Misfiring under load - 07 GTI

plant0 · Oct 15, 2017

Update: Solved my misfire issue! Boost controller connections were shorting and I had a vacuum leak in my intake temperature sensor.

Hey guys it's my first post, I'll take any advice you got. I've had my GTI for almost two years and it's never been perfect... But I have narrowed down the codes to just a cylinder 4 misfire (When a CEL does pop under load).

Work done:
Timing Belt
Pierburg Piston DV
Audi R8 Coils
AC Delco Spark Plugs (Should probably switch to Bosch)
Carbon cleanout
Aftermarket intake with dry filter
Coolant temperature sensor
Thermostat
Boost Controller replaced + hose that was glued down by previous owner(?)
Intake Manifold Motor (Recall)
MAF sensor (Just replaced)

Things to note:
Have always filled up with Shell 91 or Chevron 94
Pancake pipe/ Inter-cooler pipe has some oil leakage
Air compressor does not work anymore, AC died in the summer.

The car sounds normal in idle except sometimes it will misfire and correct itself... and around 2700RPM in low gears it will sometimes bog in and out. If I unplug the MAF it seems to limit the power of course but it does not misfire at all.

I appreciate anyone who tries to help me on this frustrating matter! I love my car and do not want to let her go

ROH ECHT · Oct 15, 2017

Is everything in your "Work done:" list done before the codes or since? List as done before or after.
Just a misfire in one of the cylinders is usually a coil, plug, plug gap, or fitment(tightened properly)...it can be its injector, but rule out that it's firing properly first.
Yes, you should swap plugs and use oem or NGK PFR7B's @ 0.028": http://www.hstuning.com/product_info.php?cPath=24_32&products_id=3688&vpath=30_31

plant0 · Oct 16, 2017

ROH ECHT said:
Is everything in your "Work done:" list done before the codes or since? List as done before or after.
Just a misfire in one of the cylinders is usually a coil, plug, plug gap, or fitment(tightened properly)...it can be its injector, but rule out that it's firing properly first.
Yes, you should swap plugs and use oem or NGK PFR7B's @ 0.028": http://www.hstuning.com/product_info.php?cPath=24_32&products_id=3688&vpath=30_31

Honestly I've been dealing with misfires for different reasons since I've had the car LOL. Thank you for the link, was looking for quality spark plugs.

The first misfires being the stock DV, then carbon build-up, then boost controller + hose, now I'm just at cyl 4 misfiring when car is under heavy load.

It seems to be running better with a brand new MAF, but it's not allowing heavy load. I will order those spark plugs and replace my shitty AC Delco Canadian Tire plugs!

carbonduc27 · Oct 16, 2017

I had misfires randomly in all cylinders for years. mostly at full throttle - high rpm.

It helped when i took out the shitty autozone iridiums and switched to bosch. I finally cured it with new coils. I had new r8 reds so i was sure that was not the problem. But i guess they were not seating correctly. Replaced them with the correct latest rev of the stockers and we are all good.

Soysauce · Oct 16, 2017

I was getting misfires at 70k miles, replaced spark plugs and ignition coils and all was well. I'm now at 86k and I'm getting a cylinder 3 misfire. I'm thinking either carbon build up or faulty plug/coil. In your case I'd guess it's a plug or coil like ROH ECHT said.

ROH ECHT · Oct 16, 2017

You will find it best to stick with the oem plugs...however, if wanting a better plug, those PFR7B by NGK are the best for our MK5's and for when tuned or bigger turbo'd...but those NGK's need to be gapped no more than 0.028". If you find the misfire still remains @ #4cyl., try a new oem coil(R8 in your case). If finding the PFR7B's hard to find...they are off a 2010 Audi A6 3.0L S-charged engine. So, a VW dealer can order them with that information.

I always keep a new coil in the garage just for this purpose...a single cylinder misfire. Easiest way to determine if a new coil is required is swap in the new one...and if fixed, you leave it in and go buy another new coil for next time.

plant0 · Oct 16, 2017

ROH ECHT said:
You will find it best to stick with the oem plugs...however, if wanting a better plug, those PFR7B by NGK are the best for our MK5's and for when tuned or bigger turbo'd...but those NGK's need to be gapped no more than 0.028". If you find the misfire still remains @ #4cyl., try a new oem coil(R8 in your case). If finding the PFR7B's hard to find...they are off a 2010 Audi A6 3.0L S-charged engine. So, a VW dealer can order them with that information.

I always keep a new coil in the garage just for this purpose...a single cylinder misfire. Easiest way to determine if a new coil is required is swap in the new one...and if fixed, you leave it in and go buy another new coil for next time.

Wow, lot of good information. Thanks man.

ROH ECHT · Oct 16, 2017

Never a problem :thumbsup:

plant0 · Oct 17, 2017

I also need to add that when I accelerate from a higher gear like fourth while going 50km/h, I can sometimes hear a whistle as if there was a vacuum leak. What kind of things could cause this?

My first guess would be valve cover? Would the pancake pipe effect this? Or how about the intake pipe connector ?

ROH ECHT · Oct 17, 2017

The sound is likely always there from whatever causes it...there is just less engine grumble drowning it out in an upper gear. Could be any of the turbo to intake connections...could also be something wrong on the rear breather tube...from the back of the valve cover to turbo. It's a ribbed alloy tube...sometimes is cracked or fitted incorrectly and isn't flush to the turbo any longer. You should do a proper smoke test inducing smoke both to the "intake to engine" and the "crankcase and vac system" as well.

Pancake pipe? You mean this ↓ The pipe alone isn't likely responsible for noise...connections to it may.

If you have vcds, you can look at data in group 032 while idling...LTFT both @ Idle(block 1) and Off Idle(block 2). If you have any sort of leak, data in block 1 will be a positive number higher than zero. The leak will affect the value in block 2 as well , so you'd see a positive number higher than zero there as well...or should. Block 2 may reflect other reasons why running lean because Off Idle includes combustion results from driving around at normal operation.

The valve cover is easy enough to remove and inspect...another vid of mine where I found my v-cover cracked on the inside:
https://www.youtube.com/watch?v=t0-G5lApFvQ

I had a new v-cover on hand just in case I did find something worthy of installing a new one...if nothing was wrong, the dealer would return the new v-cover for me.

plant0 · Oct 18, 2017

ROH ECHT said:
The sound is likely always there from whatever causes it...there is just less engine grumble drowning it out in an upper gear. Could be any of the turbo to intake connections...could also be something wrong on the rear breather tube...from the back of the valve cover to turbo. It's a ribbed alloy tube...sometimes is cracked or fitted incorrectly and isn't flush to the turbo any longer. You should do a proper smoke test inducing smoke both to the "intake to engine" and the "crankcase and vac system" as well.

Pancake pipe? You mean this ↓ The pipe alone isn't likely responsible for noise...connections to it may.

If you have vcds, you can look at data in group 032 while idling...LTFT both @ Idle(block 1) and Off Idle(block 2). If you have any sort of leak, data in block 1 will be a positive number higher than zero. The leak will affect the value in block 2 as well , so you'd see a positive number higher than zero there as well...or should. Block 2 may reflect other reasons why running lean because Off Idle includes combustion results from driving around at normal operation.

The valve cover is easy enough to remove and inspect...another vid of mine where I found my v-cover cracked on the inside:
https://www.youtube.com/watch?v=t0-G5lApFvQ

I had a new v-cover on hand just in case I did find something worthy of installing a new one...if nothing was wrong, the dealer would return the new v-cover for me.

Thanks for the info man!!

UPDATE: car is misfiring heavily in idle and lightly misfiring in idle without MAF connected... Still no CEL unless I drive X amount of KM with MAF unplugged. I am going crazy...it was driving perfect when I installed the new MAF.

plant0 · Oct 18, 2017

Update: Found the potential culprit! Got my buddy to check out my car and he was wiggling hoses near where I hear the 'whistle/squeal' noise. The intake temperature sensor could be the issue. Will post results soon!

plant0 · Oct 18, 2017

plant0 said:
Update: Found the potential culprit! Got my buddy to check out my car and he was wiggling hoses near where I hear the 'whistle/squeal' noise. The intake temperature sensor could be the issue. Will post results soon!

UPDATE 2: Finally, the solution! Fixed the vacuum leak by replacing the o-ring in the intake temperature sensor & adding a "cardboard gasket". Then I had to replace the boost controller plug wires which were pretty much shorting out every time the engine moved... Found the culprit by starting her up and shaking the engine by hand, then wiggling some hoses/wires until she felt the boo-boo & began to misfire heavily.

Hope this may help anyone out there with similar problems & thank you guys for your awesome advice. Should have made a post a year ago...:bow:

ROH ECHT · Oct 20, 2017

Nice...happy you went at it aggressively and were rewarded. Gonna be months and years of upcoming fun now. Thanks for posting the results and conclusion...need more of that on forums.

plant0 · Oct 20, 2017

ROH ECHT said:
Nice...happy you went at it aggressively and were rewarded. Gonna be months and years of upcoming fun now. Thanks for posting the results and conclusion...need more of that on forums.

Gonna get those NGK sparkplugs you linked me because my AC Delco plugs need to be replaced after so many misfires. She still doesn't go full load without knocks.

I will post results tomorrow if that improves anything

Misfiring under load - 07 GTI

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