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Mk6 Golf 2.5l lean issues?

Mk6milli

New member
So I've had my 2010 golf 2.5l for a little over a year now and looking into things a little further now, I've noticed I am running lean. The car has had the cat removed and a new catback dual-tip exhaust from rev9 (don't judge me I was broke when I "upgraded"). It also has a CAI installed and the engine cover has been removed so the SAI tube has no inlet and I have it running with just a small cone filter on it. It's always run not so great but recently I started developing a misfire while under acceleration and at idle. I've replaced both o2 sensors, spark plugs, all coil packs, fuel filter, and MAP sensor.

So my questions are:
1. Would the engine cover missing be the cause of why I'm running lean all this time? I know that there are multiple reasons I may be but was curious about this because I know the engine cover is built into the car's intake system somewhat and without it I am missing a few of the sensors that were once there.

2: The misfire has developed randomly and as stated above I've replaced all parts I could really assume would be causing the misfire. I am replacing the valve cover soon as it is leaking from the back of the head and dried up oil all over the spark plug tube areas. I also did a vacuum delete kit by Spulen and noticed that the hose connected to my PCV on the valve cover to my intake and splits into my brake booster is leaking from the PCV into my intake manifold.. I'm trying to get a little info on what may be causing this to run so poorly or just any advice or info that may help me understand how to keep my car running at its peak performance.

I do not know a whole lot about these 2.5 engines and am hoping someone here has some more experience and info that may help me. I'm pretty handy and can replace most parts myself so I've been trying to avoid the shop route which is a pain because diagnostics is not something I'm great at.. Sorry for the jumbled and somewhat poorly written stuff from above. If anything is unclear or anyone has anything I need to be more specific about please let me know. Thanks in advance!
 

Wascally Wabbit1

Go Kart Newbie
There is no problem removing the engine cover on the MK6. A leak in the vacuum delete kit would definitely be my first thought and could easily cause a lean condition as you would be letting in air that is not being detected by the map sensor. I would replace the kit or return it back to the stock configuration (ie, reinstall the vacuum pump). A leaky valve cover could also cause problems but I would think the vacuum leak to the intake manifold would be the worst offender for a lean condition.
 

MLue1

Drag Race Newbie
Anywhere that there is an oil leak is a potential cause of your problem. The first thing I would check is that all the Intake manifold bolts are snug, the bolts can loosen up or the intake manifold and/or they start leaking. If you have a one of those 12 inch Impact driver extensions you can check ALL the intake manifold bolts in 2 minutes on the 2.5, the end that goes into the impact is 6mm, just turn it around and use it on the 6mm hex bolts that secure the intake manifold.

Cheers
 

Mk6milli

New member
Anywhere that there is an oil leak is a potential cause of your problem. The first thing I would check is that all the Intake manifold bolts are snug, the bolts can loosen up or the intake manifold and/or they start leaking. If you have a one of those 12 inch Impact driver extensions you can check ALL the intake manifold bolts in 2 minutes on the 2.5, the end that goes into the impact is 6mm, just turn it around and use it on the 6mm hex bolts that secure the intake manifold.

Cheers
Yeah just replaced the valve cover, intake manifold gaskets, o2 sensors, and the map sensor still getting a misfire. Going to the shop thursday as I'm tired/dont have time to work on it anymore.
 

Mk6milli

New member
Did you fix or remove the vacuum delete kit?
Yeah replaced the whole valve cover cause it was old and cracking from taking out the coil packs over the years. No more oil leaking into the IM. Still missing though. My o2 sensors keep going out which I'm assuming is because of the 7000 leaks in my exhaust system? Not sure if that would be a problem as I am more of an "entry-level mechanic" but it is leaking right next to the downstream o2 which I've had to replace 3 times now.

My assumption is that maybe it's getting too much air from the leaks and causing the o2 to read more oxygen than it should. When I replace that o2 the car runs fine for a little and then about 6 months down the road the car starts misfiring again. Gonna have the exhaust taken off and re-fitted/re-welded and replace the o2 and go from there. The whole exhaust has been removed including the cat which has a Magnaflow 10416 in its place then to a single muffler and out the back. Put the exhaust on about a year ago and welded it myself thinking I could do it (because I'm an idiot lol) and with everything I've replaced this is my only assumption anymore. I've smoke tested it as well and am seeing no vacuum leaks anywhere so to the shop it goes I guess.
 

MLue1

Drag Race Newbie
Sounds like you've made a valant try! The only other thing I can think of is the MAP Sensor, when we first installed the UM/HEP SRI Manifold, we had damaged ours by stretching sensor wire/connection, once we cut and spliced in a section of new wire everything has been good.

To close this out let us know what the Shop finds and good luck.
 

Mk6milli

New member
Sounds like you've made a valant try! The only other thing I can think of is the MAP Sensor, when we first installed the UM/HEP SRI Manifold, we had damaged ours by stretching sensor wire/connection, once we cut and spliced in a section of new wire everything has been good.

To close this out let us know what the Shop finds and good luck.
Yeah, i'll update once the shop lets me know what's going on! So far I've done IM gaskets, map sensor, o2 sensors, all coil packs, and spark plugs so hoping it's not a valve seating issue or something... Will update for sure!
 

Mk6milli

New member
Update on the golf:
Well this is embarrassing. So I took the golf to the shop and a day later they let me know it was very strange what was going on. Well they couldn't crack it 100% so they just suggested some new ignition coils and spark plugs.

Heres were the honda boy in me failed my poor VW lol. Like I mentioned above I replaced all ignition coils and spark plugs not that long ago. Well I'm so used to slapping any part in my old civic and it would just run it which is not the case with these VW's (which I now know). I had some cheap knock off brand ignition coils and some cheap champion spark plugs because I was low on cash when I was trying to get the issue figured out.

Pulled the plugs to check them again and wouldn't you know it... The specs were all over the place and 3/5 plugs were out of spec pretty bad. So I went ahead and got some bosch plugs and ignition coils and man she is running like brand new!! Such a stupid mistake I should of known buying the cheaper option was gonna turn around and bite me in the ass lol. Guess it's a lesson learned the hard way. Will be putting bosch parts on this thing for the remainder of its years lol. Glad to be finally back on the road! We also rewelded the exhaust and man it sounds so much better now!
 
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