hint!

I'm off on a 2 hour each way drive tonight, I'll be coming back late at night on a big high speed HWY that should be near empty, I'll log a handfull of pulls, and if this issue occurs I'll stay on the gas through to redline just to see what happens and hopefully get a clearer data sample to look over!

 

[davisharr]

Alright, well I got it to do it on the highway last night, it took 5 or 6 tries at a pull, first 5 feeling perfect and pulling through to redline. Finally, I got it to misbehave, seems like it is more common to do it if you catch the car off-gaurd, say you're in 6th, drop it to 4th with paddles and floor it, its way more likely to happen than if you're already in 4th and roll onto throttle. So for this pull, I started in 6th, dropped 2 quick, and floored it, almost immediately after hitting gas you can feel you got it to display the issue, even though the car builds boost and pulls clean, its immediately noticeable as underpowered, feels a bit laggier, then when it finally does spool, the feeling of torque just isn't there like usual, then, this time I stayed in it long enough to get a bit more info... Turns out if you stay in it, it throws an EPC light eventually! At the end of this log I got an EPC, car fell on its face, and went to limp mode. Only code is P0234 Overboost. I also got a code for P2015 Intake manifold runner position sensor on the drive up there when not beating on the car or trying to get it to misbehave at all, I cleared that and it never came back, but curious... Usually a failing intake manifold flapper is associated with cold start issues from what I remember? I did have cold start missfires originally, but since cleaning my air filter they have yet to come back. Could it be related at all to my issue? The car does have the revised intake manifold done about 100,000 KMs ago by previous owner. Would a flap or all flaps closing when they shouldn't explain the overboost, while MAF G/S drops, similar to what Kosmaras above describes. Could it not opening cause the lag and lack of feeling of torque down low when it happens? Does this system ever fail intermittently like this and cause similar symptoms? Would any of this explain why the ECU is trying to add so much fuel? I thought this was a fuelling issue at first, now I am not sure if its fuelling, boost control, or something else entirely. Im lost.

Would love to hear any opinions after this added info. I am more confused than ever...

https://datazap.me/u/mk6gtiguy/jun-...t?log=0&data=6-28&trim=0&tmin=0.12&tmax=15.70

And a photo I took on the drive yesterday as well to share for fun! This was taken about 10 mins after the log you are looking at above was recorded, when I got off the HWY to clear codes and get outa limp mode.

 

[brat_burner]

Your LPFP could be on the way out. I've seen them where the car will drive pretty normally until you get under any kind of load.

 

[davisharr]

Your LPFP could be on the way out. I've seen them where the car will drive pretty normally until you get under any kind of load.

That was my very first thought months ago and is still one of the top culprits on my list. But they are very expensive, and I was really hoping to not just be guessing and throwing parts at it to see what happens. But that might be where I am at at this point...

 

[brat_burner]

That was my very first thought months ago and is still one of the top culprits on my list. But they are very expensive, and I was really hoping to not just be guessing and throwing parts at it to see what happens. But that might be where I am at at this point...

I noticed the injection time coincides with your observations about the STFT. It's commanding for fuel and it may just not have the volume(10-12 range vs 7-8 on older logs)... the drop on the HP side doesn't look to be substantial. I don't know if there is a test port or other actual values that you can see in the controller on the low side.