Random cylinder misfire - Random is the right word for it!

[danj3000]

Hi all,

Would appreciate a little help with a minor running issue with my GTI.

I'm currently experiencing a random misfire that is stopping me from enjoying the car to the full. It's best described as an intermittent fault and there doesn't appear to be a massive amount of consistency in when the exhaust management light starts flashing. It does more often happen when giving it some beans beyond 3k but again it doesn't do this all the time, only occasionally.

Last weekend I had a particularly bad misfire on cylinder 4 which meant I limped home. I whipped off the engine cover, pulled out the coilpacks, doused them in a bit of magic WD40 and it cured the misfire. This lead me to think it was the coilpacks were faulty, fortunately got them replaced for free by VW courtesy of the recall on Thursday. But alas, this fault appeared again for me today, it only flashed for a few seconds and didn't come on again for the rest of the journey. It's also worth mentioning the misfire is random and it's never on just one cylinder, the times it has happened it varies between all four cylinders.

As a foot note the spark plugs were replaced with OEM parts in April too.

So in my limited knowledge i'm thinking it's either the ignition loom which the coilpacks plug into or the injectors. If it were the injectors then I don't see how my WD40 fix would have worked though.

Any help is gladly appreciated 

[fab5freddy]

I'm also interested in any input, as i'm suffering the exact same problem 

Mine seems to happen when the engine is up to full temp and pushing on, funny thing is no record of any misfires on VCDS or any warning lights on the dash.

 

[bacillus]

I think you need to try the cheapest things first with this sort of thing so personally I would look to see the condition and colour of your plugs. Did you change the plugs yourself as it's not unheard of to be invoiced for new plugs by VW without them being changed.

Also what mileage has your car done?

[danj3000]

The plugs were replaced just before I purchased the car, whipping them out to check sounds like a good idea.

Mileage wise the car is on 107,000 and has full service history.

[dajonic]

I've had the same problem but only on the one cylinder. Funnily enough it only started after the coil packs were changed with the VW the recall. I finally had the injectors replaced with a second hand set that I had serviced and problem solved. Hope it works out for you too 

[Karl_mac_]

I'm having the same issue, however mine is slightly different as it only seems to miss after a warm start (i.e when the car has been run, then re-started shortly after).

[danj3000]

Thanks for the replies. My hunch is it's the injectors that are playing up, i'm pretty sure this would help contribute to a slightly louder than normal engine note too.

Has anyone any experience of refurbing their injectors or is this not worth doing?

[danj3000]

Small update in that i've put some Redex injector cleaner in and had a 20 minute blast around. There is already a noticeable difference in running and engine noise at idle for the better, there were also no error codes or misfires when driving spiritedly. How long this will last I don't know but it's certainly encouraging, it does support my idea that the injectors are causing the issue though.

[GrayMK5GTI]

Try a can of BG44k in the fuel tank, it's like Redex on steroids 

Supposed to be the best injector cleaner on the market 

[danj3000]

Try a can of BG44k in the fuel tank, it's like Redex on steroids 

Supposed to be the best injector cleaner on the market 

Interesting, will look at that next time.

[Streetwise-REVO]

I have known injectors cause misfire issues, but random ones like described also could be down to air leaks or bad airmass readings, or if an electrical misfire could also have a wiring issue somewhere.
Best to get it checked out by an expert.
We are Streetwise Automotive in Bristol if that helps

[danj3000]

I have known injectors cause misfire issues, but random ones like described also could be down to air leaks or bad airmass readings, or if an electrical misfire could also have a wiring issue somewhere.
Best to get it checked out by an expert.
We are Streetwise Automotive in Bristol if that helps

Thanks Streetwise-REVO, i'm going to give it a little bit of time to see how things run over the next week or two. If the problem persists i'll look at giving you guys a call as i'm based in Clifton, Bristol so very close.

[fab5freddy]

I have known injectors cause misfire issues, but random ones like described also could be down to air leaks or bad airmass readings, or if an electrical misfire could also have a wiring issue somewhere.
Best to get it checked out by an expert.
We are Streetwise Automotive in Bristol if that helps

Thanks for that 

I think the airmass reading could be my problem, as there's been a bit of rubbing on the wiring from my modified engine cover, i thought i'd got away with it and have it wrapped in loom tape. Hopefully that's the problem.

[Karl_mac_]

I've just ordered some 44K, suppose it can't hurt. Going to check MAF wiring too as suggested.

My misfire seems to be coupled with temporary loss of boost.

[Markyed30]

I had random misfires under load now n then in 3 cylinders turned out to be a £5 o ring on the intercooler only happend when I went stage 1+ and boost must have been to much for it