All Things Mk5 > How to Guides / Troubleshooting

Misfire cylinder 1

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Clarkj93:
Hmm, yeah will mull it over I think over the next week, not overly fond of giving VW 600 odd quid... thanks for the info again Pudding!

Clarkj93:
Not sure if anyone's interested but been toying with this issue with little spare time I've had recently in between a couple other rust and paint related jobs. I'm in denial about fuel injectors currently as I can't be bothered with removing and sending off/fitting new right now, hoping for a miracle!

Changed the MAF, 145 quid from VW and annoyingly no change.

I've swapped the stock air box for a creation motorsport intake as I wanted anyway and it removes the issue being the intake, again no change.

I've cleaned the IAT which was looking a bit oily, no change.

I did notice a misfire in cylinder 2 and 4, though this only happened a couple of times while monitoring and is not really often enough to say its consistently intermittent. But could be a sign its not something specifically wrong with cylinder 1?

Before the misfire started the only thing I did was add the liqui moly and fiddle with the throttle body hose, I wonder if that is the issue? The hose does not fit that well but would appear to be securely fitted? It did actually detached while driving after fiddling with it again recently, I've binned the old ones and stuck some new clips on there, still misfiring but seems possibly less often? I do have a new silicone one to replace but it's an absolute bugger to fit so will give it another go when I've had some weetabix along with cleaning the MAP as well.

I've got a suspension refresh to do also so while I'm ordering bits from awesome gti will grab a new pcv and gasket, ECS pcv hoses and a oem revision G diverter valve just for general maintenance if nothing else, may get lucky though!

pudding:
Misfiring and/or a lumpy idle has always been the bain of petrol engine owners  :grin:

I don't know what it is with cars you own.  They never seem to idle smoothly compared to mates' old beater sh1t box Vauxhalls and Fords they don't care about  :grin:

Anyway, did you look in measuring block 032 to see what the long term fuel trims are?  They normally creep up and up if there's an air leak, which can cause misfires.

If the fuel trims are tiny numbers, it's probably the injectors and/or carbon build up.

Need to get all the hardware ship shape first before calling it though, such as sorting loose throttle hoses etc etc.

Clarkj93:
So I thought I found the issue here:


Not an easy part to source, I read that vw charge well over 100 quid for this brake booster and the cheap ebay ones are 45 odd quid and like other ebay parts destined to break. So bought some samco 9mm silicone vacuum hose, very carefully cut the old one off and stuck the new one on, comes to the grand total of 9 quid so cheap easy fix!



Car is definitely running much smoother, however it is still misfiring annoyingly! Thought I had it!

 I don't have vag com but do have obd-eleven, pretty decent for a 50 quid thing, although it's by no means the complete package and does have some shortfalls as I show below. This video really helped with what you mentioned:

Obd-eleven just kept showing 0 percent or failed to connect for 032, 033 however showed quite high numbers and started rising from the point of ignition:



I noticed the upper pcv valve hose is loose, and hissing a bit, I disconnected it pcv side and stuck my thumbs over pcv hole and the end to the hissing hose, the number dropped to well into the negative figures. Note that  I did this while the engine was running and doesn't sound great when it almost stalls and almost sounds like there is some knock going on when doing this, could just be my ears though. Anyway... ordered some silicone hoses for pcv a while ago but order is delayed until end of the month, just bought a cheap 10 quidder on ebay for now as hopefully that will just prove to myself if that is the issue or not and can replace with the silicone one when it arrives. We're getting there! Slowly!

Clarkj93:
Final update then. Replacing the upper pcv hose did the job, it was just a cheap ebay part so I think after replacing the brake booster vacuum line I broke a seal on this hose while fiddling with it, another ebay part proved it was the weak point and running smoothly now! Got some ecs silicone ones to replace these coming in a week or 2 as the permanent solution.

 Cheers for all the ideas from everyone!

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